The Gas Isotope Interpretation Tool: A Novel Method To Better Predict Production Decline

Abstract

Production decline prediction is important to understand the performance and life span of oil and gas wells. The most common prediction method is decline curve fitting based on available production rate data. However, the parameters are often poorly constrained, especially when the production rate data is limited. In this study, we establish a novel gas isotope interpretation tool to better predict the resource quantity and life span of producing gas wells. This tool is based on the evolution of methane (CH4) carbon isotope ratios due to different gas releasing processes during the production. We successfully applied the tool to a producing shale gas well in the Barnett Shale. We obtained real-time methane carbon isotope data for about a year using our proprietary, field-deployable natural gas isotope analyzer (NGIA). Our prediction in this well shows that the total reserve would reach 7.34-7.75 bcf. The production rate may decline to 200-225 Mcf/day by 30 yr, whereas the empirical Arps’ equation would predict a significantly high production rate for a longer period of time. The novel production decline prediction method thus provides the important constraint on the future well production and expected ultimate recoverable reserves (EUR).