Modeling Wormhole Propagation During Closed-Fracture-Acidizing Stimulation in Tight-Carbonate Formations

Abstract

Summary Closed-fracture acidizing (CFA) is a well-stimulation technique that can be applied to stimulate carbonate reservoirs at the end of acid-fracturing treatments. In CFA, acid is injected into the closed fracture at rates lower than the fracturing pressure to enhance the fracture conductivity. The objective of this study is to develop a robust model that can capture the dissolution process and wormhole-propagation phenomena that occur during CFA. This work develops a CFA model using computational-fluid-dynamics (CFD) techniques coupled with a two-scale continuum model that can predict accurately the reactive-flow mechanisms of hydrochloric acid (HCl) in carbonate formations. The developed CFA model is constructed and populated with the actual porosity-distribution profiles of tight carbonates. The model was tested against the experimental work performed on a fracture-conductivity apparatus. Sensitivity analysis is performed for several parameters that affect the performance of CFA in tight-carbonate formations. The developed model has successfully captured the dissolution patterns and wormhole-propagation phenomena that occur during CFA. In calcite formations, high temperatures promote acid leakoff into the formation, resulting in inefficient fracture stimulation. On the contrary, low temperatures reduce the overall reaction kinetics and attenuate the HCl reaction with calcite. Also, simulation results show that high acid concentration is favorable in treating low-conductivity fractures. In dolomite formations, it is essential to adapt a strong-acid system with an extended treatment duration to ensure efficient acid stimulation to the closed fractures. This paper provides a simulation study of the CFA process in a carbonates formation by establishing a 3D CFD model using the two-scale continuum approach. Fracture-surface etching and the associated acid-wormhole behavior during CFA are experimentally validated. This study optimizes the acid volumes and injection rates that can be used in conducting CFA.

Three‐dimensional simulation of the acidizing process under different influencing factors in fractured carbonate reservoirs

“…The effect of in situ stress on hydraulic fractures has been extensively studied 36‐38 . Some scholars have tried to take the effect of in situ stress into account in the acidizing treatment, but they have only analyzed the stability of wormholes under stress or the rock's mechanical properties after acidizing 2,39,40 . To date, no numerical studies have systematically analyzed the effect of in situ stress on the acidizing process.…”

Numerical Simulation of the Wormhole Propagation in Fractured Carbonate Rocks during Acidization Using a Thermal-Hydrologic-Mechanics-Chemical Coupled Model

“…To understand the mechanism of wormhole propagation in carbonate reservoirs, extensive research has been conducted [3,4,[8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The two-scale continuum (TSC) model developed by Panga et al (2005) [22] is the most commonly used one due to its computational efficiency.…”

An Artificial Intelligence-Based Model for Performance Prediction of Acid Fracturing in Naturally Fractured Reservoirs

“…These models could be one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D). − Few studies also coupled acid fracture modeling with reservoir simulation for design optimization . Recently, a lab-scale model was developed to reproduce the roughness on the fracture surface created by acid or to simulate the complex interactions in the large-scale block experiment …”

“…26−29 Few studies also coupled acid fracture modeling with reservoir simulation for design optimization. 7 Recently, a lab-scale model was developed to reproduce the roughness on the fracture surface created by acid 30 or to simulate the complex interactions in the large-scale block experiment. 31 Carbonate reservoirs are usually abundant in natural fractures.…”