Estimation of Time of Peak Gas Production in Coalbed Methane Wells using Production Data Analysis

Abstract For coalbed methane (CBM) wells with rising gas production, time to reach peak of gas production and peak gas rate are two fundamental features of a production profile. This paper investigates the time of occurrence of peak of gas production in CBM wells using production data analysis (PDA). The methodology is simple and requires gas rate and flowing bottom-hole pressure (BHP) data. Signatures of time of peak gas production are obtained using time derivative of square of BHP over gas rate. Signatures are obtained for constant and variable bottom-hole pressure operational constraints. Derivative of square of BHP over gas rate with respect to time is calculated for observed production data. Then, plot of this derivative versus production time is constructed for the CBM well. Finally, the plot is extrapolated to a time at which the signature of peak production appears. This time is estimated to be the time of occurrence of peak of gas production. The production data for a CBM well in San Juan basin is analyzed using this technique to demonstrate the signature and the estimation of time of peak gas production. The accuracy and correctness of estimation depend upon quality of production data, goodness of fitted functions used in this approach, and time interval between time of peak gas rate and observed production data. The signatures of time of peak production introduced in this paper can contribute to production forecasting of the negative decline portion of the production profile of CBM wells.