致密砂岩储层岩石脆性评价及相关因素分析

Evaluation of rock brittleness and analysis of related factors for tight sandstone reservoirs

致密砂岩脆度是致密油气藏勘探开发的关键因素之一。以龙门山前陆盆地为例,基于野外露头岩样、钻井岩心、岩石薄片、地球化学特征等地质资料,通过镜下砂岩成分鉴定和X射线衍射矿物含量分析,发现研究区砂岩岩屑含量较高,因此建立了符合区域背景的岩石脆度公式,结果表明龙门山前陆盆地致密砂岩储层脆度较高。岩石力学特征分析表明,研究区内储层岩体具有杨氏模量高、泊松比低的特点,具有较好的脆性特征和可压裂潜力。最后,进行了砂岩体地球化学特征指数和砂岩脆度的相关性分析,论证了致密砂岩成分变异指数(ICV)和化学风化指数(CIA)与岩石脆度的关系。

Brittleness of tight sandstone is a key element for exploration and development of tight reservoirs. Taking the Longmenshan Foreland Basin as an example, microscopic identification of sandstone composition and mineral content analysis with X-ray diffraction were carried out with the geological data, e.g. outcrop rock samples, drilling cores, rock slices, and geochemical characteristics. It was demonstrated that the sandstone has higher debris content. Accordingly, a rock brittleness formula corresponding to the regional setting was established. The research results show that the tight sandstone reservoirs in the Longmenshan Foreland Basin are more brittle. According to the analysis of rock mechanics features, the reservoir rocks in the study area are characterized by high Young＇s modulus and low Poisson＇s ratio, with better brittle behavior and fracturing potential. Finally, the correlation between geochemical characteristic index and brittleness of sandstones was analyzed, and the relationship between index of compositional variability （ICV） and chemical index of alteration （CIA） of tight sandstones were discussed.