Type Curve-Based Production Prediction Tool for CBM Prospects

Abstract

The complex nature of gas production from CBM reservoirs requires significantly more reservoir properties than conventional reservoirs. Parametric studies are often conducted to evaluate the impact of the reservoir parameters on recovery factor, well performance, and future revenues. To conduct parametric studies, the production behavior must be predicted for ranges of various reservoir parameters. In order to incorporate the unique flow and storage characteristics of CBM reservoirs, it necessary to utilize complicated and expensive reservoir models to predict production performance of the CBM reservoirs. Therefore, a simple yet reliable tool is needed for predicting production behavior of CBM reservoir. The CBM Production Predication Tool developed in this study is a quick and reliable tool that can assist the typical gas producers in evaluation of CBM prospects. The tool utilizes the previously developed CBM Production Type Curves as a foundation to predict the production performance. The results can be used to evaluate the economic feasibility and to maximize potential recovery. To simplify the application of type curves for parametric studies a software package with a graphical user interface using Visual Basic programming language has been developed. The input requirements are simple and straight forward. The output is provided both in graphical and tabulated forms which can be exported into spreadsheet for further analysis by the user. Introduction CBM has grown from an unconventional gas play in the 1980's into a commercially important, mainstream natural gas source. CBM currently account for over 10 percent of the estimated total U.S. natural gas reserves and 8 percent of U.S. annual gas production. These numbers are expected to increase even further as more resources are discovered and a better understanding of the existing resources is achieved. However, for CBM to reach its true potential in the U.S. energy equation, substantial increase in CBM production in less developed basins, such as the Northern Appalachian Basin, must be achieved. Therefore, it is necessary to develop tools that make it possible for producers to seriously consider this important resource. There is a need for scientific, user-friendly tools that can assist the typical gas producers in evaluation of CBM prospects. The complex nature of CBM production behavior precludes use of conventional techniques such as decline curve methods to forecast the recovery factor, future revenues, and well performance. Production from CBM reservoir is controlled by the complex interaction of gas desorption from coal matrix and two-phase flow of gas and water through cleat system. Numerical reservoir simulators that account for various mechanisms that control CBM production are by far the best tools for predicting the performance CBM reservoirs. Often, the number of variables needed for evaluation of a given prospect is more than those typically measured. Therefore, parametric studies must be conducted to evaluate the impacts of reservoir properties on recovery factor, well performance, and future revenue evaluation. When one or more of the key parameters are not available, it is necessary to perform Monte Carlo simulation to establish a reliable estimate of production potential and to evaluate the risk However, it is time consuming and cumbersome to conduct Monte Carlo simulation or parametric studies with a reservoir simulator. Many of the producers, particularly in Northern Appalachian Basin, cannot afford the personnel and economical requirements involved in use of the reservoir simulator to evaluate CBM prospects. This paper introduces a simple yet reliable tool that can be used for parametric studies to evaluate CBM prospects.

Teste drawdown em um reservatório de coalbed methane

“…Atualmente, mais de 10% das reservas de gás natural nos Estados Unidos (EUA) são de CBM. Além disso, 8% da produção de gás anual dos EUA é oriundo de CBM (Aminian et al, 2007).…”

“…O comportamento da produção do coalbed é complexo e difícil de predizer e analisar (Aminian et al, 2004) já que é controlado por uma interação complexa entre a matriz de carvão e o fluxo bifásico de gás e água (Aminian et al, 2007). Diversos fatores podem afetar a produtividade de um reservatório de CBM, tais como a quantidade de gás presente, a litologia do carvão, a hidrodinâmica e saturação do reservatório e a permeabilidade.…”

Predicting the performance of horizontal wells in unconventional gas reservoirs

“…However, the gas production type curves were found to be influenced by m' and n'. 21 The exponent n' used in Equation 2.10 is called the Corey Gas Factor and for Equation 2.11 m' is the Corey Water Factor.…”

The Impact of Relative Permeability on Horizontal Well Type Curve Analysis in Coalbed Methane Reservoirs

“…These methods are most suited to calculation by a computer because of the repeated computations and random number selecting. However, it is time consuming and cumbersome to conduct Monte Carlo simulation or parametric studies with a reservoir simulator 16. The simulation model used for this study is the Schlumberger Eclipse 2010 Reservoir Engineering Simulation Software.…”