Fine Characterization of Reefs and Reservoir Distribution of Changxing Formation in Damaoping - Gaofengchang Area, Eastern Sichuan Basin

Abstract

The Damaoping-Gaofengchang area is located at the southeastern end of the Huankaijiang-Liangping Trough in eastern Sichuan, which is controlled by the double tectonic action of northwest and northeast. The Changxing Formation reefs and the Feixianguan Formation shoal facies reservoirs are well developed. Only 4 wells in the main area of Damaoping have good production results, while the other wells have relatively poor production and test results. Based on the existing data of drilling, logging, seismic and development performance, the subdivision of sublayers and the redefinition of reef period are carried out with wavelet transform and sequence stratigraphy. The development model and distribution character of reef are established, combining with seismic forward and inversion characteristics, and reservoir distribution characteristics are evaluated with experimental analysis, development performance, logging interpretation and geological model establishment. The Changxing Formation is divided into 2 sequences and 5 sublayers. The reefs are mainly developed in Sequence II which has three stages. The first stage develops in the flooded system tract of Sequence II, and the second and third stages develop in the high-water system tract of Sequence II. In the seismic profile, the reef is characterized by increased uplift of Changxing top formation, weak amplitude and discontinuous internal weak amplitude of Changxing formation. The three phases of reef are all developed in the main area of Damaoping, which are superposed on the plane to form an unclosed ring feature. It is characterized by three rows of reefs in Damaoping xi area which showed the characteristics of near east-west migration. The reef was formed into a fracture-porous dolomite reservoir through early freshwater dolomization. The fractures improve the seepage capacity of the reservoir, and the production capacity is well. This paper puts forward the method of reef sequence division and fine characterization, which provides a certain research basis for the exploration and development of the Changxing organic reef in the Huankaijiang-Liangping trough, and will promote the further effective development of the organic reef and similar fractured pore type dolomite.