基于裂缝相表征的页岩气藏天然裂缝新模型--以涪陵页岩气田焦石坝区块为例

A new model of natural fractures in shale gas reservoirs based on fracture facies characterization:A case study from the Jiaoshiba Block of the Fuling Shale Gas Field

页岩储层天然裂缝的定量表征与地质建模是页岩气藏勘探开发的关键技术之一,但由于中国页岩气产区构造复杂,现有裂缝建模技术不能准确表征天然裂缝,特别是裂缝空间分布的合理性和准确度受到严重影响。为此,以四川盆地涪陵页岩气田焦石坝区块为例,利用三维地震资料结合曲率等地震属性,研究了上奥陶统五峰组—下志留统龙马溪组页岩地层的构造变形特征,通过构造应力解析划分了裂缝相,基于分区相控精细表征了裂缝特征参数,构建了裂缝模型,并与传统的裂缝建模进行了对比评价,并讨论了不同裂缝相的裂缝特征与页岩含气性、产能的关系。研究结果表明:①区内存在挤压、拉张和剪切3种应力作用,不同构造区域的主要应力作用存在差异,可刻画出6条挤压和平移断层;②区内可划分出挤压性高强度裂缝相、拉张性中强度裂缝相、挤压性低强度裂缝相、挤压性—剪切性中—高强度裂缝相、挤压性中强度裂缝相等5个裂缝相;③通过裂缝相对裂缝密度和产状参数的约束和控制,采取“相控建模”的思路,建立了能刻画不同构造应力背景下的天然裂缝差异模型。结论认为,不同裂缝相区域的页岩含气性和产能存在差异,基于储层裂缝相表征建立的裂缝新模型,预测结果与已钻井信息吻合较好,该模型对提高裂缝建模精准度并高效开发页岩气资源具有重要意义。

Quantitative characterization and geological modeling of natural fractures in shale reservoirs is one of the key technologies in the exploration and development of shale gas reservoirs.Due to the complex structures of shale gas producing areas in China,however,the existing fracture modeling techniques cannot accurately characterize natural fractures,and especially the rationality and accuracy of the spatial distribution of fractures is seriously impacted.Taking the Jiaoshiba Block of Fuling Shale Gas Field in the Sichuan Basin as an example,this paper studies the tectonic deformation characteristics of Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation shale strata by using 3D seismic data combined with seismic attributes such as curvature.The fracture facies is divided based on tectonic stress analysis,and the fracture characteristic parameters are accurately characterized based on zonal facies control.Then,a fracture model is established and compared with traditional fracture modeling.Finally,the relationships between fracture characteristics of different fracture facies and shale gas content and productivity are discussed.And the following research results are obtained.First,there are three kinds of stress in this area,i.e.,compressive stress,tensile stress,and shear stress,while the main stress effects in different tectonic regions are different,and accordingly six compressive and displacement faults can be characterized.Second,five fracture facies can be identified in this block,namely,compressive high strength fracture facies,tensile medium strength fracture facies,compressive low strength fracture facies,compressive-shear medium-high strength fracture facies,and compressive medium strength fracture facies.Third,under the constraint and control of relative fracture density and fracture occurrence parameters,a model which can describe the differences of natural fractures under different tectonic stress settings is established according to the idea of"facies control modeling".In conclusion,shale gas content and productivity are different in different fracture facies regions.The prediction result of the new fracture model established based on the characterization of reservoir fracture facies is in good agreement with drilling information,indicating that this model is of great significance in improving the precision and accuracy of fracture modeling and efficiently developing shale gas resources.