Field-project designs for carbon dioxide sequestration and enhanced coalbed methane production

Worldwide concerns about global warming and possible contributions to it from anthropogenic carbon dioxide have become important during the past several years. Coal seams may make excellent candidates for CO2 sequestration; coal-seam sequestration could enhance methane production and improve sequestration economics. Reservoir-simulation computations are an important component of any engineering design before carbon dioxide is injected underground. We have performed such simulations for a hypothetical pilot-scale project in representative coal seams. In these simulations we assume four horizontal production wells that form a square, that is, two wells drilled at right angles to each other forming two sides of a square, with another pair of horizontal wells similarly drilled to form the other two sides. Four shorter horizontal wells are drilled from a vertical well at the center of the square, forming two straight lines orthogonal to each other. By modifying coal properties, especially sorption rate, we have approximated different types of coals. By varying operational parameters, such as injector length, injection well pressure, time to injection, and production well pressure, we can evaluate different production schemes to determine an optimum for each coal type. Amy optimization requires considering a tradeoff between total CO2 sequestered and the rate of methane production. Values of total CO2 sequestered and methane produced are presented for multiple coal types and different operational designs.