On Damage Propagation in a Soft Low-Permeability Formation

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In this presentation, we develop a mathematical model of fluid flow with changing formation properties. The modification of formation permeability is caused by development of a connected system of fractures. As the fluids are injected or withdrawn from the reservoir, the balance between the pore pressure and the geostatic formation stresses is destroyed. If the strength of the rock is not sufficient to accommodate such an imbalance, the cementing bonds between the rock grains become broken. Such a process is called damage propagation. The micromechanics and the basic mathematical model of damage propagation have been studied in [7]. The theory ... continued below

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5 pages

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Silin, D.; Patzek, T. & Barenblatt, G.I. November 18, 2003.

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In this presentation, we develop a mathematical model of fluid flow with changing formation properties. The modification of formation permeability is caused by development of a connected system of fractures. As the fluids are injected or withdrawn from the reservoir, the balance between the pore pressure and the geostatic formation stresses is destroyed. If the strength of the rock is not sufficient to accommodate such an imbalance, the cementing bonds between the rock grains become broken. Such a process is called damage propagation. The micromechanics and the basic mathematical model of damage propagation have been studied in [7]. The theory was further developed in [3], where new nonlocal damage propagation model has been studied. In [2] this theory has been enhanced by incorporation of the coupling between damage propagation and fluid flow. As it has been described above, the forced fluid flow causes changes in the rock properties including formation permeability. At the same time, changing permeability facilitates fluid flow and, therefore, enhances damage propagation. One of the principle concepts introduced in [3] and [2] is the characterization of damage by a dimensionless ratio of the number of broken bonds to the number of bonds in pristine rock per unit volume. It turns out, that the resulting mathematical model consist of a system of two nonlinear parabolic equations. As it has been shown in [6] using modeling of micromechanical properties of sedimentary rocks, at increasing stress the broken bonds coalesce into a system of cracks surrounding practically intact matrix blocks. These blocks have some characteristic size and a regular geometry. The initial microcracks expand, interact with each other, coalesce and form bigger fractures, etc. Therefore, as the damage is accumulated, the growing system of connected fractures determines the permeability of the reservoir rock. Significant oil deposits are stored in low-permeability soft rock reservoirs such as shales, chalks and diatomites [9, 10]. The permeability of the pristine formation matrix in such reservoirs is so low that oil production was impossible until hydraulic fracturing was applied. For development of correct production policy, it is very significant to adequately understand and predict how fast and to what extend the initial damage induced by drilling and hydrofracturing will propagate into the reservoir. The importance of fractures for rock flow properties is a well-established and recognized fact [4, 9, 5]. Different conceptual models have been developed [8]. In this study, we propose a damage propagation model based on a combination of the model of double-porosity and double-permeability medium [4] and a modification of the model of damage propagation developed in [2].

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5 pages

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OSTI as DE00837422

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  • Second International Symposium 'Dynamics of Fluids in Fractured Rocks, Berkeley, CA (US), 02/10/2004--02/12/2004

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  • Report No.: LBNL--55993
  • Grant Number: AC03-76SF00098
  • Office of Scientific & Technical Information Report Number: 837422
  • Archival Resource Key: ark:/67531/metadc777058

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  • November 18, 2003

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • April 4, 2016, 6:24 p.m.

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Silin, D.; Patzek, T. & Barenblatt, G.I. On Damage Propagation in a Soft Low-Permeability Formation, article, November 18, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc777058/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.