Prediction of coalbed methane reservoir performance with type curves

Abstract

Coalbed methane is an unconventional gas resource that consists of methane production from the coal seams. 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. In order to effectively evaluate CBM resources, it necessary to utilize reservoir models that incorporate the unique flow and storage characteristics of CBM reservoirs. These models are often complicated to use, expensive, and time consuming. The typical gas producers in the Appalachian Basin suffer from the lack of scientific, user-friendly tools that can assist them in development of CBM resources. Therefore, it is necessary to develop tools that make it possible for typical (small to medium size) producers to seriously consider this important resource. This study presents a set of production type curves for CBM reservoirs that would help the producers to predict the production from their CBM wells. As a consequence, the producers would be able to make better, more informed decisions regarding the CBM resources in the region. A reservoir model that incorporates the unique flow and storage characteristics of CBM reservoirs was employed in this study to develop the type curves. The type curves provide a reliable tool to predict the production performance of CBM reservoirs during dewatering phase. The application and issues concerning the production performance of CBM reservoirs are also discussed In order to achieve the objective of this study, four steps were performed: (a) Development of a base model for Coalbed methane production in Northern Appalachian, (b) development and verification of the dimensionless groups for water production type curves (c) Generation of the CBM water production type curve, and (d) validation of the CBM water production type curve. A modified correlation for peak gas rate estimation was also proposed as an alternative to forecast gas production along with a correlation for computing initial (maximum) water production rate.

Uncertainty quantification of coal seam gas production prediction using Polynomial Chaos

“…Aminian and Ameri [2] derived a formula for calculating the peak gas rate based on the fluid radial flow equation. Bhavsar [8] estimated the dimensionless peak gas rate using a regression equation with critical gas desorption pressure, skin factor, porosity, Langmuir volume and Langmuir pressure. Zhou [45] developed equations to predict the peak gas rate, peak gas rate arrival time and decline rate by multiple regression of 200 simulations.…”

Development of water production type curves for horizontal wells in coalbed methane reservoirs

“…Set of dimensionless rate and time were utilized by Bhavsar 20 to develop type curve for water. They do not require reservoir properties and they are presented as followed.…”

“…Arrey19 in 2004, evaluated the impact of Langmuir isotherm constants, gas production type curves.Arrey concluded that changes in V L values do not significantly impact the shape of the gas production type curves however; changes in P L values have a significant impact on the gas production type curves.Figure 2.11 shows the effect of P L changes on the CBM gas production type curves.Bhavsar20 in 2005 evaluated the impact of reservoir properties on the gas production type curves for Northern Appalachian. He also developed correlation for peak gas rate, correlation for initial (maximum) water rate, and dimensionless groups for water production type curves.…”