Impact of CO2 Injection on Flow Behavior of Coalbed Methane Reservoirs

Abstract

On the basis of observations at four enhanced coalbed methane (ECBM)/CO 2 sequestration pilots, a laboratory-scale study was conducted to understand the flow behavior of coal in a methane/CO 2 environment. Sorption-induced volumetric strain was first measured by flooding fresh coal samples with adsorptive gases (methane and CO 2 ). In order to replicate the CO 2 -ECBM process, CO 2 was then injected into a methane-saturated core to measure the incremental "swelling." As a separate effort, the permeability of a coal core, held under triaxial stress, was measured using methane. This was followed by CO 2 flooding to replace the methane. In order to best replicate the conditions in situ, the core was held under uniaxial strain, that is, no horizontal strain was permitted during CO 2 flooding. Instead, the horizontal stress was adjusted to ensure zero strain. The results showed that the relative strain ratio for CO 2 /methane was between 2 and 3.5. The measured volumetric strains were also fitted using a Langmuir-type model, thus enabling calculation of the strain at any gas pressure and using the analytical permeability models. For permeability work, effort was made to increase the horizontal stress to achieve the desired zero horizontal strain condition expected under in situ condition, but this became impossible because the "excess" stress required to maintain this condition was very large, resulting in sample failure. Finally, when CO 2 was introduced and horizontal strain was permitted, permeability reduction was an order of magnitude greater, suggesting that the "excess" stress would have reduced it significantly further. The positive finding of the work was that the "excess" stresses associated with injection of CO 2 are large. The excess stresses generated might be sufficient to cause microfracturing and increased permeability, and improved injectivity. Also, there might be a weakening effect resulting from repeated CO 2 injection, as has been found to be the case with thermal cycling of rocks.

U.S. DOE methodology for the development of geologic storage potential for carbon dioxide at the national and regional scale

“…Black and blue solid diamonds represent experimental data for Argonne premium coals at saturation (high pressure) and at low pressure (4 MPa wet), respectively. Gray solid squares with black outline represent data for two reservoir simulations (Botnen et al, 2009;Bromhal et al, 2005;Busch et al, 2003;Chikatamarla et al, 2004;Clarkson and Bustin, 1999;Day et al, 2008a;Durucan and Shi, 2009;Fitzgerald et al, 2005Fitzgerald et al, , 2006Goodman et al, 2007;Harpalani and Mitra, 2010;Harpalani et al, 2006;Jessen et al, 2008;Ozdemir and Schroeder, 2009;Pini et al, 2010;Reeves et al, 2005;Romanov and Soong, 2008;Ross et al, 2009;Siemons and Busch, 2007). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)…”

Sorption and changes in bulk modulus of coal — experimental evidence and governing mechanisms for CBM and ECBM applications

“…In this vertical case, the abovementioned heterogeneous swelling of macerals may result in opening of pre-existing microfractures (Harpalani and Mitra, 2010;Massarotto et al, 2010), or the formation of new microfractures (Hol et al, 2012b). Previous studies indicate that the latter results in irreversible and slightly non-recoverable deformation, and frequently extends pre-existing cracks on the maceral boundaries in the bedding plane (Hol et al, 2012b).…”

High pressure gas flow, storage, and displacement in fractured rock—Experimental setup development and application

“…23,20 Steady-state core flooding experiments are commonly conducted on a core sample under confined conditions and by applying gas pressure to one end and measuring the flow rate and pressure differential under the steady-state conditions. 24 For the measurement of gas flow rates during core flooding experiments, a flow meter with high accuracy, e.g., 0.5% of Full Range Output (FRO), is required to be incorporated into the flow measurement system.…”

“…The apparatus and approaches reported in the literature include (1) a True Triaxial Stress Coal Parameter (TTSCP) facility to measure the coal permeability to CO 2 using a quasi-steady flow method; 14,15 (2) a highpressure core flooding setup comprising a pressure cell, a syringe pump, and a micro gas chromatographer; [16][17][18][19] and (3) a high pressure triaxial apparatus capable of measuring the flow rate and deformation of the core samples. [20][21][22][23] Among the mentioned methods, the triaxial flooding approach has received more attention compared to other methods due to its capability to replicate the in situ stress conditions at different depths. Using a triaxial cell, the permeability of porous rock under underground stress conditions can be measured using a steady-state method, an unsteady-state method, or a transient approach.…”