Favorable reservoir facies tracts in the Changxing-Feixianguan formations of Sichuan Basin

In order to predict and optimize favorable exploration plays,we used the theory and methodology of sequence stratigraphy to divide the Changxing-Feixianguan formations in the Sichuan Basin into 8 sequences and 17 system tracts and to establish a relevant sequence stratigraphic framework.A study on the distribution of depositional facies within the sequence stratigraphic framework revealed that favorable platform-margin reef flat reservoir facies tract occurs in the Changxing-Feixianguan formations.This facies tract is controlled by Kaijiang-Liangping,Exi-Chengkou and Chuanxi(West Sichuan Basin)troughs and is in banded distribution on both sides of the troughs.Based on the prediction results of the platform-margin reef flat facies and in combination with various geologic data,we identified 3 types and 8 subtypes of favorable reservoir facies tracts.Type-Ⅰ is platform-margin reef flat facies which is distributed on the western side of Exi-Chengkou trough,both eastern and western sides of Kaijiang-Liangping trough,and both sides of Chuanxi trough.Type-Ⅱ is inner-platform reef flat facies which is distributed in Chuanxi and Chuanzhong(Central Sichuan Basin)areas.Type-III is inner-platform dolomite which is distributed in Chuannan(South Sichuan Basin)and Chuandong(East Sichuan Basin)areas.Among them,type-Ⅰ facies tract is the most favorable for exploration and the focus of current exploration,while as a supplement to type-I,the exploration of type-Ⅱ facies tract should be further strengthened though certain breakthrough has been made now.In contrast,type-III facies tract is large in area but low in exploration maturity as a whole,so comprehensive geologic study should be enhanced.