Comparison of Fractured-Horizontal-Well Performance in Tight Sand and Shale Reservoirs

TLDR

The study examines fractured‑horizontal‑well performance in conventional and unconventional reservoirs, explains the rationale for fracturing, emphasizes the distinct productivity characteristics of ultratight shale, and proposes that increasing natural fracture density can enhance productivity. A trilinear‑flow model is employed to show that a multiple‑fractured horizontal well’s drainage volume is confined to the inner reservoir between fractures, and that higher natural fracture density and the model’s predictions can guide design and performance. The results indicate that, unlike conventional reservoirs, high permeability and hydraulic‑fracture conductivity do not guarantee favorable productivity in shale, high natural‑fracture conductivity alone is insufficient, and while reducing hydraulic‑fracture spacing boosts production, the incremental gain diminishes with each additional fracture.

Abstract

Summary This paper presents a discussion of fractured-horizontal-well performance in millidarcy permeability (conventional) and micro- to nanodarcy permeability (unconventional) reservoirs. It provides interpretations of the reasons to fracture horizontal wells in both types of formations. The objective of the paper is to highlight the special productivity features of unconventional shale reservoirs. By using a trilinear-flow model, it is shown that the drainage volume of a multiple-fractured horizontal well in a shale reservoir is limited to the inner reservoir between the fractures. Unlike conventional reservoirs, high reservoir permeability and high hydraulic-fracture conductivity may not warrant favorable productivity in shale reservoirs. An efficient way to improve the productivity of ultratight shale formations is to increase the density of natural fractures. High natural-fracture conductivities may not necessarily contribute to productivity either. Decreasing hydraulic-fracture spacing increases the productivity of the well, but the incremental production gain for each additional hydraulic fracture decreases. The trilinear-flow model presented in this work and the information derived from it should help the design and performance prediction of multiple-fractured horizontal wells in shale reservoirs.