ABSTRACT:

An advanced 3D hydraulic fracturing model has been developed for simulating complex hydraulic fracturing such as multistage hydraulic fracture operation in shale and tight plays. The model utilized eXtended Finite Element Method (XFEM) to simulate injection of fracturing fluid and pretentious hydraulic fracture propagation in challenging geomechanical conditions, e.g. high ductility/brittleness, anisotropy, leak-off and tectonics. The advanced XFEM hydraulic fracturing model has been tested and validated for single and multistage hydraulic fracturing by comparing with analytical and numerical models, and large-scale laboratory tests. The validated advanced model was subsequently applied to complex multistage hydraulic fracture operations such as plug-and-perf and sliding sleeve ball-drop, to optimize multistage hydraulic fracture design in PETRONAs' unconventional assets.

1. Introduction

There are many commercially available hydraulic fracturing simulators which, however, could not aptly simulate complex hydraulic fracture operation including pore pressure changes and resulting stress-changing effects, due to their pseudo-3D or limited 3D capabilities. A full 3D and more advanced hydraulic fracturing simulator is, therefore, required to simulate complex hydraulic fracture operations in various geomechanical conditions and to optimize the hydraulic fracture design. The state-of-the-art XFEM 3D hydraulic fracturing model presented in this paper can simulate the pore pressure change and resulting stress-changing effects with full 3D poro-elastic analysis capability. The advanced capabilities lead to an improved hydraulic fracturing simulation and consequently, fracture design optimization, especially in challenging geomechanical conditions.

The advanced XFEM hydraulic fracturing model has been developed and validated in order to support PETRONAs' unconventional assets in optimizing multistage hydraulic fracture design to reduce well completion cost and improve well productivity. The model validations were conducted against multiple analytical and numerical models, and large-scale laboratory tests published in open literatures. The validation results show reasonable to good predictions for all the models and laboratory tests.

2. Methodlogy and Concept Model

A numerical method and workflow have been developed to answer the challenges of complex hydraulic fracture operations with full 3D poro-elastic analysis. The overall method is based on eXtended Finite Element Methods (Moës et al., 1999), which is a numerical technique extending the conventional Finite Element Method (FEM) based on the concept of partition of unity to allow the presence of discontinuities in an element by enriching degrees of freedom with special displacement functions.

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