东濮凹陷沙三段致密砂岩储层裂缝形成机制及对储层物性的影响

Fracturing and its Influence on the Compact Sandstone Reservoir in the Third Member of the Shahejie Formation in the Northern Dongpu Depression

为探讨东濮凹陷沙三段储层裂缝的发育特征、形成机制、主控因素及其对储层的影响,综合运用岩心观察、薄片鉴定、扫描电镜、流体包裹体分析等方法对裂缝进行了研究。结果表明:东濮凹陷沙三段储层中发育的裂缝按规模可分为宏观裂缝和微观裂缝两大类,按成因可分为构造缝、超压缝和成岩缝。构造缝走向以NNE向、NE向为主,其形成可分为两期,分别为40～35 Ma沙河街组沉积中后期和25～18 Ma东营组沉积末期。超压缝的形成与膏盐脱水、烃类充注和膏盐层封堵作用有关,形成于33～25 Ma东营组沉积时期。压实作用、溶解作用、收缩作用等成岩作用均可形成微裂缝。裂缝的形成序列为:早期构造缝-压裂缝-溶解缝-超压缝-收缩缝-晚期构造缝-溶解缝-压裂缝;裂缝的发育可以改善储层物性,宏观裂缝主要起渗流作用,微观裂缝既可作为有效的储集空间,又可作为酸性流体流动通道,产生次生孔隙带,提高储层孔隙度。

To gain further insight into the characteristics,origin,main controlling factors of the fractures in the E s 3 sandstone and their influence on the reservoirs of the Dongpu Depression,studies including core overview,thin section analysis,scanning electron microscopy and fluid-inclusion analyses were carried out.The results indicate that the fractures can be divided into macrofractures and microfractures according to their sizes,and three genetic types such as tectonic fractures,fractures related to overpressure and diagenetic fractures.The tectonic fractures are mostly NNE and NE striking and formed in 40-35 Ma and 25-18 Ma respectively.The formation of overpressure fractures is related to hydrocarbon filling and dehydration of salt and gypsum,which took place during 33 Ma to 25 Ma.The formation of diagenetic fractures is associated with diagenesis including compaction,dissolution and constriction.The formation sequence of the fractures is:the early tectonic fractures-pressure fractures-dissolving fractures-overpressure fractures-contraction fractures-late tectonic fractures-dissolving fractures-pressure fractures.The fractures can improve the physical property of the reservoir.Indeed,the macrofractures may play an important role in fluid seepage,whereas the microfractures can enhance the pore connectivity and form fluid flow channel and result in dissolution pores zone,and therefore significantly improve the physical property of the reservoir.