China^’s offshore and adjacent area experienced five basin-forming stages since the end of Mesozoic, leading to development of a number of Cenozoic basins. Source rocks in the region were developed in Paleocene, Eocene, Oligocene and Miocenes. Types of source rocks include nomareine, transitional, and marine facies. Source rocks of nonmarine facies refer to mudstones of semi-deep lacustrine facies and limnetic faices. Source rocks of transitional facies include coal beds, coaly mudstones and dark mudstones. Marine source rocks include terrigenous marine and pure marine facies. Source rocks in the East China Sea, northern South China Sea and western South China Sea are dominated by semi-deep lacustrine facies in near-shore area and transitional to marine facies in far-shore area. Source rocks in southern South China Sea are featured by transitional to marine facies in both near-shore and far-shore area. Geothermal flux in China^’s offshore and adjacent area increases from near-shore area to far-shore area, and formation overlying source rocks get thicker from near-shore area to farshore area. Because of co-control of source rock and heat, the near shore is distributed mainly with oil and the far shore distributed with gas in China^’s offshore and adjacent area. The near-shore belt extends from Bohai Bay Basin via southern Yellow Sea Basin, depression belt in northern Pearl River Mouth Basin, Beibu Bay Basin, Hanoi depression of Yingge Sea Basin, western part of Zhongjiannan Basin, western part of Wan^’an Basin, Mekong Basin, Balinjian depression of Zengmu Basin, and central and southern parts of Brunei-Sabah Basin northeastward to eastern part of Palawan Basin. This is a huge oil-generating belt with billions of tons of discovered oil reserves. The far-shore belt includes East China Sea Basin, Taixi Basin, Taixinan Basin, southern part of Pearl River Mouth Basin, Qiongdongnan Basin, Yingzhong depression of Yingge Sea Basin, southeastern part of Zhongjiannan Basin, southeastern part of Wan^’an Basin, Kangxi depression of Zengmu Basin, northern part of Brunei-Sabah Basin, and northern Palawan Basin. This is a huge natural gas generating belt with the discovered natural gas reserves accumulated to trillions of cubic meters. Currently, China^’s offshore area is located mainly in the structural trap domains of the mature zones, the structural trap domains of the middle and shallow layers and biological reefs in particular. Exploration of compound traps and lithologic traps is under the preliminary stage. There is a broad prospect for exploration of new series of strata and new types. There are a lot of new exploration area in China^’s offshore area. A number of basins and depressions with great potential for resources are at low degree of exploration. The deepwater zone of the far-shore belt, in particular, is predicted to have a great potential for exploration.

China^’s proven and undeveloped oil reserves increase with time but the undeveloped rate does not change significantly. As of the end of 2013, the undeveloped reserves in the country^’s oil in place are 85.11×10⁸t and the undeveloped rate is 21.9 percent. The undeveloped reserves in the country^’s recoverable reserves are 10.71×10⁸t and the undeveloped rate is 12.5 percent. Based on the analysis of the undeveloped reserves distributed in different basins, owned by different companies and belonging to different types of oil and gas fields, this paper proposes to use new mindset and new technology to solve the issues related to undeveloped oil reserves: (1) Undeveloped oil reserve is a realistic area to increase oil production; (2) Re-evaluate the dynamic and current conditions of proven reserves; (3) Application of suitable technology holds the key to development. So far as the suitable technology is concerned, it is necessary to stress the uniqueness of each block of undeveloped reserve, launch a new round of accurate seismic survey, appropriately introduce tight oil and gas drilling technology and reservoir transformation technology, and push ahead with heavy oil development. The advanced methods should be used for development of oil fields of medium and small sizes while importance is attached to development of condensate oil and gas fields. Finally, the paper proposes that if China^’s three major oil companies want to concentrate their efforts to increase oil production in their business development, they should appropriately reduce the areas of their exploration blocks and concentrate their efforts to improve recovery factor of the developed oil fields and energetically put undeveloped reserves into production for higher investment returns and economic performance.

Qinnan depression is one of the depressions in offshore Bohai Bay Basin where exploration maturity is the lowest. The previous exploration effect of the depression was not satisfactory with its hydrocarbon sourcing capacity questioned. Source rock is more extensively distributed and more deeply buried in Dongwa and Zhongwa, the central areas of the depression, with a larger thickness. Therefore, the central part of the depression has a higher capacity for hydrocarbon sourcing and expulsion. The structural type of the depression controlled the direction of advantageous oil and gas migration. The steadily-distributed mudstone deposit of the second member of Dongying Formation controlled the oil and gas abundance level. The development locations and degrees of long-term active faults controlled the areas and abundance degrees of the Neogene hydrocarbon accumulations. There were mainly three accumulation patterns in the region – the selfsourcing and self-storing pattern, the early-sourcing and late –storing pattern and the lower-sourcing and upper-storing near-source pattern. The study indicates that the slope zone north of Shijiutuo uplift, the slope zone east of Qinnan uplift and the areas near QinnanⅠ fault and QinnanⅡ fault are the favorable exploration zones with a great potential for exploration.

Based on the principles, advantages and disadvantages as well as applicable conditions of oil and gas resources assessment method, and in accordance with the geological characteristics and exploration history of Tarim Basin, the adaptability of several conventional statistical methods is brought under discussion with the help of some examples. It is assumed that the discovery sequence method and statistical trend prediction method are not applicable in Tarim Basin while the saturation exploration method is not applicable to the composite hydrocarbon accumulation play or area mainly with structural traps. The size sequence method needs to be used flexibly in the concrete cases. The combination of resource calculating methods applicable to different geological types of calibrated units is established to lay a solid foundation for the fourth round of resources assessment in Tarim Basin. The paper points out that one of the most important principles that selection of calibration areas should follow is to further divide the composite hydrocarbon accumulation play into two or more calibration sub-areas, making the geological characteristics of the sub-areas more simplified and typical. The combination of resources calculating methods is selected according to the geological characteristics of the calibration sub-areas, thus leading to more accurate and reasonable calculation results. Take Tazhong north slope calibration area for example. It is divided into two calibration sub-areas—carbonate rock sub-area and clastic rock sub-area. The combination of calculation methods is used to recalculate the resources. The results are substantially improved as compared to the third round of resources assessment. The natural gas resources are raised several times and more compatible to the current exploration conditions.

The Quaternary and the Neogene alluvial fan developed extensively in Dabei-Keshen gravel zone of Kuqa depression. The surface gravel layer and deep conglomerate layer are distributed at the root of the fan and in the middle of the fan separately. The lithologic characters of the gravel layer are complicated with the thickness and velocity varying significantly, leading to a low signal-noise ratio of seismic data. The methods of ^“wide line and large assemblage^” and ^“static correction and multi-domain filtering^”are used in acquisition and processing to effectively improve the signal-noise ratio of data. However, compactness of the deep conglomerate layer caused the velocity to rise abnormally, seriously affecting identification of structural trap. The surface outcrop and drilling and logging data are used to interpret the seismic facies and sedimentary facies of the alluvial fan, identify the boundary between the conglomerate layer and enclosing rock, clarify the thickness of the conglomerate layer and the law for its velocity variation, and effectively eliminate the impact of the high-velocity conglomerate layer on the underlying structural traps. Based on the efforts for the research on integration of seismic acquisition, processing and interpretation, a large number of high-quality subsalt structural traps of Cretaceous were confirmed and discovered. The high-yield oil and gas flow was found from a number of traps with exploration wells and appraisal wells. The quantity of gas fields is on the rise with important discoveries and breakthroughs made in oil and gas exploration.

Seismic data acquisition of marine-continental transitional zone faces both changes in water depth and the impact of some complex factors, such as sea bottom current, sea wave and outside working environment. 8L4S176T geometry is adopted for OBC seismic acquisition operation in the transitional zone of Block A on Bohai Sea. In the light of low efficiency, poor quality of geophone data, difficult to control precision of detector position and the harsh operational environment of the wave zone, a series of measures are proposed, such as shooting along the detector line, reducing the number of moving all detector-lines one time, laying and positioning the detector at the same time, laying two more cables in advance, shooting at an appropriate time, increasing the cable weight and some other appropriate methods. As a result, seismic data acquisition for the complex transitional zone in this block is successfully completed, with high-quality seismic data made available.

Igneous rock developed in Wulanhua depression of Erlian Basin. It belongs to eruption rock represented by basic basalt of the Neogene Hannuoba Formation. The shallow layers are of the extrusive facies while the middle and deep layers are of the volcanic aisle facies. The surface of the igneous rock area fluctuates significantly, with eruptive rock piled miscellaneously, the weathering layer is thin and the lateral velocity changes quickly, causing a low original single-shot signal-noise ratio. Therefore, the quality of data is relatively poor. In the light of the above stated geologically geophysical characteristics, technological study is made in three areas – the optimization technology for the observation system with wide azimuth, large offset and high fold to enhance weak signal of deep igneous layer, the optimization technology for vibroseis and explosive excitation factors to improve the quality of original data, and the accurate surface structural investigation and comprehensive static correction technology to solve the complexity and changeability of surface structure. The results of the study indicate that those technologies can solve the bottlenecks in 3D seismic exploration of Wulanhua depression covered with igneous rock.

The characteristics of micro pore throat structure of tight oil reservoirs are the bottleneck in study of tight oil reservoir. It also holds the key to tight oil development. Take Chang 7 tight oil reservoir in An-83 block of Jiyuan oilfield in Ordos Basin for instance. Based on microscopic observation and mercury intrusion experiment, micro pore throat structure of the reservoir is brought under analysis. Microscopic observation indicate that the main types of pores in this zone are feldspar dissolution pore and intergranular pore, while the types of throat are mainly tortuous sheet shape, sheet shape and bundled tube. The intrusive mercury curves indicate that the expulsion pressure and median value pressure are relatively high, with the curves having a higher pitch of intermediate section and a low throat radius. Heterogeneity of pore throat structure is the main factor to determine the filtration characteristics and differences of tight oil reservoir. The analysis of the correlations between parameters and physical properties in three areas of pore distribution, pore sizes and pore connectivity indicate that the sorting coefficient in the parameters of pore distribution, the pore volume ratio in the parameters of pore sizes and the mercury withdrawal efficiency in the parameters of connectivity have the best correlations with the physical properties. As a result, the appropriate appraisal standards are established to classify tight oil reservoirs, helping appraise productivity of tight oil reservoirs and optimizing the relative measures.

Based on the single-well analysis and appraisal, the Ar-ion milling/SEM technology is used to study the porous type of Longmaxi Formation in Pengshui area of southeastern Sichuan Basin. The pores of shale in the study block are divided into six types (including microfractures, intergranular pores, intercrystalline pores, intragranular pores, organic matter pores and biological fossil inner pores). The nitrogen adsorption and mercury intrusion methods are used to inspect pore sizes and its distribution. Distribution of pore sizes is normalized to obtain the continuous distribution of shale pores of the target formation. Namely the pores of 2 to 10nm size developed most. The five influencing factors of shale pore structure of Longmaxi Formation in the study block is brought under analysis and discussion – content of brittle minerals, content of clay minerals, TOC, diagenesis, and conservation conditions. The results of analysis show that TOC is the dominant intrinsic factor of the shale pore structure of Longmaxi Formation in Pengshui area.