Sedimentary Characteristics and Prediction of Favorable Areas of the Changxing Formation on the Eastern Side of the Kaijiang-Liangping Trough in Northeastern Sichuan Basin
[Objective]Reef-shoal reservoirs of the Changxing Formation are widely developed in the Kaijiang-Liangping trough,and contain abundant oil and gas resources.Core and seismic data on the eastern side of the trough are limited,and traditional geological qualitative methods have difficulty in accurately dividing and comparing the sequence stratigraphy,and consequently in predicting the locations of high-quality reservoirs.This in-depth study of the high-frequency sequence stratigraphy of the Changxing Formation helps to refine understanding of the distribution of sedimentary facies in the sequence framework and clarify the sedimentary evolution process on the eastern side of the trough.This improves the accuracy of favorable reservoir prediction and also provides a stronger basis for the exploration and development of reef-beach reservoirs.[Methods]This study was based on field profiles and core,logging and seismic data,together with Integrated Prediction Error Filter Analysis(INPEFA)logging cycle technolo-gy,to determine the characteristics of the high-frequency sequence stratigraphy and sedimentary system in the Changxing Formation in eastern Sichuan Basin.[Results]The Changxing Formation was found to be divided into two third-order sequences and five fourth-order sequences from bottom to top.Carbonate ramp sedimentation was developed in the early stage of the Changxing Formation,and carbonate platform sedimentation in the middle-to-late stage,sub-divided into open-platform facies,platform-margin facies and slope-basin facies.The favorable reservoir belt of the Changxing Formation mainly consists of platform-margin reef facies.The Changxing Formation contains crystalline dolomite reservoirs,(residual)granular dolomite reservoirs and reef dolomite reservoirs.These are strongly heteroge-neous,and their overall rating is low-porosity,producing medium and low permeability.[Conclusions]The favor-able reservoir zones are distributed in a'Y'-shape,mainly concentrated in the areas of Puguang 5-Laojun 1-Qilibei 2-Qilibei 101-Huanglong 5-Huanglong 8-Huanglong 4 distributed in discontinuous strips or dots along the platform margin.The platform margin beach in the back row of Qilibei is a sub-favorable zone occurring in a strip within the study area.The spatial and temporal evolution of the sedimentary facies belt,and the predictability of the locations of favorable reservoirs in the Changxing Formation,provides a geological basis for further exploration and development of reef-shoal reservoirs.
northeastern Sichuaneastern side of Kaijiang-Liangping troughChangxing Formationsedimentary characteristicsfavorable area prediction
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