Abstract
Field performance analysis in unconventional reservoirs is complicated by the dynamic onset of interference: fracture to fracture and well to well. Interference between the stages of a multistage hydraulic fractured well leads to the onset of the so-called Stimulated Reservoir Volume (SRV). Interference between multiple wells may, eventually, lead to an apparent drainage volume. The methodology developed and applied in this study provides novel and rapid techniques to assess the dynamics of these interactions and their interference.
This study combines two newly developed methodologies for the analysis of the onset of interference in unconventional reservoirs. The first is an extension of waterflood flow diagnostics, previously restricted to incompressible fluid flow, to the analysis of primary depletion. These diagnostics utilize the control volume finite difference calculations based on 2D/3D geologic or simulation models, but do not require explicit flow simulation. The second is a modification of the flow analysis based upon the Fast Marching Method (FMM) and the diffusive time-of-flight (DTOF) to a new computational approach based upon the Pseudo Steady State (PSS) pressure as a 1D coordinate. The result provides a fast modeling methodology which has aspects of the classic Stabilized Zone but which also honors the reservoir heterogeneity, natural fractures, and the complex completion and hydraulic fracture geometry of unconventional reservoir development. As with the FMM, the DTOF obtained from the PSS coordinate can be utilized to rapidly assess the interaction between fractures or between wells. In contrast to the FMM, a better resolution of the interference effects that lead to the development of the SRV is obtained.
We first demonstrate our method of analysis on a synthetic reservoir model consisting of a single multitransverse hydraulic fractured well. The model uses reservoir and completion parameters typical for wells in unconventional shale reservoirs. The analysis reveals a significant time lag between the outwardly propagating pressure and the convective time-of-flight. The pressure propagation and the PSS coordinate provide excellent visualization of the development of a Stabilized Zone and its relationship to the timing of the development of the SRV. The second demonstration uses the DTOF, now obtained from the PSS coordinate instead of from the FMM, to examine multiwell interaction. For a single well, this calculation of the DTOF provides more quantitative resolution of the SRV than did the FMM. For multiple wells, a grid-free analysis based upon superposition and dynamic well productivity obtained from the DTOF can be used to rapidly evaluate multiwell interaction. Novel methodology for depletion flow diagnostics is applied to the improved interpretation of the onset of the SRV. Improved prediction of the interference of the drainage volume for parent/child wells, provides a rapid means to determine an optimal well spacing.
