Modeling and Analysis of Pressure- and Rate-Transient Behavior of Interfering Horizontal Wells in Multi-Layer Unconventional Reservoirs

Abstract Multi-well systems are essential for unconventional asset development by optimizing the reservoir drainage, well productivity, and cumulative recovery to maximize the economics of the project. Although the underlying principles of infill drilling and multi-well production is the same as that for conventional reservoirs, in unconventional reservoirs, the contrast between the stimulated and unstimulated volumes (SRV and ORV, respectively) of the reservoir, differences in well completions and resulting SRV vs. ORV properties, asynchronous start of production, different production conditions, and unmatching schedules of production and shut-in periods further complicate the design (the spacing, completion, and production conditions) of the multi-well systems. Moreover, development decisions are usually made with uncertainties caused by the complexity of well-interferences in the existence of extreme reservoir heterogeneity. Therefore, to make multi-well unconventional reservoir development decisions, both the knowledge of the interwell reservoir characteristics and their effect on the multi-well productivity of the system must be known. These requirements call for models that are accurate and efficient for estimating reservoir and completion parameters by pressure- and rate-transient analysis (PTA and RTA, respectively) and capable of efficiently evaluating multiple development scenarios subject to the uncertainties of reservoir characteristics. We have developed robust semi-analytical models to analyze the performances of multi-well systems in single and multi-layer completion conditions in unconventional reservoirs. This paper discusses the diagnostic features of pressure- and rate-transient behaviors of multiple wells in single- and multi-layer unconventional-reservoir, delineates the sensitivities of well performances to well spacing, stimulation treatment, and production conditions of interfering wells, and demonstrates the application of the models to PTA and RTA of field cases. The PTA/RTA methodology presented in this work consists of obtaining initial estimates of the well completion and reservoir properties through diagnostic and straight-line analysis of specific flow regimes, guided by the multi-well solution, and refining the estimates by matching the transient well responses by the semi-analytical model. This methodology provides a remarkably efficient and reasonably accurate estimation of properties within the bounds of the system uncertainties.