The Flow Characteristics of Supercritical Carbon Dioxide (SC-CO2) Jet Fracturing in Limited Perforation Scenarios

Can Cai,Qingren Liu,Yong Kang,Song Xie,Dong Lian,Banrun Li

doi:10.3390/en13102627

Abstract

Supercritical carbon dioxide (SC-CO2) jet fracturing is a promising alternative for shale gas fracturing instead of water. However, most studies pay more attention to the fracture generation and ignore the flow characteristic of SC-CO2 jet fracturing in limited perforation scenarios. To accurately explore the flow field in a limited perforation tunnel, a numerical model of a SC-CO2 jet in a limited perforation tunnel before fracture initiation is established based on the corresponding engineering background. The comparison between the numerical simulation and experiments has proved that the model is viable for this type of analysis. By using the numerical method, the flow field of the SC-CO2 jet fracturing is analyzed, and influencing factors are discussed later. The verification and validation show that the numerical model is both reliable and accurate. With the dramatic fluctuating of turbulent mixing in a fully developed region, there is an apparent increase in the CO2 density and total pressure during limited perforation. When the z increases from 10 times r0 to 145 times r0, the velocity on the perforation wall surface would decrease below 0 m/s, resulting in backflow in the perforation tunnel. The structure of the nozzle, including the outlet length and outlet diameters, significantly affects the axial velocity and boosting pressure in the perforation tunnel. The highest total pressure exists when the nozzle length-to-radius ratio is 2. The maximum velocity of the jet core drops from 138.7 to 78 m/s, and the “hydraulic isolating ring” starts disappearing when the radius changes from 1 to 1.5 mm. It is necessary to increase the aperture ratio as much as possible to ensure pressurization but not over 1. Based on a similar theory high-speed photography results clearly show that the SC-CO2 develops to fully jetting in only 0.07 s and a strong mixing exists in the annular region between the jet core and the surroundings, according with the numerical simulation. This study should be helpful for scholars to comprehensively understand the interaction between the SC-CO2 jet and perforation, which is beneficial for studying SC-CO2 fracturing.

Highlights

IntroductionAs a clean energy resource, has been an emphasis in research and development in the primary energy field
Shale gas, as a clean energy resource, has been an emphasis in research and development in the primary energy field
The velocity in the axial section and pressure distribution on the perforation surface are important for fracture generation, which are essential for further exploration and study. We extend these previous works and investigate the mechanical behavior of supercritical carbon dioxide jet fracturing in the perforation tunnel before fracture initiation based on its engineering background

Summary

Introduction

As a clean energy resource, has been an emphasis in research and development in the primary energy field. Energies 2020, 13, 2627 poor fracturing performance, supercritical carbon dioxide (SC-CO2 ) has been proposed for shale gas fracturing to replace the slick water. In addition to decreasing domestic energy cost, it works better in stimulating low-pressure, low-permeability, strong water-locking/water sensitive reservoirs than water-based fracturing fluid [1]. SC-CO2 is expected to be an efficient technique for shale gas fracturing. The SC-CO2 fluid which is used as a supercritical solvent in chemistry and chemical engineering firstly has unique physical characteristics. It is believed that the SC-CO2 can enhance the fracturing and improve the production of shale gas [2]. It is found that a high rate of penetration (ROP) can obtained by using SC-CO2 as the drilling fluid [3,4,5,6]

Results

Discussion

Conclusion