Dongpu Depression Of Duqiaobai Deep Gas Reservoir Prediction

s ~ stratigraphic unit means 3-4 subsection of Third Section of Shahejie Formation Lower Tertiary in DQB area of Dongpu depression Bohaiwan Basin North China. The deeply buried S ~ in DQB area possesses ascendant hydrocarbon geologic conditions having generated a huge amount of natural gas. Although Zhongyuan Petroleum Exploration Bureau has been searching gas in this area for many years, No big discovery, however, has been broken through. The reasons for tills may be numerous, but predominant one should be that no large-scale reservoir sand-bodies were founded. The deep target horizon of the area is dominated by deep to hemi-deep lacustrine deposits with scarce sandstone and poor reservoir conditions. For instances, the deltaic and turbidite sand-bodies are mainly lenticular and thin, and a single layer of sandstone is generally less than 3 meters thick. The maximum cumulative sandstone thickness is less than 80m, and normally 10-30m. They are largely made up of silt-fine sandstone, densely compacted with low porosity (10-99%), low permeability (<0.001 I.?in2) and high remained water saturation ( as high as 40%). Therefore oil and gas pooi might be build up as long as some reservoir sandstone of coarse depositional system exist in the thick hydrocarbon source rocks. Thus it is most important how to predict thick and connect sandstone for seeking for middle-large gas fields.Since well PS 12 uncovered 28m sandstone in S ~ and produced commercial gas of 3500 m3/d in the initial test, a lot of geophysical methods and software have been utilized for characterizing and predicting the reservoir distribution at depth. But at last well PS15 drilled on the foundation above failed. Despite various reasons for it, the crucial one should be lack of comprehensive research of geology, log, core, and seismic data. In this paper we first look for large coarse depositional systems such as main channel, delta or fan-delta through entire basin analysis and sequence stratigraphy analysis associated with sedimentary review of modern half graben lakes by means of variety of geology, log and seismic data. Then thick amalgamated skeleton sand-bodies are outlined on base of analysis of depositional faces, seismic facies, forward model and impedance inversion. Finally combining the resevoir sand-bodies anticipated above with structures and factors that control formation of known oilgas pool, favorable gas area, trap or well locations are defined. Following such a criterion a good research result is achieved.The reviews of modern half graben lakes show that coarse depositional facies do not developed everywhere along the lake margin, but only at the main river mouths. Axial3channel and delta are foremost field for coarse deposits because either high stand or low stand coarse sediments are easy to remain on these fields. Instead on hinged or escarpment margin coarse sediments are difficulty to remain or merely exist as partial remnant as result of post- deposition rework and erosion. Another site for coarse sediments to preserve easily is delta of hinged margin or fan-delta of escarpment margin and turbidite fan in front of them developed at low stand stage. The sand body distributions of DQB region also follow this principle on the whole. The sand bodies presently predicted through seismic fades mostly extend in north-south direction. Two delta systems that are separately interpreted on well B11 B17 area and well B4 B16 area are far away from the rift margin fault, and thus display a characteristic of low stand system. According to core, log fades, well sand percentage, sublayer sand cumulative thickness inferred with 3D seismic amplitude and seismic reflection of progradation, depositonal anticline and onlap etc, deep S3~ of DQB region possess a background depositional fades of deep to hemi-deep lake intervened with semi-salt-water shallow lake. Reservoir sandstone consists of dominant delta mouth bar, distributary channel, axial channel, and inferior turbidite fades.Each event of 3D seis...