Modeling Production and Characterizing Well Performance of Fractured Horizontal Well in Unconventional Reservoirs

Abstract

This dissertation presents a comprehensive study for modeling the production and characterizing the well performance for the fractured horizontal well in unconventional reservoirs. Based on the different fundamental governing equations utilized, the standard diffusivity equation for normal diffusion or the fractional diffusivity equation for anomalous diffusion, our work is separated into two main parts. In the setting of the standard diffusivity equation, we develop an efficient algorithm to quickly assess the production performance of a specified well-fracture configuration and a sectionbased approach for providing a preliminarily optimized development plan (number of horizontal wells and clusters to be created in a section). According to our method, under the assumption of planar hydraulic fractures with infinite conductivity, the dimensionless total fracture length and the feasible range of fracture half-length are the two most important factors for the decision of an optimal development plan. In the second part of our work, we employ anomalous diffusion to structurally accounting for the effect of the heterogeneity due to complex fracture networks on the production. Firstly, by simulating the particle-wise diffusion on a graph object, complex fracture networks are formally verified as a major cause of anomalous diffusion in the reservoir scale, which compromisingly provides the fundamental mechanism for the further investigation based on the fractional diffusivity equation. Secondly, to resolve the issues in a traditional planar fracture framework, hydraulic fractures are merged into the fracture network and the fractional diffusivity equation is solved in a domain based on a horizontal lateral. From this perspective, two fractional production decline models are developed. Model I, without considering the influx from the matrix, successfully interprets the relevant production data of the synthetic and field cases, which manifests its capability of accurately describing the transient regime for the fracture flow. Then, after incorporating the influx and a tempering factor, Model II can describe the whole sequence of the flow regimes. According to its type curves, the essence of using hydraulic fracturing for economically developing unconventional reservoirs can be explained as reducing c while increasing w and o, and other insights like selecting the re-fracturing candidates are also provided.