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Title: Gas Flow Tightly Coupled to Elastoplastic Geomechanics for Tight- and Shale-Gas Reservoirs: Material Failure and Enhanced Permeability

We investigate coupled flow and geomechanics in gas production from extremely low permeability reservoirs such as tight and shale gas reservoirs, using dynamic porosity and permeability during numerical simulation. In particular, we take the intrinsic permeability as a step function of the status of material failure, and the permeability is updated every time step. We consider gas reservoirs with the vertical and horizontal primary fractures, employing the single and dynamic double porosity (dual continuum) models. We modify the multiple porosity constitutive relations for modeling the double porous continua for flow and geomechanics. The numerical results indicate that production of gas causes redistribution of the effective stress fields, increasing the effective shear stress and resulting in plasticity. Shear failure occurs not only near the fracture tips but also away from the primary fractures, which indicates generation of secondary fractures. These secondary fractures increase the permeability significantly, and change the flow pattern, which in turn causes a change in distribution of geomechanical variables. From various numerical tests, we find that shear failure is enhanced by a large pressure drop at the production well, high Biot's coefficient, low frictional and dilation angles. Smaller spacing between the horizontal wells also contributes to faster secondarymore » fracturing. When the dynamic double porosity model is used, we observe a faster evolution of the enhanced permeability areas than that obtained from the single porosity model, mainly due to a higher permeability of the fractures in the double porosity model. These complicated physics for stress sensitive reservoirs cannot properly be captured by the uncoupled or flow-only simulation, and thus tightly coupled flow and geomechanical models are highly recommended to accurately describe the reservoir behavior during gas production in tight and shale gas reservoirs and to smartly design production scenarios.« less
Authors:
 [1] ;  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
1182652
Report Number(s):
LBNL--6961E
Journal ID: ISSN 1086-055X
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
SPE Journal
Additional Journal Information:
Journal Volume: 19; Journal Issue: 06; Journal ID: ISSN 1086-055X
Publisher:
Society of Petroleum Engineers (SPE)
Research Org:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Earth Sciences Div.
Sponsoring Org:
USDOE; US EPA, Office of Water
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; 03 NATURAL GAS; 02 PETROLEUM fracturing, geomechanics