Open AccessNumerical Simulation and Analysis of Cave Penetration by Hydraulic Fractures
Author(s) -
Jiawei Kao,
Wenzhi Wang,
Yan Jin,
Hailong Liu
Publication year - 2020
Publication title -
iop conference series. earth and environmental science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.179
H-Index - 26
eISSN - 1755-1307
pISSN - 1755-1315
DOI - 10.1088/1755-1315/570/2/022029
Subject(s) - cave , multiphysics , geology , permeability (electromagnetism) , hydraulic fracturing , petroleum engineering , carbonate , geotechnical engineering , fluid dynamics , penetration (warfare) , viscosity , materials science , mechanics , engineering , finite element method , composite material , structural engineering , chemistry , archaeology , operations research , biochemistry , physics , membrane , metallurgy , history
The cavernous carbonate reservoir in the Tahe oilfield in northwestern China has high development potential. Fluid is distributed in caves due to low matrix permeability, and recombination acid fracturing is a primary development method. The effects of fracturing depend on the number of caves connected by fractures. An estimate of whether a hydraulic fracture can penetrate a cave and continue propagation is therefore important for production safety and efficiency. We developed a numerical model using COMSOL Multiphysics to calculate the fluid-solid coupling stress distribution after fractures connect with caves and determine whether the fractures can continue to expand. We first developed an analysis group based on parameters from fracturing experiments in which caves were placed in man-made samples. A comparison of the calculation and experimental results verifies that the model is reasonable. The penetration ability of hydraulic fractures and influencing factors under different conditions were analyzed in combination with characteristics of the cavernous carbonate reservoir in the Tahe oilfield. The results show that when holding fixed certain working parameters, such as displacement and fluid viscosity during fracturing, the hydraulic fractures more easily penetrate smaller caves, the in-situ stress ratio increases, and the distance between the well and caves that would lead to a higher penetration ability decreases. If the fractures of a given cave are connected but not penetrated, several methods can be applied to effectively increase the hydraulic pressure in the cave, such as increased fracturing injection fluid displacement or replacing low-viscosity fracturing fluid. This can form new fractures in the wall that continue to expand and connect more caves. We calculated the fluid-solid coupling stress distribution after the fractures had connected caves to determine whether hydraulic fractures could also achieve penetration. The main influencing factors and optimization methods affecting the ability of fracture penetration are clarified, which provide an important reference for fracturing design in the Tahe cavernous carbonate reservoir.