准噶尔盆地玛湖凹陷三叠系百口泉组储层特征及油气成藏规律

Reservoir characteristics and hydrocarbon accumulation rules of Triassic Baikouquan Formation in Mahu Sag,Junggar Basin

通过岩心分析测试、地震厚度预测、包裹体成藏期次分析以及源储配置关系研究,对准噶尔盆地玛湖凹陷三叠系百口泉组储层特征及油气成藏规律进行了刻画。研究结果表明:①玛湖凹陷斜坡区三叠系百口泉组主要发育扇三角洲沉积,岩性普遍较粗,相对优质的储集层主要分布于扇三角洲前缘水下分流河道微相及少量河口砂坝微相中,其成分以长石岩屑砂砾岩为主,其次为岩屑砂砾岩。岩石普遍较致密。岩心孔隙度为3.17%~23.40%,平均为9.04%,渗透率为0.01~934.00mD,平均为0.73mD,属低孔特低渗型储集层。储集空间类型以次生溶孔为主,可见粒间缝和其他微裂缝。②研究区油气主要来源于下二叠统风城组碱湖沉积的泥页岩,最厚处超过400m,为残留海—潟湖相沉积,水体盐度较高,岩性以云质泥岩和泥质岩为主。有机质类型以Ⅰ和Ⅱ1型为主,总有机碳含量(TOC)多大于1.0%,生烃潜量(S1+S2)多大于6.0mg/g,氯仿沥青“A”平均为0.2%,HI平均为322mg/g,有机质演化处于成熟阶段,为中等—好烃源岩。③研究区具有3期成藏特征,晚三叠世之前为第1期油气充注,未能聚集成藏,早侏罗世为第2期油气充注期,对应黄色荧光烃类包裹体;早—中白垩世为第3期油气充注期,对应蓝白色荧光烃类包裹体,后2期油气充注对百口泉组油气成藏起主要贡献作用。④研究区源储配置紧密性是导致玛湖西斜坡和玛湖东斜坡油气差异性聚集的核心要素。

Through core analysis and testing,seismic thickness prediction,inclusion accumulation period analysis and source-reservoir configuration study,the reservoir characteristics and hydrocarbon accumulation rules of Tri‐assic Baikouquan Formation in Mahu Sag of Junggar Basin were studied.The results show that:(1)The Triassic Baikouquan Formation in the slope area of Mahu Sag mainly develops fan delta deposits,with generally coarse litho-logies.Relatively high-quality reservoirs are mainly distributed in underwater distributary channel microfacies and a small number of mouth bar microfacies of fan delta front,dominated by feldspathic lithic sandstone con‐glomerate,followed by lithic sandstone conglomerate.The rocks are generally relatively dense.The core porosity ranges from 3.17%to 23.40%,with an average of 9.04%,and the permeability ranges from 0.01 mD to 934.00 mD,with an average of 0.73 mD.It belongs to low porosity and ultra-low permeability reservoirs.The main reservoir spaces are secondary dissolved pores,with intergranular fractures and other microfractures developed.(2)The oil and gas in the study area mainly come from the shale of alkali lake in Lower Permian Fengcheng Formation,with the maximum thickest greater than 400 m.It is a residual sea lagoon facies deposit with high water sali-nity,and the lithologies are mainly composed of dolomitic mudstone and mudstone.The organic matter is mainly of typeⅠandⅡ1.The total organic carbon(TOC)content is greater than 1.0%,the hydrocarbon generation potential(S1+S2)is generally greater than 6.0 mg/g,the average chloroform asphalt“A”is 0.2%,and the average HI is 322 mg/g.The organic matters are in the mature stage,and are medium-good source rocks.(3)There are three stages of hydrocarbon accumulation characteristics in the study area.Before the Late Triassic,it was the first stage of oil and gas filling,which failed to accumulate and form reservoirs.The Early Jurassic was the second stage of oil and gas filling,corresponding to yellow fluorescent hydrocarbon inclusions.The Early-Middle Cretaceous was the third stage of oil and gas filling,corresponding to blue white fluorescent hydrocarbon inclusions.The latter two stages of oil and gas filling played a major role in hydrocarbon accumulation of the Baikouquan Formation.(4)The tightness of the source-reservoir configuration in the study area is the core factor that leads to the differential accumulation of oil and gas in the west slope and east slope of Mahu Sag.