The U.S. Department of Energy's Office of Scientific and Technical Information

Stimulated Reservoir Volume (SRV) is an engineering concept developed for the purposes of quickly evaluating the effective well drainage area and analyzing the actual performance of a multistage horizontal well in tight formation. Usually SRV is defined using microseismic event mapping. However, there are many other factors hindering the realization of the correct SRV value and largely impairing its engineering application. A simplified integrating model with multiple regions that combines the near wellbore engineered reservoir area, the SRV region, the original tight formation area and the outbound reservoir region, named as region I, II, III and IV, respectively, were built and analyzed systematically, where the region I confines the horizontal wellbore with multiple artificial hydraulic fractures and allows the integration of complex skin factor distribution, region II intends to capture the influence of SRV under various parametric settings such as fracture networking and matrix-fluid mobility variations, region III accommodates the general geological information for the original large scale tight formation environment and region IV supports the information input for the outbound reservoir environment. The multiple region modeling has been successfully built and applied to understand the relationship among wellbore, fracture, SRV and original reservoir formation. Theoretical study on the transient pressure and rate responses were conducted to address the technical challenge encountered. The results, presenting in a type curve format under various conditions, have shown that SRV region is strongly related to the fracture influenced/dominated boundary flow regime and appears as a region possessing a less than 1 slope in pressure and reciprocal rate derivative curves, which indicates that the flow process has reached the theoretical SRV boundary, i.e., the fracture influenced area/boundary. However, the derivative value would not reach one due to the inflow from the outside original reservoir region. This phenomenon is a symbolic feature of tight formation with SRV connectivity, as many field cases have been so indicated. This work allows a quick estimation of SRV region, a better understanding of the influence of the complicated wellbore configurations and a way to characterize the reservoir connectivity between SRV and original/outbound tight formation reservoir.

Adsorbed gas may account for a significant part of the gas resources in shale gas and coalbed methane plays. Understanding gas sorption behaviors and integrating gas desorption into analytical reservoir modeling and an associated transient performance analysis are important for evaluating a system’s gas desorption ability and further analyzing its CO₂ injectability, utilization, and storage capacity. However, gas desorption, along with other pressure-dominated gas properties, increases a system’s non-linearity in theoretical studies. Few studies on analytical modeling have integrated the gas desorption feature into a non-linear system and validated the model’s accuracy. In this study, the desorbed gas due to pressure decay was treated as an additional source/sink term in the source-and-sink function methods. This method was combined with the integral image method in a semi-analytical manner to determine the amount of gas desorption. Fundamental reservoir and gas properties from the Horn River Basin shale gas play were chosen to evaluate the methodology and the performance of the associated production well. The results were compared with the commercial fine-gridding numerical simulation software, and good matches were achieved. The results showed that the desorbed gas released from rock will supply free-gas flow when the pressure significantly decreases due to gas production. The production wellbore pressure can be maintained at a higher level, and the production rate was higher than in cases where gas desorption was not considered, depending on the operating conditions.