Abstract
A large majority of the recent deepwater developments in West Africa require sand control applications. Openhole gravel packing is the preferred sand control technique adopted by many operators in this region. It is considered one of the proven methods of sand control from both reliability and productivity standpoints, and allows access to larger reserves through fewer wells. Since most of these reservoirs contain reactive shale streaks, they require synthetic/oil-based drilling fluids (S/OB). Considering that the openhole gravel packing in the industry deals primarily with water based fluid environments, new challenges for gravel packing of the associated wells are thus introduced. A significant level of progress has been made in recent years towards overcoming the challenges through new developments in fluids application, tools and techniques. These developments have resulted in successful gravel packing of wells drilled with oil-based (OB) fluids, which have yielded well productivities, which, in many instances, exceeded those completed in water-based drilling fluid environments. Currently, techniques and fluid systems are available for gravel packing with either a water-based (WB) or an oil-based gravel packing fluid. Both approaches have been practiced in various regions in the world. A common and critical element of both approaches is the proper assessment of potential plugging of the sand control screens during installation and subsequent displacement processes, since the screen installation often must be accomplished with solids-laden fluids (conditioned oil-based mud) in the wellbore, due to logistical challenges and economics.
An OB carrier fluid was recently used for openhole gravel packing of a well in Okpoho field, offshore Nigeria. The application resulted in the best producer in the field. This paper details the steps taken through the design and execution stages of the treatment, incorporating the lessons learned from two previous applications of the OB carrier fluid. A detailed description of the yard tests conducted in Nigeria and the onsite QA/QC procedures with screen samples are also included. A simple approach is proposed for quantification of the impact of screen plugging test results on field practice. This allows operators to evaluate how much, if any, screenplugging can be expected with the particular conditioned OBM as the screens are run in hole and during subsequent displacement processes, so that the operator can decide whether further conditioning, and thus the additional rig time, is worth the associated cost.
