天然裂缝是变质岩潜山储层重要的储集空间和有效的渗流通道。多尺度裂缝组合在空间形成连通性良好的连续网络是致密变质岩形成优质连片储层和获得高产、稳产的关键因素。综合利用成像测井、岩心、薄片和扫描电镜等资料,对变质岩潜山储层中不同尺度裂缝进行精细表征,建立了多尺度裂缝的幂律分布规律,明确了不同尺度裂缝对储层的贡献,分析了裂缝网络空间结构模式及其对产能的影响。结果表明:不同尺度裂缝系统相关参数发生规律性变化,随着裂缝规模的降低,裂缝发育程度呈幂律函数增加。宏观裂缝的规模大,连通性好,为致密储层提供重要的渗流通道,但裂缝密度相对较低,为储层提供的孔隙度有限。微观裂缝密度大,可以为致密储层提供储集空间,但裂缝规模较小,裂缝连通性有限,主要起到沟通基质孔隙的作用。根据不同尺度裂缝的空间组合模式,建立了5种缝网结构。其中,多尺度-高密度-多组系缝网和大尺度-中密度-多组系缝网能够形成大面积连续型优质储层,可以获得高产和稳产;小尺度-高密度-多组系缝网和大尺度-低密度-多组系缝网需要压裂改造才能获得稳产;小尺度-低密度-单组系缝网不能有效改善致密储层,很难获得工业油气流。

Natural fractures are important reservoir spaces and effective seepage channels for metamorphic buried hill reservoirs. For metamorphic rock reservoirs an interconnected network of multi-scale fractures is key to forming high quality contiguous reservoirs and achieving high, stable reservoir productivity. In this study, the power law distribution of fractures is established based on detailed characterization of multi-scale fractures using image log, core, thin section and SEM data. The contribution of malti-scale fractures to reservior storage is clarified, and the spatial pattern of fracture network and its impact on productivity is analyzed. According to the results, fracture systems of different scales in the study area show similar change patterns, i.e., the increase of fracture intensity follows the power law with the decrease of fracture size. In tight reservoirs, large and well connected macroscopic fractures provide important permeability, but their contribution to porosity is limited due to low fracture density; whereas microfractures with high fracture density can provide important reservoir space, but they mainly play the role of connecting matrix pores due to their small aperture and limited connectivity. According to spatial combination of multi-scale fractures, five types of fracture networks are recognized. Among them, the multi-scale/high-density/multi-set combination type and large-scale/medium-density/multi-set type networks can form large-scale continuous high-quality reservoirs and achieve high, stable production, while small-scale/high-density/multi-set type and large-scale/low-density/multi-set type networks require hydraulic fracturing to achieve stable production; small-scale/low-density/single-set type fracture network can not improve tight reservoir due to difficulty of obtaining industrial oil flow.