טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDana Asaf
SubjectDynamics of Fracture Relaxation During Shale-Oil and-Gas
Production by Hydraulic Fracturing
DepartmentDepartment of Energy
Supervisor Assistant Professor Guy Ramon


Abstract

Hydraulic fracturing for production of oil and gas from shale formations releases fluid waste, by-products that must be managed carefully to avoid significant harm to human health and the environment. These fluids result from a variety of fracture relaxation processes, and are commonly referred to as `flowback' and `produced water', depending primarily on the time scale of their appearance. Here, a model is presented for investigating the dynamics of backflows caused by the elastic relaxation of a pre-strained medium, namely a single fracture and two model fracture network systems: a single bifurcated channel and its generalization for n bifurcated fracture generations. Early and late-time asymptotic solutions are obtained for the model problems and agree well with numerical solutions. In the late-time period, the fracture apertures and backflow rates exhibit a time dependence of t^(-1/3) and t^(-4/3), respectively. In addition, the pressure distributions collapse to universal curves when scaled by the maximum pressure in the system, which we calculate as a function of n. The pressure gradient along the network is steepest near the outlet while the bulk of the network serves as a `reservoir'. Fracture networks with larger n are less efficient at evicting fluids, manifested through a longer time required for a given fractional reduction of the initial volume. The developed framework may be useful for informing engineering design and environmental regulations. For example, prediction of backflow rates can be utilized both in creating better waste management policies and in regulatory frameworks. Additionally, it could be utilized to enhance production from existing network structures or even, in the future, assist in analyzing flow data from wells to gain insight of the fractured formation.