Verification of Coupled Hydraulic Fracturing Simulators Using Laboratory-Scale Experiments

Abstract

In this work, we aim to verify the predictions of the numerical simulators, which are used for designing field-scale hydraulic stimulation experiments. Although a strong theoretical understanding of this process has been gained over the past few decades, numerical predictions of fracture propagation in low-permeability rocks still remains a challenge. Against this background, we performed controlled laboratory-scale hydraulic fracturing experiments in granite samples, which not only provides high-quality experimental data but also a well-characterized experimental set-up. Using the experimental pressure responses and the final fracture sizes as benchmark, we compared the numerical predictions of two coupled hydraulic fracturing simulators—CSMP and GEOS. Both the simulators reproduced the experimental pressure behavior by implementing the physics of Linear Elastic Fracture Mechanics (LEFM) and lubrication theory within a reasonable degree of accuracy. The simulation results indicate that even in the very low-porosity (1–2 %) and low-permeability ($${10}^{-18}\ {\mathrm{m}}^{2}- {10}^{-19}\ {\mathrm{m}}^{2}$$ 10 - 18 m 2 - 10 - 19 m 2 ) crystalline rocks, which are usually the target of EGS, fluid-loss into the matrix and unsaturated flow impacts the formation breakdown pressure and the post-breakdown pressure trends. Therefore, underestimation of such parameters in numerical modeling can lead to significant underestimation of breakdown pressure. The simulation results also indicate the importance of implementing wellbore solvers for considering the effect of system compressibility and pressure drop due to friction in the injection line. The varying injection rate as a result of decompression at the instant of fracture initiation affects the fracture size, while the entry friction at the connection between the well and the initial notch may cause an increase in the measured breakdown pressure.

Laboratory Study of the Influence of Fluid Rheology on the Characteristics of Created Hydraulic Fracture

“…Before industrial application of new fluids in the field conditions, the testing of fluids in laboratory conditions could be useful [17]. Existing works are mainly focused on the laboratory hydraulic fracturing experiments with promising waterless fracturing fluids such as liquefied and supercritical gases.…”

A comprehensive review of numerical simulation methods for hydraulic fracturing

“…Fluid flow involves applying consistent pressure across fracture surfaces in hydraulic fracturing simulation 64 . When the fracture's aperture is smaller than its height and length, lubrication theory is suitable for modeling flow within the fracture 65 . Applying Poiseuille's and Lubrication laws establishes a relationship between flow rate and pressure drop within the hydraulic fracture.…”

A Review of Hydraulic Fracturing Simulation

“…However, this overly simplified approach can cause significant modelling error, with the exception of certain special cases with low-viscosity fluid and high-toughness formation. A more rational approach to modelling fluid flow in fractures is based on the lubrication theory, which recognizes the fact that the aperture of a hydraulic fractures is always much smaller than its height and length [85,378,394,395]. The application of lubrication theory in hydraulic fracturing modelling is extremely popular, and the Poiseuille's law (or cubic law) is widely used to relate the flow rate with the pressure gradient along the hydraulic fracture.…”