Characterization of irregular complex fractures in unconventional oil and gas reservoirs

Abstract

Unconventional oil and gas resources have large reserves and are difficult to develop. Reservoir fracturing is a key technical means for the development of unconventional oil and gas resources. Natural fractures and induced fractures are irregular and complex. To address the issue that existing fracture characterization methods cannot accurately depict the true shapes and width variations of fractures, a method based on unstructured PEBI grids for characterizing irregular and complex fractures was proposed. First, a natural fracture characterization process based on PEBI grids was established, allowing for accurate characterization of natural fractures in any region or a specified area. Second, a characterization and optimization method for induced fractures based on Delaunay triangulation and PEBI grids was developed, analyzing the impact of grid size and optimization iterations on fracture characterization accuracy. Third, a method for characterizing non-planar fractures using unstructured grids was established, enabling the depiction of curved fractures, making the fracture morphology and distribution more consistent with actual conditions. Fourth, a method for characterizing non-uniform fracture width was proposed, achieving fine characterization of fractures with non-uniform distribution of width and conductivity along the same fracture. Fifth, a complex fracture network characterization method coupling irregular induced fractures and irregular natural fractures in the whole area and specified regions was realized. For fracture network characterization under complex conditions such as large-scale intersections of natural and induced fractures, non-uniform fracture width distribution, and non-planar frac- tures, adjusting the number of grid optimization iterations could improve the quality of the fracture network characterization. Utilizing the advantage of PEBI grids to flexibly and accurately approximate complex fracture boundary conditions, this method enabled the rapid and accurate handling of a large number of irregular natural and induced fractures. The developed method for characterizing irregular and complex fractures helps improve the accuracy of fracture network characterization and numerical simulation calculations in unconventional oil and gas reservoirs.

Keywords

• unconventional oil and gas reservoir
• irregular fracture
• complex fracture network
• fracture characterization
• delaunay triangular grid
• pebi grid