凝灰质砂砾岩复合型储集空间特征及其成因——以莱州湾南斜坡沙河街组为例

    CHARACTERISTICS AND GENESIS OF COMPOUND RESERVOIR SPACE IN TUFFACEOUS GLUTENITE—A CASE FROM SHAHEJIE FORMATION ON THE SOUTH SLOPE OF LAIZHOU SAG

    • 摘要: 渤海海域莱州湾南斜坡沙河街组近源凝灰质砂砾岩中发现了高丰度油藏, 与传统近源砂砾岩储层物性差的认识不同, 研究区凝灰质砂砾岩受凝灰质成分和沉积作用双重控制, 发育复合型储集空间。通过岩心、薄片、场发射扫描电镜、阴极发光和压汞等多种方法落实了沙河街组凝灰质砂砾岩发育继承型、成岩型、构造型和复合型4类13种储集空间类型, 并首次提出了继承型储集空间的概念, 指出砂砾岩优质储层具有继承型和后期改造型储集空间相互叠加的显著特征。继承型储集空间主要继承了母岩中的风化淋滤孔、凝灰质脱玻化孔、构造破碎缝、黏土收缩缝以及搬运过程中产生的机械破碎缝等多种储集空间类型。继承型孔缝约占总孔隙的41%, 对整个砂砾岩优质储层的发育起到决定性作用。研究发现, 成岩型和构造型储集空间与继承型孔缝的发育程度密切相关, 继承型孔缝越发育后期成岩流体和构造运动对其改造程度越大, 越容易发育优质储层。在此基础上明确了(母岩)同沉积期风化作用、砾间凝灰质成岩蚀变、砾石支撑作用和溶蚀改造作用是砂砾岩复合型储层的4种主要成因机制, 并建立了该类储层的沉积成岩演化模式。这4种特殊的储层成因机制, 支撑了渤海近源砂砾岩优质储层的勘探与实践。

       

      Abstract: A large number of hydrocarbon reservoirs have been discovered in the near source tuffaceous glutenite of Shahejie Formation in the Laizhou Sag of the Bohai Sea. Different from the traditional understandings that near source sand and gravel deposits are usually poor in physical properties, the tuffaceous glutenite is rich in hydrocarbon accumulation under the control of the composition and sedimentation of the tuffaceous matter. Complex reservoir spaces are well developed. By means of cores, thin sections, field emission scanning electron microscopy, cathodoluminescence and mercury injection, 4 types of reservoir space are identified in the tuffaceous glutenite of Paleogene, i.e. the inherited, the diagenetic, the structural and the mixed. We proposed and defined for the first time in this paper the concept of glutenite compound reservoir. The glutenite reservoir, as observed, is commonly superimposed by two or more types of reservoir spaces under the control of various geological factors. Inherited reservoir spaces, which includes leaching holes, devitrification holes, structural fractures, clay shrinkage cracks, primary fractures, and mechanical fractures formed during transportation, are often changed by later reformation. Inherited reservoir spaces account for about 41% of the total, which play a critical role in the glutenite reservoir. Diagenetic and structural reservoir spaces are closely related to the development degree of inherited reservoir spaces. If the inherited reservoir space exists, the late diagenetic fluid and tectonic movement may further increase the reservoir space and the quality of glutenite reservoirs will be much improved. Therefore, the genesis of sandstone conglomerate reservoirs may be classified into 4 types i.e. reservoirs formation by weathering and deposition, reservoirs formation by alteration of tuffaceous matter, the change in supporting matter and later dissolution. A sedimentary and diagenetic evolutionary model is then established upon the above study of the compound reservoir space.

       

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