Numerical study of long-time growth of hydraulic fractures in a line drive

J.L Mogensen,C.F Niordson,C.S Andreasen,O Jørgensen

doi:10.1016/j.gete.2021.100270

J.L Mogensen, C.F Niordson + Show 2 more

Open Access

https://doi.org/10.1016/j.gete.2021.100270

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Abstract

This work concerns detailed numerical modelling of injection fracturing in chalk formations under 2–3 km burial. The conditions and properties are chosen to resemble field conditions as typically found in oil fields subject to water injection in the Central Graben in the North Sea off-shore Denmark, Norway and the UK, but the studied phenomena are general to injection fracturing irrespective of geographical location and technological application. The complexity of reality is a challenging factor when mathematical models of hydraulic fractures in the subsurface are formulated. To this end the finite element method and a multi physics approach is instrumental, and data from fields developed and operated under conditions prudent for modelling are equally important. In the present study, a poroelastic finite element model is applied and used under plane strain conditions for a linear fracture mechanics investigation. This approach is suitable for analysing fracturing in arrays of parallel and horizontal wells as can be found in many oil fields undergoing water-flooding. Based on realistic field data, e.g. reservoir properties and rate and pressure scenarios representative for typical fields in the North Sea region, fracture initiation and fracture growth are analysed in details in a realistic field setting. Using a formulation of the J-integral, that includes Functionally Graded Material and poroelastic effects, it is demonstrated that formation fracture toughness determines fracture initiation and fracture height. The fracture propagation speed is controlled by continuity, e.g. the injection rate must balance the leak-off from the fracture wall. By combining the fields of geotechnical engineering, petroleum engineering and mechanical engineering with realistic data measurements, this study provides a novel realistic study of how the producer and injector pressure influence the fracturing process for induced hydraulic fractures in a line drive.

Highlights

Hydraulic fractures in oil and gas recovery processes have been used successfully to increase production since the 1950s
The horizontal pre-stress state, imposed by the initial displacement of the rock, and the pore pressure can be seen in Fig. 7(a), as well as the domain used for calculation of the J-integral for the upper fracture
A key conclusion of this study was that the state of stress and the fracture growth is affected by flow in the entire reservoir, and thereby the producers in a line drive are critical to the fracture process

Summary

Introduction

Hydraulic fractures in oil and gas recovery processes have been used successfully to increase production since the 1950s. While the fractures on one side have a huge potential of enhancing oil production, a downside is the inherent difficulty of controlling the fracture process, and the associated risks related to uncontrollable fractures. This has led to the demand of a more thorough understanding of the fracture process and how it can be controlled. Some theoretical models for the fracture generation includes the Perkins–Kern–Nordgren (PKN) model in Perkins and Kern[1] and Nordgren,[2] and for linear and radial propagating fracture geometries (KGN) in De Klerk.[3] The

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