Modelling of hydraulic fracturing and its engineering application

The Hydraulic Fracturing process and its engineering applications have been studied and reported in this thesis. The Distinct Element Method (DEM) was adopted as the main and preferred numerical technique because of its distinctive features and advantages. This method allows the phenomenon to be modelled and viewed microscopically at the inter-particle level by conceptualising the rock mass as an assembly of discrete particles interacting with each other via contacts. This method allows for a more detailed and dynamic monitoring of the hydraulic fracturing process.

Sequel to a detailed review on the study of the hydraulic fracturing phenomenon, the research was extended to investigate specific cases of applications of hydraulic fracturing in geo-mechanical and environmental problems. Examples of such cases include carbon dioxide injection and storage in a reservoir system, and the behaviour of naturally occurring faults subjected to hydrostatic fluid pressures. The key factors governing the geo-mechanical responses of porous media (rocks), including reservoir formations were identified and further examined to ascertain the following: the role and inter-relationship between operating and material/fluid variables such as injection flow rate, fluid pressure, and interstitial velocity; type and pattern of fracture propagation; influence of environmental conditions as well as the configuration of the well-reservoir system, amongst others.

Because of broad similarities in enabling conditions, analyses and applications of the phenomenon were also extended to study the sand production process. However, since the emphasis of the study was on identifying and examining the controlling variables as well as establishing patterns of sanding production rates rather than the study of the cavitation process, investigations were conducted using a finite element procedure; moreover, the limit of computational capacity has prevented a large scale DEM model for such problems. Modelling results show that fracturing mode, pattern and intensity are highly dependent on operating and environmental conditions; the reservoir erosion processes also indicate likewise tendencies. The numerical modelling techniques adopted and results obtained facilitate an improved understanding of geo-mechanical mechanisms at sub-surface systems, and could be further improved for industrial applications, such as site evaluation and assessment of the efficiency of stimulation techniques.