Distribution and accumulation of materials in shoal-reef compound gas deposits and reservoir characteristics——A case study of the Changxing-Feixian Formation in the Puguang gas field, northeastern Sichuan

Abstract：The Puguang gas field is the biggest and deepest gas field recently found in the Sichuan basin, southwestern China. Recently a major breakthrough has been made in this gas field. The intensive study of the model of accumulation of materials in the shoal-reef compound gas deposit of the field has certain guiding significance for the prediction of favorable exploration areas of carbonate rocks in northeastern Sichuan and even the whole Sichuan basin. Controlled by the Kaijiang-Liangping inter-platform basin, a carbonate sedimentary system similar to Wilson's facies model is developed in the Changxing Formation and Feixianguan Formation in the Puguang area at the east side of the inter-platform basin, where there mainly occur platform evaporates, restricted platform, open platform, platform-margin reef-shoal, slopes and inter-platform basin sedimentary facies, but continental shelf facies is not well developed. The paleogeographic differentiation mainly evolved centering around the development and filling of the Kaijiang-Liangping inter-platform basin. The study of the sedimentary microfacies and microscopic geological characteristics of the reservoirs indicates that the platform-margin shoal reef facies is the most favorable facies belt for the development of reservoirs in the area and that sponge baffle dolomite, sponge skeletal reef limestone, oolitic dolomites and relic oolitic dolomite are main reservoir rock types. The development of favorable reservoirs are mainly controlled by the distribution of the sedimentary facies belt and later dolomitization, dissolution and tectonic processes