A composite model based on semi-analytical method for multiwell horizontal pad with stimulated reservoir volume

Abstract

The multiwell horizontal pad is an effective method to enhance oil recovery for unconventional reservoirs. Microseismic evidence indicates that the stimulated reservoir volume (SRV) may have originated in the overlap region created by multi-well fracturing. However, the majority of SRV modeling studies have concentrated on a single well, ignoring the interference from offsetting wells. In this study, a novel model for modeling the SRV and multiwell horizontal pad in unconventional reservoirs is developed using an effective semi-analytical method. The proposed semi-analytical model is capable of simulating the behaviors of a multiwell horizontal pad with an irregularly shaped SRV and an impermeable boundary. The transient pressure behaviors of the multiwell horizontal pad with SRV are significantly different than that of a single isolated well, as demonstrated by the results. The linear flow between wells, the pseudoradial flow (PRF) of the multiwell pad in SRV, the transitional flow, and the final pseudoradial flow (PRF) of the multiwell pad all correspond to an extremely unusual transient pressure response. Due to the high flow capability of SRV, pressure diffusion occurs at a faster rate, resulting in the appearance of these flow regions in advance. Sensitivity analysis confirms that as the scale of SRV increases, the duration of the flow influenced by the SRV increases. The SRV and compensating wells result in a negligible PRF, while the pressure behaviors exhibit a gradual rise. This phenomenon may serve as a demonstration of the extremely rare occurrence of radial flow or PRF in unconventional reservoirs. The horizontal line value for the PRF in SRV is proportional to the total production of the well pad. The horizontal line value for the final PRF is also related to the unstimulated region's mobility ratio, the well pad's production rate and 0.5. The case in Junggar Basin shows that the natural fracture permeability in the SRV is 2.5 mD, the matrix permeability is 0.044 mD, the rectangular SRV side lengths are 1600 m and 880 m, the mobility ratio and dispersion ratio are 15, and the wellbore storage coefficient is 0.5 m3/MPa.