四川盆地龙门山前构造带中三叠统雷口坡组四段碳酸盐岩储层裂缝形成机理

研究储层裂缝特征并弄清裂缝形成机理,对于明确储层类型和性质、开展裂缝分布预测、优化井位部署及明确裂缝对气藏开发的影响等都具有重要的意义。为此,以四川盆地龙门山前构造带中三叠统雷口坡组四段碳酸盐岩储层为例,利用岩心、薄片、成像测井及分析测试等资料,对该区碳酸盐岩储层天然裂缝的成因类型和发育特征进行研究,并结合埋藏史及构造演化史,在研究裂缝分期配套的基础上,分析成岩裂缝及构造裂缝的形成机理。研究结果表明:(1)龙门山前构造带雷四段碳酸盐岩储层主要发育构造裂缝和成岩裂缝两种成因类型,其中构造裂缝包括张性裂缝和剪切裂缝,以剪切缝为主,成岩裂缝包括溶蚀缝、构造—溶蚀缝以及缝合线;(2)溶蚀裂缝主要在准同生期、古表生期及埋藏期不同溶蚀流体溶蚀作用下形成,构造裂缝主要在印支晚期第二幕、印支晚期第三幕—燕山早中期、燕山中期—燕山晚期和喜马拉雅期龙门山构造带形成以及不断演化下的北西向挤压应力场作用下形成。结论认为,该区雷口坡组构造裂缝与成岩裂缝在各主要形成时期相互穿插,相互切割、限制,形成了储层中复杂的裂缝系统,有利于改善储层局部物性和提高气藏开发效果。

Formation mechanism of fractures in the carbonate reservoir of the 4th Member of Middle Triassic Leikoupo Fm in Longmenshan piedmont,Sichuan Basin

Studying the characteristics of reservoir fractures and clarifying the formation mechanisms of fractures are of great significance to defining reservoir types and properties, predicting fracture distribution, optimizing well location and figuring out the effect of fractures on gas reservoir development. In this paper, the 4th member of Leikoupo Fm, Middle Triassic in the Longmenshan piedmont of the Sichuan Basin was taken as an example. The genetic types and development characteristics of natural fractures there were studied based on core, thin section, image logging and testing data. Then, combined with burial history and tectonic evolution history, the formation mechanisms of tectonic fractures and diagenetic fractures were analyzed after fracture mating by stages was studied. And the following research results were obtained. First, tectonic fracture and diagenetic fracture are two main genetic types that are developed in the carbonate reservoir of the 4th Member of Leikoupo Fm in the Longmenshan piedmont. Tectonic fractures include tension fracture and shearing fracture, and the latter is dominant. Diagenetic fractures include dissolution fracture, structural-dissolution fracture and stylolite. Second, dissolution fractures are formed by the denudation of different dissolved fluids in the penecontemporaneous stage, ancient supergene stage and burial stage, and the tectonic fractures are formed under the effect of the NW compressional stress field with the formation and continuous evolution of Longmenshan piedmont during the second episode of the late Indosinian period, the third episode of the late Indosinian period to the early and middle Yanshanian period, the middle–late Yanshanian period and the Himalayan period. It is concluded that tectonic fractures and diagenetic fractures of Leikoupo Fm in this area are intercalated, cut and limited mutually in main formation stages, resulting in complex fracture systems in reservoirs, which are favorable for the improvement of local reservoir physical properties and gas reservoir development results.