Minimizing Wellbore Damage in a Sandstone Reservoir Using Effective Mud Management Practices

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractInducing formation damage in sandstone reservoirs through poor drilling fluids management is a crucial factor that can affect well productivity. An integrated team assigned to manage drilling horizontal producers for field development, developed a mud management plan to monitor drilling fluid properties and maintain mud system specifications to minimize formation damage in the field's sensitive sandstone reservoir. This paper discusses the implementation of the engineered oil-based drillin fluid, particle size monitoring, and drilling and completion methods designed to minimize reservoir formation damage and help maximize well productivity.A particle size distribution (PSD) analyzer was used in the field to monitor the PSD values of the particulates in the drillin fluid (DIF) while drilling the sandstone reservoir. Core samples were selected and analyzed using a scanning electron microscope (SEM) to determine an average pore size value.A diesel-based DIF was specifically designed to minimize formation damage. The DIF was formulated with a 70/30 oil water ratio and was treated with a sized calcium carbonate bridging agent to help minimize spurt/total loss. The engineered bridging agent was added to prevent formation damage that results from the invasion of fines. Overbalance pressures were also minimized to avoid the risk of differential sticking.For better bridging results, the D90, D50 and D10 particle size distributions were instantaneously maintained in the programmed range while drilling the entire sandstone pay section with controlled rates of penetration (ROP). The % of drill solids as a function of total solids was also maintained at low levels with the use of centrifuges and addition of whole treated mud. Upon reaching the total depth (TD), the bottomole assembly (BHA) was changed to a reaming assembly and the entire open-hole section was reamed to TD.After making a wiper trip, the operator 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 emulsion mud maintained at the same density as the DIF. This fluid was circulated over a 230-mesh screen prior to running the screens to ensure that all fine sand and excess filter cake were removed.To date, 26 wells have been successfully drilled and completed with sand screens using the abovementioned methodology. Testing results of the first three wells indicated minimum skin damage and good and stable production rates.