Application of Flowing Material Balance in Unconventional Reservoirs

The application of the horizontal drilling and hydraulic fracturing to unconventional reservoirs, such as Marcellus Shale, has resulted in a significant increase in gas production in the United States. The estimation of the original hydrocarbons in place is an essential element for evaluating the economic success of any reservoir. There are a number of techniques available for estimating the original hydrocarbon in place such as decline curve analysis, volumetric method, and the material balance equation. Flowing Material Balance (FMB) is a more advanced techniques which has become popular in recent years because it does not require static (shut-in) pressure data which is required by the traditional material balance equation application. This is particularly useful for the shale reservoirs where shut-in pressure data are rarely available. However, the application FMB in shale reservoirs is challenging because of the presence of the adsorbed gas due to high organic content and the long time that is required to establish boundary dominated flow (BDF) due to extremely low permeability. In this study, a reservoir model was developed based on the Marcellus Shale reservoir properties obtained from the analysis of the available data from well MIP-6H in Morgantown, WV. The simulated pressure and production data were then utilized to estimate the original gas in place by the application of the FMB technique. Several modifications to FMB were also investigated to account for the adsorbed gas and the long BDF time.