The laws of natural gas reservoir formation of Songliao Basin are summed up from the perspectives of structural evolution, features of deep fault depressions and palaeohighs, reservoir conditions, fault development, and cap conditions. Geological evaluation of zones is conducted based on the criteria for selecting geological parameters of evaluating deep gas zones of the basin. On the basis of analogic methodology, the deep gas resources of the basin is evaluated as 1116.144 billion cubic meters, which is mainly distributed in the zones of Xujiaweizi, Miaotaizi, Changling, Yingshan, and Gulong. The target of exploration for the deep gas of the basin is ultimately determined as follows: Shengping-Xingcheng structural belt of Xujiaweizi fault depression, Xuxi slope, and the slope east of Changling fault depression are strategic areas for expanding exploration; Songzhan and Fengle uplifts of Xujiaweizi fault depression as well as the central uplift of Changling fault depression are strategic areas for making breakthroughs; Yingshan-Miaotaizi and Gulong fault depressions are strategic areas for preparing for exploration

There are three types of fault depressions distributed in Hailaer Basin, i.e., mono-faulted depressions, double-faulted depressions, and fault depressions with bulging superposition in the center. Based on the comparative study on different types of fault depressions, it is regarded that continuously sedimentary subsags with big width and depth features in well-developed hydrocarbon source rocks and abundant oil resources. Favorable reservoirs may be composed of sandstones, conglomerates basement metamorphic buried hills, and volcanic rocks. There are three hydrocarbon generation and expulsion stages in the basin, and the crude oil is migrated laterally and vertically in it. 2~4 source-reservoir-cap assemblages and 12 types of oil and gas reservoirs develop based on favorable reservoir formation. Oil-bearing zones with different lithologic and structural features are easily to develop in the internal part or on the margin of subsags. Four oilfields have been discovered in the internal part or on the margin of the main subsags in Beir and Wuerxun fault depressions so far. It is therefore proposed in this paper to strengthen the exploration of such wide and deep subsags as Chagannuoer and Hongqi subsags, to lay emphasis on the exploration of superposed and residual fault depression, and to pay attention to the discovery of various oil and gas reservoirs including metamorphic buried hills, fracture slope breaks, and volcanic rocks, etc.

The exploration and development of Huangjindai Oilfield in Liaohe Basin was mainly focused on the intermediate and upper submembers of Es-1, while less attention has been paid to Dongying Formation of shallow layers, lower submember of Es-1 and Es-3 of deep layers. This provides space for potential exploration. On the basis of further study on the hydrocarbon reservoir formation model and the reservoir forming assemblage of the area, abundant shallow gas layers are discriminated in Dongying Formation through several years of adjustment and deployment, developing huge production capacity. What's more, four potential block faulted regions are discovered in deep layers. Diversified technologies including reservoir modeling and inversion of reservoir are used to conduct rational arrangement, which does not only increase oil-gas productivity but also reveals the potential of deep layers. Based on summing up the results of tapping potential of mature areas of the oilfield achieved before the Tenth Five-Year Plan period, it reveals that the further study on the non-essential series of strata of mature exploration areas are of great significance. Meanwhile, it is important to persist in integral cognition, to lay the same emphasis on deep and shallow layers, and to pay attention to fundamental petroleum geology study, such as reservoir formation models and reservoir-forming assemblages during the exploration and development for oil and gas.

Xinglongtai-Majuanzi buried-hill belt lies in the sag west of Liaohe depression. It features in complex oil-gas properties and the exploration of it is influenced by the quality of deep seismic data. Gravomagnetic and electric exploration was conducted in the area in 2004. The distribution and thickness variation of Mesozoic Formation is identified on the whole. It is predicted that the error between the buried depth of the top surface of Archaeozoic era and the actual drilling result of Magu-2 and Magu-3 wells is only ten meters or more. Post-tracing of newly drilled wells shows that the effect of seismic interpretation of gravomagnetic and electric data is equivalent to the drilling result. Hence the credibility and precision of the drilling result can be improved and the complicated geological problems can be solved on the basis of gravomagnetic and electric exploration. It is indicated that the target for exploration should be focused on NE-SW extension area of the buried-hill belt

Based on the geological interpretation of more than ten thousand seismic profiles of 1000 meters in Sanhu region of Qaidam Basin, this paper shows that two strike-slip faults developed in the basin, among which one in the south of the basin and another in the middle of the basin, while the latter one has played an important role in the formation of the structure of the region. Three en-echelon anticline belts, i.e., the faulted anticline belt and the slope anticline belt with low amplitude as well as the central anticline belt with low amplitude developed in the region in Early Pleistocene owing to the right-lateral strike-slip and inversion thrust of the fault in the middle of the basin under E-W compression. Fold intensity gradually decreases from the belt in middle Qaidam to the south. This paper finally reveals that the Quaternary biogas reservoir is mainly controlled by structural background, regional slope belts, gas generation intensity, and cap rock, based on structural conditions, preservation conditions, and the relationship between essential gas-generating regions and known gas fields. It suggests that the central anticline belt with low amplitude in the south of the basin is favorable for discovering structure conglomerate gas reservoirs in the future.

Petroleum geochemistry parameters and indexes exert great effect on the study of petroleum system. The study mainly consists of six decisions on hydrocarbon kitchen, critical moment, migration pathway, boundary of hydrocarbon migration-and-accumulation units (HAMU), resources potential, target potential and level. Based on the discussion of the six aspects mentioned above, this paper presents the practical application of petroleum geochemistry in petroleum system study. It is considered that petroleum geochemistry can be applied from the beginning to the end of the study. Emphasis needs to be laid on the close combination between geochemistry experiment and petroleum system study.

The basic characteristics of Gama Ray (GR) and dual laterolog (DLL) in volcanic lithofacies are obtained based on the analysis of the well logging data of volcanic rocks in Xingcheng area of Songliao Basin. The logging characteristics are as follows: Except that basalt shows low value of GR and tuff shows low value of DLL in volcanic neck subfacies, the others show high value of GR and media value of DLL in volcanic vent facies. Explosive facies shows low value of DLL except showing media-low value of DLL in subfacies of air fall. The lithology of effusive-facies volcanic rock can be distinguished by GR logging. Effusive facies shows low or media-low value of DLL. Extrusive-facies volcanic lava shows high value of GR and low or media-low value of DLL. Extrusive and subfacies tuff lava shows media value of GR and DLL. This paper illustrates the practical application of logging data in the identification of special lithology of lithofacies from volcanic facies so as to identify lithofacies and lithology by making comparative analysis of the logging characteristics mentioned above.

By using well logging curves, this paper analyses the relationship among strata information and all genetic signs as well as hydrodynamic factors in relevant sedimentary environment, studying well-logging facies, sedimentary microfacies, and the distribution and development of their reservoir sandbody. It also confirms that the underwater distributary channel microfacies and channel overlying debouch bar microfacies of delta front subfacies are favorable for developing low permeability reservoir sandbody in studies area. They can control the striking and distribution of sandbody and feature in fine continuity and connectivity, high thickness. The extension and scale of favorable areas of Chang3 and Chang 4+5 reservoirs can be controlled only if adequate trap conditions are available. Based on the predictive research on sedimentary microfacies and favorable petroliferous area of Chang33 2 reservoir, it reveals that the reservoir lies in the central and southwestern host facies of underwater distributary channel belonging to five water systems developed from northwest to southeast. The favorable petroliferous reservoirs controlled and blocked out by favorable sedimentary facies tend to be more upgraded from middle to the middle and lower reaches of southwestern part, blocking out the increasingly extending tendency of middle channel reservoir and southwest Huachi reservoir. All of this provides reliable geological foundation for future rolling and border expanding development for the reservoir in the area

This paper introduces the three main procedures of the cross-holeseismic technology, i.e., seismic data acquiring, processing, imaging, and the application of some new techniques. The new technology does not only develop oil-gas reservoir information but also fills the blank of it. What's more, it plays an irreplaceable role in highresolution well-to-seismic calibration and reservoir production monitoring. This paper at last discusses the difficulties facing the currently-used cross-hole seismic technology, and points out that it is the development trend to integrate the cross-hole seismic technology, the terrestrial 3-D technology, and the well logging technology.

Influenced by the complicated geomorphology of the loess tableland area, the approach for evaluating the reservoir of the area is relatively simplistic because the Mesozoic terrestrial formation of Ordos Basin changes rapidly and reservoir types are mainly lithological reservoirs featuring in extra-low permeability and great difficulty to be discovered. In view of the problems of tough surface relief of the area and low conductivity of loess, four solutions are taken to improve the surface-borehole electrical approach, that is, the surface elevations static correction, the static displacement correction, the irregular network routing, and the increment of excitation intensity. The new approach is applied to predict the size of reservoirs and good results are obtained. The prediction range increases to 25~36 km2 from 9 km2. What's more, the prediction result is reliable and has broad prospect for popularization.

Light oil reservoirs with high productivity are discovered in Shawan Formation of Well Pai-2 in Chepaizi area of Junggar Basin. They have "bright spot" seismic characteristics due to the shallow burial depth, light density, large mudstone segmentation, good physical properties of reservoir, low speed of reservoir and its big difference with wave impedance of surrounding rock. The reservoir is identified using such approaches as composite seismogram calibration, forward modeling, analysis of seismic properties, and inversion, and good results are obtained.

It is the key to identify effective reservoirs from large sandstone body during exploration of Santaizi subsag of Damintun sag. There is no difference in acoustic transit time between this kind of wall rock and reservoir, so it is impossible to recognize by using the properties of wave impedance. Comparative logging analysis shows that there exist remarkable differences in spontaneous potential (SP) and conductivity between petroliferous glutenite segment and wall rock segment. Therefore, it is available to effectively identify reservoirs by selecting SP or induction curves with electric properties sensitive to the reservoir characteristics of the studied area, forming a linkage between the curves and seismic information, and then applying multi-parameter lithologic seismic inversion. Industrial oil output are obtained from the two exploration wells which are deployed on the basis of using the inversion results. This can be a good reference to the recognition of similar reservoirs

This paper discusses the achievements obtained in the development and application of geophysical technologies in China during the Tenth Five-Year Plan period, based on summarizing the application, development background, deployment characteristics, and working methods of the geophysical technology of Sinopec west frontiers during this period. Some understandings on the achievements are put forward as follows: The geophysical technology is a stimulating impetus to the exploration for oil and gas. Deeper understanding to geology and the application of geophysical technologies supplement each other. It is the development method of geophysical technologies to organize and implement the integration of seismic acquiring, processing, and interpretation with scientific approach. Such new understandings will exert great effect on accelerating the further exploration for oil and gas resources in new frontiers during the 11th Five-Year Plan period.

Experiments are conducted on the damage mechanism of fracturing fluids by using the real sandstone model to identify the reservoir damage factors caused by fracturing fluids, to optimize fracturing fluid system, and reduce or even eliminate the damage with the most effective method. What's more, the micro-mechanism of reservoir damage caused by fracturing fluids is analyzed on the basis of analyzing the reservoir geological characteristics, fluid properties, and reservoir sensitivity. Experimental results show that the rate of water-block damage caused by fracturing fluids is 46.6%, the rates of reservoir damage and fracture damage caused by residue due to the low reservoir pressure coefficient and fracturing fluids are 25.7% and 60% respectively. Rock wettability is altered by selecting out suitable surfactant so as to reduce the waterblock damage caused by fracturing fluids. The reservoir damage caused by fracturing fluid residue is reduced by developing the fracturing fluid system with low residue so as to improve the permeable capability of seepage flow from reservoirs to fractures. All of this provides theoretical support for the development of novel low-damage fracturing fluid systems and relevant technologies suitable to low permeability oilfields.

Low-grade petroleum reserves has a large proportion in the total petroleum resources in China. This paper systematically analyses the size and characteristics of the low-grade petroleum reserves in China and further discusses the three development organization modes of petroleum enterprises, i.e., the development mode of oil companies, the development mode of joint stock system (Dongsheng Mode), and the coexistence of multiple petroleum development modes (Northern Shaanxi Mode). It proves that Dongsheng Mode chiefly based on joint stock system is successful and good effect has been obtained. Then this paper conducts research on the policies and laws relevant to the development and production of low-grade petroleum reserves in China, including approval and management systems, enterprise operational mechanism, tax systems, science and technology policies, and regional coordination conditions between environment and production

The basin area near the sea on the passive continental margin of West Africa is one of the oil-gas producing areas of world focus and one of the investment concentrated areas in the world. However, the oil and gas producing currently concentrates in the basin area north of Walvis Ridge, while only Kudu gas field has been discovered in Namibia Basin to the south. Based on comparing Namibia Basin with northern oil-gas hosting basins, meaningful discussion is conducted on the prospect of exploration for oil and gas in the area near the sea of Namibia from the perspectives of structural evolution and features of the passive margin of West Africa. It is considered after comprehensive analysis that the main causes of no remarkable breakthroughs made in the exploration for oil and gas in the basin near the sea of Namibia are the impact of politics, low degree of exploration, less information publicized, and low degree of study. Namibia basin area is found to be similar to northern basin area in rifting, seafloor spreading modes, and marginal structure, based on the marginal evolution characteristics, but it is earlier than the latter one. Both southern and northern basin areas have gone through the pre-rift stage, syn-rift stage, transitional stage, and post-rift stage, and finally developed similar structural and sedimentary assemblages and similar source rocks. Maturity and thermal history modeling show that the oil and gas in the area of Namibia margin off a certain distance from the coastline is of medium and high maturity. So the area has the conditions of oil-gas generation. In addition, reservoir and cap rocks, and evaporite rocks which exert great effect on oil production of West Africa well developed in the area. The distribution of turbidite during the plate drafting period is controlled by the major structural traps generated from gravity gliding structures developed in the formation of the period. On the basis of comprehensive analysis, it reveals that Namibia Basin has similar geological background with the basin area in the north and has the conditions of oil-gas generation. Therefore, exploration and development should be strengthened, as well as the area ranging from Namibia basin area near the sea to the coastline is the optimized target for oil and gas exploration.