Progresses in Researching Phase Change Materials for Drilling Fluid Cooling

As wells are drilled deeper and deeper to explore nonconventional oil and gas resources, drilling fluids, downhole tools and detection instrument are experiencing higher formation temperatures, and high efficiency cooling technology is urgently required. The methods of cooling a drilling fluid presently in use include natural cooling and cooling with surface instrument, whose cooling effect is limited. Phase change materials have advantages of high heat storage density and adjustable phase change temperature, hence can be used in a specific well section to achieve temperature response. With phase change materials, precise cooling in a depth near a downhole device such as RSD and LWD can be achieved, and phase change materials are thus becoming the research hotspot in drilling fluid cooling technology. Presently phase change materials though have been widely used in photothermal storage of solar energy, building temperature regulation as well as heat management for electronic devices etc., their use in deep and ultra-deep well drilling and exploration is still in an initial exploration stage. This paper focuses on the classification of phase change materials, the research status of medium and high temperature phase change materials, the properties of phase change materials required for use in drilling fluids, as well as the existing literatures on application studies of drilling fluid cooling. In the future, cost effective phase change materials of high thermal conductivity can be developed through numerical simulation and field test. By strengthening multifunction design of these phase change materials, optimizing their compatibility with drilling fluids, and investigating environmentally friendly, highly efficient, stable and intelligent new phase change materials with multiple functions such as cooling, lubricating and reservoir protection etc., an innovative solution to drilling fluid technology can be developed.