Coalbed Methane Parametric Study: What's Really Important to Production and When?

Abstract

Abstract Coalbed methane (CBM) reservoir performance is controlled by a complex set of reservoir, geologic, completion and operation parameters and the inter-relationships between those parameters. In order to identify, analyze and mitigate risks associated with any CBM prospect, one must first understand the relative importance of each of these parameters, how their relative importance changes under different constraints, and how they interactively affect CBM production. To date, no comprehensive parametric study on coalbed methane is known to have been conducted within the industry. The parametric studies that do exist in the literature have only considered a limited set of parameters and a limited range for those parameters while holding all the other parameters fixed, thus potentially skewing their results. This comprehensive parametric study has been conducted to enhance our understanding of CBM reservoir performance. In essence, it is an analysis of an extensive Monte Carlo simulation of more than 100,000 reservoir simulations in which the reservoir, geologic, completion and operational variables that impact the production performance of CBM reservoirs were varied. While it is stated that this was a coalbed methane parametric study, coalbed methane reservoirs typically occur in conjunction with sandstones of varying quality. For that reason, one-half of the reservoir simulations modeled the production from coalbed methane reservoirs in conjunction with sandstones of varying quality and degrees of wetness (fully water charged to various degrees of gas-charge). The study's goal was to establish the relative importance of the identified parameters and their inter-relationships, developing rank correlations between these parameters against several production end states (e.g., peak gas rates, dewatering times, cumulative gas, etc.). To avoid some of the potential problems of other similar studies, this study aimed to be as comprehensive as possible in the coverage of parameters varied with the tools available. In so doing, it provides a fuller understanding of the parameters involved in coalbed methane production and enables uncertainties and risk to be more accurately assessed for project economics, and will ultimately lead to the development of more accurate and efficient CBM screening models.