Simulation of multiple hydraulically driven fractures

Hydraulic fracture;simulation;abaqus;finite element;optimization;multiple fractues;Civil Engineering

Sayed, Sara

University of Waterloo

关键词: Hydraulic fracture;    simulation;    abaqus;    finite element;    optimization;    multiple fractues;    Civil Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/9691/1/Sayed_Sara.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Hydraulic fracturing is a process that is used to release and extract naturalgas from the pores of shale rocks. The process involves drilling vertical andhorizontal wells through shale formation beds. After which, a mixture offluid and sand is pumped into the rock formation through the horizontal well,pressurizing the shale around the well, causing multiple permeable cracks toform. Studying hydraulic fracturing helps Oil and Gas companies to improvethe efficiency and productivity of this process.Because the hydraulic fracturing process takes place hundreds of metersbelow the ground’s surface, its behavior is difficult to physically assessed.Computer modeling is an efficient and economical way to study andanalyze the behavior of the process. Finite element modeling, as anumerical tool, can be used to solve such non-linear fracture problems.In this thesis, finite element modeling is used to study two-dimensional,single, and multiple crack propagation problems that occur during fluid injection.The single fracture problem is compared with a well known analyticmodel (KGD model) in order to verify the efficiency of the numerical finite elementmodel. The effects that rock and fluid material properties have on thefracture propagation, crack width, and fluid pressure is studied. As a result,the finite element numerical model is found to be in good agreement with theKGD analytical solution. Moreover, the analysis revealed that small changesin the material properties (e.g., rock elasticity modulus, permeability, andfluid viscosity) have significant effects on fracture propagation.Multiple crack problems, using three parallel cracks, are also investigated.The effects of the fracture spacing and type of fluid control (flow rate or pressurecontrol) are studied. Stress shadowing (induced stresses from the adjacentfracture) between multiple fractures is evaluated. For the edge cracks,it is found that as the fracture spacing decreases, the crack length increases.While, for the middle crack, as the fracture spacing decreases, the cracklength decreases. It is shown that fluid flow controlled injection leads to stable crack injection, while pressure control injection leads to unstablecrack propagation.In summary, this thesis finds that an optimal spacing for three crackhydraulic fracturing is between equal fracture spacing and two-third the distancebetween the middle and any of the edge cracks. It is recommendedthat future engineers extend this research to simulate a three-dimensionalproblem with randomly oriented fractures.