Optimizing fluid viscosity for systems of multiple hydraulic fractures

Abstract

Optimal hydraulic fracturing stimulations of horizontal oil and gas wells maximize created fracture surface area and/or maximize the uniformity of stimulation. Here, we use a new, rapidly‐computing hydraulic fracture model to investigate how surface area and uniformity are impacted by interplay among multiple growing hydraulic fractures driven through permeable rocks by fluids of various viscosities. The results show the existence of a surface‐area‐optimizing viscosity that is large enough to control leak‐off but not so large that leads to unnecessarily large fracture aperture.

Non‐Newtonian Backflow in an Elastic Fracture

“…Under the same approximation, the volume of fluid within the fracture at any time is V ≈ r 2 e h, and the flow rate exiting the fracture through the outlet, or outflow rate, is q = −dV ∕dt ≈ r 2 e dh∕dt. Gravity effects are absent in horizontal fractures and negligible when compared to pressure gradients for fractures lying in any other plane (Abbasi et al, 2012;Cheng & Bunger, 2019;Shi & Shen, 2019). As to the flow conditions, the Reynolds number is low enough to ensure that the flow is viscous and inertial terms are negligible.…”

Model‐Based Evaluation of Methods for Maximizing Efficiency and Effectiveness of Hydraulic Fracture Stimulation of Horizontal Wells

“…As an illustrative example, we show that injection volume can vary significantly depending upon both the nominal regime (location in the plots in Figure as defined by Φ and τ in equations and , respectively) and the fracture spacing. Specifically, we contrast uniformly spaced and a particular nonuniform spacing, which is inspired from prior work (Cheng & Bunger, ; Cheng & Bunger, , b; Lecampion et al, ), demonstrating that some nonuniform spacing configurations can balance the impact of stress shadow acting on the fractures, thereby leading to more uniform fracture growth. This parametric study entails varying viscosity and characteristic leak‐off parameter C L 0 , keeping all other quantities unchanged with practically relevant values given by until a fracture surface area of 100,000 m 2 is achieved.…”

“…A major challenge to optimization is that many simulation runs are required, thereby motivating development of fast, approximate models. Building on previous versions (Cheng & Bunger, , b), the new model C5Frac is developed to extend consideration to include the impact of the fracture toughness of the rock and fluid leak‐off.…”

“…For this reason, a first step enabling optimizing the resource use and resource recovery is to address the need for rapid, even if approximate, simulation including capturing the transition behavior between multiple fracture growth regimes. We previously demonstrated the feasibility and basic concept of a new HF simulator, C4Frac, which very rapidly simulates the growth of an array of HFs (Cheng & Bunger, , b). In this prototype reduced order model (ROM), the fractures created from all perforation clusters were restricted to radial, planar growth under the limitation that fractures propagate without toughness (i.e., energy dissipated in fluid flow greatly exceeds energy dissipated due to rock breakage).…”

“…The solution method and associated assumptions and simplifications follow from our prior work (Cheng & Bunger, ; Cheng & Bunger, , b) but with an important extension that allows for consideration of finite fracture toughness. The prior models were limited to consider cases where energy dissipation associated with rock fracture was negligibly small compared to viscous dissipation associated with fluid flow.…”