the Flowing Material Balance (FMB) has become popular in recent years because it does not require static (shut-in) pressure data that are needed for the traditional material balance application. This method is particularly useful for the shale reservoirs where shut-in pressure data are rarely available. The application FMB to the 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 ultra-low permeability. However, the interference between the fracture stages in a horizontal well with multiple hydraulic fracture stages leads to an early BDF period during the production. Therefore, the production data from this early BDF period can be utilized to determine the gas in place which can be attributed to the stimulated reservoir volume (SRV) and is of more economic significance.

The objective of this study was to investigate the applicability of the FMB for estimation of the gas in the SRV associated with a Marcellus shale horizontal well with multiple hydraulic fracture stages. The available information from several existing horizontal wells at MSEEL site in West Virginia were utilized to develop a reservoir for model for a Marcellus shale horizontal well with multiple hydraulic fracture stages. To accurately simulate the production data, the adsorbed gas as wells as geomechanical factors, derived from the laboratory and published data, were incorporated in the model. The geomechanical factors account for the impairments in hydraulic fracture conductivity and the reduction in the formation (matrix and fissure) permeability caused by the reservoir depletion. The simulated production data were then analyzed by both conventional method and King method which accounts for gas desorption.

The FMB method which accounts for gas desorption was found to provides reliable estimates of the gas in place in SRV. The analysis of the production data indicated the presence of two BDF. The analysis of the data from the early BDF provided the gas in place in SRV. The analysis of the data from the late BDF provided the total gas in the reservoir. The results were found to be comparable to the values determined from the model. Therefore, the reliability of the data analysis method was confirmed.

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