Date of Award

January 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Vamegh Rasouli

Abstract

Multistage hydraulic fracturing (MsHF) is a technique often combined with horizontal drilling for the extraction of oil or gas from unconventional plays. MsHF alters the magnitude and orientation of the principal stresses along the length of an induced fracture. This stress alteration in the vicinity of the hydraulic fracture is commonly called the stress shadow, and the shadow impacts the propagation of the subsequent fracture. This study utilized numerical simulations and theory-based analytical models to establish a relationship between hydraulic fracture and stress shadow development.

This study developed a methodology for optimizing hydraulic fracture spacing by considering the stress shadow effect. A numerical simulator, XSite, an Itasca Consulting Group geomechanics simulation software, was used to understand the effect of formation properties and hydraulic fracture parameters in stress shadow development. Investigation of the impacts of each parameter was performed on each hydraulic fracture stage. Then the influence of the first stage on the next stage was investigated to understand stress shadow behavior.

Sneddon-Elliott's (SE) equation was modified and utilized to calculate stress alteration around the length of an induced fracture. This modification allowed a stress alteration calculation around a hydraulic fracture and a multistage hydraulic fracture along the wellbore. The modification, called analytical SE, was deduced by understanding the 2D model of the PKN model and Sneddon-Elliott penny-shape fracture. The results from the analytical model and numerical simulations were compared to examine the theory and for comparison purposes.

The study shows that formations with higher Young’s modulus generally produce longer hydraulic fractures, whereas Poisson’s ratio does not affect fracture length. Fracture geometry and stress anisotropy play an important role in controlling the stress shadow regime. Stress anisotropy influences the propagation direction of a hydraulic fracture but does not affect fracture length. Net pressure, defined as the pressure contrast between shut-in fracture pressure and minimum horizontal stress, is important in controlling the stress shadow area. Larger net pressures lead to larger stress shadow regimes. The research results from both the modified SE and numerical simulations show that the optimum normalized fracture spacing is 0.71, i.e., the optimum fracture spacing is 210–245 ft for the Bakken Formation, where the fracture length is 300–350 ft.

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