The broad offshore is very rich in oil-gas resources in China. Amounts of oil and gas were discovered in this area during 40 years of exploration. However, owing to the limitation of technology, information and research extent, it has always been considered that all the basins in China offshore are similar in types and geologic conditions and classified as the Cenozoic rift basins on the continental margin. The analysis on a massive amount of seismic and drilling data shows that there are two depression belts in China offshore. The two depression belts are evidently different from each other in their tectonic situations, geothermal gradients, basin types, forming periods, sedimentary environments, petroleum geologic conditions and petroleum properties. The first depression belt containing Bohai Bay Basin, South Yellow Sea Basin, Taibei Depression, ZhuⅠ Depression, Zhu Ⅲ Depression and Beibuwan Basin is the lacustrine rift basin located on the continental crust and mainly generates oil. The second depression belt containing Zhedong Depression, Zhu Ⅱ Depression, Qiongdongnan Basin and Yinggehai Basin belongs to the marine depression basin located on the continent-to-ocean transitional crust and mainly generates gas. The first depression belt has already become a very important oil-producing area, and the second depression belt is expected to be a large gas-producing area in China offshore.

The comprehensive study of some samples from the Ordovician granule limestone in Tarim Basin showed that the burial dissolution could be classified as in-source dissolution and out-source dissolution based on the macro-microcosmic petrology and geochemistry features. There are different origin and migration path for the acid fluids in two stages of dissolution. The burial dissolution fluids might be organic acid, CO₂ and H₂S originated from the maturation of organic matters and decomposition of hydrocarbon. The fluid of in-source dissolution came from the organic matter in granule limestone, while the fluid of out-source dissolution mainly came from the shale source rocks far away from granule limestone strata. The burial dissolution reservoir was resulted from the actions of the in-source dissolution and the out-source dissolution. The granule limestone firstly formed the unattached pinholes under the action of in-source dissolution and afterwards suffered wide dissolution from the out-source fluid moving along the unconformities, seams, ruptures and associate fissures. The mineral composition of the stratum and the thermal convection of fluid are the important factors for forming the favorable reservoir.

The genetic types of natural gas and their source rock compositions were discussed in the northern slope of Baiyun Sag to Panyu Low Uplift in Pearl River Mouth Basin on the basis of former studies.According to the stable carbon isotope of methane and ethane, natural gas in the studied area can be classified into 5 main genetic types, including biogas, biothermal-catalytic gas, matured mixture coaliferous gas, matured to high-matured mixture petroliferous gas and matured to high-matured coaliferous gas. Sterane and terpane biomarkers of associated condensate oil in natural gas have two types of obviously different source compositions, which came from organic matter both enrichment-type coal and type-Ⅲ dispersed kerogen. So, hydrocarbon in the studied area was mainly generated from the matured to high-matured source rocks located in coal beds of Oligocene Enping Formation, shore-shallow lacustrine source rocks of Oligocene Enping Formation and Eocene Wenchang Formation. The further analyses of petroleum geological and geochemical characteristics show that this area has a great exploration prospect of natural gas and good potential of petroleum resource.

According to 3D high-resolution seismic data, polygonal faults were discovered firstly in Qiongdongnan Basin of the northern continental margin of South China Sea by using the coherent slice and flattening technique. The polygonal fault is tensional fault system with small throws, which is of nontectonic origin. The polygonal fault in the deep-water area of Qiongdongnan Basin has a length from 150 meters to 1500 meters, an interval space from 50 meters to 3 000 meters, a fault throw from 10 meters to 40 meters and a dip from 50° to 90° in three layers. Qiongdongnan Basin underwent the syn-rift stage and the post-rift thermal subsidence stage. The tectonic faults were undeveloped in the post-rift stage, which leads to the absence of pathway between source rock and reservoir. The unfavorable migration system is one of the factors restricting oil and gas accumulation in the post-rift stage. The polygonal fault can efficiently serve as the pathway for linking source rock and reservoir to enhance hydrocarbon migration along the polygonal fault. So it is very favorable for oil and gas migration and accumulation in the post-rift stage of the northern South China Sea.

With the statistic results about a total of 392 geothermal gradient values and 234 heat flow values, the geothermal gradients range from 2.94℃/hm to 5.22℃/hm with an average of 3.91±0.74℃/hm, and the heat flow values vary from 24.2 mW/m² to 121 mW/m² with an average of 77.5±14.8 mW/m² in the deep-water area of the northern South China Sea. The present geothermal field in the deep-water area of the northern South China Sea is characterized with "hot basin". The heat flow value increases from continental shelf to continental slope against the trend of the crust thickness, its distribution is also characterized with prominent local anomalies. The "hot basin" in the deep-water area of the northern South China Sea might be a result of the combination of the Cenozoic lithospheric thinning with the magma activities and faulting during the Neotectonic event. The variation trend of heat flow value was controlled by the magnitude of the lithospheric thinning. The magma activities and faulting during the Neotectonic period might be the main factors for the existence of the local anomaly of heat flow value.

The data from core, slice, SEM and XRD were used to study the characteristics of the Jurassic reservoirs in Santanghu Basin. In the Lower-Middle Jurassic low-pressure reservoir, lots of feldspars were dissolved, the content of kaolinite is from 3% to 16%, and the average value is 9.6%. During the formation of kaolinite, the formation water was abundantly consumed, and fluid content in pores decreased. The porous space increased by 1%, and the average value of fluid pressure almost decreases by 2MPa during feldspar dissolution. So, feldspar dissolution is the most important factor for declining of the reservoir pressure in the Lower-Middle Jurassic reservoir of Santanghu Basin.

The carbonate rock in Lower Ordovician Majiagou Formation of Ordos Basin is ineffective source rock because of its turbulence and rich-oxygen environment resulting in low organic matter abundance, inferior kerogen type and low hydrocarbon generation potertial. But the geological and geochemical analyses showed that there existed a set of high quality marine source rock in the platform slope facies of Middle Ordovician Pingliang Formation. The oil and gas generated from the source rock of Pingliang Formation was accumulated firstly in the central Palaeo-uplift and its surrounding regions. The thermogenic asphalt in palaeo-uplift carbonate reservoir indicated that oil accumulation completed transition from oil to gas in the Lower Crataceous. Along with the palaeo-uplift axis convection and the formation of westward monocline in the Late Crataceous, gas from the palaeo-reservoir was finally accumulated in the weathering crust of Majiagou carbonate reservoir. Pingliang series in southern and western margins of Ordos Basin was provided to be the main source for oil-type gas in Jingbian Gas Field.

There are two sets of effective source rocks in Tarim Basin, including Cambrian-Ordovician sapropelic matters and Triassic-Jurassic humics. The spatial distribution and the thermal maturity of two sets of effective source rocks controlled the genetic type and regional distribution of natural gas. Two genetic types of natural gas in the basin can be clearly identified according to the carbon isotope composition of methane and its homologue, namely oil-type gas and coal-type gas. Generally, the coal-type gas is derived from the humic matters, whereas the oil-type gas stems from the sapropelics. The coal-type gas is preserved in the traps along the margin of the basin, including Kuqa Depression, Southwest Depression and Southeast Depression, while the oil-type gas is mainly distributed in Tabei Uplift, North Depression, Central Uplift and the northern part of Southwest Depression. Based on the theoretical and empirical carbon isotope fractionation patterns, the oil-type gas can be further divided into the primary gas and oil-cracking gas. The primary gas geographically limits in Tabei Uplift, while oil accumulated in Lunnan, Mandong, Hetianhe and Tazhong attributes to the secondary cracking. The distribution of different oil-type gas greatly depends on the thermal maturity of the sapropelic matter.

Raoyang Sag is one of the oil-enriched sags in Bohai Bay Basin. In Raoyang Sag, hydrogen-enriched shale is high-quality source rock, but it has been ignored. Using the successful exploration experience of Nanpu Oilfield for reference, the organic geochemistry features of hydrogen-enriched shale were analyzed. It is indicated that this type of source rocks mainly contributes to the large buried-hill oilfield in Renqiu area. The organic carbon content is over 3%. The pyrolysis hydrocarbon-generation potential is 24.89 mg/g averagely. The type of parent material is type Ⅱ1 with amorphous solid as dominant, and the major source rocks (Es₃) is at the stage of hydrocarbon-generation peak. The newly calculation of resource shows that the oil-generating amount is 28.61×10⁸t and accounts for 27% of total oil-generation amount in the sag. Thus remaining oil resource amount reaches 7.59×10⁸t in Raoyang Sag. The current exploration situation presents an optimistic prospect for oil and gas exploration.

Fractures in the low-permeability reservoirs are usually high dip-angles. But there exist low dip-angle fractures formed by tectonism in the thrust zones of the western basins of China. These low dip-angle fractures are mainly distributed in the medium-granular sandstones and grit stones nearby the thrust or sliding layers. These fractures are often oblique to bedding plane with tiny angle and have equal spacing. Some fractures are filled with calcite, quartz and asphalt.Some fractures are characterized by dissolution and cut by the high dip-angle fractures. The geological analysis and numerical simulation show that the low dip-angle fractures are mainly formed by shearing due to thrusting or interlayer gliding under tectonic compression. These low dip-angle fractures are widely distributed along the thrust or sliding layer and have good lateral connectivity and high permeability in the horizontal direction. They can be also connected with high dip-angle fractures to form a good network system,which is advantageous to the enrichment for oil and gas in the low-permeability formation and to generation of high production wells.

The high-quality source rock of Chang 7 Member in Ordos Basin produced abnormal high pressure during the main period of hydrocarbon generation. There are about 10MPa differential overpressure between Chang 7 Member and Chang 8 Member, which was the main dynamic force for oil migration to the lower reservoirs. Overpressure can result in the hydraulic fracturing in source rock and its underlying strata. Many hydraulic fractures were founded in the cores, thin section and FMI data. Mixed phase fluid of hydrocarbon and water were expulsed quickly along fractures. The boiling oil and gas inclusions were founded in the source rock of Chang 7 Member and the reservoirs of Chang 8 Member and Chang 9 Member, which indicated the episodic expulsion and migration of oil and gas. According to the homogenization temperature of organic inclusion, it is suggested that oil and gas in the northwestern Ordos Basin has been mainly charged in twice episodes. The period of hydrocarbon accumulation was from the early to the middle of Early Cretaceous.

Shengtuo Oilfield of Dongying Depression is ternary mixed oil derived from the multiple source rocks and multistage accumulation. The early-accumulated oil was from the upper Es₄, and it suffered biodegradation in the tectonic movement. The late-accumulated oil was from the lower Es₃ and the upper Es₄. Absolute quantitative analyses of biomarkers in the selected three typical end-members show that the average contribution of source rock in the upper Es₄ is 39% in the early accumulation, and the contribution rates of source rocks in the upper Es₄ and the lower Es₃ during the late accumulation are respectively 30% and 31% in the Es₂ reservoirs in Tuo 2 Block. In the Es₂ reservoirs of Tuo 3 Block, the contribution rate of the mixed oils in the upper Es₄ source rock is 41% in the early accumulation, and the contribution rates of source rocks in the upper Es₄ and the lower Es₃ in the late accumulation are about 33% and 26%, respectively. The contribution of the lower Es₃ source rock is reduced from Tuo 2 Block to Tuo 3 Block. The contribution rate of source rock in the upper Es₄ to the Es1 reservoir of Tuo 2 Block is 8% in the early accumulation and 24% in the late accumulation, the contribution rate of the lower Es₃ source rock is 68%. The mixing ratio of oils in this block differs from that in the main oil-bearing layers.

Many features of reef in seismic time profile were numerically simulated by the way of F-K wave equation modeling to effectively recognize seismic response features of reef. A calculation program by combining seismic forward with depth migration was proposed to test the explanation for reef. Based on the 2-D seismic modeling, the continuation method of 3-D wave equation was applied to realize poststack forward modeling of 3-D atoll model. Many representative response features in different seismic profiles were obtained. The simulated synthetic records only contain the primary reflections and diffractions with high signal-to-noise ratio, which is available for eliminating the multiplicity of reef seismic interpretation.

Increasing liquid production is considered as the basic condition for stabilizing oilfield production with water injection. When the current well pattern adaptation becomes worse, well pattern infilling should be implemented to support and ensure oilfield stable production. If increasing liquid production is considered as the basic condition for oilfield stable production, well pattern infilling, improvement of control degree of water flooding and increasing recoverable reserves are the prerequisites for it. The key elements for stabilizing production include water cut, liquid production capacity, well spacing density, water injection rate and timing of water injection. The formula for stabilizing production which is established on the correlation between water cut and liquid production rate can describe the technical limit for stable production of oilfields with different water cut at different stages. The correlation formula between well spacing density and incremental rate of recoverable reserves was proposed with the statistics method. The formula can be used to predict the increment of recoverable reserves using well pattern infilling method in different development stages of waterflooding oilfield. The macroscopic water injection technology was discussed for sustaining stable production of oilfield.

The gas-resistance characteristics of nitrogen foam produced in sand pack was studied at different gas injection pressure. The stability evaluation of foam in beaker and porous medium indicated that the initial residual resistance factor of foam to gas increased in power exponent with the increment of gas injection pressure. The residual resistance factor of foam to gas and water decreased in power exponent with equilibrium time. The stability of foam in beaker was greatly lower than that in the porous medium and increased linearly with the enhancement of environment pressure. The analysis on a simple pore model showed that good dispersion conditions and thicker membrane in the porous medium could be the main causes for above phenomena. The initial resistance factor of foam increased with the pore-throat ratio, and coalesce probability declined with the rising of throat length, which thus improved the stability of foam. The greater the heterogeneity of reservoir in pore scale network, the larger the gas pressure difference in pores. When the coalesce probability of gas enhancement gets bigger, the stability of foam will get worse.

The conventional grid method is difficult to describe condensate gas reservoirs with thin oil ring. Based on the bedding grid and horizontal grid, mixed grid-modeling method was established by analyzing oil ring distribution and the existing reservoir simulation grid technique. The bedding grid was used to describe distribution of gas reservoirs, and the horizontal grid was used to describe distribution of oil rings. Both grids were effectively coupled into a mixed grid. In the mixed grid, the bedding grid was pinched out at the gas-oil contact surface and coupled with the horizontal grid in geometric shape. The non-adjacent grid conductivity model was used to calculate the flow transmissibility coefficient of fluid flow from the horizontal grid to the bedding grid. The mixed grid method could avoid limitations of bedding grid for describing distribution of oil ring with zigzag, decline the grid number in description of oil ring and enhance calculating velocity in numerical simulation. The dynamic development performance of thin oil ring and the characteristics of bottom water coning could be effectively simulated by this method, the simulated results are more reasonable.

The effects of lateral symmetry and camber on the production of herringbone wells were analyzed by using the semi-analytical model. Different angles, number and spans for laterals had different effects on the production of herringbone wells. The contribution of the main wellbore in the asymmetrical herringbone well is smaller than that of the symmetrical herringbone well, but the total production of the asymmetrical herringbone well is bigger than that of the symmetrical herringbone well. The curved laterals will cause less production than the deviated laterals. The bigger lateral angle results in the higher production for herringbone wells. The contribution of 1/3 section to the lateral end accounts about 50% of the total lateral contribution. Under the same total length of laterals, the production of well with two laterals on different sides of the main wellbore is the highest. The laterals should be put as near as possible to the middle part of the main wellbore, there exists an optimum span for the laterals.

The stress sensitivity of micro-fractured, fractured and dense cores from low-permeability reservoir was experimentally analyzed. The non-equivalent diameter and circuitous capillary module was used to express the stress sensitivity of single capillary and porous media by calculating elastic deformation amounts of big capillary and small one. The function mechanism on stress sensitivity of low-permeability reservoir was discussed by using the effective percentage of capillary diameter. The research results show that the stress sensitivity for permeability is more important than that for porosity in the low-permeability reservoir. The difference of stress sensitivity between low-permeability reservoir and medium-high permeability reservoir depends on some distinct factors such as microscopic pore structure, solid-fluid interfacial force and start-up pressure gradient, which can reflect the effective percentage of capillary diameter. The quantitative module of stress-sensitivity considering the effective percentage of capillary diameter can explain the difference of stress sensitivity between low-permeability and medium-high permeability reservoirs based on the microscopic mechanism.

Based on the fact that NMR T₂ distribution and capillary pressure curves can reflect the reservoir pore structure, a novel method was presented to calculate reservoir permeability by combining NMR log and capillary pressure data. A correlation model between Swanson parameter and rock permeability was established by analyzing plenty of core samples with mercury-injection and NMR log data. Considering the problem that capillary pressure data are limited by their quantity, the novel method was presented to acquire Swanson parameter from NMR T₂ geometric mean value and to calculate reservoir permeability consecutively. The permeability data in low-porosity and low-permeability reservoir of Well A calculated by the method are close to the result of air permeability obtained from core analysis, which indicates the accuracy and applicability of this method.

Acquiring the condensate gas phase behavior in original formations condition is difficult,but it is the most important in condensate gas reservoir development.The in-line phase recovery method was proposed after the changing law of condensate gas components in constant volume depletion experiment were analyzed by taking the condensate gas fluid samples from Well 169 in Zanarol Block,Well Banshen 7 in Dagang Qianmiqiao Block,and Well Yingmai 7 in Talimu Yingmai Block.The method was applied in Zanarol condensate gas reservoir,and has made the very good applicatiom effect. The applicatiom conditiom was studied by comparing the recovery results in different formation pressure.The results show that the in-line phase recovery method is representative and effective.But there exists an attentive problem in application, which is the formation pressure can't decrease too much,or the recovery result is unreliable.`

The curve of the world oil production has been shifted from the idealized Hubbert curve since 1973, when the crude oil production was restricted organically by OPEC. The actual curve took on the characters of "partitioned, truncated and shifted". According to the modified Hubbert Model, there might be multiple peak points of oil production during OPEC's constraint action. So, the classical concept, "peak point", would be dimmed on significance.It would be replaced by the critical point, on which the world oil production will be changed from plateau to permanent decline. The research suggested that the world ultimate recoverable reserves might be 395.5 billion tons,the turning point of the world oil production might arise during 2026-2032 period, and the oil production on the point would be about 4.69~6.58 billion tons per year,as well as the exploitation degree of reserves would be as high as 67.7%. If taking a more conservative estimation of 291 billion tons of total ultimate volume,then the milestone of oil production decline may arise in 2013. This will be a great baptism for the continual development of oil companies.

A set of non-linear finite element formulae with incremental form was derived on the basis of the fluid-solid coupling equations of porous fluid diffusion and deformation. The pore pressure cohesive elements were used to simulate the initiation and propagation of hydraulic pre-defined fractures resulted from hydraulic loading. A finite element model was proposed for hydraulic fracturing of oil well.Both the viscosity of fracturing fluid and volume concentration of proppant varied with time in the model. All of the simulation parameters are from data of oil wells. Some parameters including pressure at the fracture mouth, perforation friction, string friction, hydrostatic pressure of fluid column in well bore and wellhead pressure have changed with fracture time. The presented "curves of stimulation treatment history" are in good coincidence with those obtained from the field measurements.

Hydraulic pulsating-cavitation jet compound drilling is a new drilling technology and makes full use of mechanic energy and hydraulic to improve penetration rate. The pulsating-cavitation jet generator is located between bit and screw drilling string. The mechanism of the new drilling technology relies on the combination of high rotating speed of the conventional compound drilling and effectively bottom clearing of the pulsating-cavitation jet to improve the penetration rate. Field experiments in 4 boreholes of Yingmai and Lunnan districts demonstrated that the hydraulic pulsating-cavitation jet compound drilling could improve the penetration rate by 12.67 percent more than the conventional compound drilling and by 26.2~55.36 percent more than the conventional string drilling. This technology is valuable for popularizing in drilling engineering.

The problem of multidirectional contact of drill string with borehole wall is usually studied by using penalty function method, gap-element method, formal stiffness method and loosing constraint method. But these methods have slow calculation speed and are difficult to meet the requirements of engineering application. A new solution for nonlinear finite element equations of multidirectional contact of drill string with wall of borehole was proposed by establishing three-dimensional finite element model of drill string in the curved well bore and definite condition of the contact between drill string and borehole wall on the basis of cellular automata. This solution method is suitable for solving the nonlinear contact problem of drill string in the three-dimensional curved well bore and has the advantages of simple programming and convergence speed. It can be used to solve the complex boundary conditions of collision in three-dimensional curved borehole.

The alternating mechanisms of flow resistance to porous wall and the mechanism of enhancing water injection by using nano-particle of SiO₂ were investigated with the nano-particle adsorption method. When the hydrophobic nano-particles were adsorbed on the surface of porous walls, a layer of nanometer particles was formed instead of hydrated layer. The wettability of porous wall then could be translated to strongly hydrophobicity from hydrophilicity, and the slip effects on the nano-particles layer happened. The flow resistance could be reduced obviously, and the fluid velocity was enlarged obviously. A series of experiments were made to validate the feasibility to form the slip effects on the porous wall by nano-particle adsorption method. The results of displacement experiment show that the water-phase effective permeability could increase about 47 percent averagely. The Lattice Boltzmann Method was used to simulate the slippage length on the porous wall induced by nano-particle adsorption method.

Formation creep will make the external pressure on the casing get up to the overburden pressure in the process of well production. When the external extrusion load exceeds the casing compressive strength, the casing will be yielded and deformed or even cracked. The prevalent interaction model between creep formation and casing has some theoretical mistakes and can not be used for calculating the external pressure of casing. Based on the well construction procedure and mechanics principle, a correct interaction model between creep formation and casing was established. If the formation is rigid or elastic, earth stresses can not exert on the casing. If the formation is of creep property, the external pressure on the casing will be the overburden pressure after a long time. The non-axisymmetry deformation of casing detected from well site is mainly resulted from non-uniform thickness,non-uniform material of casing, scraping damage on casing and clay swelling in one side of casing, but not from the non-uniform earth stresses.

The dynamic reliability of offshore platform within its life cycle was analyzed. Three dynamic reliability models in consideration of fracture failure, corrosion failure and both of them were proposed. The dynamic fatigue reliability to platform system was investigated. The corresponding assessment methods and the relative formulae were given. The investigated example illustrated the validation of the proposed method. A new method to prediction of fatigue stress of offshore platform was proposed by combining the spectral method with the time domain method. The new method possesses the advantages of less computation work and more simple application.

In order to improve the accuracy of magnetic flux leakage (MFL) detection for the long-distance oil and gas pipeline, the impact of the moving velocity of detector on MFL signals should be carefully considered. According to the principle of 3D finite element analysis, a transient mathematic model for the MFL testing system was established and used to stimulate and analyze the crack detection process of oil and gas pipeline. A model for the static MFL distribution of pipeline crack was derived from the Maxwell's equations.Based on the model, the circumferential eddy current of pipeline generated from the movement of the detector was quantitatively analyzed, furthermore, the characteristics of inverse magnetic field formed by the eddy current and its effect on the external magnetic field were evaluated. Finally, a finite element simulation model for the magnetic flux leakage of crack was derived under the condition of dynamic magnetization. The model can acquire the tested results of MFL signals corresponding to different cracks. The consistency between the actual physical experiments and simulation analysis of the MFL signals proved the effectiveness and correctness of the transient simulation model. The relations of the crack geometric parameters, such as depth, width and the peak-valley value of MFL signals were discussed, and their relative curved surface plots were also drawn. The results of simulation analysis may be as a reference for practical MFL detection of cracks in long-distance oil and gas pipelines.

When the metal magnetic memory(MMM) inspection method is applied to make early diagnosis of oil pipeline, the magnetic memory signal is easy to be disturbed by various sources of noises, and the detectability of defect signals is greatly lowered. An improved method composed of wavelet threshold function and adaptive threshold was presented on the basis of the classic denoising method using soft and hard threshold algorithm and the characteristics of magnetic memory signals. The Daubechies wavelet was used as a wavelet function with four series, and the adaptive method was used to calculate the threshold. The magnetic flux leakage-magnetic memory detector was used to certify the algorithm. The testing results demonstrated that the new method could overcome the shortcomings of soft and hard threshold algorithm, and the signal-to-noise ratio of the rebuilt signal was improved, and the noises of signal were greatly eliminated. This denoising algorithm can provide the theoretical basis for estimation of stress concentration zone and early diagnosis of oil pipeline.

A mathematic model of particle erosion under inter-particle collision was established. This mathematic model includes the flow field simulation of the continuous carrier fluid under Eulerian coordinate system, the inter-particle collision simulation using the discrete particle hard sphere model under Lagrangian coordinate system and the erosion rate calculation using semi-empirical formulations. The movement simulation of solid particle and the erosion characteristics of the solid-liquid two-phase fluid in flow controller under hydraulic sand fracturing operation showed that the particles were accumulated in a narrow region from inlet to outlet of the flow controller. The erosion rate was proportional to the inlet velocity with the exponential growth. The erosion rate increased with the increase of particle diameter. The most serious erosion in flow controller occurred on the upper region of the edge with 10 mm away from the outlet.

In order to analyze the influence of visco-elastic effect of polymer solution in produced fluid on the eccentric wear of sucker rod in polymer flooding wells, a mathematical formula of the lateral force acting on the surface of sucker rod was derived by analyzing the stress state of fluid. Taking Maxwell model as the constitutive equation for produced fluid containing polymer, the mathematical models for the produced fluid flowing in eccentric annular were set up. The velocity field was obtained by using the numerical method. The lateral force was calculated on the basis of the velocity field. The analysis results showed that the lateral force was caused by the eccentric of the rod in annular and the elasticity of the fluid. Lateral force changed periodically with the reciprocating movement of the sucker rod and lagged behind the rod for about one quarter cycle. There are lateral forces along the rod equably acting on the rods during the upstroke and the down stroke. The lateral force can exceed the minimum load easily and result in the distortion of the rods and the eccentric wear between the rods and tubes. The eccentric wear of sucker rod in polymer flooding wells was more serious than that in water flooding wells.

The predictions of petroleum production change and peak rely on a precondition that the reserves and development methods are relatively unchanged, or the change rate of oil production and the maximum proved reserves are fairly prescribed. The estimation might be reliable in some "closed systems" with the above-mentioned features. However, for some "open systems" characterized with every unpredictable possibility, these estimations could be inaccurate or even misleading. In addition, the impact of social factors on petroleum production should also be considered in the application of the estimation. Hubbert, who proposed the production peak theory, was lucky enough to correctly predict America's production peak of 1969-1971 peoriod in 1956 when the oil situation was much simpler than that of present days. Meanwhile, other estimations about the production peak were failed due to their blindness to the ever-changing technologies and environment of the petroleum industry. The irony is that, quite contrary to the production peak and depletion theories, the petroleum production has always been increasing during the recent 20 years. However, these theories were widespread through media and induced concerns over petroleum supply security. Thus, those served as one of the reasons for pushing sky-high oil price.

There are the potential domains for oil and gas exploration in the areas with the elevation of 0~5 km and the deep formations of 5~10 km in depth, where some petroleum geology theories and technologies require to be studied. The modification effect and influence of the neotectonic movement on the oil-bearing formations and palaeo-reservoirs are more profound in the high-elevation areas such as Qiangtang Basin and the north part of Qinghai-Tibet area,so the preservation of oil reservoirs is rigorous.The burial depth of ultra-deep reservoirs is normally 5~10 km in the non-marine basins characterized with rapid deposition, thick sedimentary rock and multiple structural layers,which corresponds to the late stage of diagenesis and deep burial period (with temperature and pressure higher than 175℃ and 100MPa, respectively). The development of high-quality clastic reservoirs in ultra-deep formations of China is controlled by deposition, the duration of deep burial (long-term diagenesis and short-term deep burial), the pressurization of fluid and secondary dissolution. The generation of high-quality carbonates reservoirs in the deep and ultra-deep formations mainly depends on dolomitization and dolomite karst.

The hydrocarbon source rocks of coal-bearing strata are widely distributed in the Upper Paleozoic of Ordos Basin.There exist multiple layers of fluvial-deltaic reservoir sand bodies, which forms the favorable reservoir-seal combinations.The main part of the basin is a large gentle slope tilting westward and develops large lithologic traps. There are favorable gas reservoir-forming conditions and great exploration potential.Two regional unconformity surfaces including the regional marine regression surface at the bottom of Shanxi Formation and the erosion unconformity surface at the bottom of Shihezi Formation control the formation of the main gas reservoirs.Analysis on gas distribution and gas-water relationship of the main gas-bearing strata showed that three factors of provenance, palaeogeomorphology and sedimentary facies controlled the distribution of gas reservoir.Lithologic gas reservoirs are mainly developed in the middle-upper part of the low system tracts of SQ11(lower part of 8^th member of Shihezi Formation) and SQ8(2^nd member of Shanxi Formation). Giant lithologic gas reservoirs are developed in the gentle slope region, where the hydrocarbon-generating intensity is more than 20×10⁸m³/km². Natural gas are mainly distributed in quartz-rich coarse depositional systems, and the gas-bearing strata transfer upward from east to west. From SQ8 to SQ9(1^st member of Shanxi Formation)and to SQ11, gas-accumulating facies transfer from delta front to delta plain and fluvial facies.

The relationships between facies and potential of 527 sand bodies in Jiyang Depression were analyzed. The connotations of facies-potential coupling effects on reservoir were discussed on the bases of two-dimensional simulation experiments on different sand configuration as well as high pressure and high temperature simulation of oil migration and accumulation in cores. The results showed that there exist different characteristics of facies-potential coupling effect on reservoir in different scales. In the sand body scale, there mainly reflects the different type of sedimentary facies, the characteristics of oil and gas accumulation are also different. In the sand layer scale, there mainly reflects the different of oil migration pathway and oil pay zone attributed to heterogeneity of the sand,variations of sand-shale composition and permeability difference. In the core scale, the flow characteristics of oil-gas migration and oil saturation are different. The oil-filled sand-bodies mainly lie in the two-high and one-low areas of PFR model for facies-potential coupling effect on reservoir developed by using energy condition, mobility and reservoir capacity. Facies-potential coupling effect on reservoir is a quantitative model with power function and can be used to predict hydrocarbon-bearing.

Banghu Syncline is the main source sag in Qianjiang Depression. The source rocks of Eq₃ and Eq₄ around Banghu Syncline has matured and generated oil and gas. Many updip pinch-out traps of lithologic sandstone are developed on the southern and eastern slopes around Banghu Syncline. The permeable sandstones accepted hydrocarbon in a way of surface supply, and oil and gas migration was driven by buoyancy. Hydrocarbon migration and accumulation in these slopes were mainly controlled by three factors. The tectonic framework controlled the migration trends of oil and gas.The hydrocarbon migration paths were controlled by special disposition of permeable sandstone conductor and migration trends.Each lithologic trap corresponding to the convergence area was limited by oil and gas migration path network.The petroliferous property of lithologic trap was controlled by volume of source rocks and hydrocarbon-generating and hydrocarbon-expulsing performances of corresponding source rock. The convergence area was in positive proportion with the petroliferous property of lithologic trap in the same combination of petroleum migration and accumulation. On the basis of prediction technology for hydrocarbon migration path in source sag, the petroliferous property of lithologic trap could be correctively evaluated.

The lithologic pools have a great potential of resource in Southwestern Qaidam Basin,however,the study on hydrocarbon accumulation process is insufficient.In the paper,the hydrocarbon generation and expulsion history of the main source rocks in the lithologic pools of the Southwestern Qaidam Basin was analyzed,and the formation characteristics of local lithologic reservoirs was investigated on the basis of microscopic fluorescence and homogenization temperatures of fluid inclusions in reservoir. The result showed that there were two hydrocarbon-charging times in the Middle Miocene and the Late Pliocene. This area is characterized by the early-stage and multi-stage lithlogical traps which mainly formed in the Late Oligocene and the Late Pliocene. The formation process can be divided into two stages of accumulation period and preservation-destruction period.

The Chang 6¹ layer is a low-permeability reservoir of Yanchang Formation in the Upper Triassic System and is also the main oil layer in Yanhewan area of Ordos Basin. The distribution and development degree of tectonic fractures restrict the petroleum exploration and valid development. The observation of outcrop and drilled core, thin-section analysis and paleo-magnetis core orientation were applied to the quantitative statistics of tectonic fractures,including the basic characteristics,mechanics and valitidy of tectonic fractures of Chang 6¹ low-permeability reservoir in the Yanhewan area. Chang 6¹ reservoir developed the regional conjugate high-angle tectonic fracture system with NEE and NS directions. The density of tectonic fractures is from 0.12 to 3.56 ribbons per meter. The most tectonic fractures are tensional and filled seriously,which belong to the invalid tectonic fractures in Chang 6¹ reservoirs of Yanhewan area. According to the density of tectonic fractures in cores obtained from different drilling wells in Yanhewan area, a mathematical model for quantitatively predicting and evaluating the distribution and development degree of tectonic fractures was developed by using the finite element simulation method,the rock burst method and the strain energy method. The model was used to predict the areas of developed, sub-developed and un-developed fractures and to determine the strikes of tensile-shear fractures. These results can provide the important geological references for establishment of fracture network model and further petroleum exploration in Yanhewan area.