Through the discussion of the current state of lithologic & stratigraphic reservoir of Dongpu sag and the contrastive analysis of some typical basins in China, the geological conditions favorable for the formation of lithologic & stratigraphic reservoir in the sag are illustrated. The main area to explore lithologic & stratigraphic reservoir is within the area of hydrocarbon generation where structural trap is not developed. The countermeasures for exploring the lithologic & stratigraphic reservoir in the sag are analyzed and summarized.More attention should be paid to high-precision 3D information and reservoir characterization in order to effectively explore the lithologic & stratigraphic reservoir

Dongpu sag is one of the few sags in Bohai Bay Basin that are abundant with both oil and gas. Although it has been explored and developed for more than 30 years, there is great potential in the sag. In order to realize sustainable development of accurate exploration in the sag, suitable technical strategies should be adopted on the basis of different characteristics of structural belts. It is important to seek faulted zones in western clinoform zone so as to find some new oil-bearing fault blocks continually. To join the multilayer oil-bearing fault blocks together, attention should be paid to fill the blank of reserves in northern central uplift belt. It is essential to focus on the modification of structural details on the basis of high accuracy seismic data, so that the target area can be evaluated accurately in southern central uplift belt. It is effective to secure sustainable development of accurate exploration by developing technologies for high accuracy seismic exploration and multi-target directional well drilling that are suitable to accurate exploration in the sag, implementing project management and integrated management mechanism of exploration and development that combines exploration departments with institutes and oil producing factories together.

Jiyuan sag is a Mesozoic-Cenozoic superposed basin that has experienced multi-stage structural movement and reformation, after Early- Middle Triassic carbon basin shrinking. Upper Paleozoic (C-P) and Mesozoic (T3, J1-2) are main hydrocarbon source beds, multi-stage structures and fault-block activity lead to multi-stage hydrocarbon generation and a number of oil and gas migration and accumulation periods. Reservoirs were mainly accumulated during the secondary hydrocarbon generation from mid-Yanshanian to Himalayan. Intersected fault blocks are themain traps in the structures dominated by fault nose and fault blocks. Secondary pores or structure fracture zones developed in deep reservoirs are the key factors for hydrocarbon accumulation.Many a sets of reservoir combinations are connected through late-stage fault activities, so hydrocarbon reservoirs including faults, lithologic faults and buried hills are distributed congruently. And the distribution pattern of the reservoirs is the controlling factor for the formation and preservation of hydrocarbon reservoirs. The unique secondary hydrocarbon generation leads to the formation of abundant oil and gas resources, and the gas prospect in the sag gets broad. However, no breakthroughs have been made in the exploration of the sag in the past years.So there still exist many difficulties in finding out new geological theories and evaluating methods that are urgently needed for the recognition and understanding of multi-stage reservoir formation and preservation.

Dongpu sag is a sophisticated oilfield which has been explored and developed for 30 years. At present, complex fault-block reservoirs are the major target for exploration and development, of which the fault blocks are small and cracked, the fault plane is steep, and oil column thickness is small. All the features require more accurate seismic exploration. To meet the requirements of exploration and exploitation, combined with the trends of geophysical technology, we shall learn from the relevant advanced techniques both at home and abroad and focus on high precision 3D seismic techniques to tackle the imaging problems in complex fault-block reservoirs. Finally, a series of techniques are developed to implement high precision 3D seismic exploration. The application of the techniques in the areas such as Machang and Qiaokou shows that they are effective in solving the exploration and development problems in complex fault-block areas, and are valuable to be more widely applied in the same problematic area.

The structures in Pucheng-Weicheng area of Dongpu sag are complicated and the exploration mainly focuses on the crushing complex fault blocks and lithologic hydrocarbon reservoirs, such as the fault of the narrow space between two adjacent things, and the small fault blocks. The working area features in large-volume seismic data, complex wave field, and interference wave develops. In view of the characteristics of high-precision seismic data of Pucheng-Weicheng area and geological characteristics of the working area, research has been conducted on the fine processing method and high precision seismic imaging technology. High-precision seismic data processing technologies taking high-precision point-to-point velocity analysis, tomographic inversion static correction, prestack time migration, and prestack interference wave suppression as main features are developed. And obvious progress has been made in data processing.

The uniformity of 3D geometry is essential to seismic acquisition in the spatial continuity, balance, as well as follow-up data processing (prestack migration) and comprehensive explanation. In this paper, the analytical evaluation method of 3D geometry is presented to be applied, through analyzing and evaluating the uniformity of 3D geometry on fold, offset, azimuth and offset-fold qualitatively or quantitatively, so as to comparatively analyze the sampling uniformity difference of 3D geometries on the whole, then feed back the analysis results to design process of 3D geometry, make the choice of 3-D geometry more scientific and reasonable

In 2005, Zhongyuan Oilfield Company carried out high-precision 3D seismic exploration in Machang area of Dongpu sag, in which the design and demonstration of geometry scheme is a key step. The main geometries utilized in the sag in the past are first analyzed by using forward modeling techniques. By comparison of simulated data, the knowledge that imaging effects can be improved with increasing spatial sampling density is cognized. The acquisition geometry is determined by analyzing the two geometries with higher spatial sampling during the survey design of high-precision seismic exploration in the area. Focal analysis shows that the designed geometry has good property in amplitude accuracy and in horizontal illumination, which is favorable for lithology recognition in final seismic data. With the practice of high-precision seismic exploration in the area, imaging quality is significantly improved and very good results are achieved, which also proves the correctness of the geometry design

Aiming at different targets during developing period, Zhongyuan Oilfield has acquired 3D seismic data of small-scale for 10 disperse batches in Baiyinchagan depression since 1993, itwas unfavorable for local research and depression exploration, stamp patterned data was not content with depression exploration development. In order to meet the requirement of exploration in the sag, Geophysical Research Institute of Zhongyuan Oilfield Company adopts the 3D data merged processing technique using 9 batches, which eliminates field data difference and lays solid foundation for exploration breakthrough

Acquisition footprint is inherent in a 3D seismic observation system, which results from uneven distribution and different construction methods of shot and positioning point in the observation system, and seriously affects the fidelity of the information collection amplitude, accordingly affecting the processing and interpretation result of information collection. This article applies 3D seismic observation system footprint analysis and evaluation technology, to quantitatively compare and analyze the impact on acquisition footprint rising fromchanges of different trace interval, perpendicular offset, seisline interval, rolling offset of three-dimensional seismic observation system and different target stratum depth. It reveals the inherent connection between 3D seismic observation system and acquisition footprint. It provides good measures for minimizing acquisition footprint from the origin of designing 3D seismic observing system and optimizing 3D seismic observation system design.

When velocity anisotropy exists in subsurface rocks, the conventional isotropic migration methods may lead to not only wrong imaging position but also inaccurate image quality. This paper presents a method of anisotropic pre-stack time migration with real 3D seismic data in Dongpu sag. First, velocity and anisotropy parameters are obtained by using bi-spectral velocity analysis, and then the pre-stack data is migrated with an anisotropic method. Good imaging results are fulfilled in real 3D data

To enhance the imaging precision of complex fault blocks and carry on fine description of small complex fault blocks, the key is to increase the density and precision of velocity analysis. Through actual data processing analysis, 2% of the imgration velocity error will exert obvious effect on the intended interval migration imaging results during the application of prestack time migration to imaging of complex fault blocks. Therefore, improving the accuracy of velocity analysis is the key to high-precision seismic imaging. The conventional velocity analysis method is used hyperbolic NMO formula to carry on velocity analysis, and manual pick-up velocity is needed to be used. So the density is restricted, the quality of velocity analysis is also influenced by human factors greatly. In addition, as a result of the anisotropic characteristics underground media, reflecting the travel time is no longer a hyperbola, the application of conventional hyperbolic NMO may lead to uneven correction in the far-offset. In is paper, the high-density anisotropic velocity analysis method is proposed to be used. High-density automatic velocity analysis may be conducted, so non-hyperbolic NMO problems caused by anisotropy could be solved.

During the operation of high precision 3D acquisition projects in Dongpu area in the past few years, the number of channels for one crew has been increased from 1,000 to 4,000, even 10,000. Meanwhile, corresponding human resource and equipment are soaring. These changes have brought great difficulties in the implementation of acquisition and the management of human and equipment. In view of the problems exist in high-precision 3D seismic acquisition, such as more labors and equipment, swath management, and re-shot drilling, new concepts are put forward including human and equipment management, cross line array management, one swath executing rate. The quality and operation efficiency has been improved in practice

In view of the features (complicated and changeable superficial structures, closely set obstructions on earth surface) of central uplift belts in Dong sag, the design target is refined, the process of links target administration is discussed, the single line design, conclusions, themeans and requirements of point layout and the administration target of procedure links are elaborated in this paper. CDP offset distribution target may be used to control the evading obstructions design, so as to make the minimum binning fold more uniform, meet the delicate requirements of point exactitude, obtain accurate surface investigation scheme and little explosive compensation plan. All these indexes, treatments and measures may ensure the quality of high-precision acquisition in complex surface area.

The surface of swamp transitional zone in Sudan is highland, shallow swamp and deep swamp, its geological and surface conditions vary greatly, so there is too much difference in absorbing energy and frequency of seismic waves. Three different operation methods (highland, transitional zone and deep swamp) are used for the area. The geological structure of surface absorption attenuation model is established by analyzing various surface conditions, and it provides the basic theory to probe into the relationship between absorption/attenuation of seismic waves and exploration operation in swamp area. After various comparison tests, reasonable parameters are fixed, optimization source and receiver conditions are selected, and the objective for absorption attenuation of seismic waves are achieved.