四川盆地西部彭州气田中三叠统雷口坡组四段上亚段白云岩孔隙表征、分布及成因

彭州气田雷口坡组四段上亚段的微生物白云岩和微粉晶白云岩是油气主要的储集岩。在此，采用了多种分析手段及统计方法，深入研究了主要岩性的孔隙类型、物性和孔隙结构参数及其与岩相（尤其是微生物岩）、白云石晶体大小等关系，综合划分出4种储集体类型及致密层段（隔层），初步提出了孔隙形成与分布的主控因素。研究表明：具残余藻结构的白云岩占近四分之三多为泥微晶、粉晶白云石；高频旋回中，自下而上，以藻凝块-藻球粒（藻砂屑）-藻纹层-纹层泥晶；晶粒以颗粒-粉（细）晶-微晶-泥晶呈规律变化；中三叠世的干燥-炎热、超盐度和碱性沉积环境利于微生物岩发育，潮下带上部凝块-叠层石至潮间藻纹层-叠层石至潮上带的薄（藻）纹层的向上变浅的米级旋回，导致中、上部往往发育高孔渗带；早期快速的渗透回流白云岩化及大气淡水作用、浅埋藏期的烃类充注及多期构造裂隙对孔隙演化均起了重要的作用。

Characteristics,distribution and origin of dolomite reservoir in the upper Lei 4 member of the Middle Triassic,Pengzhou gas field,western Sichuan Basin

Microbiological and micritic-calcisiltic dolomites have been regarded as the dominant reservoir lithology in the upper section of the 4th member of the Leikoupo Formation in Pengzhou gas field. Multiple analytical and statistical methods are applied to study the pore types, physical properties, and pore structure parameters, as well as their impact on lithofacies (especially for microbialite) and crystal size of the dolomites. Besides, four types of reservoirs and the tight zones (interlayers) are identified. The main factors controlling pore formation and distribution are hereby proposed. The results show that dolomites with various microbial textures account for nearly 3/4 of the total formation, most of which are silty-micritic and calcisiltic dolomites. In a high-frequency cycle, the dolomite textures vary upwards from algal clot, to algal spheroid (or algal arene), to algal lamina, and then to laminated silty types. In terms of grain size, a cycle is composed regularly of grained, very fine-(fine-) crystal, micritic, and silty dolomites from the bottom to the top. A dry, hot and alkaline sedimentary environment of hypersalinity prevailed during the Middle Triassic, favorable for the development of microbialites. The meter-scale shallowing-upward cycles of thin (algal) laminae, that is, from the thrombolites and stromatolites in the upper part of the subtidal zone to the intertidal algal laminae-stromatolites, and then to the thin (algal) laminae in the supratidal zone, caused the well development of zones of high porosity and permeability in the upper and middle parts of the sequence. In addition, factors including rapid seepage reflux dolomitization and meteoric freshwater dissolution, early hydrocarbon charging in the shallow burial stage, and multi-stage tectonic fracturing, all play an important role in pore development and preservation.