1、Deformation Dependent Permeability of Coal for Coalbed Methane (CBM) Recovery and CO2 SequestrationG. X. Wang1, Z. T Wang1,2, V. Rudolph1 and P. Massarotto11 Division of Chemical Engineering, University of Queensland, Qld 4074, AUSTRALIA2 Department of Mining Engineering, China University of Mining
2、and Technology, Xuzhou 221008, CHINAAbstractAn alternative approach is proposed in this paper to address the difficult issue on permeability of coal so as to improve the numerical simulation of Coalbed methane (CBM) and/or enhanced CBM (ECBM) recovery and CO2 storage processes. This approach integra
3、tes the coal structural properties with its mechanical behavior in cleat scale, resulting in two basic models, i.e. stress induced deformation model and deformation dependent permeability model. The deformation model is described using stress-strain correlations that cover the elastic and brittle de
4、formations of coal. The permeability model, build up based on the stress-strain correlations, accounts for the contributions from the deformations of individual cleats and coal matrix in coal and formulates in a generalized strain-permeability relationship. Coupling these two models with the associa
5、ted structural and mechanic properties of a given coal allows determination of directional permeability of the coal under any progressive stress conditions. Verification of the models has been discussed with experimental investigations and the results showed the reasonable agreements between the mod
6、el predictions and the experimental measurements for the given coal under laboratory conditions.Keywords: Coal; Coalbed methane (CBM); CO2 enhanced CBM (ECBM); Stress/strain; Deformation; Permeability.1. INTRODUCTIONCoalbed methane (CBM) recovery and CO2 sequestration have become more attractive tec
7、hnologies in recent decades due to advantages in optimal utilization of energy sources and effective storage of carbon dioxide, a greenhouse gas (GHG). It is particularly attractive to develop a combined CBM recovery and CO2 sequestration in deep, unmineable coalbeds, i.e. CO2-enhaced CBM (ECBM) pro
8、cess in which CO2 or flue gas (i.e. a mixture of carbon dioxide and nitrogen) can be injected and stored into the coalbed to replace the adsorbed methane . Thus the revenue of methane production can significantly reduce capital cost by offsetting the expenditures of CO2 storage operation. There are
9、many factors that affect the efficiency of CBM or ECBM process. Darcy flow, for example, may control the gases and water flows through coal seams , and hence determine the well pattern and the (production and/or injection) well rates. Generally speaking, the Darcy flow is basically related to the pe
10、rmeability and pressure gradient which are controlled by the structural and mechanical properties of the coal. The most important requirement in the CBM/ECBM process is to achieve the required gas flow rate without obvious loss of permeability in coal seams. Therefore it is essential to understand t
11、he relevant mechanical properties and its impacts on the transport characteristics of fluid through coal seams for this particular process. In the past three decades, the mining industry has expended a large number of resources to understand the physical behavior of coal, such as its deformation, el
12、asticity, as well as the correlations between laboratory and field data. Focus of such efforts, however, has been on most aspects of coal pillar loading behavior and design approaches to develop more accurate and reliable coal pillar design methods for underground coal mining . Very less attention i
13、s paid to the impact of the physical behavior of coal on permeability which is one of major concerns in processes for CBM/ECBM recovery and CO2 sequestration . There exists another knowledge gap between the structural properties and mechanical behavior of coal which significantly limit generalized a
14、pplication of the common geological/mechanical models in deep coals. Today the structure of coal, consisting of two distinct constitution, i.e. matrix and cleat, can be well characterized by means of many advanced techniques and their combination, such as geographical measurement, light microscope (
15、LM), scanning electronic microscope (SEM) and x-ray diffraction (XRD). Thus the structure of coal can statistically described with average dimensional parameters such as cleat spacing of both butt and face cleats and so-called cleat density . On the other hand it is apparently easy and reliable to m
16、easure the mechanical properties of singe constituent materials than ones of multi-constituent coal. These features are helpful in developing somehow or other correlations between coal structure and its mechanical behavior. It is particularly significant to understand and describe the influence of structural properties on mechanical behavior in optimizing CBM or ECBM process in deep coal. Both experimental and field data have reveal
