Supercritical CO2 Proposed Instead of Water for Hydraulic Fracturing
Scientists from Perm Polytechnic University, in collaboration with colleagues from China, have developed a method of enhanced waterless hydraulic fracturing. This could improve the efficiency of oil and gas production from unconventional reservoirs, according to a report from PNIPU obtained by the Devon news agency.
Shale oil and gas deposits are characterized by high density and low permeability, making resource extraction difficult. To develop these deposits, hydraulic fracturing (fracking) is used, where liquids with special additives are injected into the well under high pressure. This process creates fractures in the rock, allowing hydrocarbons to flow more easily.
Despite its effectiveness, hydraulic fracturing presents numerous technical and environmental problems, such as high water consumption, chemical contamination, reservoir damage from pore blockage, and high viscosity. Therefore, scientists are seeking waterless methods to increase rock permeability.
One of the most promising methods under development is the injection of supercritical carbon dioxide (SC-CO₂). This is carbon dioxide in a state above its critical temperature and pressure, which gives it unique physical and chemical properties.
Supercritical carbon dioxide has greater miscibility with hydrocarbons and reduces oil and gas blockage.
“This eliminates problems with clay swelling and formation contamination and helps create a large network of fractures,” explained Vladimir Poplygin, Director of the Kogalym branch of PNIPU.
Carbon dioxide can be injected underground on an industrial scale, supporting environmental policy goals for dual-use carbon.
Scientists from Perm Polytechnic, the China University of Petroleum, and the Chinese Academy of Sciencesstudied how supercritical carbon dioxide affects the morphology, length, width, and pressure of the fractures created. They presented a technology for enhanced hydraulic fracturing that reduces environmental impact and increases resource recovery efficiency.
The method consists of three stages. First, SC-CO₂ creates microfractures around the wellbore without damaging the rock. Then the gas injection pump is stopped.
Under holding pressure, the well is saturated with CO₂, which reacts with minerals, reducing the rock’s strength and density. Only at the final stage is liquid injected at high speed to create fractures, widen them, and increase complexity.
The researchers tested the technology using a specially developed hydraulic fracturing setup. It includes a liquid injection system, data collection, power supply, and a triaxial fracturing device. The device applies three-sided pressure to the rock sample. Tests on shale rock were conducted using both the traditional and the proposed technology.
Compared to water-based fluids, enhanced hydraulic fracturing with carbon dioxide reduces pressure by 43%. The total fracture length is approximately 3.5 times greater, with numerous branches.
With standard hydraulic fracturing, fractures form only on the shale surface and cannot penetrate deeper. When supercritical carbon dioxide is injected, the fractures spread along the bedding plane, passing through the entire rock sample.
