泾河地区中生界致密油藏天然裂缝发育主控因素及模式

Study on the main controlling factors and development models of Mesozoic natural fractures in the Jinghe oilfield,South of Ordos Basin,China

研究鄂尔多斯盆地南部泾河油田长8油藏天然裂缝的发育主控因素及模式。通过野外露头、岩心、常规测井和成像测井资料,开展井剖面天然裂缝的识别。在数据的处理上,利用单一变量法分别对比工区内断层和裂缝的力学性质、统计裂缝发育指数与相邻断层距离的关系、不同岩性中裂缝的发育情况、裂缝发育指数与砂地比的关系、长8地层的构造曲率与裂缝发育指数的关系,结果表明:断层伴生2组共轭剪切裂缝,只有一组较发育,这些裂缝离断层越近,裂缝发育指数越高;随着泥质含量的增加,岩性逐渐向泥岩转化,天然裂缝的发育程度逐渐降低,平面上看,天然裂缝多发育在砂地比值较高的地方;构造曲率越大,天然裂缝发育的程度越高。泾河地区长8段裂缝发育的主控因素为岩性、构造变形和断层。其中断层对裂缝发育的影响表现在裂缝发育指数随断层距离的增加而减小,并且为控制裂缝发育的最主要因素;岩性中的脆性成分越高,裂缝越发育;构造变形程度越高,构造张裂缝也越发育。

The development of natural fractures in the typical tight sandstone reservoir of Jinghe oilfield is the key to the high yield of this kind of reservoir. The identification of natural fractures in drilling well profile is carried out through the studies of field outcrop data, drilling core data, conventional logging data and imaging logging data. Based on the comparison of the mechanical properties of faults and fractures and the analysis of relationship between fracture development indexand the distance of adjacent faults in work area, two sets of conjugate shear fractures are identified. One set of fracture is close to the fault with higher fracture development index and is well developed than the other set. Comparison in different lithologies of the fracture development and analysis of fracture development index and ratio of sandstone with strata thickness shows that with the increase of clay content, lithology are gradually changed to mudstone, fracture development degree is reduced gradually, and fractures are usually developed in place with higher ratio of sandstone to strata thickness. The relationship between the structural curvature of the Chang-8 strata and the fracture growth index is analyzed. It is indicated that the larger the structural curvature is, the higher the degree of the development of the fractures. The understanding of development characteristics of natural fractures in Chang-8 reservoir of Jinghe oilfield and its main controlling factors are of important significance on the evaluation of the reservoir, and on the future production development strategy and development plan.