Abstract

Reservoir engineering (and simulation) have historically paid little attention to the geomechanical behaviour of porous media. However, a number of important (primarily unconventional) recovery processes can be properly engineered only by including this effect (e.g., thermal recovery in oil sands, compaction drive in soft and unconsolidated reservoirs, chalk reservoirs, stress sensitive and microfractured media, waterflooding at fracture pressure, waste injection, coal seam stimulation, etc.). In addition, analysis of drilling and completion problems such as wellbore stability, sand production, fracturing or casing failure require knowledge of geomechanical behaviour of the reservoir. This paper gives an overview of the geomechanics of reservoir behaviour, describes recent advances in coupled reservoir and geomechanical modeling and presents case studies of field applications of this new tool. The examples show the potential of the coupled modeling to become a comprehensive tool for integrated reservoir management including reservoir, production and drilling aspects of field development. In each case, the use of the new, more comprehensive tools provided better understanding of recovery mechanisms and changed significantly the economic evaluation of the project.

Introduction

The geomechanical behaviour of porous media has become increasingly important to hydrocarbon operations. Numerical modeling of such processes is complex and has been historically caried out in three separate areas: geomechanical modeling (with the primary goal of computing stress/strain behaviour and its consequences in production engineering), reservoir simulation (essentially modeling multiphase flow and heat transfer in porous media), and fracture mechanics (dealing in detail with crack propagation and geometry).

In reservoir management, the geomechanical aspects of the engineering often bridge the various engineering specialities. In fact, the term "geomechanics" is often being applied very broadly to describe a wide range of reservoir phenomena.. Examples of the engineering problems involving geomechanics include:

  • Wellbore stability during drilling (in shales and in the reservoir)

  • Wellbore stability of open hole completions during production (in particular for horizontal wells)

  • Reservoir compaction and subsidence

  • Management of stress-sensitive reservoirs (in which permeability and porosity change with stress)

  • Naturally fractured reservoirs (fracture systems are stress sensitive)

  • Integrity of completions during production (casing failures)

  • Sand production (prediction of stability and minimization or prevention)

  • Analysis and engineering of waterflooding above fracture pressure (so called "thermal fracturing")

  • Recovery processes in unconsolidated sands (heavy oils and oil sands), including sand failure, dilation,

  • microchanelling and wormholing, and cold production

  • Conventional and unconventional hydraulic fracturing (frac-pack, high permeability soft formations...)

  • Completion and reservoir engineering of coalbed methane wells (fracturing, wellbore cavitation, productivity)

  • Waste disposal at fracturing pressure (oilfield, radioactive, chemical,...)

  • Drilling cuttings reinjection

  • Produced water reinjection (PWRI), in particular in "soft" formations.

The common feature of all of these problems is the strong interaction of the behavior of the solid (porous matrix and fractures) with the reservoir fluid flow and potentially induced fractures. Consequently, the analysis using conventi

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