In-situ pressure-preserved coring for deep exploration: Insight into the rotation behavior of the valve cover of a pressure controller

Abstract

In-situ pressure-preserved coring (IPP-Coring) is considered to be the most reliable and efficient method for the identification of the scale of oil and gas resources. During IPP-Coring, because the rotation behavior of the pressure controller valve cover in different medium environments is unclear, interference between the valve cover and inner pipe may occur and negatively affect the IPP-Coring success rate. To address this issue, we conducted a series of indoor experiments employing a high-speed camera to gain greater insights into the valve cover rotation behavior in different medium environments, e.g., air, water, and simulated drilling fluids. The results indicated that the variation in the valve cover rotation angle in the air and fluid environments can be described by a one-phase exponential decay function with a constant time parameter and by biphasic dose response function, respectively. The rotation behavior in the fluid environments exhibited distinct elastic and gravitational acceleration zones. In the fluid environments, the density clearly impacted the valve cover closing time and rotation behavior, whereas the effect of viscosity was very slight. This can be attributed to the negligible influence of the fluid viscosity on the drag coefficient found in this study; meanwhile, the density can increase the buoyancy and the time period during which the valve cover experienced a high drag coefficient. Considering these results, control schemes for the valve cover rotation behavior during IPP-Coring were proposed for different layers and geological conditions in which the different drilling fluids should be used, e.g., the use of a high-density valve cover in high-pore pressure layers.