Fracture Height Propagation in Tight Reservoirs Using the Finite Element Method
Date
2021-01-26
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Abstract
In recent years, multi-stage hydraulic fracturing technology is widely applied in oil/gas industry all over the world as a successful treatment, especially in tight and shale reservoirs. The induced fracture geometries directly affect the post-stimulation production and economic profitability of the project and accurately predicting the fracture properties is quite important. In addition to fracture length and conductivity, fracture height is another critical parameter of the hydraulic fracturing treatments in the unconventional tight/shale formations. Multiple transverse fractures are usually created along the horizontal wells, where the mechanisms of fracture-height-containment can be complicated under conditions such as interactions with the natural fractures, as well as adjacent hydraulic fractures. In addition, the directions of the bounding layers may not be parallel with that of horizontal wells. Traditional fracture propagation models applied in industry do not include all the aforementioned factors comprehensively. This research targets to study the mechanisms of hydraulic fracture propagation, focusing on the fracture-height-containment in the scenarios of multiple fractures along the horizontal wells. Firstly, a two-dimensional numerical model is proposed to analyze the methodology of single fracture height propagation via the finite element method. Then, an analytical model is built to understand the mechanisms of the fracture height containment considering inclined bounding layers. Modeling results suggested that for the closely spaced multiple fractures which are growing simultaneously, the critical fluid pressure becomes larger, implying that the fracture height propagation is more difficult under such scenario. Fracture height propagates more easily when bounding layer inclination angle increases. Thirdly, a three-dimensional numerical model with cohesive method on the fracture height propagation is used to analyze the multiple fracture interactions and the effective fracture height and width in tight reservoirs. The influence of stress shadow and stress difference on effective fracture height has been investigated and results show that the interaction from adjacent fracture becomes more significant when fracture spacing is small. Fluid injection rate is also an important influencing factor on the hydraulic fracture width especially when flow rate is low. When stress shadow effect is strong, the interior fractures can hardly propagate, and the majority of the fluid volume goes into the exterior fractures.
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Cai, J. (2021). Fracture Height Propagation in Tight Reservoirs Using the Finite Element Method (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.