The Changqing Oilfield Company has extensively and efficiently developed reservoirs with ultra-low permeability between 0.3mD and 1mD. Based on the practice of petroleum exploration and development in Ordos Basin, the tight oil herein refers to the oil that accumulates in oil shale or interbedded tight sandstone reservoirs adjacent to source rocks and with surface-air permeability less than 0.3mD. Generally, this accumulated oil has not yet experienced large-scale and long-distance migration, and thus its accumulation includes tight sandstone and tight shale oil reservoirs. The tight oil of Yanchang Formation mainly develops in a semi-deep to deep lake zone, typically in the oil shale and tight sandstone of Chang-7 interval and the tight sandstone of Chang-6 interval of the central lake. Tight oil in Ordos Basin is characterized by a wide distribution, superior conditions of source rocks, tight sandstone reservoirs, complex pore-throat structures, poor physical properties, high oil saturation, better oil properties and low pressure coefficient. Wide development of nano-sized pore-throat systems is one of the fundamental characteristics for the oil and gas continuous accumulation of tight oil reservoirs. Most of the connected pore-throat diameters of tight sandstone reservoirs in Yanchang Formation are greater than the critical pore-throat diameter, gratifying the need of oil and gas to migrate in tight reservoirs. Reservoirs of the tight oil in Yanchang Formation can be divided into 3 different types depending on the contact relationship between tight reservoirs and source rocks, i.e. compact massive sandstone reservoirs, sand-shale interbedded reservoirs and tight reservoirs in oil shale. Tight oil is widely distributed in Chang-6 and Chang-7 intervals of Yanchang Formation in Ordos Basin, and it is preliminarily forecasted that the total resources of tight oil in Ordos Basin are about 30×10⁸t, of which the shale oil resource in Chang-7 interval exceeds 10×10⁸t, while the tight sandstone oil resource in Chang-7 and Chang-6 intervals amounts to about 9×10⁸t and 11×10⁸t, respectively. Therefore, tight oil resources are the realistic oil replacement resources that can ensure Changqing Oilfield to achieve an annual output of 5000×10⁸tons of oil equivalent and a long term stability of oil production.

Lots of hydrocarbon inclusions and bitumen have been measured in 90 sandstone samples from the Lower Cretaceous of Shaya uplift, Tarim Basin, and the evidence from these measurements can be used to trace the hydrocarbon migration and accumulation history of the basin. Four types of inclusions were determined in fluorescence observation, i.e. gas-liquid biphase oil inclusions, pure gas inclusions, oil-asphalt inclusions and aqueous inclusions. According to fluorescence properties（fluorescent colors, λmax and QF535) of the oil inclusion and combined with the employment of homogenization temperature of aqueous inclusions projected on a burial history diagram, three oil charging events were determined, and they took place in 12-5Ma, 5-2Ma and 2-0Ma, respectively. By the fluorescence spectral comparison of the oil inclusion with the crude oil from oil-prone source beds, it could be concluded that the first and the second charging oils originated from terrigeneous source rocks while the third charging oil was derived from marine ones. The marine oil is characterized by a lower maturity and later charging time compared with the continental oil. Its hydrocarbon accumulation occurred mainly during the middle-late Himalayan period, and is characterized by continuous and rapid charging.

Used high-resolution seismic data and combined with outcrop and drilling data, we analyzed structural characteristics of Kedong structure(the east segment of Keliyang-Fusha fault belt) in the piedmont of western Kunlun mountain, which, as a transpression structure, consists of mainly basement faults and shows a gently dipping backlimb(crest) and intensely-deformed forelimb. Growth strata reveal that Keliyang-Fusha faults formed a monocline(nose) structure by thrust in Pliocene with the deformation of limb rotation, that is to say the Kedong structure is a basement-involved structure. Later Keliyang-Fusha faults broke through the Kedong monocline and cut it into fault blocks, resulting in a suite of steeply-reversed strata exposed to the surface, which contained Jurassic-Cenozoic beds. Because deep fault blocks didn’t suffer intense deformation, they formed good traps for hydrocarbon accumulation. Drilling data of Well KD-1 indicated that such blocks are of good exploration potential.

This paper deals with mudstone sampled from the first member of the Cretaceous Qingshankou Formation in the Songliao Basin. We qualitatively and quantitatively investigated characteristics of its micropores using scanning electron microscope (SEM), field-emission SEM (FE-SEM), gas adsorption and high-pressure mercury-injection methods. The results indicate that there are mainly five pore types in the mudstone, including matrix intercrystal, organic, dissolution, intergranular and intracrystal pores as well as micron to nano microfissures. Pores in the mudstone are mainly composed of micropores and meso-pores with pore volume generally ranging from 0.0018 to 0.0300mL/mg, specific surface area from 0.91m²/g to 31.02m²/g and porosity from 1.2% to 3.9%. It is believed that compositions and concentrations of various minerals in the mudstone determine, to a certain extent, development of micropores. For instance, the mudstone porosity increases with increasing content of organic matter(OM), illite or pyrite but decreases with increasing content of chlorite, quartz, calcite or anorthose. Moreover, the mudstone porosity has a poor correlation with content of kaolinite, indicating that abundance of kaolinite may not affects variations of mudstone porosity.

Crude oils from Dongying and Shahejie Formations of BZ35/36 structures in Huanghekou sag, Bohai Bay Basin are characterized by high density, high viscosity and high sulfur, these physical properties and geochemical features are quite different from crude oils in other structures of Huanghekou sag. The comparison and analysis of biomarkers, including Pr/Ph, C₂₄Te/C₂₆TT, C₂₉20S/（20S+20R） and C₂₉ββ/（ββ+αα） ratios, and gammacerane, show that sulfur-rich oils in these two structures have an affinity with the high-sulfur oil in Miaoxi sag adjacent to the eastern Huanghekou sag. The high-sulfur low-maturity crude oil of Miaoxi sag was charging from northeast to southwest, while the low-sulfur mature crude oil of Huanghekou sag was charging in the opposite direction. Because these sags had comparatively high hydrocarbon generative potential, crude oils derived from them gathered in BZ35/36 structures that lie in the hydrocarbon charging path. By analogy with the same type of high-sulfur crude oils, a preliminary conclusion can be drawn that source rocks of the sulfur-rich crude oils are formed in a dry climate and strongly reducing saline lake with abundant living beings.

Water-rock interaction acts as a bridge between the diagenetic mineral evolution and formation water ion change，through which minerals and formation water keep the water-rock system equilibrious, taking on a reciprocal relationship between them and giving proof of water-rock interaction. The present paper discussed the mechanism and conceptual model of water-rock interaction by comprehensively investigating microcosmic characteristics of minerals and chemical characteristics of formation water in Xujiahe Formation of the study area，the result showed that different water-rock systems，host-rock matrices and backgrounds of formation water are the key reason for the difference in water-rock interaction mechanism between member 2 and 4 of Xujiahe Formation. Feldspar in Member 2 of Xujiahe Formation is effectively preserved due to a higher K⁺/H⁺ activity ratio，while the feldspar-depleted material source is the most significant reason for the absence of feldspar in Member 4 of Xujiahe Formation, moreover, the dissolution of feldspar caused by a lower K⁺/H⁺ activity ratio can also result in the lower concentration of feldspar. Feldspar dissolution, authigenic mineral precipitation and clay mineral transformation are controlled mainly by the slowest reaction process in the ternary system of feldspar corrosion，ionic migration(K⁺) and illitization. Carbon and oxygen isotopes of carbonate cements indicated that Member 4 has an open water-rock system because of more acidic fluid than Member 2. The lack of organic CO₂ in Member 2 of Xujiahe Formation was supposed to be related with less acidic fluid，marine lime argillutite as a source rock and the denudation caused by tectonic uplift，and to be less affected by the fractionation of CO₂ migration. Based on these，we established conceptual models of water-rock interaction for aluminosilicate and carbonate rocks, respectively. Argillutite was proposed not to be a sealing factor but the first open object in a water-rock system, moreover, some argillutite(coal bed), as a material contributor and receiver, was thought indispensable in a whole water-rock system.

Tectonic stress is one of the comparatively active energies in the earth’s crust. It is of guiding significance in oil and gas exploration and development to study tectonic stress patterns and transformation processes. Through studies on upright folds, conjugate joints, slickenside on fracture planes and other structural vestiges, we rebuilt the Late Mesozoic-Cenozoic tectonic stress field of Xuanhan-Daxian region and examined regular patterns of its tectonic activities. The result shows that this region experienced at least two tectogeneses in Late Mesozoic-Cenozoic, one occurred during Late Yanshanian, when a series of NE-direction faults and folds developed in Xuanhan region of east Sichuan under the SE to NW direction compression; and the other happened in Himalayan period, when the east Sichuan tectonic belt subsided gradually while NW-direction faults and folds were formed by the NE to SW direction extrusion in Daba mountain. The superposition of various tectonic stress fields with different directions and intensities in different periods comprehensively controlled the formation and evolution of oil and gas reservoirs of this region. The superimposition of staggered tectonic activities in the study area has improved reservoir properties, substantially controlled the development of hydrocarbon traps and adjusted lithologic reservoirs into structural-lithologic composite ones. Moreover, tectonic stress and fractures formed consequently in rocks have provided oil and gas migration with dynamic power and pathways.

Among widely-distributed low-permeability and low-porosity tight sand gas reservoirs, there usually develop some local reservoirs with relatively higher qualities. In order to understand control factors on the genesis of favorable tight gas reservoirs, we comparatively studied tight gas reservoirs in two intracratonic basins（Sichuan and Ordos Basin) in the sense of depositional fractionation and diagenesis. Sedimentary and diagenetic characteristics of the Xujiahe Formation in Guang’an, Sichuan Basin and the He-8 and Shan-1 members in Sulige, Ordos Basin were examined in detail. The results showed that:（1) the sedimentary heterogeneity determined by differences in provenance and hydrodynamic environments affects diagenesis significantly, which forms a basis for the formation of effective reservoirs. “Coarse-lithofacies” sandstones in stacked high-energy channels are thought to be favorable to forming high-quality reservoirs;（2) compaction and cementation are the main causes of reservoir quality reduction;（3) rigid and coarse grains such as quartz may contribute to retaining more initial intergranular pores by resisting compaction during early diagenesis, which can be pathways for diagenetic fluids in late diagenesis, but quartz overgrowth in a coal-measure acidic diagenetic environment may largely reduce the reservoir quality during late diagenesis;（4) authigenic clay minerals may reduce the permeability of reservoirs, while clay coatings may help retain initial intergranular pores by preventing quartz overgrowth; and（5) secondary dissolution controlled by dissolvable minerals, diagenetic fluids and fluid pathways is the main cause for enhancing reservoir quality. As for the studied tight gas reservoirs, sandstone diagenesis is strongly controlled by the initial heterogeneity derived from sedimentation process, which consequently controls the formation of favorable reservoirs as well. In order to predict the distribution of favorable reservoirs, sedimentary characteristics should be carefully studied.

Shale oil and gas are one of the unconventional hydrocarbon resources. Characteristics of continental rifted basins determine the complexity of the shale oil and gas exploration in such a basin and no existing experience can be used for reference. Through a study on the Luojia area in the Jiyang Depression, an evaluation method for shale oil and gas in continental rifted basins was preliminarily established. With which a favorable area of shale oil and gas was determined based on the analysis of petroleum geological conditions and a high-frequency sequence stratigraphic framework of the target area was consequently built up, where shale spatial and temporal distribution could be confirmed. A shale lithofacies classification criterion was established according to rock textures, structure, composition and color, and high-quality lithofacies were demarcated, tracked and forecasted with logging data. Abundance, types and maturity of organic matter were analyzed by means of geochemical analyses and hydrocarbon generation simulation, and geochemical parameter criteria for shale hydrocarbon generation and occurrence were determined as well. A model for the interpretation of reservoir logging parameters was established through studying space types, combination and evolution of shale reservoirs by means of core observation, thin-section analysis, electron microscopy and fluorescence spectrometry. The reservoir performance was evaluated combined with the analysis of reservoir physical properties. A saturation model was established based on core analysis, logging interpretation, and well-test and production-test data in order to evaluate movable hydrocarbon contents and carry out integrated identification of oil potential. Finally, the prediction of shale oil and gas production and exploration prospects in the study area was made by analyzing influential factors of deliverability and rock compressibility. Through comprehensive evaluations on lithofacies, source rocks, accumulation quality and deliverability, shales in the Luojia area were divided into three types, i.e. type I (high porosity and high resistance), type II (medium porosity and medium resistance) and type Ⅲ (low porosity and medium resistance). Guided by this division, three horizontal wells including Well Boyp-1 were located.

It is critical in hydrocarbon exploration to understand the intricate role of a fault, that played during hydrocarbon migration and accumulation. And it is generally difficult to determine valid optimum parameters for the characterization of fault connectivity among numerous geological factors while quantitatively evaluating fault opening and sealing. Taking Wangjiagang oilfield in Dongying depression as a studied area, we deduced the hydraulic connectivity of fault plane during hydrocarbon migration according to the occurrence of hydrocarbon accumulation within reserviors at two sidles of faults walls and the genetic correlation between them. An index, the fault-connecting probability, was used to evaluate the possibility fault acted as a migration pathway. On the basis of fault-connectivity determination and data statistics for a typical faulted reservoir, a relationship between the index and any an individual parameter proposed in previous works to characterize fault sealing was built to evaluate the effect of these parameters in characterizing fault connecting properties for hydrocarbon migration. By compariing the statistical correlation between each of these parameters and the fault-connecting probability, we found that the effectiveness of a parameter representing only a single geological factor is generally weak to determine whether the fault acted as a migration pathway. Some comprehensive parameters that deal implicitly or explicitly with two or more geological factors, such as the shale gouge ratio (S_GR), can improve the effectiveness of normal stress of a fault plane substantially. The fault opening index (F_OI) may be the best parameter to characterize the fault connecting for hydrocarbon migration.

As for carbonate fractured-cavity reservoirs, especially for those characterized by chaotic weak reflection, it is very difficult to make a reservoir prediction. Based on analyzing formation mechanism of seismic reflection, a new method to recognize carbonate fractured-cavity reservoirs by using seismic trend anomaly was proposed. This method uses a technique of trend surface analysis to approximately obtain the interface reflection wave, effectively decomposes seismic reflection of fractured-cavity reservoirs according to principles of wave superposition, and finally predicts fractured-cavity carbonate reservoirs efficiently. The technique can not only recognize reservoirs represented by “beadlike” seismic reflection but also those by “chaotic” seismic reflection with weak amplitude. The method has produced good effects in practical application, such as providing a significant reference value for the geometric arrangement of wells and complementing the prediction of fractured-cavity reservoirs in the carbonate area of Tarim Basin.

Traditional deconvolution methods usually need to assume a sparse distribution for seismic reflectivity, and then apply the L 1 norm deconvolution to get sparse reflectivity so as to improve resolution, but this doesn’t conform to reality. In addition, when traditional methods improve the resolution, they reduce the signal to noise ratio at the same time, making the continuity of a seismic profile poor. In view of these problems, the sparse deconvolution based on the Curvelet transform was proposed in the present paper. The Curvelet transform is characterized by an optimum sparseness expression for multidimensional signals to have the best nonlinear approximation, thus it can be used to express seismic reflectivity. When the Curvelet transform was introduced to the L 1 norm deconvolution, a sparse Curvelet coefficient representing reflectivity could be obtained without assuming the sparseness of reflectivity. In addition, according to the distribution characteristics of effective signals and noise the signal to noise ratio could be improved by using a threshold method to suppress noise, and consequently the multidimensional seismic deconvolution was obtained to maintain the continuity of seismic profiles. Finally, a threshold iterative algorithm was proposed to solve the L 1 norm deconvolution problem. The results show that this proposed method can effectively improve resolution and continuity of seismic profiles while suppressing random noise.

Represented by the Tahe oilfield，the carbonate fractured-cavity reservoir is a special type of reservoirs that have large caves and fractures as the major accumulating space. The reservoir distribution is complex and the fluid flow in main fractured-cavity media is incompatible with the Darcy seepage flow law, so that the reservoir development can not use the mature development theory and technology of clastic rock reservoirs for reference. Through scientific and technological researches in recent years, some theoretical problems on the formation mechanism of fractured-cavity reservoirs and the related fluid dynamic mechanism have been solved, and three key technical achievements have been obtained, including the geophysical description of ultra-deep fractured-cavity reservoirs, the fractured-cavity reservoir modeling under the multiple-scale karst-facies control and the numerical simulation of fractured-cavity reservoirs, all of which have effectively guided the water injection development and enhanced the development effect of fractured-cavity reservoirs in the Tahe oilfield.

A near-wellbore simulation model was designed for the Bohai Suizhong 36-1 Oilfield. The recovery performance process of partially hydrolyzed polyacryamide(HPAM) and hydrophobically associating water-soluble polymers(HAWP) with different molecular structures was studied with the wellbore simulation model at an injection rate of 5m³/(m·d)，10m³/(m·d) and 20m³/(m·d), respectively. The results show that the viscosity, residual resistance factor and resistance factor of HPAM can not be recovered while solution properties of HAWP after high-speed shearing can be restored. With the injection rate of 5m³/(m·d), the final retention rate of the viscosity, resistance factor(RF) and residual resistance factor(RRF) of HAWP is 92.3, 43.7 and 81.1, respectively. The viscosity, RF and RRF of HAWP may decrease with the increase of injection rate. When the injection rate is 10m³/(m·d), the final retention rate of the viscosity, RF and RRF is 70.6, 35.2 and 72.7, respectively, however, when the injection rate increases to 20m³/(m·d), the final retention rate of the viscosity, RF, RRF is 55.6, 26.3 and 55.8, respectively. The microstructure of polymers after shearing was observed with an atomic force microscope. Therefore, the cause of performance recovery for polymer solution after shearing was primarily attributed to the association of hydrophobic groups, which makes the network structure of polymer solution regenerate after high-speed shearing.

Heavy-oil reservoirs with extremely strong water sensitivity in the Shengli oilfield are mainly distributed in the Jinjia oilfield and their reserves amount to more than 20 million tons. In addition, the thermal recovery effect only by steam injection seems poor and it is difficult to effectively produce these reserves because the water sensitivity index for this kind of reservoirs exceeds 0.9. In view of the above contradiction, a thermal compound chemical method research was carried out, in which real cores from the Jinjia oilfield were used to evaluate different displacement manners based on thermal compound chemical flooding, such as the vapor+high-temperature antiswelling agent, steam+high-performance oil displacement agent, and steam+high-performance oil displacement agent+high-temperature condensation agent. Composition changes of clay minerals, clay distributions in pore throats and radius distributions of pore throats were measured by means of X diffraction, scanning electron microscope, cast thin section and mercury-injection in order to explore principle mechanisms of the enhanced oil recovery with the thermal compound chemical method under high-temperature conditions. The results showed that the thermal compound chemical displacement manner with the steam+high-temperature oil displacement agent+high-temperature condensation agent can promote the transformation of montmorillonite to illite and the dissolution of part kaolinite at the same time, which can greatly improve pore-throat flow channels of reservoirs to form large “hot-wormholes” that remarkably increase the permeability and flooding displacement efficiency of heavy-oil reservoirs with strong water sensitivity.

The spatial-vector-based stochastic modeling of point-bar reservoir architectures is proposed in this paper. Compared with traditional object-based modeling approaches, this proposed modeling approach has no cell or grid definition at the simulation stage. Architecture elements are simulated directly by dropping them into the modeling domain. Borrowing the idea from the vector image format in computer graphics, we used spatial lines, points and surfaces to form simulated architecture element bodies. The architecture elements are defined with spatial vectors which are expressed using their spatial distribution parameters. And the shape parameters are in real data set. Thus, different scale of heterogeneities can be reproduced from the realization. Because the well data conditioning is obtained through the modification of the architecture elements’ spatial locations and their shape parameters, it is easier to be satisfied. And the simulation has a faster convergent speed compared with traditional object-based approaches because of grid free and parameter adjustment in simulation. A developed block of one oilfield in eastern China, which has a geological background of meandering-river point-bar sand, is used to illustrate the theory and modeling procedures of this approach. 

This paper introduced basic concepts, principles and modeling steps of the Alluvsim algorithm for the depositional-process-based reservoir stochastic modeling. Compared with traditional stochastic modeling methods, this modeling method, which efficiently integrates various kinds of data with experts’ knowledge based on depositional processes, enables a more geologically reproduction of the geometry and relationship of architectural elements of reservoirs, such as channel, point bar, levee and crevasse splay. Generally, the Alluvsim algorithm can not exactly describe internal architectural elements of a point bar, such as lateral-accretion units and associated mud drapes. Thus, an improvement was made to characterize the key parameters of mud drapes in a point-bar, including dip angle, extending length and frequency, which significantly affect the movement of fluids. In addition, channels could be partly or wholly abandoned in the new method. At last, some limits of the present depositional-process-based modeling algorithm were discussed.

Coal beds are discontinuous media with well-developed cleats and fractures. The prediction of safe-density window of drilling fluid with the continuous medium mechanical model currently used can not achieve good effects in coal beds, and the sidewall destabilization is one of the difficulties in coalbed methane drilling. For this reason, we established a divergent elementary model for coalbed collapse pressure based on the discontinuous medium mechanical theory, and a discontinuous coalbed mathematical equation for collapse pressure and breakdown pressure was deduced via ground stress, interval and dip angle of cleat, size of wellbore, cohesive force and friction angle of face cleat. Moreover, sidewall stabilization coefficients related to wellbore liquid-column pressure and collapse pressure in the equation were defined. The analysis indicated that sidewall stabilization can be reinforced by increasing liquid-column pressure when the sidewall stabilization coefficient is positive, otherwise, both the liquid-column pressure and the formation pressurization capacity should be enhanced in order to keep sidewall stabilized. The size effect analysis showed that collapse location is sensitive to the size of wellbores, however, collapse pressure changes a little with various sizes of wellbores.

Using acoustic waves to transmit downhole information through the drill-string transmission channel is a promising approach to meet the modern drilling requirements for the high-speed and large-volume transmission of data. Herein, we established a model to analyze acoustic transmission characteristics and examined acoustic characteristics of different drill-string assemblies by means of transmission matrix calculations. The results showed that a distinctive feature of the drill-string transmission channel lies in the existence of passbands and stopbands, in other words, the drill string, serving as a linear comb filter, is a narrow-frequency multi-band communication channel. The transmission performance of a drill string depends considerably on structure dimensions, physical parameters and signal frequencies. Along with the increase of signal frequency and transmission distance, the attenuation rate received increases obviously. In addition, the transmission performance is also co-influenced by the elastic modulus and density of drill-string materials. As for a periodic drill string, when the length of drill pipes increases, the passband center tends to shift to low frequency and both the passband and the stopband become narrower. When the sectional area of joints decreases, the passband widens while the stopband narrows, and the passband center within a band cycle tends to shift to frequencies of the band center. The closer to the band center the passband center is, the greater the offset is. As for a non-periodic drill string, the increase of differences in structure dimensions and physical parameters will change characteristics of the channel frequency domain of the drill string remarkably and reduce the acoustic transmission performance considerably. The signal to noise ratio is the key factor in designing an acoustic signal transmission system within the drill string. In order to realize the acoustic telemetry, the communication frequency of acoustic transmission should be chosen, to the greatest extent, within the low frequency range.

While casing goes down into the curved section of a horizontal well, whether casing threads have been yielded has a great influence on following drilling and oil-gas production. However, there have been very few researches on mechanical behaviors of casing threads while casing goes down through the curved portion of a horizontal well, such as connection strength and sealing ability of the casing. Based on the principle of virtual work, nonlinear contact theory and von Mises yield criterion, we established a 3-D calculation model for the API short-round casing thread connection, examined the stress distribution of short-round casing threads under combined load of stretching and bending moment, and figured out that hole curvature (bending moment) would significantly influence the connection strength and sealing ability of casing. In addition, a maximum allowance hanging load for various given hole curvature was worked out through a large number of calculations. Based on synthetic considerations of thread connection performance and sealing ability,we recommended the optimized parameters of the API short-round casing thread criteria, including thread taper, thread pitch, thread length and thread ridge thickness. This research has an important engineering reference value for reducing casing thread failure and selecting the casing thread type for the curved section of a horizontal well.

According to the Mohr-Coulomb criterion, we established a governing equation of wellbore stability for horizontal well based on borehole-wall stress equations of horizontal well. And a method to determine safe and dangerous drilling azimuths for horizontal well was proposed, with which safe and dangerous drilling azimuths for horizontal well can be determined under any stress conditions. The result of algorithmic studies showed that the in-site stress regime determines safe and dangerous drilling azimuths of horizontal well. Therefore, the study result can provide a theoretical basis for the optimization design of wellbore trajectory.

Well Guanshen-1 is the second well in the world that was successfully drilled with the ultra-high density drilling fluid after the drilling of Well Guan-3. The drilling fluid with density more than 2.50kg/L was applied to drill 835.3m of Well Guanshen-1 that has a well diameter of 316.5mm. In order to safely and successfully complete the drilling of this well, a series of experiments had been done to deal with technological difficulties of the ultra-high density drilling fluid, in which a high solid dispersing agent (SMS-19) and an ultra-low viscosity deflocculating agent (SML-4) were developed, and finally a prescription of ultra-high density drilling fluid with high resistance to contamination and better setting stability was invented. During operation, the ultra-high density drilling fluid successively penetrated three high-pressure fluid formations and implemented to improve the mud density until killing the well. After drilling passed through the third high-pressure formation (T₁J¹-T₁J²)，the mud density was increased from 2.55kg/L to over 2.85kg/L and the drilling successfully shifted to the normal one. In view of technological particularities of the ultra-high density drilling fluid, some measures were taken in on-scene care to keep the ultra-high density drilling fluid system in a good rheological performance during drilling operation, such as to adopt the optimized screen-cloth standard, to optimize gel compatibility and maintenance amount, to hold proper pH values, to adjust bentonite contents properly and to control low-density solid contents reasonably.

Signal frequency spectra were analyzed based on establishing a mathematic model for multiple phase shift keying (MPSK) signals for pulse width modulation (PWM) and pulse position modulation (PPM) of drilling fluid pressure. The feasibility of applying the PWM and PPM methods to transmit down-hole MPSK signals of drilling fluid pressure was studied in terms of frequency domain. Impacts of drilling fluid channel parameters and modulation methods on data transmission were examined by establishing transfer functions for the MPSK signal distribution along directional drill string. Numerical calculation results show that the relative energy of signals within the main-lobe bandwidth of MPSK signal for PWM of drilling fluid pressure is too low to fit the frequency-band transmission in terms of frequency spectra, while only the MPSK signal for PPM of drilling fluid pressure can be used for data frequency-band transmission. However, this transmission pattern usually has relatively stricter requirements for the signal detection, treatment and rotating speed control of the rotary valve because of a greater transmission loss.

The nonlinear estimation of Casson model rheological parameters is usually a complex process. To solve this problem, an improved algorithm which is based on nonlinear regression is proposed. Then rheological parameters estimation algorithm is turned into seeking the minimization of one variable function and a method for determining the upper and lower bounds of the search interval is given. The test results based on a large amount of practical data showed that the object function is a unimodal function in the search interval, which can be solved with one-dimensional search method such as dichotomy, the golden section and Fibonacci method. This algorithm has such advantages as calculation stability, no need to set initial values, fast convergence and easy for computer programming. Through example tests, the proposed rheological parameter estimation was proved to be the optimal estimation based on the least squares method.

A threshold pressure gradient (TPG) associated with low permeability reservoirs can be used to describe non-Darcy flows at low velocity. A porous flow kinematic equation containing TPGs is an efficient supplement and development of the classical Darcy’s law, which lays a solid theory foundation for the exploitation of low-permeability reservoirs. The study shows that in the classical porous flow theory, the essence of TPGs, which depends on properties of fluids, surface interaction and pore structures of media, is not affected by the variety of porous flow patterns. Therefore, non-Darcy flows at low velocity can not be scientifically described by the threshold flow rate derived from previous studies. The existence of TPGs can intensify degrees of the pressure decline, resulting in “the pressure cone of depression” smaller and sharper. However, the pressure distribution curve intersects with, instead of being tangent to, the initial reservoir pressure line when the TPG is greater than zero, and cut angles will become larger with the increase of TPGs, indicating the existence of outer boundaries of pressure disturbance.

To follow direction of well-logging technology development, get rid of dependence on foreign well-logging software, improve capability of independent innovation, and enchance core competitiveness, CIFLog, the 3rd generation well-logging software which has independent intellectual property rights, has been successfully developed by PetroChina supported by the major national oil and gas project. Based on advanced Java-NetBeans programming technology, CIFLog adopts three-layer structure, and it can run under three major operating systems, i.e. Windows, Linux and Unix. Combine with well-logging evaluation of open-holes and cased holes, CIFLog offers the interpretation methods of complex reservoir including volcanic, carbonate, low-resistivity clastic rocks and flooded zones, and it is the first well-logging software that can be successfully applied to processing and interpretation of all domestically produced high-end imaging logging equipment in China. The successful development of the software not only breaks technical barriers of foreign software, and also fill gaps in relevant fields, meanwhile, it greatly enhances well-logging technology and research and development of large-scale software in China.

Petroleum exploration in the southwest Tarim Basin has a history more than sixty years. Up to now, five oil and gas fields and two oil and gas reservoirs have been discovered, namely Kekeya, Bashituopu, Yasongdi, Hetianhe, Akemomu, and the Shan-1 well and Kedong-1 well. Petroleum geologists and explorationists have cherished high hopes for these favorable and prospecting areas and all along pursued goals how to understand their petroleum geological conditions in detail, to accelerate exploration activities, and to get much more discoveries. In addition, a great breakthrough has been made in gas exploration of Kuqa area in Tarim Basin since 2000. Therefore, the petroleum geologic comparison between these two depressions is one of the important methods to analyze and uncover key petroleum geologic conditions of Southwest depression. Based on available exploration data and the current knowledge of these two depressions, we compared the very similarities and differences between them from the point of view of comparative tectonics and petroleum geology. Both of them share the following common points: (1) boundaries between the basin and mountains are characteristic of overthrusting or strike-slipping-overthrusting; (2) they have the intra-continental foreland basin structures at present; (3) they are formed by the transformation and superimposition of different proto-type basins; (4) basin structures are characterized by segmentation, zonation and stratification; and (5) fault zones play a major role in controlling hydrocarbon accumulation. However, differences between these two depressions are also much more remarkable in twelve aspects, such as geo-tectonic settings, deep geological structures, basement properties, tectonic evolution, geological framework, structural deformation, source rocks and their thermal evolution, reservoir-seal rock associations, petroleum systems, oil and gas accumulation mechanisms and preservation patterns, and oil and gas distributions. Of which the overwhelming important factors that control the oil and gas reservoir-formation are the geo-tectonic background and geological structures. The former shows that Kuqa depression is tightly related to the Paleo-Asian Ocean tectonic system, while Southwest depression to the Tethyan Ocean tectonic system. The latter indicates that Kuqa depression is formed predominantly by the superimposition of Cenozoic strata upon Mesozoic strata, while Southwest depression chiefly by the superimposition of Cenozoic strata upon Paleozoic strata. The above-mentioned comparison shows clearly that exploration in Southwest depression must be supported by a new theory of petroleum geology and exploration philosophy. This new theory needs to definitely disclose the exact locations, status, types, and possible mechanisms of the oil and gas sealed and preserved under late-period extensive structural movements, which have been sourced from old and lower-seated source rocks. It is urgent for this new exploration philosophy to establish new concepts of 3D geological structures, ideas of unitary and dynamic exploration, and also the stereoscopic thinking, which strengthen not only complex structural traps in foreland belts, but also subtle traps in slope zones, i.e. Ordovician buried-hills and Devonian-Carboniferous stratigraphic-lithologic traps, as well as dolomitic traps adjacent to Cambrian source rocks.

Molecular parameters such as triterpanes Ts/(Ts+Tm), total concentration of carbazole compounds, 1,8-/2,4-DMC and 4-/1-MDBT were used as “tracers” to investigate oil-gas migration and accumulation of the Yageliemu Formation (K 1y) in the Yakela gas condensate field in the Tabei uplift. The results indicated that in the K 1y oil reservoir, oil migration and reservoir filling have major and minor pathways with significant fractionation effect. It was suggested that the main charging point should be around S-7 and YK-13 wells located at the eastern end of the reservoir. Oil migrated in parallel with the Luntai fault and along the long axis of the anticline with NEE-SWW direction. And there exits a secondary filling point in the southeast of the oil reservoir. Oil migrated towards NW direction and accumulated at the structural high. Both the above-mentioned oil-gas filling pathways were apparently controlled by the Luntai fault in the south of the Yakela gas condensate field, which is supposed to be a major oil-gas migration pathway in the Tabei uplift.

Marine carbonate reservoirs in China are of a distinctive heterogeneity and complex formation mechanism, which have been all along a focus concerned by oil and gas exploration of China. We examined reservoir characteristics of the Yingmai-2 well field by applying various data of 3D seismic attributes, cores, imaging loggings and thin sections. It was concluded that reservoirs in the Yingmai-2 well field are not typical weathering-crust karst but faulted or fault-controlled karst. The reservoir space includes mainly fractures unfilled or semi-filled with calcite, small corroded vugs and cracks, and its distribution is strongly controlled by faults. Based on comprehensive analyses of structural activity background and fluid inclusion salinity, we thought that faulted karst in the study area experienced successively two corroded processes, one is surface water corrosion downward along faults and the other is hydrothermal fluid corrosion upward along faults. The former is predominantly constructive to the formation of reservoirs, while the latter is mainly destructive. The study result showed that it is not enough to search only for weathering-crust karst reservoirs in oil and gas exploration of the Tabei area, thus, more attentions should be paid to other types of reservoirs, among which fault-controlled karst is very promising to be the next significant exploration target in this area.

Affected by multistage tectonic movements, hydrocarbon accumulation in Silurian reservoirs of Tarim Basin is of uniqueness. Through systematical analysis methods for fluid inclusions, especially micro-beam fluorescent analysis method on a single fluid inclusion, we aimed to classify Kepingtage Formation hydrocarbon charging events of Well Shun 9 in Shuntuoguole low uplift and define their individual hydrocarbon accumulation ages. Results showed that Kepingtage Formation of Well Shun 9 located in the slope of Shuntuoguole low uplift is characterized by three oil charging episodes and one natural gas accumulation episode, the first oil charging episode occur in 417.5～409.5Ma; the second oil charging episode occurr in late Hercynian (335.0～231.5Ma), which is the major hydrocarbon accumulation period of this well field, oil might be from the Cambrian-Lower Ordovician and Middle-Upper Ordovician source rocks; the third episode occurr in middle-late Himalayan (20.1～19.7Ma) oil are from the Middle-Upper Ordovician source rock,natural gas accumulation time is 23.5～15.3Ma,and gas may be from the Cambrian-Lower Ordovician source rock.

The deepwater area of the northern South China Sea underwent multistage rifting in Paleogene and came into depression stage in Neogene. Lacustrine and transitional source rocks were formed mainly in the rifting period, while marine source rocks developed mainly in the depression stage. The transitional source rock is one of major source rocks in the deepwater area of the northern South China Sea．Oil and gas found in the northern South China Sea are mainly generated from transitional source rocks of Yacheng Formation and Enping Formation, while Zhuhai Formation marine source rock makes an important contribution to oil in the deepwater area of the Zhu II Depression. Natural gas in the Qiongdongnan deepwater area is a typical coal-type gas generated from Yacheng Formation humic source rock, but gas in the ZhuⅡ Depression of the Pearl River Mouth Basin is neither a typical coal-type gas nor an oil-type gas, instead it is a transitional gas generated from Enping Formation humic-sapropel source rock.

Saturated and aromatic fractions of typical marine and terrestrial oils and seepages collected from exploratory wells and outcrop in the northeastern Sichuan Basin, respectively, were characterized in molecular geochemistry using GC/MS and GC/MS/MS and their origins were also discussed in combination with analytical data of source rocks. The results indicated that oils from the Middle Jurassic Qianfoya Formation in Well Xinqingxi-1 in Puguang structural belt and Well Yuanba-9 in Yuanba structural belt show a pristane predominance over phytane (Pr/Ph>1.5), low amount of tricyclic terpanes with ETR values below 1.2 and abundant fluorene series in aromatic hydrocarbons. Based on the correlation of carbon isotopes between oils and kerogens from related source rocks, the oils were validated to be derived from lacustrine source rocks of the Qianfoya Formation. However, these two oils could have different organic sources and depositional settings due to a significant difference in diahopane abundance. The Permian oil in Well Chuanyue-84 of Puguang structural belt shows a relatively low Pr/Ph ratio (0.82), abundant tricyclic terpanes and detectable C₂₆ norcholestane. Carbon isotopes indicated a genetic correlation between the oil and marine source rocks of the Upper Permian Longtan Formation. The seepages from the Feixianguan and Changxing formations in Erlangmiao, Jiangyou area are characterized by dominant C₂₉ sterane over C₂₇ and C₂₈ homologues, a high 24-isopropyl-/24-n-propyl-cholestane ratio (1.1), predominant 3β- and 2α-methylsteranes in methylated steranes, a low 24-/（24-+27-）norcholestane ratio (below 0.2) and the absence of triaromatic dinosteroids. These age-related biomarkers, in conjunction with the isotopic depletion for whole oils (-34.1‰ to -34.6‰), suggested that the seepages could originate from Sinian-Cambrian source rocks.

Gas pools were found in the Member 3 of the Lower Triassic Feixianguan Formation in Heba area of the northeastern Sichuan Basin, indicating a great exploration potential in the Member 3 of the Lower Triassic Feixianguan Formation (T 1f 3 for short). Based on detailed microscopic, scanning electron microscopic and election microprobe observations of ordinary, mold and cathodoluminescence thin sections of core samples and combined with measurement results of porosity, permeability and trace element analysis of some samples, we examined diagenetic characteristics of carbonate reservoirs in the Member 3 of the Lower Triassic Feixianguan Formation in this area. The results showed that the Member 3 of the Feixianguan Formation is dominated by intra-platform shoal and inter-shoal deposits of open platform, of which the intra-platform shoal deposit is favorable for reservoir evolution. Main reservoir rocks are composed of oolitic limestones and calcarenite having intragranular dissolved pores and mould pores with low-porosity and low-permeability. The main kinds of diagenesis in reservoirs of the Member 3 of the Feixianguan Formation are micritization, dissolution, cementation or filling, compaction-pressolution, dolomitization and fracturing. The pore development of these grain carbonate reservoirs is affected by penecontemporaneous meteoric dissolution and burial dissolution, of which penecontemporaneous meteoric dissolution is a key factor that controls reservoir pore formation. Burial diagenesis including dolomitization, strontianite cementation or replacement and burial corrosion has greatly improved pores. Thus, favorable exploration zones in this area should be distributed in micro-paleogeomorphic upland and other places where faults and fractures are relatively developed.

The Lower-Middle Jurassic Shuixigou Group in the Kekeya area is rich in gas resources of tight sandstone reservoirs, analysis of their reservoir “sweet spot” types and genesis is of certain reference significance in the tight sandstone gas exploration & development in the Turpan-Hami Basin and other areas. By contrast of porosity and permeability, core observation, thin-section analysis, fracture statistics, log interpretation and production feature comparison, we summed up “sweet spot” reservoirs developed in the Shuixigou Group of the Kekeya area as two “sweet spot” types, i.e. the pored and fractured. Based on analyses of sedimentary microfacies, mineral compositions, formation water and simulations of basin burial history and basin evolution history, we concluded that specific sedimentary microfacies, relatively weak compaction and relatively strong dissolution are chief reasons of forming pored “sweet spot” reservoirs, while strong tectonic movement and local special tectonic locations control development of fractured “sweet spots” reservoirs. This comprehensive study showed that in the Turpan-Hami Basin, the formation of pored and fractured “sweet spot” reservoirs is a consequent result caused by interaction of deposition, diagenesis and tectonism.

Red-bed deposits developed on a large scale during the Ek₁-Es₄^x stage of Paleogene in Dongying sag under arid climate. Integrated with analyses of burial and evolutionary histories of the basin, diagenetic characteristics and formation mechanism of red-bed reservoirs in the study area were systematically investigated based on data of drilling cores, casting thin sections, physical properties and clay minerals. These red-bed reservoirs are characterized by the formation in multiple alkaline and acidic diagenetic environments, moderate to strong compaction, and apparent thermal compaction. Cement types mainly include carbonate, ferrocarbonatite, authigenic quartz, gypsum and anhydrite. Cementation is strong at the boundary belt of sandstones but relatively weak at the middle part of sandstones, where cement contents increase gradually from the lower part to the upper part of fault blocks. Dissolution in red-bed reservoirs occurs mainly as quartz dissolution in an alkaline diagenetic environment or feldspar and carbonate cement dissolution in an acidic diagenetic environment. Dissolution plane porosity increases gradually from the fringe to the bosom of sand bodies but decreases gradually from the lower part to the upper part of fault blocks. Metasomatism occurs mainly in quartz and feldspar grains with carbonate and sulfate cements, authigenic quartz, and carbonate with ferrocarbonatite. The diagenetic sequence of red-bed reservoirs was specified from the early carbonate and gypsum cementation, early quartz dissolution to the feldspar and carbonate cement dissolution, authigenic quartz cementation to the late carbonate and anhydrite cementation, late quartz dissolution then to the late carbonate cement and feldspar dissolution. The alternate evolution of multiple alkaline and acidic diagenetic environments and the action mechanism of upwelling current have controlled the development of these reservoirs.

Based on superpressure and heavy-oil characteristics of inter-salt shale reservoirs, the paper studied lithology, accumulation space, porosity, permeability and a variety of shale reservoirs by means of core description, X-diffraction analysis, SEM, measurements of porosity in lab and well logging data, and then made a classification and evaluation for inter-salt shale reservoirs in the upper part of the third member of the Shahejie Formation(Es₃). The result showed that inter-salt shale reservoirs have a complex lithology because they are complex salt rhythms which are composed of clastic, carbonate and evaporitic rocks. Rigid minerals and total organic carbon are high, and organic matter type is good, with medium-to-low maturity. the formation pressure is high overpressure. Structural fractures and overpressure fractures are developed ubiquitously within shale reservoirs. Organic pores and matrix-related pores are relatively well developed, providing shale rocks with main storage space. Combination of organic pores and fractures increases permeability of shale reservoirs. On the basis of studies above, the upper Es₃ inter-salt shale reservoirs can be divided into 4 types, providing an evaluation foundation for shale reservoirs in this area.

Nanostructure morphology of shale reservoirs was investigated using a field-emission environmental scanning electron microscope and adsorption-desorption isotherms were measured with low-temperature nitrogen adsorption experiments. Combined with high-pressure mercury injection, further investigation into characterization of pore structures in shale reservoirs was gained. Results show that pores in shale reservoirs are generally in a nanometer grade, it can be classified into five types: organic nanopores, interparticle pores between clay minerals, mineral pores in rock skeletons, apertures in palaeontologic fossils and microfractures, of which the most common ones are organic nanopores and interparticle pores between clay minerals. The pore-size distribution of shales are complex, which includes not only predominant mesopores (2～50nm), but also a certain amount of micropores (<2nm) and macropores (>50nm). Micropores and mesopores with a diameter less than 50nm amount to most of specific surface area and pore volume of shale pores, and mainly are places for gas adsorption and storage. Shale is characterized by high threshold pressure, good-sorting pore throats, poor connectivity and low efficiency of mercury withdrawal. In addition, mesopores in shale apparently contribute a lot to gas percolation, while micropores in shale are mainly for gas storage.

A model to characterize lithology of volcanic rock reservoirs by using nine types of volcanic rocks was presented to indicate lithologic control over high-quality reservoirs. Based on this model, we selected 15 petrogeophysical logging parameters sensitive to lithology, fabrics, genesis and pore structures of volcanic rocks, and adopted three machine learning algorithms, i.e. multiple regression analysis (MRA), artificial neural network (ANN) and support vector machine (SVM), respectively, to identify lithologic characteristics of volcanic rocks. Taking the Niudong oilfield of the Malang sag in the Santanghu Basin as an example, we employed data from three wells where volcanic rock reservoirs in Well N9-10 and Well N9-19 served as learning samples while that in Well N8-10 as a prediction sample. In particular, 1361 samples from Well N9-10 and 881 samples from Well N9-19 were employed and each of them contained 15 parameters of logging and lithology, the knowledge to predict lithologic characteristics of volcanic rocks could be obtained, respectively, by these algorithms. Then, 961 samples from Well N8-10 were used and each sample only had 15 logging parameters, while their lithologic characteristics were gained based on the aforementioned knowledge obtained by learning. The result shows that as for the learning samples, the absolute value of mean relative errors (%) between calculated and field-measured results for MRA, ANN and SVM are 51.84%, 48.66% and 0, respectively; and as for the prediction samples, these errors are 52.44%, 46.31% and 6.30%, respectively. Therefore, in this case only SVM is applicable because a nonlinear relationship between lithologic characteristics of volcanic rocks and 15 petrogeophysical logging parameters is very strong.

Although the mercury content in natural gases used as an identification index of coal-type gas and oil-type gas has been accepted by many gas geochemists, it is not used so much in practical exploration. The reason is probably that the index is not clearly understood. In order to clarify the applicability of this index, firstly, we discussed the genetic mechanism of mercury in natural gases. Through examining the mercury content in coal and the gas production ratio of coal, and conducting a thermal releasing mercury experiment on crumble coal, we concluded that mercury in natural gases comes mainly from source rocks, especially coal, only the formation temperature reaches to a certain value, can mercury in source rocks begin to be released enormously by the force of heat, and migrate into a gas pool with generated gas and accumulate there. Therefore, the mercury content in gases is determined both by the source rock type and formation temperature. Secondly, we measured the mercury content of gas samples collected from more than 500 gas wells in 8 giant basins of China, and performed the carbon isotopic measurement of alkane-gas from some wells. The statistical analysis of these data showed that the gas can be generally judged as a coal-type gas when the mercury content in the gas is more than 30μg/m 3; it is more likely to be a coal-type gas when its mercury content ranges between 10～30μg/m³; and it should be pointed out that an reasonable conclusion can be drawn only by combining this measurement value with other geological data. However, the mercury content in natural gases can be used only as an auxiliary identification parameter when it varies between 5～10μg/m³ or even much lower.