Flowback Study of Hydraulic Fracturing in Shale Gas Reservoirs
Date
2017-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Shale gas production has achieved great success in the U.S.A and Canada. It is increasingly critical in reshaping the global energy landscape. Multi-stage hydraulic fracturing in horizontal wells is widely accepted as the most economic and effective technique to unlock shale gas reservoirs. As shale gas production continues, higher requirements are proposed to improve the long-term productivity after hydraulic fracturing. Fracture cleanup after hydraulic fracturing is an important factor to impacting long-term production forecasting. It plays a significant role in optimizing flowback of a fracturing fluid to maintain the optimal conductivity in hydraulic fractures.
This research is focused on the development of a novel simulator using a mathematical model to optimize a choke size as wellhead pressure changes over time. This new optimization model is capable of performing dynamic adjustment of a choke size while wellhead pressure changes over time. It has a two-phase (gas and liquid) flow model along the horizontal, slanted and vertical sections as fractures close. The model simultaneously considers forces acting on proppant particles, filtration loss of water, compressibility of the fracturing fluid, wellbore friction, a gas slippage effect, water absorption and adsorption. The theoretical feasibility of gas releasing from shale faces when the pressure in fractures is greater than the formation pressure is identified due to the capillary pressure and substitution. Using an idealized straight smooth capillary model, the join forces of capillary pressure and formation pressure are greater than the pressure in fractures in the non-water-wetting section allowing the gas to move and be produced. In order to maximize flowback of the fracturing fluid to the surface and the volume of proppants remaining in the fractures, this research determines the maximum flow velocity of the liquid based on the forces acting on proppant particles. To build the optimization model, the equations of a pressure drop in the two-phase (gas and liquid) flow were derived considering a slippage effect and friction loss while temperature and/or pressure alter along the horizontal, slanted and vertical wellbores. After investigating the workflow of hydraulic fracturing and fracture cleanup, the interface and functions of the novel simulator were designed. The interface is realized with QT and operated by coding with C++ language. The flowback section is complete and a novel simulator testing procedure has been applied to a shale gas well from the Shuangyang Formation in China. Comparison curves with both real and simulation data are demonstrated respectively. Both real and simulation data have the identical changing tendencies and match each other very well.
Description
Keywords
Citation
Jing, G. (2017) Flowback Study of Hydraulic Fracturing in Shale Gas Reservoirs (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.