Fracture Height Growth Prediction Using Fluid Velocity Based Apparent Fracture Toughness Model

Abstract

This paper outlines the development of a fracture height growth prediction model that uses the modified rock mechanical properties obtained from a combination of fluid flow and rock material property behavior and applies them during the calibration process to match actual treatment data resulting fracture height growth evolution and profile. The traditional fracture growth models are closely linked with the fracture toughness parameter which is not only difficult to estimate but is also considered dynamic in nature as it may assume various geometry-dependent values rather than a fixed input value. To account for this limitation, this study uses the fluid tip velocity to estimate apparent fracture toughness during the initial model setup process and continuously scales the model during the fracture growth prediction phase. The influence of controllable parameters such as injection rate and fluid viscosity on vertical growth of fractures was studied and applied to field examples. Analysis from the modeling work on two of the case histories presented, indicated a rapid fracture growth in the first few minutes of the treatment that was proportional to the rate of net pressure gain. The influence of the fracture tip on the fracture pressures in the tip region is visible only in the early part of the treatment and are relatively short-lived especially once the contribution from viscous flow pressures dominates the pressure behavior. The findings are presented in detail and are helpful from a treatment planning and execution viewpoint as they provide a detailed insight into fracture propagation. Relevant theory, equations and workflow adopted during the study are presented for ready adaptation in the field.