Hydro-Mechanical Simulation of Hydraulic Fractures in Low-Permeability Shale Reservoirs using Generalized/Extended Finite Element Method

As the major driving force of the Saudi Arabian economy, natural gas, plays a key role in transforming the countrys development and that of its many other sectors. Being a non-renewable energy source, the depletion of gas fields which results in decline in natural gas production prompts the need to source for the non-conventional gas sources. Fortunately, natural gas obtainable from hydrocarbon-rich shale formations is a viable option. Popularly known as shale gas, this type of gas occurs in highly less permeable deposits/reservoirs that makes its extractions impossible without special intervention, in contrast to the extraction of conventional natural gas. As a result, the technique of hydraulic fracturing (also known as fracing) is widely adopted in the oil and gas industry in order to increase the permeability of a reservoir. Hydraulic fracturing consists of injecting a combination of fluid and proppant into an initially drilled well-bore in order to create high pressure that drives the nucleation and propagation of fractures in the formation with low permeability, thereby serving as pathways that enhance the recovery of hydrocarbons. This practice has seen tremendous success as the productivity of the reservoir is increased tremendously. Despite the many advantages associated with hydraulic fracturing, a poor design of the process can lead to uneconomical outcome or failure in achieving the desired gas production quantities due to fractures that may turn sharply to prevent the transport of the proppant further enough for adequate opening. Other setbacks include unwanted pressure drop in the process, improper spacing of the initial fracture clusters, etc. In addition, the process creates a concern for environmental pollution caused by the use of toxic chemicals during the fracking that can contaminate groundwater. In order to overcome many or most of the aforementioned challenges, predictive tools such as numerical simulation techniques are utilized in practice. Consequently, the literature is inundated with many attempts to simulate the hydraulic fracturing and assess its effectiveness. The generalized/extended finite element method (G/XFEM) is one of the most popular tools used in order to achieve that purpose. Unlike the conventional FEM, the method does not require the use of special quarter-point elements that are time-consuming and laborious to generate in evolving 3D fractures. In addition, G/XFEM allows modelling discrete fractures that do not conform with the element boundaries in an efficient and robust manner. This proposed research plans to simulate the fracture propagation, during the hydraulic fracturing, using a state-of-the-art three-dimensional G/XFEM. This technique will be used to study the impact of 3D non-planar hydraulic fractures and their interactions with each other, particularly during the early stages of the fracturing. The models will be developed using an in-house 3D code (under development by the Consultant of this project and his research team at the University of Illinois at Urbana-Champaign) that has many capabilities which other commercial software programs that uses XFEM do not have. For effectiveness, mesh adaptivity will be utilized in order to minimize the use of expensive mesh throughout the domain of the problem. Despite the complexity of the program, it can still run on a desktop personal computer. A number of typical reservoir formations with different in-situ conditions will be simulated in order to come up with conclusions about the fracture behaviour during the hydraulic fracturing. In particular, the study will come up will guidelines about the factors to consider in order to minimize pressure drop from the wellbore, the optimum spacing of the initial fracture clusters, as well as their interactions during propagation. This study will be beneficial to the Kingdom of Saudi Arabia due to the importance of the topic in its economy. If funded, this research will serve as a pioneer study about the use of G/XFEM as a simulation tool for the hydraulic fracturing in KSA and the region at large. The experience of the Consultant (Prof. C. Armando Duarte) as one of the pioneers of G/XFEM, as well as on the topic of hydraulic fracturing, will be greatly beneficial to the team, having worked on similar projects funded by ExxonMobil Oil Company for several years. Please see Section 5.2 of this proposal and the Consultants resume (Page 27) for the the highlights about the immeasurable benefits that KSA, KFUPM, and the research team will benefit by adopting Prof. Duarte as the Consultant.