川西致密砂岩气藏有效砂体分布特征与形成机理

Distribution Characteristics and Formation Mechanism of Effective Sand Bodies in Tight Sandstone Gas Reservoirs in Western Sichuan

摘要: 有效砂体的横向展布、纵向叠置特征是开发层系、开发井型、井网设计的重要依据，为此，利用砂体长宽比、宽厚比及钻遇率研究砂体的几何形态，利用有效厚度、有效厚度与砂厚比值以及储能系数解剖有效砂体的发育程度、规模及含气性，结合沉积、成岩作用分析，明确有效砂体的形成机理。认为研究区有效砂体呈毯状分布，厚度较大且横向展布稳定，各小层砂体纵向叠置程度高，有效砂体的形成受其沉积环境的控制和成岩作用的改造，该区属三角洲平原分流河道沉积，沉积微相控制岩石粒度大小、成份及分布，溶蚀作用改善致密化岩石，改善了储集和渗流能力，最终形成有效砂体。落实有效砂体分布及成因是该区井位部署、高效评价与开发的基础。

Abstract: Design of development strata, well pattern and path are based on the distribution and superposition of effective sandbody. Therefore, the geometric parameters, such as the length-width ratio, width-thickness ratio and drilling rate, are used for the study of sandbody shapes. The development, scale and gas-bearing properties of effective sandbody are analyzed by the NTG (net to gross), effective thickness and storage coefficient. Meanwhile, the mechanism of effective sandbody is defined combined with sedimentation and diagenesis analysis. The effective sandbody in the study area is blanket shaped, thick and distributed laterally; sand layers in high overlapped are formed by the sedimentary environment and reformed by diagenesis processes. The effective sandbody that deposits in distributary channel of delta plain vary in particle size, composition, is controlled by the microfacies and improved by dissolution in reservoir property. To implement the distribution and genesis of the effective sandbody is the basis for well location, efficient evaluation and development of gas reservoir in this area.