The Impacts of Gas Adsorption on the Productivity of Marcellus Shale Horizontal Well

Abstract

The shale formations, in addition to the gas present in the pores of the rock, contain gas in the adsorbed state in the organic matter within the rock. As the pressure depletes in the reservoir the adsorbed gas is released and augments the gas production. In addition, gas desorption can potentially lead to permeability enhancement due to shale matrix shrinkage. At the same time, the pressure depletion increases the effective stress causing shale permeability and hydraulic fracture conductivity impairments. The purpose of this study was to investigate the impact of the gas desorption on the productivity of Marcellus shale horizontal well with multiple hydraulic fracture stages. The impacts of hydraulic fracture properties including half-length, conductivity, and stage spacing on gas desorption were also investigated. To investigate the impact of the gas desorption on gas production from Marcellus shale, a reservoir model for a horizontal well completed with multiple hydraulic fracture stages was used. The model has been developed based on the available information from several existing Marcellus shale horizontal wells in West Virginia. The laboratory and published data relative to adsorbed gas and the geomechanical factors were analyzed and geomechanical multipliers were generated and incorporated in the model. The geomechanical multipliers account for the impairments in hydraulic fracture conductivity and the reduction in the formation (matrix and fissure) permeability as well as the shale shrinkage caused by the reservoir depletion. The model was then utilized to investigate the impact of different parameters including Langmuir pressure and volume, fracture half-lengths, fracture spacings, and fracture conductivity on gas desorption and gas production. The inclusion of geomechanical multipliers provided more realistic production predictions and better understanding of the desorbed gas impact. The gas desorption was found to have a significant impact on the productivity during later stages of the production. This is contributed to pressure depletion required for desorption to become significant. The contribution of the desorbed gas to production increases as the fracture half-length increases and the fracture spacing decreases. Therefore, it can be concluded that desorption of gas depends on the stimulated reservoir volume.