Numerical simulation of hydraulic fracture height using cohesive zone method

Abstract

Hydraulic fracturing is a popular method used in the petroleum industry to increase the well performance by improving the permeability of the reservoir. However, while there has been extensive research on the development of the length of the fracture, the fractured height has been frequently assumed to be equal to the reservoir thickness. The objective of this paper is to study the influence of formation rock characteristics and the impact of underground stress state on the development of the fracture height. To achieve this objective, a finite element model was built using a cohesive zone method to predict the development of fracture height in time and space. Different scenarios were then effectuated by varying the values of the primary formation variables which are the Young’s modulus, the porosity, the Poisson ratio, the fracture energy, and the maximum horizontal stress of the reservoir and of the beddings. This research therefore covered principally uncontrolled factors which are the formation properties and stress state underground, which contribute mostly to the erroneous prediction in fracture height. The findings revealed that the fracture height was strongly influenced by the properties of the formation and of the adjacent layers. However, the influence levels are not the same for different kinds of properties. This study showed that the most influential mechanical property of the rock on the fracture height is the Young’s modulus. Regarding the porosity, its effect on the fracture height is extremely small. However, it is worth noting that the porosity is still an important parameter in hydraulic fracturing because it can be used to estimate others parameters and to model the development of fracture geometry which are width, length, and height. Practical suggestions for real-life hydraulic fracturing jobs can be deduced from this study, in order to control the fracture height as accurately as possible, and to decrease financial cost by concentrating mostly on the high influential factors instead of doing all kinds of tests for other less influential mechanical properties of the rock.