Dissertation/Thesis Abstract

Factors Affecting the Critical Flowback Velocity of Fracturing Fluids and the Long-Term Productivity of Shale Gas Wells
by Zhang, Zheng, Ph.D., University of Louisiana at Lafayette, 2018, 154; 10809942
Abstract (Summary)

Proppant production during the flowback process in hydraulic fracturing treatments has been generally recognized as a problem that causes low fracture conductivity of fracture near the wellbore. This undesirable process also causes the proppant accumulation in the well bore (sand-out) and consequent interference with tubing and other equipment. Among several techniques available to reduce proppant loss from fractures, controlling the flowback velocity of fluid to be lower than a critical value during the flowback process is an essential one. However, this critical velocity has not been established for all conditions, including proppant types, fluid properties, and closure stresses.

The objective of this study was to determine the critical flowback velocity for different types of proppants under different confining pressures with various viscosities of fracturing fluid. This objective has been achieved based on experimental studies conducted in a specially designed apparatus.

A simple analytical model for long-term shale gas production evaluation is still lacking. This work fills this gap. A simple and accurate mathematical model was developed which considers linear flow in both shale matrix and fractures. It can describe the long-term shale gas production with pseudo steady state flow. The model is verified against a Fayetteville field case data. The difference between the production rate given by the model and measured data was found to be less than 10%. The effect of fracture geometry parameters on the long-term production rate is also investigated. The results show that fracture spacing, and fracture length are the most dominant factors on the long-term shale gas production performance. This model provides reservoir engineers a simple and accurate tool for predicting, evaluating and optimizing the long-term performance of shale gas wells. The result of the investigation indicates that, for a fracture with a given width, the closure stress helps hold the proppant in place. This is due to the friction force that is proportional to the normal force created by the closure stress. The fluid velocity required to mobilize the proppant therefore increases with closure stress. However, the effect of closure stress influenced by the shape of proppant particles and their friction coefficients at the fracture surfaces. Proppants containing angular particles from tighter packs in the fracture, increasing the critical fluid velocity. Under the condition of constant closure stress, high viscous fracturing fluids have higher capabilities to carry away proppant from the fractures. The critical flowback rate decreases with fracturing fluid viscosity. Therefore, super high viscosity fracturing fluid should be avoided to improve fracturing performance in shale gas or oil wells.

Indexing (document details)
Advisor: Guo, Boyun
Commitee: Boukadi, Fathi, Feng, Yin, Guo, Boyun, Seibi, Abdennour, Zhang, Pengfei
School: University of Louisiana at Lafayette
Department: Petroleum Engineering
School Location: United States -- Louisiana
Source: DAI-B 80/08(E), Dissertation Abstracts International
Subjects: Engineering, Petroleum engineering
Keywords: Flowback, Hydraulic fracturing, Proppant
Publication Number: 10809942
ISBN: 978-1-392-04113-0
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