多因素约束下的致密砂岩气藏离散裂缝特征及地质模型研究

Geological model and characteristics of dissrete fracture network in tight sandstone gas reservoir constrained by multi-factors

根据地震、测井、野外、岩心和薄片观察解释结果,从断裂成因机制出发,围绕天山前KX气藏开发需要,重新划分裂缝类型,界定尺度范围,划分裂缝期次,建立裂缝发育地质模式;分析构造、沉积、开发与裂缝参数的相关性,优选裂缝发育主控因素,采用'熵权赋值法'构建三维裂缝发育强度地质模型;采用确定法、序贯高斯插值法建立大、中、小尺度缝离散模型,最终构建气藏裂缝属性模型。结果表明:山前KX地区致密砂岩构造裂缝系统具有明显的多尺度性、期次性和多样性,它们符合断层-褶皱-裂缝共生演化系统;多因素权重约束下的多尺度建模方法适合于致密砂岩DFN裂缝模型建立,断层、大裂缝适合优选确定性建模方法,中、小尺度裂缝适合优选序贯高斯模拟方法,地质模型与实际井点数据和开发动态数据吻合度高,可直接应用于双介质渗流数值模拟和气藏防水方案的优化。

As important flow channels in tight sandstone reservoirs,fracture networks have complicated distribution characteristics and are controlled by multiple geological factors,which have restricted the modeling of fractured sandstone reservoirs.Based on seismic,geological,logging and thin sections data in the KX area,scale limits for fractures or faults were revised and re-evaluated in terms of from fracture mechanics and scale features. The formation periods of fractures were inferred by means of structural evolution history and fluid inclusions tests in order to establish geological model for fractures. Then relationships between the fracture parameters and tectonics,lithology,physical properties were analyzed in detail,and the main controlling factors for distribution of fracture parameters were concluded and optimized. A set of fault-fold-fracture symbiotic systems at different scales were then established. By using entropy weight theory,each factor was assigned relative weights in the above analyses,through which the single fracture intensity curve of every well and 3-D fracture intensity model were built. Finally a complete discrete fracture network model( DFN) for different scales is found using four key techniques,including using determination approach to build large-scale fracture model; and using SGCS to interpolate or build middle and small-scale fracture model. The results show that fractures of tight sandstone in the KX area have obvious multi-scaleand multi-stage characteristics. The optimized modeling method restricted by multiple geological factors is effective for establishing a discrete fracture model,offers feasible improvement over traditional DFN constructions,and provides a reliable geologic basis for progressive optimization and adjustment of tight sandstone reservoir development scheme.