Simulating Carbon Dioxide Sequestration/ECBM Production in Coal Seams: Effects of Coal Properties and Operational Parameters

Abstract

Carbon dioxide sequestration is a promising technology for reducinganthropogenic greenhouse gas emissions while fossil fuels are still being used.The costs associated with CO2 sequestration are often high; however, in certain circumstances (e.g., enhanced oil recovery) these costs can be morethan offset by the benefits of additional incremental hydrocarbon production.Primary production of coalbed methane is a well-developed technology, butsecondary production, through the injection of CO2 or N2has undergone relatively little study. Recent research suggests that carbondioxide preferentially sorbs to coal, displacing methane, makingCO2-enhanced coalbed methane production an ideal candidate forCO2 sequestration. We use PSU-COALCOMP, a dual-porosity coalbed methane simulator, to modelprimary and secondary production of methane from coal, for a variety of coalproperties and operational parameters. Our base well pattern consists of fourhorizontal production wells that form a square, with four smaller horizontalproducers/injectors at the square's center. Primary production of methane andwater is simulated until a specified reservoir pressure is reached, after whichCO2 is injected in the center wells to displace methane, extendingthe reservoir's production of methane. Production continues until theCO2 concentration in the produced gas is too high. By modifying coalproperties, such as permeability, porosity, degree of anisotropy, and sorptionrates, we have approximated different types of coals. By varying operationalparameters, such as injector length, injection well pressure, time toinjection, and production well pressure, we can evaluate different productionschemes to determine an optimum for each coal type. Any optimization requires considering a tradeoff between total methaneproduced (or CO2 sequestered) and the rate of methane production.Values of aggregate methane production and methane production rate arepresented for multiple coal types and different operational designs. Introduction Concern about the quantity of anthropogenic greenhouse gas emissions hasgrown steadily over the past few decades because of their potential forcontributing to global warming. One of the most promising new technologies forreducing carbon dioxide emissions while allowing for continued fossil fuel useis carbon sequestration. Coal seam sequestration is an option with greatpotential because CO2 becomes chemically bound or sorbed to the coalsurface, reducing its mobility and decreasing the chances that it will escapeinto the atmosphere, and because CO2 displaces methane in the coalseam, making the sequestration more economically viable.

Economics for Enhanced Coalbed Methane (ECBM) and CO2 Sequestration with Horizontal Wells

“…For higher permeabilities, lower injection pressures are better. As our previous studies 22 have shown, higher injection pressures cause higher average reservoir pressures, which allow more CO 2 to be sorbed per unit volume of coal. For the case when there are no credits, more CO 2 injection worsens the economics, and therefore those projects with higher reservoir pressure perform worse.…”

“…The length of injectors was kept constant in this study, at 735 ft. This value represents an optimum tradeoff value between methane production and CO 2 sequestration 22 . In a previous study we found that small variations of the injector lengths do not have a large influence on the economics of the project 36 .…”

Simulating Carbon Dioxide Sequestration/ECBM Production in Coal Seams: Effects of Permeability Anisotropies and the Diffusion-Time Constant

“…8 The present authors have previously examined the performance of this well configuration in a series of papers. [18][19][20][21] That work served to identify reservoir and operational parameters that have important effects on project performance. These parameters can be divided roughly into two groups: those that determine the theoretical maximum amount of methane that can be produced and the maximum amount of carbon dioxide that can be sequestered, and those that determine the fraction of the theoretical maximum that can be obtained in an actual project.…”

Development of the Wyodak Coalbed Methane Resource in the Powder River Basin

“…This is consistent with other published results for the Wyodak coals. 2,5 The sorption time was related to the simulation input parameters describing the matrix-fracture coupling and the gas diffusion coefficient using the relationships presented by Sams, et al 6 The remaining properties critical to obtaining a successful history match with the simulation model were the coal transmissivity and storativity variables (Φ, k, C f ), and the influence of the surrounding regional aquifer. Measured data for coal compressibility or porosity were not available.…”