Study of the Transient Flow Behavior of Complex Fractures by Use of Semi-Analytical Models

• Author / Creator

  Teng, Bailu

• Hydraulic fracturing treatment has been widely applied to enhance the well productivity in tight/shale formations, and history matching method is one of the most commonly used technique to help us obtain the information (e.g., fracture geometry and fracture conductivity) of the induced fractures. Due to the fact that the history matching work commonly requires running numerous fracture models to find the best match between the history production data and the simulated production data, it is highly necessary to work out a high computation-efficiency method to characterize the transient flow behavior of the hydraulic fractures in order to reduce the simulation time. Since the semi-analytical method has natural advantage in terms of computational efficiency, various semi-analytical models have been proposed in recent years to conduct the history matching work on the hydraulic fractures. At present, the existing semi-analytical models are normally developed for vertical planar fractures. However, due to the appearance of the complex stress field in the formations, a complex fracture can be induced after the fracturing treatment. This complex fracture can be a horizontal fracture (HF) with irregular geometry, a partially-penetrating-inclined fracture (PPIF), an orthogonal refracture, a reoriented refracture, or a non-uniform-width fracture. In order to conduct the history matching work on such complex fractures, it is imperative for us to develop the corresponding semi-analytical models to characterize the transient flow behavior of these complex fractures.
  In this thesis, the author discretizes the complex fractures into small segments and characterizes the fluid flow in the fracture system with the numerical method (implicit finite difference method). Whereas, the fluid flow in the matrix system is characterized by an analytical method (Green function method). Coupling the numerical fracture flow equations with the analytical matrix flow equations yields the semi-analytical models for characterizing the transient flow behavior of the complex fractures, including horizontal fractures, partially penetrating inclined fractures, reoriented refractures, and orthogonal refractures. Afterward, the author investigates the flow regimes that can be observed during the production period of the fractures by use of the proposed semi-analytical models. These flow regimes include wellbore after flow, fracture radial flow, bilinear flow, inclined formation linear flow, vertical elliptical flow, vertical pseudo-radial flow, inclined pseudo-radial flow, horizontal formation linear flow, horizontal elliptical flow, horizontal pseudo-radial flow, and boundary dominated flow. With the aid of these proposed models, the author also conducts history matching work on some real field cases to obtain the fracture conductivity and fracture dimension.
  In addition, the author proposes a new fracture permeability model to characterize the relationship between the fracture permeability, fracture width, proppant-pack porosity, and proppant-pack permeability. The results calculated with the fracture permeability model show that the fluid flow in a fracture can be divided into viscous-shear dominated (VSD) regime, transition regime, and Darcy-flow dominated (DFD) regime. If Darcy parameter is sufficiently large, the effect of proppant-pack permeability on fracture permeability can be neglected and the fracture permeability can be calculated with viscous-shear-dominated fracture-permeability (VSD-FP) equation (i.e., ), whereas, if Darcy parameter is sufficiently small, the effect of viscous shear on fracture permeability can be neglected and the fracture permeability can be calculated with the Darcy-flow-dominated fracture-permeability (DFD-FP) equation (i.e., ). Both the VSD-FP equation and DFD-FP equation are special forms of the proposed fracture permeability model.

• Subjects / Keywords

  • petroleum

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-aqc5-n767

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.