Shenjia Hydraulics

Release Date:

2023-01-10

Since its introduction, displacement‑enhancement technology has become one of the primary methods for boosting oil and gas production. However, conventional water‑flooding techniques suffer from high water consumption, low produced‑water recovery, and rapid fluctuations in oil and gas output. Supercritical CO2 flooding, by contrast, offers numerous advantages—environmental protection, water‑resource conservation, increased hydrocarbon production, and CO2 sequestration—making it a promising approach with broad prospects for enhancing reservoir performance and advancing field development.

Understanding the applications of carbon dioxide displacement systems

Since its introduction, displacement‑enhancement technology has become one of the primary methods for boosting oil and gas production. However, conventional water‑flooding techniques suffer from high water consumption, low produced‑water recovery rates, and rapid fluctuations in oil and gas output. Supercritical CO2 flooding, by contrast, offers numerous advantages—environmental protection, water‑resource conservation, increased hydrocarbon production, and CO2 sequestration—making it a promising approach with broad prospects for enhancing reservoir performance and advancing field development.

Displacement device

　　Supercritical CO2 flooding technology is primarily suited for reservoir stimulation in unconventional oil and gas plays characterized by water sensitivity, water‑lock effects, low production rates, low permeability, and low hydrocarbon abundance. Due to its physicochemical properties, CO2 adsorbed into the formation can create a mildly acidic environment, mitigating clay mineral swelling and fundamentally addressing water sensitivity and water‑lock phenomena, thereby enhancing reservoir permeability. This approach is currently one of the key methods for large‑scale development of unconventional oil and gas resources.

　　Furthermore, supercritical CO2 itself exhibits the low viscosity and high diffusivity of a gas, as well as the high density of a liquid. Its fracture pressure is lower than that of hydraulic fracturing and liquid‑CO2 fracturing, resulting in greater fracture‑propagation capability and a more complex fracture network. However, as a novel displacement technique for enhanced oil recovery, many of the associated technologies and theoretical frameworks of supercritical CO2 flooding remain incomplete. Scholars hold differing views on the fracture initiation mechanisms and fracture‑extension patterns during the displacement process; therefore, an in-depth investigation into the underlying principles of supercritical CO2 flooding is warranted.

　　What is supercritical CO2?

　　As environmental temperature and pressure vary, certain substances can exist in three phases: gas, liquid, and solid. The point at which these three phases coexist in equilibrium is called the triple point, while the point at which the gas–liquid interface disappears is known as the supercritical point. The temperature and pressure at the critical point are referred to as the critical temperature and critical pressure, respectively; different substances have distinct critical temperatures and pressures.

　　Supercritical CO2 refers to CO2 that, under conditions where the pressure exceeds 7.38 MPa and the temperature surpasses 31.04°C, transitions into a supercritical state—a phase that exists between gas and liquid. Gases are characterized by their ability to completely fill any container, while liquids can dissolve other substances. When CO2 is in its supercritical state, the distinct gas–liquid interface vanishes, giving rise to a unique phase that exhibits properties of both gases and liquids.

　　Application of Low-Field Nuclear Magnetic Resonance in the Study of Supercritical CO2 Displacement Systems

　　Supercritical CO2, owing to its unique physical and chemical properties, displaces formation fluids upon injection, thereby enhancing oil recovery. Its mechanisms can be broadly categorized into four key processes: shearing and fracturing natural fractures; reducing the net pressure within fractures to promote fracture propagation; lowering the critical pressure to stabilize fracture formation; and inducing localized phase transitions that facilitate the dynamic, sustained evolution of fractures. Through these effects, the reservoir’s electrical conductivity and permeability are significantly improved.