基于复杂岩性识别的低渗储层综合分类评价

Q油田沙一段-沙二段广泛发育陆源碎屑与湖相碳酸盐岩的混合沉积，陆源碎屑与碳酸盐岩不同程度、不同形式的混合构成了多种岩性组合，总体上属于低孔低渗储层。针对该油田岩性复杂、低孔低渗等特点，利用岩芯、铸体薄片、阴极发光、扫描电镜及ECS测井等资料建立了一套基于复杂岩性识别的低渗储层综合评价方法。该方法选用岩性、有效厚度、渗透率、孔隙度、排驱压力、中值半径、分选系数共7种评价参数，其中排驱压力、中值半径和分选系数是属于微观孔喉结构参数，通过压汞资料得到，在地质条件约束下采用层次分析法求取各个参数的权重值并求得储层综合评价参数。基于该评价方法将该区储层划分为3类，其中I类储层以生屑云岩、鲕粒砂岩等岩性为主，溶蚀孔发育，孔隙连通性好，测试产能高，为低渗储层中的“甜点”。

Comprehensive Classification and Evaluation of Low Permeability Reservoirs Based on the Identification of Complex Lithological Characteristics

The SHA1 and SHA2 reservoirs of the Q oil field have widely-developed mixed sedimentary rocks composed of terrestrial debris and lacustrine carbonates. The mixing of these sediments in varying degrees and forms has resulted in a variety of lithological combinations; as a whole, the SHA1 and SHA2 reservoirs are low-porosity/low-permeability reservoirs. In view of the complex lithology and low porosity/permeability of this oil field, the data obtained from rock cores, casting sheets, cathodoluminescence and elemental capture spectroscopy (ECS) logging were used to establish a comprehensive evaluation method for low permeability reservoirs based on the identification of complex lithological characteristics. This method uses 7 evaluative parameters including lithological characteristics, effective thickness, permeability, porosity, displacement pressure, median radius, and sorting coefficient, in which displacement pressure, median radius, and the sorting coefficient are the structural parameters of microscopic pore throats which are obtained via mercury porosimetry. An analytic hierarchy process was then used to obtain the weights of each parameter and the comprehensive evaluative parameters of the reservoir, under constraints applied by the reservoirs' geological conditions. Based on this method of evaluation, the reservoirs in this region were classified into three types; in particular, the lithology of Type I reservoirs is mainly composed of silkites and oolitic sandstones with well-developed dissolution pores, high levels of pore connectivity, and have excellent deliverability test results. Hence, this is the "sweet spot" of these low-permeability reservoirs.