Establishment of multi-scale fracture model based on digital outcrop and its guidance for subsurface fracture prediction

Abstract

Objective Large deep carbonate reservoirs have been developed in the Tarim Platform area. Structural fractures are important seepage paths and reservoir spaces for deep carbonate reservoirs. Due to the strong heterogeneity of reservoirs, which is influenced by multiple geological factors, there is no effective technical method to solve the problem of quantitatively characterizing multiscale fractures in reservoirs. Methods In this study, digital outcrop technology was used to establish a 3D digital model of the outcrop area, and on this basis, outcrop fracture identification and quantitative description of fracture parameters were carried out. Emphatically, based on the outcrop fracture results, different modelling methods have been adopted for the development of multiscale fractures. Large-scale fractures were modelled via the deterministic modelling method. Optimal fusion modelling methods based on fractal dimension theory were used for medium-scale fractures. Due to the complex problem of small-scale fracture modelling, three significant models were distinguished via the multisource information fusion method: the fault strike model, the distance from fault model and a stratigraphic curvature model.A comprehensive development probability body of small-scale fractures was established. Construction of a small-scale fracture model based on collaborative simulation of multiple data points was constrained by the comprehensive probability volume. Consequently, restricted by the established comprehensive probability volume, a small-scale fracture model was constructed based on collaborative simulations of multiple sets of data. Finally, under the same grid system, a prototype geological model of the outcrop was obtained by superimposing the multiscale fracture model and the structural model. Results The results of the outcrop prototype geological model were applied to fracture modelling of underground reservoirs in the Yueman area of the Tarim Basin. The primary modelling parameters, such as fracture occurrence and density, and the main controlling factors of fracture development were described at multiple scales. By integrating the analysis results of the well point fractures, a reservoir multiscale fracture network model was constructed, which agreed well with the fracture interpretation and production data from a single well. Conclusion The results showed that outcrop prototype geological model can provide important research ideas and a geological basis for subsurface reservoir fracture modelling.

Keywords

• digital outcrop
• prototype geological model
• deep carbonate reservoir
• fracture modeling
• fractal dimension
• multi-scale
• subsurface fracture