多尺度离散裂缝性致密砂岩气藏数值试井新方法--以塔里木盆地克拉苏气田为例

A new numerical well test method of multi-scale discrete fractured tight sandstone gas reservoirs and its application in the Kelasu Gas Field of the Tarim Basin

塔里木盆地克拉苏气田白垩系气藏是罕见的超深、超高压裂缝性致密砂岩气藏,基质—裂缝—断层多尺度离散裂缝发育,储层动静态描述难以满足开发的需要。为此,将天然裂缝网络随机生成和非结构化离散裂缝建模方法相结合,突破传统连续介质试井模型,建立了一种基于基质、裂缝、断层(大裂缝、小断层)三种孔隙介质的直井数值试井模型,并采用混合单元有限元方法对模型进行求解,得到了不同随机裂缝网络下的试井典型曲线。研究结果表明:①基于实测资料可将裂缝性致密砂岩气藏的缝网分布模式划分为三类,讨论了缝网随机生成对试井典型曲线的影响,并将离散裂缝试井模型与传统连续介质试井模型的结果进行了对比,明确了传统连续介质模型的适用条件;②离散裂缝模型与双重孔隙介质模型结果存在较大差异,双重孔隙介质模型是离散裂缝模型中裂缝均匀分布且间距无限小的一种特例;③讨论了三种缝网分布模式下的试井曲线特征,应用所建立的随机离散裂缝试井解释模型成功解释了常规双重孔隙/三重孔隙连续介质无法解释的试井曲线,曲线拟合效果理想,解释得到的参数合理。结论认为,新模型、新方法揭示了不同尺度介质间逐级动用、协同供气的开发机理,解释了井间产能差异大、井间压力响应异常迅速的开发特征,为同类型气藏开发提供了借鉴。

The cretaceous gas reservoir in Kelasu Gas Field of the Tarim Basin is a rare ultra-deep and ultra-high pressure fractured tight sandstone gas reservoir where multi-scale discrete fractures of matrix,fracture and fault are developed,so its development cannot be conducted just based on static and dynamic reservoir description.In order to solve this problem,this paper establishes a numerical well test model of vertical wells based on matrix,fractures and faults(large fractures and small faults)by combining the random generation of natural fracture networks with the unstructured discrete fracture modeling method to break through the traditional continuous medium well test model.In addition,the model is solved by using the finite element method with mixed element,and the typical well test curves under different random fracture networks are obtained.And the following research results are obtained.First,based on the measurement data,the fracture network distribution modes of fractured tight sandstone gas reservoirs are classified into three categories.The influence of random generation of fracture networks on typical well test curves is discussed.The results of discrete fracture well test model are compared with those of the traditional continuous medium well test model,and the applicable conditions of the traditional continuous medium well test model is determined.Second,there are great differences between the results of discrete fracture model and those of dual porosity medium model.The dual porosity medium model is a special case of the discrete fracture model,in which the fractures are evenly distributed within finitely small spacing.Third,the characteristics of well test curves under three fracture network distribution modes are discussed.The well test curves that cannot be interpreted by the conventional dual\triple porosity continuous medium model are successfully interpreted by using the established well test interpretation model of random discrete fracture.The curve mathing effect is ideal and the interpreted parameters are reasonable.In conclusion,the new model and the new method reveal the development mechanism of step-by-step production and coordinated gas supply between media of different scales,explain the development characteristics of large inter-well productivity difference and abnormal rapid inter-well pressure response,and provide a reference for the development of similar gas reservoirs.