酒泉盆地下白垩统致密油类型、分布特征及勘探领域

Types, distribution and play targets of Lower Cretaceous tight oil in Jiuquan Basin, NW China

基于钻井和分析化验资料,对酒泉盆地致密油形成条件开展综合分析,指出勘探领域。酒泉盆地早白垩世经历了3期湖平面升降旋回,下白垩统发育中沟组、下沟组和赤金堡组3套优质烃源岩,主要形成自生自储型和下生上储型源储组合,发育泥云岩和砂砾岩致密储集层,形成泥云岩和砂砾岩2类致密油,"甜点"控制油气富集。泥云岩致密油具有"源储一体"的特征,裂缝沟通了基质微孔,孔隙-裂缝型和裂缝-孔隙型"甜点"规模展布;砂砾岩致密油以源储侧接为主,可划分为下生上储型、侧接型和"三明治"型,扇三角洲前缘有利相带和次生孔隙发育叠合区为"甜点"规模发育区。砂砾岩致密油以青西、花海和营尔等凹陷环凹分布的扇三角洲前缘沉积为主要勘探方向,有利勘探面积达550 km^2;泥云岩致密油以青西凹陷北西向裂缝发育带为主要勘探方向,有利勘探面积达100 km^2。

Based on drilling and laboratory data,the formation conditions of tight oil reservoirs in the Jiuquan basin were comprehensively analyzed and the exploration domains were sorted out.The Jiuquan basin underwent three cycles of lake level fluctuation in early Cretaceous,leaving three sets of high-quality source rocks,the Zhonggou,Xiagou and Chijinbao Formations in the Lower Cretaceous.There are two types of reservoir assemblages,source-reservoir in one type and source below reservoir type,and two types of tight reservoirs,argillaceous dolomite and conglomerate.The'sweet spots'control the enrichment of oil and gas.Argillaceous dolomite tight oil reservoirs have the characteristic of'integrated source-reservoir',with fractures connecting the matrix micro-pores,pore-fracture type and fracture-pore type'sweet spots'distributed in large scale.The sandy conglomerate tight oil reservoirs were formed by source-reservoir lateral connection,and can be divided into source below reservoir type,source-reservoir side by side type and'sandwich'type.The overlapping areas of the favorable facies belts of fan-delta front and the secondary pore developing belts are the'sweet spot'sites.The favorable areas for seeking conglomerate tight oil are fan-delta front deposits around the Qingxi,Ying'er and Huahai sags,with an exploration area of550km2;while the area to seek argillaceous dolomite tight oil is the NW fracture developed belt in Qingxi sag,with an exploration area of100km2.