John Mansoori

Bio: John Mansoori is an academic researcher. The author has contributed to research in topics: Pore water pressure & Permeability (earth sciences). The author has an hindex of 2, co-authored 2 publications receiving 960 citations.

How Permeability Depends on Stress and Pore Pressure in Coalbeds: A New Model

Abstract: In naturally fractured formations, such as coal, permeability is sensitive to changes in stress or pore pressure (i.e., effective stress). This paper presents a new theoretical model for calculating pore volume compressibility and permeability in coals as a function of effective stress and matrix shrinkage, using a single equation. The equation is appropriate for uniaxial strain conditions, as expected in a reservoir. The model predicts how permeability changes as pressure is decreased (i.e., drawdown). Pore volume compressibility is derived in this theory from fundamental reservoir parameters. It is not constant, as often assumed. Pore volume compressibility is high in coals because porosity is so small. A rebound in permeability can occur at lower drawdown pressures for the highest modulus and matrix shrinkage values. We have also history matched rates from a {open_quotes}boomer{close_quotes} well in the fairway of the San Juan basin using various stress-dependent permeability functions. The best fit stress-permeability function is then compared with the new theory.

How Permeability Depends on Stress and Pore Pressure in Coalbeds: A New Model

Abstract: In naturally fractured formations, such as coal, permeability is sensitive to changes in stress or pore pressure (i.e., effective stress). This paper presents a new theoretical model for calculating pore volume compressibility and permeability in coals as a function of effective stress and matrix shrinkage, using a single equation. The equation is appropriate for uniaxial strain conditions, as expected in a reservoir. The model predicts how permeability changes as pressure is decreased (i.e., drawdown). Pore volume compressibility is derived in this theory from fundamental reservoir parameters. It is not constant, as often assumed. Pore volume compressibility is high in coals because porosity is so small. A rebound in permeability can occur at lower drawdown pressures for the highest modulus and matrix shrinkage values. We have also history matched rates from a {open_quotes}boomer{close_quotes} well in the fairway of the San Juan basin using various stress-dependent permeability functions. The best fit stress-permeability function is then compared with the new theory.

Volumetric strain associated with methane desorption and its impact on coalbed gas production from deep coal seams

Abstract: The permeability of deep (1000 m; 3300 ft) coal seams is commonly low. For deep coal seams, significant reservoir pressure drawdown is required to promote gas desorption because of the Langmuir-type isotherm that typifies coals. Hence, a large permeability decline may occur because of pressure drawdown and the resulting increase in effective stress, depending on coal properties and the stress field during production. However, the permeability decline can potentially be offset by the permeability enhancement caused by the matrix shrinkage associated with methane desorption. The predictability of varying permeability is critical for coalbed gas exploration and production-well management. We have investigated quantitatively the effects of reservoir pressure and sorption-induced volumetric strain on coal-seam permeability with constraints from the adsorption isotherm and associated volumetric strain measured on a Cretaceous Mesaverde Group coal (Piceance basin) and derived a stress-dependent permeability model. Our results suggest that the favorable coal properties that can result in less permeability reduction during earlier production and an earlier strong permeability rebound (increase in permeability caused by coal shrinkage) with methane desorption include (1) large bulk or Young's modulus; (2) large adsorption or Langmuir volume; (3) high Langmuir pressure; (4) high initial permeability and dense cleat spacing; and (5) low initial reservoir pressure and high in-situ gas content. Permeability variation with gas production is further dependent on the orientation of the coal seam, the reservoir stress field, and the cleat structure. Well completion with injection of N2 and displacement of CH4 only results in short-term enhancement of permeability and does not promote the overall gas production for the coal studied.

Drawdown Induced Changes in Permeability of Coalbeds: A New Interpretation of the Reservoir Response to Primary Recovery

Abstract: A model for pore pressure-dependent cleat permeability is presented for gas-desorbing, linear elastic coalbeds under uniaxial strain conditions experienced in producing reservoirs. In the model, changes in the cleat permeability of coalbeds, which are idealised to have a bundled matchstick geometry, is controlled by the prevailing effective horizontal stresses normal to the cleats. Variations in the effective horizontal stresses under uniaxial strain conditions are expressed as a function of pore pressure reduction during drawdown, which includes a cleat compression term and a matrix shrinkage term that have competing effects on cleat permeability. A comprehensive analysis has revealed that the shape of the stress – pore pressure curve is predominantly determined by the magnitude of recovery pressure and rebound pressure relative to the initial reservoir pressure. A total of five possible scenarios have been identified with regard to response of the horizontal stress function to reservoir drawdown. When applied to four coalbed wells at two separate sites in the fairway of the San Juan basin, the model predictions at one site, where the three wells have shown increased absolute permeability during gas production, are in excellent agreement with the published pore pressure dependent permeability changes that were obtained independently from history matching the field production data. At a separate site the model correctly predicts, at least qualitatively, a strong permeability rebound at lower drawdown pressures that has been inferred through history matching the production data. An analysis of the effects of initial reservoir pressure on the response of effective horizontal stress to drawdown was carried out, with reference to the range of pressure likely to be encountered in the San Juan basin. The implications of this in terms of pore pressure dependent permeability are discussed.