Sedimentary characteristics and prediction of favorable areas of Changxing Formation on the east side of Kaijiang-Liangping Trough in northeastern Sichuan Basin

Key words: 
• Keyword: Northeastern Sichuan /
• the east side of Kaijiang-Liangping Trough /
• changxing group /
• sedimentary characteristics /
• favorable area prediction

Abstract: [Objective] The reef- shoal reservoirs of Changxing Formation are widely developed in the Kaijiang-Liangping Trough, and the oil and gas resources were abundant. The coring and seismic data on the east side of the trough are limited, and the traditional geological qualitative methods are difficult to accurately divide and compare the sequence stratigraphy, which brings some difficulties to the prediction of high-quality reservoirs. The In-depth study of high-frequency sequence stratigraphy of Changxing Formation is helpful to refine the distribution law of sedimentary facies in the sequence framework, clarify the sedimentary evolution process on the east side of the trough, and improve the accuracy of favorable reservoir prediction, so as to provide a basis for deepening the exploration and development of reef-beach reservoirs. [Method] Based on the field profile, core, logging and seismic data and integrated with INPEFA logging cycle technology, the characteristics of high frequency sequence stratigraphy and sedimentary system of Changxing Formation in eastern Sichuan are studied. [Result] The results show that the Changxing Formation is divided into two third-order sequences and five fourth-order sequences from bottom to top. The carbonate ramp sedimentary was developed in the early stage of the Changxing Formation, and the carbonate platform sedimentary was developed in the middle-late stage, which can be subdivided into open platform facies, platform margin facies and slope-basin facies. The favorable reservoir facies belt of the Changxing Formation is mainly platform margin reef facies. The Changxing Formation develops crystalline dolomite, (residual) granular dolomite, and reef dolomite reservoirs. The reservoir heterogeneity is strong, and the overall performance is low porosity-medium and low permeability. [Conclusion] The favorable reservoir zones are distributed in the shape of ' Y ', mainly concentrated in the areas of Puguang 5-Laojun 1-Qilibei 2-Qilibei 101-Huanglong 5-Huanglong 8-Huanglong 4, which are distributed in intermittent strips or dots along the platform margin. The platform margin beach in the back row of Qilibei is a sub-favorable zone, which is distributed in a strip within the study area. The spatial and temporal evolution law of sedimentary facies belt and the prediction results of favorable reservoir distribution in Changxing Formation in northeastern Sichuan can provide geological basis for the next exploration and development of reef-shoal reservoirs.