Inducing formation damage in sandstone reservoirs through poor drilling fluids management can impair well productivity. A detailed mud-management plan that addresses fluid design and particle-size monitoring can help minimize formation damage and improve well productivity. This management plan was demonstrated successfully on 29 wells where the operator implemented an engineered oil-based drill-in fluid (DIF) and a particle-size distribution (PSD) analyzer in the field while drilling the reservoir.
The oil-based DIF was formulated with a 70/30 oil/water ratio and then treated with sized calcium-carbonate bridging agent. The PSD analyzer was used continuously while drilling to monitor and maintain optimal PSD values in the DIF. Maintaining controlled ROP was essential while drilling a reservoir section along with the hourly addition of sized calcium carbonate and efficient solid control equipment running all the time while drilling. Overbalance pressures were also minimized to reduce the risk of differential sticking.
To achieve better bridging results, D90, D50, and D10 particle-size distributions were maintained in the programmed range throughout the entire reservoir section. Upon reaching total depth (TD), the bottomhole assembly was changed and the entire section was reamed to TD. A wiper trip was done to casing shoe then tripped back to bottom without pumping to simulate hole conditions that would occur while running screens.
Once the open hole was deemed in good condition, the well was displaced to a solids-free invert mud maintained at the same density as the DIF. This fluid was circulated over a 265-mesh screen prior to running the screens to ensure all fine sand and excess filter cake had been removed.
Testing results indicated minimum skin damage and good stable production rates.