Characteristics and movability evaluation of shale oil in Jurassic Da'anzhai Member,Sichuan Basin
The integrated quantitative evaluation of movable shale oil is the fundamental basis for optimizing favorable blocks,intervals and lithologic combinations in the study area.The Jurassic shale oil is a key exploration layer series in Sichuan Basin,and currently there is no literature report on complete integrated evaluation and recoverable layer prediction for the mobility of shale oil in Da'anzhai Member.This paper is a case study of reservoirs in Da'anzhai Member.The reservoir space,occurrence mechanism and pore structure characteristics of different lithologic combinations were studied using the microscopic experimental methods such as SEM,low-temperature and nitrogen adsorption.The oil-bearing property and adsorption difference of reservoirs in Da'anzhai Member were analyzed based on the characteristics of source rock.According to the basic analysis of oil-bearing property,dynamic core experi-ments were further conducted to deeply analyze the mobility of the target reservoir and clarify the influencing factors of mobility.Fi-nally,by analyzing the influencing factors of shale oil mobility,a comprehensive evaluation system and an integrated quantitative method for shale oil mobility in Da'anzhai Member was established based on the fuzzy analytic hierarchy process,sum product meth-od and translational range transformation method.On this basis,the paper selects the major influencing factors of shale oil mobility,optimizes the favorable lithologic combinations in Da'anzhai Member,predicts the corresponding favorable production intervals and movable resources amount,and confirms exploration breakthrough in wells.The research results indicate that shell limestone in Da'anzhai Member is compact,and shale microfractures are underdeveloped;the layered limestone shell shale has the best oil-bearing property,of which the OSI is 121.86mg/g;the heterogeneous mud shale interbedded with shell limestone has the best shale oil mov-ability,of which the POI is 34mg/g.Therefore,the exploitable shale oil in Da'anzhai Member is the interbedded/interlayered lithol-ogic assemblage of shale oil,and the high frequency of interlayer between the roof and floor of dense shell limestone in the lower sub-member 1 of Da'anzhai Member and upper submember 2a of Da'anzhai Member and the submember 2b of Da'anzhai Member are predicted as recoverable strata,which are distributed in Nanchong-Langzhong-Yilong-Pingchang area,Fuling and Santai area.The movable resources of shale condensate oil and gas in Type Ⅰ favorable areas amount to 1.91 × 1 08t and 3232.39 × 108m3,respective-ly,showing good prospects.
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