The Studies Of Carbonate Reservoir In The Changxing And The Feixianguan Formations In The Northeastern Sichuan Basin In China

The Xuanhan-Daxian and the Tongnanba prospect areas lie in the northeastern Sichuan basin in China .The largest marine gas reservoir of Puguang the Changxing and Feixianguan formations in the former area that was thought to be a forbidden exploration region because of the reservoir's great depth and deepwater facies, has been found by Southern Company of Sinopec Corp.,demonstrating that it is necessary to further study the facies belts and diagenesis of reservoirs in the two formations.The depositional settings of Late Permian Changxing Formation and the Early Triassic Feixianguan Formation in Tongnanba and Xuanhan-Daxianare carbonate ramp and platform respectively, and there is a depression between the settings. The reservoirs in the two formations are mainly dolomitized reef and oolite. The following tasks have been accomplished in this paper:Based on the sequence investigation of outcrop and the boring and seismic data in the overlying regions, the 6 2^nd-order sequences and 21 3^rd-order sequences and corresponding plays in the sequences have been determined, and a northwest to southeast sequence framework and a northeast to southeast one and the distribution of plays have been established;on the basis of thin sections, isotopes, and inclusion data, the sequence of diagenesis events such as micritization, cementation, compaction and pressure solution, dolomitization, resolution, hydrocarbon implacement, and fissure have been established and porosity evolution models have been set up, the resolution by TSR and organic acid from infilled hydrocarbon have been analyzed, and the resolution times and their relation with porosity have been defined;According to water saturation of rock and the porosity in thin section combined with core, debris, and routine well logging data, the generalized permeability prediction model for quantitative calculation of the permeability of reservoir in the high-resolution isochronic sequence framework has been established, and by use of the model the permeability of the reservoir interval in well Puguang 2 has been quantitatively calculated;the gas saturation of carbonate reservoir in well Puguang 2 has been calculated by use of the formation resistivity factor Fr, porosity, and cementation index m of various types of the porosity;finally the thickness, distribution, and grades of the reservoir in the two formations in the two areas have been determined by the integrated uses of synthetic seismogram corrected by the known reservoir intervals, and the sedimentary facies and diagenesis of the intervals;basied on the seismic facies of 2-D profiles in the southwestern Tongnanba area, the progradational complex of shoal in Feixianguan Formation has been recognized.