Understanding Fluid Exchange as Screens are Run in Hole – Mitigation of Formation and Completion Damage Risks

To reduce the risk of screen plugging with drilling fluid solids, wellbore fluids are typically displaced to low or no solids systems before sand screen lower completions are run in to wells. Displacing the entire wellbore volume to low solids fluids can add significant cost particularly in high pressure wells. An option can be to displace the open hole section of the well only with the low solids fluid and run the lower completion through the original drilling fluid. A refinement of this process is to fill the upper hole section with the low solids fluid in order to pre-saturate the screens assembly. The movement or exchange of the two fluids as the screens are run in to the wellbore has been a significant uncertainty, until now! This work was conducted to investigate the potential for fluids to exchange as sand screen completions are run in to wells in the Field 1 Satellite and Field 2 developments. The hypothesis that fluids in the wellbore would displace fluids inside the screen assembly as the screens are run in to the well was tested. Computational Fluid Dynamics (CFD) modelling was used to simulate the movement of the lower completion in to the well and determine the rate and quantity of fluid exchange. The simulations demonstrated that when stand alone screen (SAS) completions are run in to wellbores, fluids will exchange from outside to inside the screens. This process happens at all tripping speeds examined and in all parts of the cased and open hole wellbore. The fluid exchange continues throughout the running in process, including in the open hole lower completion. There is no value in filling the top hole section with low solids completion fluid unless fluid exchange during running in can be controlled. When a one-way inflow control device (ICD) check valve is fitted to each screen joint allowing fluid to flow in to the tubing but not back out to the annulus then fluid exchange is significantly limited. Careful consideration should be given to the exchange of fluids as lower completion assemblies are run in to wells. If it is considered undesirable that the fluid in the well should enter the lower completion string as it is run in to the well then appropriate valves or flow reduction should be considered. Eliminating the requirement to fill the top hole section with low solids fluid can lead to significant cost reduction in well where expensive fluids, such as Cs formate, are required to meet the low or no solids specifications. Understanding fluid exchange in wells as screens are run in can significantly reduce the risk of formation/completion damage. The work illustrates the value in a novel application of CFD to determine the optimum well construction process.