Omar Akash

Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Vamegh Rasouli

Abstract

Unconventional reservoirs such as tight formations and plays, are known by their ultra-low permeability. To economically produce hydrocarbon from these reservoirs, technology-based solutions need to be deployed. hydraulic fracturing is a widely accepted and applied technology for successful development of unconventional reservoirs.

The fractures initiated near wellbore can have different lengths, widths, and heights. As a result, a complex fracture network is expected to be formed near wellbore. The hydraulic fracturing design is related to several parameters. Some of these parameters cannot be altered such as the geological attributes and mechanical properties of the targeted formation and the field in-situ stresses. Other parameters can be designed and controlled such as the fracturing fluid injection rate and viscosity, wellbore’s completion type, number of hydraulic fracturing stages and the spacing between closely adjacent wellbores. Understanding how these parameters affect the initiation and the propagation of hydraulic fractures can enhance the hydraulic fracturing operation.

Optimal design of perforation tunnels can significantly reduce undesired near wellbore situations such as: fracture tortuosity, early screen-out and increased fracture initiation pressures. Also, understanding the mechanism by which the fracture initiates from perforated wellbores can result in larger fracture areas, therefore enhanced hydrocarbon production. Field studies, laboratory experiments, analytical models, and numerical simulations have been utilized to better understand fracture initiation from perforated wellbores.

In this research project, some of the important analytical solutions are presented and used to investigate the fracture initiation from perforated wellbores. The newly lattice numerical simulation method was used to run multiple simulations to understand the effect of different parameters on fracture initiation and near wellbore propagation from perforations.

The results showed that the geometry of the perforations tunnels have great effect on fracture initiation, for longer perforations tunnels lengths, more desirable fracture initiation was observed as compared to shorter perforations tunnels. The orientation of perforations tunnels relative to field stresses can have an effect on fracture initiation, orienting the perforations tunnels in a certain way with respect to field stresses can reduce fracture initiation pressures and initiate the fractures in a more desired way. The spacing between perforations tunnels can affect the way that the fractures initiate and propagate, perforations tunnels placed very close to each other can prevent certain fractures to initiate, due to increased stress shadow effect.

When the oriented perforations tunnels method is used as a stimulation technique in a vertical wellbore, and for a normal stress regime, fractures tend to initiate randomly, as they tend to propagate, fractures combine and form an axial fracture. In a strike slip stress regime, the initiation of fractures is more symmetric, and fractures eventually combine and form an axial fracture. For a reverse stress regime, fractures initiate from outer perforations and form transverse fractures.

When the spiral perforations tunnels method is used as a simulation technique in a vertical wellbore, and for a normal stress regime, fractures tend to initiate from perforations oriented perpendicular to minimum horizontal field stresses. Less propagation happens from other perforations tunnels. In a strike slip stress regime, and due to higher horizontal stress anisotropy, fractures initiate from perforations oriented perpendicular to horizontal field stresses and from other perforations tunnels as well. In a reverse stress regime, fractures initiate and propagate from fractures placed at the middle of the wellbore.

At the end of the project, the author recommended some important ideas that might be used for future considerations in related topics of investigation.

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