In view of global scale, primary oil and gas reservoirs of the Meso-Neoproterozoic, and even the Lower Cambrian, have been reported in cratons of Siberia, Africa, East Europe, India, Arabia and Australia, especially in the East Siberia and Oman regions, so far the proved oil and gas reserves are up to a scale of 10⁸ t to 10⁹ t of oil equivalents, which testifies that the Meso-Neoproterozoic petroleum is an energy resource realm worthy of notice. In China, the thermal evolution levels of the Meso-Neoproterozoic, and even the Lower Palaeozoic strata are commonly in overmature phase unfavorable for the preservation of liquid oils, thus, Meso-Neoproterozoic primary oilfields are not yet discovered up to now. However, a large number of oil seepages and/or large scale bituminous veins are found in the Meso-Neoproterozoic, the analysis of the primary petroleum prospectivity would be helpful to guiding the exploration of Meso-Neoproterozoic oil and gas resources. The cumulative thickness of overlying sedimentary covers is not big enough so that the Meso-Neoproterozoic strata have never been deeply buried, or the lithosphere is unusually thickening, resulting in a geological condition of “cool lithosphere and cool basin”. Therefore, as the Longmenshan piedmont belt in the Yangtzi Craton and the North Yanshan Depression zone in the North China Craton are taken as examples, the Meso-Neoproterozoic primary hydrocarbons would be always within the category of “liquid oil window”, which should still favor the preservation of the Meso-Neoproterozoic primary oil and gas resources.

The present paper made a re-recognition of Jurassic oils in Sichuan in terms of the four aspects, such as resource potential, reservoir types, fractured reservoirs and techniques of exploration and development. The paper has drawn the following conclusions. ①The Jurassic oil resource in Sichuan may be much more than the presently discovered amount of 1.0~ 1.1 billion tons.②The Jurassic oil resource is a special large-area and non-conventional compact oil accumulation that has no clear trap boundaries, no clear edge-water, bottom-water and oil-water boundaries like a “water-free reservoir”, and no clear differentiation between buoyancy and gravity. Their reservoirs are characterized by inner-source or near-source accumulation rather than large-scale secondary migration, ultra-low permeability, dual media, large-area entire oiliness, superimposed and linked multi-measures, “continuous” occurrence on slopes or in depressed areas, being restricted by lithology rather than local structures, and delimitating oil-bearing and well distribution areas frequently by output instead of reserve.③Jurassic reservoirs can not be simply defined as “fractured type” because various pores contribute significantly to both the reserves and long-term low but stable production though fractures are the prerequisite for a high output at the testing or production beginning. ④These exists a great reserve for this kind of non-conventional compact oils in the central-northern Sichuan, however, a non-conventional technique consisting mainly of hydraulic fracturing should be adopted in development. It was proposed that Shaximiao Formation in the Longgang area should be a prospecting target, which will be a breakthrough to open a new era for petroleum exploration in Sichuan Basin.

Troughs in faulted basins are generally taken as a province of hydrocarbon generation and expulsion instead of accumulation. Therefore, troughs are frequently neglected in the exploration focusing on the search of hydrocarbon reservoirs provided that they have been verified to be of hydrocarbon generation and expulsion capacity. Based on the practical exploration in Paleogene of Jizhong Depression and Cretaceous of Erlian Basin for years, this paper puts forward a new concept on the hydrocarbon accumulation in troughs of faulted depressions, which includs the following findings. In troughs of faulted basins, the sandbody distribution is controlled by multiple factors, lithologic accumulations are more readily to form than structural accumulations, three factors control the formation of large hydrocarbon accumulations, and structural and stratigraphic-lithological reservoirs are not only co-exist but also complement each other. Moreover, the novel concept also indicated that in troughs, fan-delta front in a flank part of an inverted structural belt, delta front on the break of a gentle slope, a sublacustrine fan and a channel sandbody along toes of faults are favorable locations for hydrocarbon accumulations in stratigraphic-lithologic traps. With the application of this concept, hundreds of million tons of oil reserves have been discovered in trough areas of the Huabei Oilfield.

The Jurassic system in the central Junggar Basin mainly developed various deposits including braided river, delta and lake facies, and their rocks are mainly lithic sandstones and feldspathic litharenites. Strong compaction is the most important diagenesis to control reservoir qualities in the study area. Based on comprehensive investigation of casting thin sections and physical properties of rocks, the present paper proposed that there was a high-quality sandstone reservoir zone with relatively high porosity and permeability at the depths of 3500m to 4500m in the Mosuowan region and this deep burial high-quality reservoir zone was identified as a primary porosity zone rather than a secondary dissolution porosity zone. The combination of logging data indicated that there was an uncompacted belt in the Mosuowan region and anomalies of high acoustic interval transit time and low resistivity occurred in the uncompacted belt of wells Mo-13, Mo-15 and Pen-5. Overpressure resulted from uncompaction had greatly reduced the effect of a normal compaction on deep strata, significantly resulting in the development of high-quality reservoirs in deep strata of this area. The distribution of uncompacted sandstone reservoirs in the study area showed an obvious tendency, i.e. the lower the sand-to-shale ratio, and the thicker the depth of mudstones, the more readily the uncompacted sandstone reservoirs develop.

Hydrocarbon source rocks usually occurred in a marine carbonate environment in Tarim Basin during Ordovician, no effective source rocks have been found in the Middle-Upper Ordovician thick marine clastic. The analysis of pyrolyzed organic carbon in some mudstones systematically sampled from the Queerquek Formation in the eastern Tarim Basin, the detailed observation and description of cores from the Queerquek Formation of Well Yingdong-2, and the comprehensive interpretation of various 2-dimensional seismic sections indicated that a suite of marine hydrocarbon source rocks with a total accumulated thickness of nearly 100m occurs at the middle and lower parts of the Middle-Upper Ordovician thick Queerquek marine clastic. This suite of source rocks, which has TOC as high as 1.23%, is electronically characterized by a higher natural gamma-ray value and lower electric resistivity, indicating a relatively pure mudstone, and is obviously of high amplitude reflection in seismic sections. Widely distributed in the eastern Tarim Basin, these source rocks overlapped and pinched out eastward in the Luoxi platform margin and westward in the Gucheng-Lungudong platform margin, respectively. Meanwhile, the distribution of these source rocks along the south-north strike disappeared at the Che’erchen fault in the south and the Peacock River fault in the north, respectively, while on the northwestern rim they overlapped upon the Peacock River ramp. The marine source rock in the Queerquek Formation is a suite of deep-water shelf–basin facies mudstones deposited during the intermission of extensive development of submarine fans when transgression happened and water body was relatively quiet.

The middle-upper Jurassic Lagongtang Formation, composed mainly of a turbidite depositional system of bathyal-deep sea facies, is characterized by an incomplete Bouma sequence. The statistic data of observations at different parts of the residual basin as well as the measurement and analysis on source rock samples showed that the Lagongtang Formation source rock had a huge accumulative thickness and contained organic matter dominated by typeⅠand type Ⅱ₁ kerogens. The source rock was characterized by abundant organic matter with TOC  mostly ranging from 0.40% to 1.20%, and a high or even over maturity with R_o mainly varying between 2.0%～5.0%. Under special evolutionary settings of the Tethys tectonic domain, the regional metamorphism and local structural deformation arising from the Mesozoic folding, stacking, thickening and the Yanshanian-Himalayan magmatic and hydrothermal alterations were likely to be the important factors that gave rise to high maturity of the Mesozoic organic matter and regional differences in maturity. Therefore, the paper suggested that the prospecting and assessment on hydrocarbon resources in Tibet Plateau should focus on the influence of the Himalayan tectonic evolution on oil-gas accumulation and preservation.

It is generally thought that the lower-middle Jurassic is the major source rock in the northern Qaidam Basin, of which the seventh member of the Dameigou Formation is a high-quality source rock. Aiming at further evaluating the hydrocarbon-generative potential of the lower-middle Jurassic in the east part of the northern Qaidam Basin, the present study systematically sampled mudstones，oil shales，black mudstones and coals from the lower-middle Jurassic Dameigou Formation and performed conventional geochemical analyses, including organic carbon，S₁+S₂，I _H，bitumen A，total hydrocarbon，the ratio of H/C and O/C，carbon isotopic composition of kerogen (δ¹³C)，composition of regular steranes and etc.. The results showed that the hydrocarbon-generative potential of the first member of the Dameigou Formation was as good as that of the seventh member，which was the first positive recognition on source rocks of the first member of the Dameigou Formation in the northern Qaidam Basin. This recognition was also supported by the palynofacies and kerogen type investigations of the Dameigou Formation. Therefore, it is suggested that the first member of the Dameigou Formation should deserve more attentions in the evaluation and exploration of the lower-middle Jurassic in the east part of the northern Qaidam Basin.

Gaseous alkanes from the Xujiaweizi fault depression in the Songliao Basin are characterized by heavier stable carbon isotopes, mostly showing a inverse order or a reverse order. It is still in debate whether these gases are biogenic or abiogenic. To determine the potential origin of these natural gases, a series of experiments concerning the generation and synthesis of gaseous alkanes have been conducted. Mantle-derived carbon dioxide sampled from the Xujiaweizi fault depression was used to synthesize hydrocarbon gas through the Fishcher-Tropsch reaction, and the produced gaseous alkanes yielded a normal stable carbon isotope trend. Meanwhile, some source rocks with low maturity were sampled from the Shahezi Formation to conduct pyrolysis experiments, the produced gases were then determined for chemical components and stable carbon isotopes. Based on the possible end-member gases in the Xujiaweizi fault depression and geological conditions, the produced gases generated by shales and coals at different heating rate were mixed to determine the trend of stable carbon isotopes. The results showed that the mixed biogenic end-member gases could also lead to an inverse stable carbon isotopic order, whereas the mixed abiogenic gases are not necessarily reversal. Integrated with the results of pyrolysis experiments discussed in this paper, comprehensive analyses both on gases released from modern volcanic springs and on source-rock characteristics of the Xujiaweizi fault depression have suggested that natural gases from the Xujiaweizi fault depression are mainly biogenic.

Since the commercial oil flow was discovered in the Damoguaihe Formation (K₁d) in the Hailar Basin recent years, the hydrocarbon source, genesis mechanism and resource potential of this formation have been a focus of attention. The present paper discussed the oil genesis mechanism by making oil-source correlation and combining the gas and oil inclusions  with homogenization temperature and alteration of maturity. Oil-oil correlations indicated that physical properties of crude oils, distribution of n-alkanes, parent material types and sedimentary environments of the K₁d and the Nantun Formation (K₁n) were very similar in the southern Wuerxun Sag. The maturity of crude oils in the K₁n was a bit higher than that in the K₁d, while they were both mature crude oils and might be derived from the same source. Oil-source correlations demonstrated that crude oils from these two layers mainly originated from the source rock of the K₁n. The distribution of grains with oil inclusions (GOI )and maturity variations of these oils indicated that oils in K₁n and K₁d were not associated and the formation of oil pools in the K₁n occurred earlier than that in the K₁d. Oil pools in the southern Wuerxun Sag were secondary reservoirs that accumulated due to the regulation of paleo-oil pools of the K₁n. Crude oils in the southern Wuerxun Sag were characterized by “the hydrocarbon accumulation of two periods” and “the early accumulation and the late regulation”. During the middle period of the Yimin Formation (K₁y) sedimentation, oils derived from the source rock of the K₁n migrated laterally for a short distance and accumulated in reservoirs of the same layer because of the sealing of faults. At the end of the K₁y and Qingyuangang Formation (K₂q) sedimentation, inversion occurred in the basin and a folding inversion was generated in the sub-sag of the southern Wuerxun Sag, resulting in a strong movement of faults in the east limb, the destruction of the K₁n reservoirs and the regulation of the oil from the K₁n to the K₁d to form secondary oil pools later, therefore, oils of the K₁d were mainly accumulated on inversion structures.

The Leikoupo Formation in Sichuan Basin was deposited in a restricted evaporative platform or margin platform environment. Exploration practice has indicated that in the Leikoupo reservoir developed two kinds of grain shoals, i.e. intra-platform shoal and marginal-platform shoal, which are distinctly different. With thorough analyses on characteristics and formation conditions of these two shoals, the present paper showed that the marginal-platform shoal had a wave base up to 20 m in maximum and a large available space for sediments, forming shoals with big thickness for an individual one and less exposure. Greater static pressure of overlying formations resulted readily in a trellis support for grains and the decreased throat port, favoring the preservation of intergranular space within shoals and the formation of reservoir space dominated by residual intergranular pores (dissolved enlargement). While the intra-platform shoal had a wave base ranging generally between 2～3 m due to a shelter of the marginal-platform environment and grain shoals developed in local micro-topographic highland with minor thickness and frequent exposure. Fresh water in the early atmosphere might influence the middle and upper parts of a mono-cyclic intra-platform shoal, resulting in the reservoir space dominated by intragranular karst and moldic pores.A material basis laid by environments is a key to diagenetic and porous evolutions at the late stage, exerting an effect on the final reservoir features of grain shoals.

An important progress has been made in exploring the crystal basement of the Xinglongtai buried-hill in the Liaohe Depression recent years. The deep drilling, such as in wells Xg7 and Xg8, has proved the existence of large-scale buried-hill inside reservoirs with a thousand-meter-range oil show, which have approximately one hundred million tons of reserves. An in-depth study on drilling cores and rock cuttings revealed that the Archaeozoic Xinglongtai crystal basement was made up of metamorphic and magmatic rocks, the former constituted mainly the buried-hill, while the latter formed hysterogenic viens dominated by well-developed neutral-acid magmatic rocks with a thickness from 1 to 50 meters and distributed at intervals in archaic metamorphic rocks of the buried-hill. A correlation of lithology with logging traces was established by studying physical properties of rocks, the lithology of crystal basement was identified through the dynamic integration of logging curves such as GR, DEN and CNL. The reservoir space of the buried-hill consisted mainly of tectonic fractures and broken intergranular pores. The development of reservoirs significantly depended on differences in lithology and the extent of tectonic reworking, namely, lithology was the primary factor under the same stress or vice versa. A predominant lithologic series was formed usually based on the quantity of dark minerals. These updated achievements have effectively guided the reserve calculation, exploration and development of the Xinglongtai buried-hill.

The Fushan-Keliyang area is situated in the eastern segment of the western Kunlun arc tectonic belt, providing key constraints for studying deformation characters of the western Kunlun piedmont thrust belt. Combined with geologic survey, drilling data and recent high-resolution seismic profiles, this study analyzed the Cenozoic deformation characters of the Fushan-Keliayang area. The present paper proposed that the studied area consisted of three ranges of structural belts from south to north, i.e. Fusha, Kekeya and Guman-Heshitag, of which the Fusha structural belt showed obviously lateral variations in configuration characters. Among these structural belts, the deformed timing of individual structural belts got younger northward, displaying characters of “break-forward” deformation. Within the each range of structural belts, deformation propagated from west to east. Based on the balanced section calculation, the total shortening of the Cenozoic structural belts in the Fusha-Keliyang area accounted for 54.5 km and the shortening rate was 35.9%. Therefore, the Cenozoic deformation greatly controlled hydrocarbon accumulation, and deep structures of the Fusha structural belts were considered to be the best target for hydrocarbon exploration.

The Tuositai Anticline, which locates in the western section of the southern Junggar Basin foreland, has been strongly deformed. It is a complex superimposed fault-related fold in the piedmont of the northern Tianshan Mountains with rich fault-related folding marks exposed on the surface.Basing on geometric analyzing of a 2-D seismic line through the Tuositai Anticline constrained by the surface data and the well information, the present paper established the reasonable structural geometric model of the Tuositai Anticline.And then, a geometric numeral simulation cooperated with the geometry of the fault-related folding was developed, and its kinematics are also reconstructed by constructing a series of forward balanced geological cross-sections. The study results indicates that the Tuositai Anticline is a superimposed fold, and its thrusting and corresponding structural overlapping has been experienced several times. During the Jurassic to the Cretaceous, two southern dipping thrust faults had developed at the southern limb of the Tuositai Anticline,which forming a duplex structure, with the Jurassic and the Pre-Jurassic formations were thrust from south to the surface. After that, during the late Himalayan orogeny, another south dipping blind thrust have developed under the pre-existing duplex Tuositai Anticline, thus forming the present Tuosital Anticline with a total 12 km displacements.

Many fault traps occur in the Zhu Ⅰ Depression in the Pearl River Mouth Basin because of well-developed faults. Researches on drilled fault traps in the depression revealed that both the lateral seal and the breakdown intensity of faults in the oil source province and its vicinity mainly determined how risky the drilling was. This paper used arithmetic products (SDD) of the shale content in fault rocks, the burial depth of fault rocks and the cosine of fault dip to quantitatively express the lateral sealing of faults indirectly, and applied products of the quotient derived from the division of the fault throw resulting from re-activities after the reservoir formation of fault traps by the ancient fault throw during the reservoir formation of fault traps and the frequency number of fault activities to quantitatively express the extent to which fault rocks were destroyed. By drawing a scatter diagram revealing the correlation of the success rate of drilling with the SDD and the breakdown intensity of fault rocks, the paper determined critical values of both the SDD and the breakdown intensity of fault rocks, which were required by a successful drilling of fault traps in various zones of interest. Consequently, a risk assessment plot of drilling in undrilled fault traps was worked out based on these two critical values in order to predict the drilling risk of undrilled fault traps. The prediction result showed that among the twelve fault traps to be drilled in the zone, five of them were less risky if drilled and the rest were too risky to be drilled.

Ordovician carbonate fracture-cavity reservoirs in the Tahe Oilfield are a special type of reservoirs, in which fractures and cavities constitute the main reservoir space. In the Tahe area, the development of ancient karst is closely related with the regional tectonic evolution because Ordovician carbonate reservoirs in the Tahe Oilfield experienced karstification in the middle Caledonian and early Hercynian, and the karstification of the long-term exposed weathering crust during the early Hercynian played a major role in controlling the development of these karst reservoirs. Based on the geological survey of palaeokarst outcrops of the Yijianfang, Liuhuanggou, Sandaoban and Wudaoban regions in the northern margin of the Tarim Basin, developmental characteristics of reservoirs in the Tahe Oilfield revealed that there were three developmental patterns of the fracture-cavity system in Ordovician carbonate reservoirs: i.e. underground river system, karst caves, and corroded pores and fissures, of which the former two were the most dominant types for the reservoirs. The fracture-cavity system developed well in the vicinity of fault belts, and the horizontal distribution of the fracture-cavity system was controlled by palaeo-geomorphology. For instance, karst caves were extremely well-developed in peak-cluster of a karst platform, and then in knob-and-kettle topography on gentle karst slopes and in rugged country of valleys. Vertically, the development of karst cavities was apparently of zoning and superficial karst belts were the most important segment for karst development.

Base on theories related to fluid mechanics and seepage mechanics, a mathematical analysis model that couples the wellbore conduit flow and formation seepage was established to deal with the situation that a stepped horizontal well traverses three independent fault-block oil layers. Based on the mass conservation law and micro-unit line-congruence theory, the model analyzed the influence of inflow on the pressure drop within wellbore for horizontal production sections and educed an equation to calculate the pressure drop of a production section in stepped horizontal wellbore. A method to calculate the pressure drop under the condition of different curvature radius was proposed for linking sections of various oil layers. Meanwhile, since different fault-block oil layers traversed by a stepped horizontal well have different production capacity, the resolution based on a mathematical model was educed along with a corresponding computing program. With the utilization of this analysis model, the distribution of on-way pressure of stepped horizontal wellbore as well as the output at different positions could be predicted. The analog computation indicated that the output was influenced both by the production capacity of each oil layer and by the flow friction of horizontal wellbore, moreover, it is more favorable to exploitation if oil layers with better and worse physical properties were located, respectively, at the heel and toe of horizontal wells.

Relative permeability curves are the main characteristics of two-phase fluid flow in laboratory test. In light of the relative permeability curve and material balance principle, the present paper, based on different relative-permeability curve patterns, deduced the generalized Arps decline model under the voidage balance condition, i.e. exponential, hyperbolic and harmonic decline equations. The paper also analyzed the conditions under which the generalized model was simplified into a conventional one and described the important impact of oil-phase relative permeability characteristics on parameters of production-decline types and models. The application results indicated that the generalized Arps model could effectively describe the production-decline rule of low-permeability reservoirs. The curve patterns of oil-phase relative permeability determined the decline type, the faster the oil-phase relative permeability declined, the greater the output-decline rate was.

In view of nonlinear seepage characteristics during the flow of fluids in low-permeability reservoirs and the effect of the starting pressure gradient, the present paper established a mathematical model for the 3D oil-water phase seepage numerical simulation of reservoirs by integrating both nonlinear seepage and pseudo-linear seepage. The model for numerical simulation of low-permeability reservoirs was constituted by means of the fully implicit difference format and the preconditioned conjugated gradient method was applied to solve this model. The calculations of homogeneous reservoirs in the five-spot pattern and a certain block in the Daqing Oilfield indicated that the starting pressure gradient had a strong influence on the pressure distribution of low-permeability reservoirs. By the constant output, the greater the starting pressure gradient, the bigger the pressure variation and the larger the influenced area. Since the nonlinear flow formulation could describe both the flow behavior of fluids under a lower pressure gradient and the effect of the minimum starting pressure gradient in low-permeability reservoirs much better, the pressure calculated by the mathematical model using nonlinear flow formulation varied more gently than that using pseudo-linear flow formulation, thus, the model using nonlinear flow formulation is more practical for the exploration of low-permeability reservoirs.

A novel preformed particle gel (PPG) as a chemical EOR was screened out by means of the rheometer, interfacial tensiometer, laser particle analyzer, microscopic oil displacement and physical simulation of oil displacement. The present paper evaluated its properties in application, investigated the mutual interaction between the PPG and other polymers or surfactants, designed a heterogeneous combination flooding system (HCFS), and appraised the EOR effect of this new system under the condition of high-temperature, high-salinity and after-polymer-flooding reservoirs in the Shengli Oilfield. The results indicated that PPG could not only migrate and penetrate through porous mediums, but also generate a more significantly sweeping efficiency by means of piling up, plugging, pressure rising and deforming at throats to modify the existing dominant migration paths, and it was of a greater volumetric-expansion capacity than conventional polymers. Because the combination of the PPG and polymers could enhance the viscosity and viscoelasticity of a system, the heterogeneous combination flooding system (HCFS) composed of the PPG, surfactants and other polymers is of a displacement efficiency similar to the combination flooding. Under the experimental condition of a dual sand-packed tube flooding with the interlayer heterogeneity of (1000∶5000)×10^-3 μm², the HCFS could improve the oil recovery by 22.5% for HT/HS reservoirs in the Shengli Oilfield and by 19.1% for the Ng3 reservoirs after polymer flooding in the Zhong-1 section of the Gudao Oilfield.

Compared with the transportation of slurry,the flow of mixture of heavy oil and sand in horizontal wellbore is different.From the toe to the root of wellbore with the inflow of formation fluid,the flow rate of wellbore gradually increased,which make the flow condition in the horizontal wellbore alter with the increase of flow rate.According to the method of liquid-solid two phase flow,the flow pattern in horizontal wellbore change in turn from the combination of heterogeneous suspension layer,moving bed layer and stationary bed layer to heterogeneous suspension layer.With the alternation of flow pattern,the flow parameters in wellbore such as pressure gradient,the height of moving bed layer and stationary bed layer will also change,which make the sand carrying capacity of heavy oil change.Based on above-mentioned theories,this paper sets up a sand carrying model of heavy oil considering variable mass flow in horizontal wellbore,and calculates the distribution of pressure gradient,the height of moving bed layer and stationary bed layer in wellbore,which help to appraise the sand carrying capacity of heavy oil.

Reservoir hydrocarbon saturation is the basis of reserve estimate.Rock electricity parameter is one of important factors when using Archie equation to calculate reservoir oil/gas saturation.This article utilizes airdrying and imbibition to establish water saturation of carbonate rock core,compares the experimental method of rock electricity parameters.The porosity of carbonate rock samples used in experiments ranges from 0.5% to 6.2% and the permeability is less than 1×10^-3 μm². Results show that,due to the complexity of pore configuration and the wettability of carbonate rock,the rock will not absorb more water when water saturation reached a critical value,actually the maximum of water saturation always less than 50% by imbibition.Compared the resistivity of lower saturation rock by imbibition with the samples which were full saturated by simulation formation water,the latter R_o  always displays a higher value,on the relationship between resistivity and saturation,most of the resistivity values with full saturation diverge from the extension value which matched from the resistivity point of low saturation samples.The coefficients n and b derived from airdrying and imbibition are quite different,but the change tendency is unanimous,and the coefficient  n has a great correlationship with porosity,that is, n decreases with the increase of porosity.However,it is difficult to set various saturation of carbonate rock with low porosity and permeability in rock-electrical experiment.Due to water/gas migration law of carbonate rock gas reservoir and water/gas equilibrium process within gas reservoir,the rock electricity experimental relationship by airdrying method is better to meet the needs of gas saturation evaluation of carbonate rock gas reservoir.

Decomposing the complex geologic body to relatively simple units,based on analyzing the allocation relation between fracture occurrence and ground stress,the formulas of fracture permeability in the principal stress coordinate system were obtained by formula deduction,and computational formulas of the fracture permeability in the whole coordinate system were deduced through projecting the fracture permeability in each unit to the whole Cartesian coordinate system.Comparing several Cartesian coordinate systems which were used often in the process of numerical simulation modeling,each axis of the optimal selection coordinate system was demarcated: - dip、-strike、-vertical of the dominant fracture,permeability along each coordinate axis was calculated in this coordinate system not only can reflect the direction of the fracture permeability,but also reflect the effect of the different strike fracture on permeability,then make the calculated fracture permeability more practical significant.One optimal selection method was given and the relationship of several coordinate systems was illustrated by the application to practical modeling of Shigang-Qiaohekou area.

To shorten the waiting-on-cement time under deepwater and low temperature cementing conditions,the present paper dealt with the influence of a new lithium-salt accelerator on the low-temperature hydration capacity and property of oil-well cement and showed that the lithium-salt accelerator could enhance the low-temperature hydratability of C₃S and C₂S mineral clinkers by means of speeding up the breakdown of protective membranes and shortening the induction period of hydration.Affecting the initial consistency of cement slurry little,the accelerator could shorten the thickening time of the class-G cement slurry,significantly improve the early strength of set cement at low temperature,and show remarkable virtue of acceleration.The lithium-salt accelerator also hardly affected types of hydration products of oil-well cement and these hydration products were mainly composed of calcium silicate gel,calcium-hydroxide crystals and minor ettringite (AFt) crystals,consistent with the hydration product of pure oil-well cement except for denser microstructures than the conventional cement stone.

The synthetic drilling fluid system is currently widely applied in deep-water drilling operation.Meanwhile,the low temperature rheological property of the synthetic drilling fluid was one of the problems widely concerned in deep-water drilling.The present paper investigated effects of various factors,such as emulsifier types,organic clay addition,oil-to-water ratio and mud density,on the low temperature rheological property of the liner α-olefin synthetic drilling fluid by measuring its viscosity-temperature properties at different compositions.Then,the paper discussed the influence of base-oil types and viscosity on viscosity-temperature properties of the water-in-oil drilling fluid.The experimental results demonstrated that the low temperature rheological property of the liner α-olefin synthetic drilling fluid was significantly influenced by the emulsifier type,followed in turn by organic-clay addition and oil-to-water ratio,while weighting materials affected the low temperature rheological property of the synthetic drilling fluid much less.The low temperature viscosity of base oil was most decisive to the viscosity of the deep-water synthetic drilling fluid system.The liner α-olefin synthetic drilling fluid was superior to the mineral-oil-base and gas to liquid-base drilling fluids in low temperature flowability,being applicable to deep-water drilling operation.

The formation of gas hydrate caused by shallow gases is one of the most potential hazards in deepwater drilling.Gas hydrate can exist steadily under the circumstance of low temperature and high pressure.Once it generates in deepwater drilling pipes,severe blocking will occur in an air tube, conductor,riser or subsea blowout preventer (BOP) and can not be readily eliminated,which may badly endanger the security of both engineering operators and drilling platforms.The present paper primarily investigated the effects of agitation conditions,bentonite contents and additives of drilling fluids on the gas hydrate formation by means of a newly-developed simulating apparatus for the assessment on inhibiting the gas hydrate formation.The investigation indicated that the existence of either agitation or bentonite could promote the formation of gas hydrate,while most of drilling fluid additives could only inhibit to a certain extent the formation of gas hydrate.The performance of commonly used inhibitors was dealt with and experimental results showed that the dynamic inhibitor could not restrain the formation of gas hydrate completely and its optimum dosage was 1.5%;meanwhile,the thermodynamic inhibitor could ultimately terminate the formation of gas hydrate if its dosage was great enough,in which NaCl was better than glycol.A good synergism of the dynamic and thermodynamic inhibitors could be achieved by confecting them in different proportions and a formula,fit for the 3000 m deepwater drilling,was worked out based on the experimental selection.

Wellbore collapse is one of the main obstacles that prevent horizontal wells from the extensive use in coal seams.Coal rock mass has a great number of cleats and some fragmented zones,and is of low strength,so it is a great risk to drill in coal seams.Middle or high rank low-strength coal dominates in the Qinshui Basin,Shanxi Province.Hence,when water is used as a drilling fluid,it is easy for wellbore to collapse and the bottom hole assembly is readily buried underground.Especially for horizontal wells,the number of wells that collapsed has occupied about 32.65% of the total in the Qinshui district by January,2008.According to the concept of the discrete element method(DEM),problems of wellbore stabilities in coal beds can be attributed to a discontinuous problem.Coal rock mass is usually divided into small blocks by face cleats and butt cleats.Face cleats and butt cleats,on one hand,are regarded as boundaries between blocks,and on the other hand，act as a medium with which blocks interact.3DEC is a three-dimensional numerical program based on the discrete element method for discontinuum modeling.The present paper applied 3DEC to analyze horizontal wellbore stabilities in coal beds based on the core experimental and field-test data from the Qinshui Basin.Techniques of the virtual joint modeling and inside-outside two-layers modeling were used.The virtual joint modeling allowed a random generation of possible joints and a dynamic fracture analysis,and the inside-outside two-layers modeling could decrease amounts of computations and eliminated effects of boundaries.The actual distribution of both face and butt cleats in the No.3 coal seam of the Qinshui Basin was modeled by applying the above-mentioned modeling techniques.Influences of the strike of wellbores,hole diameter,bottom-hole pressure,and the density of cleats on wellbore stabilities were analyzed,respectively.The results demonstrated that when the strike of face cleats was perpendicular to that of wellbores,face cleats exerted hardly any influence on wellbore stabilities; when the strike of face cleats was parallel to that of wellbores,wellbores were the most unstable. Furthermore,the larger the hole diameter,the more unstable the wellbore; the larger the density of cleats,the poorer the stability of wellbores; and the higher the bottom-hole pressure,the more stable the wellbore was as seepage was excluded.

In drilling process，the stick-slip oscillation of a drill bit can lead to stalling and an equipment failure of the drilling-rig rotary system,which reduces the drilling permeability and increases the drilling cost.In order to solve those problems,the present paper built a model to describe drilling-rig torsion characteristics and presented an adaptive PID control strategy to restrain the stick-slip oscillation of a drill bit.The paper proposed that the input state of the drilling-rig rotary system should be controlled linearly to compensate for the stick-slip oscillation caused by nonlinear characteristics of drilling rigs.The adaptive PID control was designed to ensure the tracking control and the optimal operating status of the system output when parameters of the drilling-rig rotary system were greatly variable and uncertain.Moreover,the adaptive PID control could elevate the speed of dynamic response and shorten the adjustment time of the system.A simulation experiment was conducted on models of drilling-rig torsion characteristics and the friction torsion between a drill bit and rocks.The results demonstrated that the adaptive PID control could restrain the stick-slip oscillation of a drill bit effectively,improve characteristics of the dynamic and static response and enhance the stability and reliability of the drilling-rig rotary system.

Location optimization of drilling platforms is one of the key problems in the cluster-well drilling technology.The present paper,based on the distribution of geological targets,took constraints of the minimal sum or quadratic sum of the total horizontal displacement of targets,the minimal sum of the total length of wellbores,or the minimal sum of the total drilling cost as the conditions to determine optimized criteria (target functions) for optimizing platform locations of wells to be drilled immediately,set up a mathematical programming model for the location optimization of drilling platforms of cluster wells,and discussed solution ways to this model by means of the genetic algorithm.Analyses of examples demonstrated that the mathematical programming model and solution ways established by this paper could optimize drilling-platform locations under the precondition of taking surface constraints such as environmental factors into integrative considerations,meet requirements of safety-drilling field constructions,reduce the cost of drilling largely and make a full use of superiority of the cluster-well drilling technology.All of these are of theoretical and practical significance to the drilling and exploitation of cluster wells.

The present paper proposed an efficient algorithm employing the proper orthogonal decomposition (POD) for the computation of the normal operation,shutdown and restart processes of buried heated pipelines.Firstly,the finite volume algorithm and finite difference algorithm were adopted to generate fundamental samples,and then eigenfunctions of the oil and soil temperature fields after pipeline shutdown and the restart flux were obtained by means of the singular value decomposition (SVD) algorithm.Further,spectral coefficients under the condition of arbitrary computation parameters were calculated by interpolation and finally the relevant physical quantities were rebuilt.By using this new algorithm,pipeline restart parameters under other conditions could be obtained very efficiently and accurately only by means of numerical computations with fewer input data.Case studies demonstrated that the deviations between the POD simulation and the direct numerical computation were less than 0.05℃ for temperature and 3% for the flow rate,respectively.Therefore,the computation efficiency was improved greatly by using the POD algorithm,and the average time consumption for the computation of one-group input data was about 20 min by using the numerical algorithm,while the POD algorithm averagely took only 0.1s or even less time.

In view of frequent occurrences of drill-string failure under complicated geological conditions and the less effectiveness of preventive measures,the present paper applied the fault tree analysis (FTA) of the graph theory to interpret the logical relationship of an inducement of drill-string failure and related control measures,established a fault tree model for drill-string failure,and analyzed paths of drill-string failure and the optimal prevention ways by using the least cut-set and the least path-set.The drill-string failure analysis in the northeastern Sichuan exploration area was taken as a case study.The results indicated that the probability of drill-string failure in the study area obtained by quantitative analysis of fault tree was 56.81%,consistent with the actual statistics.The case study proved that the drill-string failure analysis based on FTA was feasible,the structure of the fault tree involved was reasonable and the calculation results were truthful and reliable.Meanwhile,the calculation of importance magnitude by fault tree for basic events provided the drill-string failure prevention and control with a theoretical basis,which enhanced the pertinence and practicality of prevention and control measures.

In the condition of the stratum temperature,ADSA (axisymmetric drop shape analysis) has been utilized to investigate the equilibrium interfacial tension of CO₂ / crude oil and N₂ / crude oil systems under different pressures.It turns out that crude oil and supercritical CO₂ had intense mutual diffusion in the initial stage of their mixing.The light components of crude oil were extracted by supercritical CO₂.And the higher the pressure was,the stronger the extraction was.Crude oil and N₂ also had the diffusion but not obvious within the pressure range (less than 36MPa) in this experiment.The test results indicated that the equilibrium interfacial tension of two systems decreased as the systematic pressure increased.In addition,the equilibrium interfacial tension values of CO₂ / crude oil decreased more than N₂ / crude oil system.The relation between equilibrium interfacial tension and pressure was approximately linear in N₂/crude oil system; while in CO₂ / crude oil system,the equilibrium interfacial tension decreased sharply with the pressure less than 17.7 MPa,and the equilibrium interfacial tension only decreased appreciably with pressure over 17.7 MPa.

Geological model is the most representative and comprehensive achievement of development geology researches,which is compromised of reservoir sedimentary characteristics,reservoir heterogeneity,petrophysics and formation fluid characteristics.As the only effective mean to supply quantitative data directly to reservoir engineering and numerical simulation,geological modeling has shown its importance increasingly.Base on the analysis of quantitative geology,multidisciplinary reservoir geology,different types of geological model and reservoir modeling method,the main achievements on reservoir geological modeling of China in the past two decades were summarized.At the same time,it was pointed out that geophysical application,coal bed methane and shale gas reservoir modeling,reservoir architecture modeling and multidisciplinary integration would be a development trend.

In order to deeply research a model for both controlling hydrocarbons and predicting favorable exploration zones of the Tazhong palaeouplift in Tarim Basin, this paper focused on the tectonic evolution of the Tazhong palaeouplift and the distribution of different reservoirs. A three-epoch tectonic evolution was identified for the Tazhong palaeouplift, i.e the Late Caledonian, Late Hercynian and Himalayan, and a reservoir controlling model for two classes (inner or outside of buried hill) and eight types was established for the Tazhong palaeouplift. Outside the Tazhong palaeouplift buried hills, Carboniferous and Silurian clastic anticline reservoirs, stratigraphic or lithologic reservoirs and fault-block reservoirs occurred at top parts of the palaeouplift and slope, while within the palaeouplift buried hills, Ordovician and Cambrian carbonate weathering-crust reservoirs occurred at the top, reef-flat reservoirs in the lateral margin, and karst and fractured reservoirs at the lower part of the palaeouplift. The mechanism of the reservoir control by the palaeouplift, which contains various traps and carrier systems indicating favorable direction of hydrocarbon migration, was discussed. The research predicted that the Tazhong main horst zone was the most favorable exploration area for fault-block reservoirs, anticline reservoirs and carbonate weathering-crust reservoirs, the Tazhong No.10 structure zone was the favorable exploration area for stratigraphic reservoirs, anticline reservoirs and carbonate karst reservoirs, and the Tazhong No.1 slope break zone was the favorable exploration area for lithologic reservoirs,carbonate karst reservoirs and buried-hill inside fractured reservoirs.

In the northern slope of the Tazhong palaeouplift, large-scale high-quality reservoirs with karst fractures and cavities are well developed along the unconformity of the top part of the Ordovician Yingshan Formation, where the cumulatively proved oil in place is nearly 200 million tons. The reservoir space of these karst reservoirs is dominated by large fractures and vugs, penetrating through a depth of 200 m below the unconformity. These fractures and vugs are characterized by the superimposition of fractures and vugs with heterogeneous change and by a banded distribution. These reservoirs are not only related to ancient karst topography, but also controlled by many other integrated factors, such as multi-origins, multi-phase diagenetic dissolution, fracture cracks, superimposition of burial dissolution. The fracture and fracture network is a major percolation channel of karst water. And the unconformity karst controls the horizontal distribution scale of reservoirs, and burial dissolution is a key for the optimization of reservoirs. By detailed investigations on these main controlling factors, a model for the superimposed development and evolution of reservoirs was established and a comprehensive forecast for favorable zones of reservoir development was made as well. It was pointed out that it was necessary to pay attention to differences in reservoir types and main factors between different well blocks, and finally an optimal selection of main controlling factors was made for exploration guidance.

The influences of thermal alteration, evaporation fractionation and water washing on the Carboniferous oils were evaluated by using chemical and isotopic compositions of light hydrocarbons (C₆—C₈) in Carboniferous crude oils from the Tz4 Oilfield, NW China. The results suggest that hydrocarbons in the CI Fm and CII and CIII Fms have distinct accumulation processes. Compared with C₆—C₈ in the CII and CIII Fms, C₆—C₈ in the CI Fm contain more normal alkanes, but less cycloalkanes and aromatics resulting in greater ratios of normal (branched) alkanes to cycloalkanes, and are comparatively depleted in  ¹³C. These results indicate that hydrocarbons entrapped in the CI Fm are derived from a relatively less matured kerogen, which is consistent with the conclusion based on the biomarkers in the aromatic fraction of these oils. Water washing during petroleum secondary migration along carrier bed has a relatively minor influence on oils in the CI Fm, while oil cracking and evaporation fractionation have important role in regulating the chemical and isotopic compositions of light hydrocarbons in the CII and CIII Fms. Therefore, it is commonplace that different generative oils mix together within the CII and CIII Fms. Oil cracking probably occurred in the deeply-buried Lower Ordovician and Cambrian paleo-reservoirs through geological time scale, these thermally altered oils migrated upward along faults and finally accumulated in the Carboniferous; natural gases from hydrocarbon secondary cracking should have a critical implication in forming gas accumulations in this region recently.

The Cretaceous Bashijiqike Formation is one of the high-quality sandstone reservoirs and a primary oil/gas-producing bed in the Kuqa Depression of Tarim Basin. As its burial depth is more than 5000m and cores are limited, the prediction of effective reservoirs in the Dabei-Kelasu deep structural belt is considerably difficult. Four methods, including the model-based prediction, envelop curves of porosity from logging data, the ration of effective reservoirs to sandstones and the forward modeling for Basin Modeling Software，have been used to predict the lower limit of buried depths of researched area. Due to the diversity of methods themselves and the data qualities, differences in methodological reliability and veracity by different methods existed in different structure areas. The “weighting” hypothetical valuation method that be common used in reservoirs valuation, by giving different weight coefficients based on the reliability of various methods, has also been used. Finally the lower limit of burial depth of effective reservoirs in the Dabei-Kelasu deep structural areas was predicted to be about 8000-8300 m, that Dabei area was about 8200 m, Keshen area was about 8300 m, the north and south of Keshen area were about 8100 m, the northern of Baicheng area was about 8000 m. The ratio of effective reservoirs to sandstones is an important parameter for the evaluation of deeply-buried reservoirs, the burial depth of deep reservoirs and the ratio of effective reservoirs to sandstones of the Bashijiqike Formation in the Dabei-Kelasu deep structural belt had a third power relationship, by which the burial range of reservoirs could be used to inversely predict the thickness of effective reservoirs.

Spore-pollen assemblage and compositions of organic matter revealed that organic matter of Tertiary marine source rocks in the northern South China Sea mainly originated from terrestrial higher plants, and the formation of such source rocks was closely related with depositional environments favorable to the living of terrestrial higher plants, such as fluvial-delta, costal plain, etc.. Horizontally, marine source rocks deposited at the edge of a basin or depression generally had a high content of organic matter, but the content of organic matter was lower for marine source rocks deposited in the central part of a basin or depression, therefore, good marine source rocks with abundant organic matter occurred mainly in the edge area of a basin or depression. A transgressive system tract in the sequence stratigraphic framework could form a more reducing depositional environment that was preferable to the preservation of organic matter and could produce good marine source rocks. The study indicated that the marine source rock in the Zhuhai Formation contributed obviously to oils found in the deep-water area of the Baiyun Depression of the Pearl River Mouth Basin. Marine source rocks were probably the major source rock for adjacent basins or depressions of the deep-water area in the northern South China Sea.

The north slope of the South China Sea is structurally characterized by a passive continental margin and has various Cenozoic oil- and gas-bearing depositional basins, where hydrocarbon resources are abundant, and the geological and tectonic settings, the temperature and pressure regimes as well as the methane-generative potential of thick organic-rich sediments are all favorable for the formation of gas hydrate. As a result, this region is also an ideal area for studying gas hydrate accumulations. In order to understand natural conditions of the gas hydrate formation, based on the typical 2-dimensional seismic image of the Shenhu area, a geological model of gas hydrate reservoirs was established and a dynamic simulation of gas hydrate accumulations was carried out as well. The results indicated that the temperature and pressure of the Shenhu area are appropriate for gas hydrate accumulations, source rocks there have a huge gas-generative potential and hydrocarbon migration conditions are favorable, providing an abundant gas source and good pathways for the gas hydrate formation. A forecasting model of the gas hydrate formation was given based on basin analysis, indicating that the Shenhu area is a better prospect area of gas hydrate because of its huge potential of gas hydrate resources.

The exploration practice and integrated sequence-stratigraphic studies for years demonstrated that the Oligocene-Miocene boundary was an important transfer interface of sedimentary-tectonic-climate conditions in the Pearl River Mouth Basin and corresponded to the Baiyun movement(in about 23.8 Ma), during which the seafloor spreading ridge of the South China Sea jumped, was deflected and accompanied with material source changes of the paleo-Pearl River. This event resulted in the shift of the shelf slope-break zone from the neighborhood of the southern uplift area of the Baiyun Depression in late Oligocene to the northern slope in Miocene. Moreover, the shelf slope-break zone has basically stood there since about 21 Ma. In Oligocene-Miocene, two shelf slope-break zones with different development types and locations controlled the development of the two different sequence units in the Baiyun Depression, i.e. a depositional shelf slope-break zone extending in NNE orientation shifted from NW to SE until 23.8 Ma and developed a regressive progradation sequence unit in the Zhuhai Formation, and subsequently, another shelf slope-break zone with NE strike has stood steadily around the north slope of the Baiyun Depression since 21 Ma and formed a transgressive aggradation sequence unit. Moreover, the migration of shelf slope-break zones also controlled the development of prospective reservoirs and hydrocarbon accumulation belts(including shallow marine delta with relatively
abundant sand, lowstand shelf-edge delta and deepwater fan sandstones in the continental slope of the Pearl River) within various sequences of the Baiyun deepwater area. It was confirmed that both SQ23.8 and SQ21.0 third-grade sequences were the product of sedimentation corresponding to the Baiyun Movement, and they were of conditions to develop lowstand deepwater fans with most abundant sand in the Baiyun deepwater area. Integrated investigations basically demonstrated that reservoir-seal assemblages of the Oligocene Pearl River coast-delta-deepwater fan depositional system and Neogene deepwater deposits were major objective strata for further exploration. Up to now, natural gas discoveries in the Baiyun deepwater area and Panyu gas province have confirmed the control effect of the shelf slope-break zones on gas reservoirs, indicating a great potential of petroleum exploration in the Baiyun deep-water slope area of the northern South China Sea.

A great breakthrough has been made in oil exploration activities in deep zones of the Yanchang Formation in the western and southern-centeral Ordos Basin in recent years, where several hundred millions geological oil reserves have been confirmed. Therefore, it is of great practical value to study oil accumulations in deep zones of the Yanchang Formation in the Ordos Basin. The present paper revealed oil accumulation rules in deep zones of the Yanchang Formation by systematically investigating interrelationships between source and reservoir rocks, oil migration and accumulation, etc. The study showed that accumulations in deep zones of the Yanchang Formation were dominated by lithologic reservoirs with source rocks above, the oil accumulation was characterized by “provinces controlled by source rocks, plays controlled by sedimentary facies, and positions controlled by pressure difference of reservoirs”, specifically, deep provinces of the Yanchang Formation occurred in areas adjacent to source rocks, plays mainly occurred in superimposed linked areas of delta front subfluvial distributary channels, and most of reservoirs in the Member Chang 8 occurred in areas with relatively high abnormal pressure under the background of low abnormal pressure difference between the Member Chang 7 and Member Chang 8.