# Modeling the boosting pressure in cavity and its application in predicting fracture geometry in hydrajet fracturing

• Chang Wen

Student thesis: Master's Thesis

### Abstract

Hydraulic fracturing has been widely used in oil fields. For conventional hydraulic fracturing, it is hard to separate intervals in multi-layered formation. Hydra-jet fracturing technique can avoid this problem. The boosting pressure in cavity behind the casing is a key factor in hydra-jet fracturing process, making the fracture initiation successful. However, there is little research about the pressure field in cavity. This paper aims to establish a mathematical model for predicting boosting pressure in the cavity under different scenarios and predict the fracture geometry. In literature, few mathematical models based on experimental data have been proposed, and the factors affecting boosting pressure in cavity have been studied. In the present work, a numerical model is developed to study the effects of nozzle differential pressure, ratio of nozzle diameter to cavity diameter, annulus pressure and cavity length on boosting pressure. Based on the numerical results, a mathematical model is developed to predict the boosting pressure in cavity under various reservoir conditions. Finally, this mathematic model is combined with 2D PKN-Carter model, Pseudo-3D-Carter model and analytical 3D-Carter model independently to predict the fracture geometry. It has been observed that the boosting pressure increases linearly with nozzle differential pressure and diameter ratio respectively when fixing other parameters. However, annulus pressure and cavity length are proved to be of little effect on the boosting pressure in cavity. For some specific diameter ratios, the relationship between boosting pressure coefficient and dimensionless standoff distance has been developed. Insightful sensitivity analyses have also been presented about the effect of formation leak-off coefficient, Young's Modulus and nozzle differential pressure on the fracture geometry. In P-3D-C model, fracture propagates the most in fracture height direction with pressure increasing. While in analytical 3D-C model, fracture propagates the most in half-length direction with pressure increasing. This work reveals the effect of nozzle differential pressure and diameter ratio on boosting pressure in cavity, which finally affects the prediction of fracture geometry in pinpoint hydra-jet fracturing. This leads to the design of treatment parameters in hydra-jet fracturing. This work also advances the global application of hydra-jet fracturing technology. The UAE has deeper tight gas sand offshore which could be investigated using this model.
Date of Award 2015 American English MD Rahman (Supervisor)

### Keywords

• Applied sciences
• Cavity pressure
• Fracture mechanics
• Hydra-jet fracturing
• Unconventional reservoir
• Petroleum engineering
• 0765:Petroleum engineering

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