A workflow of fracture geometry diagnostics of unconventional wells with complex fracture networks coupling fracture mapping and well testing

Abstract

Although many attempts have been made for fracture diagnostics, the complex fracture-network geometries are still ineffectively identified. To improve this situation, this study develops a new workflow to determine the geometries of complex fracture networks of unconventional wells. The theoretical basis of this workflow is containing fracture mapping based on Hough transform and well testing based on semi-analytical model. The flexibility and reliability on identifications of complex-fracture geometries are demonstrated through the case studies. Subsequently, the proposed workflow is applied to perform field application with microseismic data and identify the most likely fracture geometry. Results show that different geometries of fracture networks have different features of flow regimes, which are totally distinct from those of traditional bi-wing fractures. A special “hump” occurs if the fracture geometry is dendritic, and a feature of “fluid feed” from fracture branches to wellbore-connected fracture may occur, and the “pseudo boundary dominated flow” appears for an orthogonal fracture networks. The “fluid feed”, “fracture interferences”, and “pseudo boundary-dominated flow” are respectively demonstrated by a dual-porosity feature, namely “V-shape”, a “hump”, and a unit-slope line, which are good tools for fracture-geometry diagnostics. By performing a field application, the estimated fracture-network geometry of well QW1 from the Ordos Basin is obtained using the proposed workflow. The results demonstrate that mutually orthogonal fracture networks may not be generated. This study demonstrates a new way for fracture geometry diagnostics of unconventional wells with complex fracture networks.