New Approach for Parameter Evaluation of Tight Gas Reservoirs Stimulated with Fracture Networks

Tight gas reservoirs are divided into a stimulated zone and an unstimulated zone after hydraulic fracturing treatments. Due to the complexity of reservoir geology, many models have been established to evaluate the parameters of the fracture network and reservoir around vertically fractured wells (VFWs). However, owing to the impact of stress sensitivity, when tight gas reservoirs have strong heterogeneity, using well test curves to interpret the parameters of fracture and reservoir still has uncertainty. Bahrami et al. used a second semilog pressure derivative (SSPD) to reduce uncertainty in determining flow stages; however, SSPD has not been used to analyze VFWs in tight gas reservoirs with multizone and stress sensitivity. So, we calculated the dimensionless second semilog pressure derivative chart, which aided in identifying the flow characteristics during the middle and late stages. When pressure spreads to the transition flow stage, the pressure second derivative will show a "bulge" with the change of neighbor zone properties, and the number of "bulges" in the second pressure derivative is equal to the number of the outer zones. Meanwhile, it is worth noting that when the permeability modulus changes, the timing of bulge changes in the second derivative remains largely consistent, suggesting that stress sensitivity does not significantly affect the division of zones. The analytical model of VFWs was established in the Laplace domain, encompassing multiple zones and considering stress sensitivity. By utilizing Laplace and perturbation transforms, we obtained the bottom hole pressure (BHP) of the VFW through the implementation of the Stehfest algorithm. Then, a sensitivity analysis was conducted to study the impacts of zone radius, inner-to-outer zone mobility ratio, inner-to-outer zone storativity ratio, permeability modules, and fracture network volume ratio on the pressure transient analysis. This method can play a guiding role in devising zones in multizone composite gas reservoirs.