Prediction and analysis of the coalbed methane (CBM) production is challenging especially at the early stages of the recovery when production is subject to two-phase flow conditions. CBM reservoirs are dual-porosity systems that are characterized by a complex interaction of coal matrix and cleat system that are coupled through desorption process. As a result, the conventional methods cannot be utilized to predict CBM production. Currently, only numerical models (simulators) can be used to predict (CBM) production behavior since they incorporate the unique flow and storage characteristics of CBM reservoirs. Often, the number of variables needed for evaluation of a given prospect is greater than that typically measured. In such cases, parametric studies are conducted to evaluate the impacts of reservoir properties on recovery factor, well performance, and future revenues. However, parametric studies with a reservoir simulator is cumbersome, time consuming and expensive. Therefore, there is a need for scientific, user-friendly tools that can assist the typical gas producers in evaluation of CBM prospects.
This study presents a set of production type curves for CBM reservoirs. A reservoir model that incorporates the unique flow and storage characteristics of CBM reservoirs was employed to generate the type curves. Our previous study (SPE 91482) introduced a new set of dimensionless groups that led to development of unique set of type curves. The impact of basic reservoir characteristics was also investigated to confirm the uniqueness of the type curves. This study investigates the impact of key parameters including isotherm constants and relative permeability data on the type curves. The type curves can be used to predict and/or analyze gas and water the production from CBM wells both during de-watering and stable gas production phases. The issues concerning the application and limitation of the type curves are also presented. Finally, a type curves-based simple yet reliable tool with graphical user interface (GUI) was developed. This tool can be used for predicting and analyzing production performance of CBM reservoirs with simple and straight forward input requirements. This tool is particularly useful for parametric studies to evaluate CBM prospects.