Case History: Efficient Coiled-Tubing Sand Cleanout in a High-Angle Well Using a Complete Integrated Cleaning System

Abstract

Abstract As in many oil fields, the primary coiled-tubing (CT) operation in the Kuparuk River Unit on the North Slope of Alaska is a wellbore cleanout. These cleanouts remove produced fines, fracturing sands, scales, and paraffin. As drilling technology advances and wells become longer and more deviated, the process required to clean out these highly deviated wells becomes more complicated. One such case, West Sak Well, is an undulating horizontal well in unconsolidated West Sak sands with a low bottomhole pressure (BHP). During previous attempts with standard cleanout methods, returns were lost during the job and the final results were less than optimal. Post-job reviews of the unsuccessful conventional cleanouts illustrated where previous approaches were insufficient. This paper describes the use of an integrated cleanout system that efficiently addressed all the challenges of the West Sak Well, which resulted in a successful cleanout returning the well to production. This integrated system approach to wellbore cleanouts was recently commercialized, and this well was the first job using the system in Alaska. Introduction Wellbore fill is a pervasive issue in many reservoirs throughout the world. The production-inhibiting problem is commonly dealt with through CT interventions. However, as wellbores and completions become more complex and as reserves are produced under increasingly difficult conditions there are environments in which conventional CT cleanout techniques are not adequate for effective fill removal. The difficulty of a cleanout depends on many factors, including the completion size, deviation angle, fluid properties, fluid flow rate, BHP, bottomhole temperature, type of solids, and the length along which solids have to be transported.[1] Typically, the cleanout operation involves the circulation of a fluid through the CT to the sandface where the sand is picked up by the jetting action of the nozzles. It is then transported to the surface through the annulus between the CT and production tubing or casing.[1] Depending on the well and fill, multiple wiper trips are required to clean the hole.[2,3] The well in this case history illustrates the challenges and the effectiveness of the integrated system approach for fill removal solution in an unconsolidated sand reservoir with a difficult horizontal well and a low BHP. The objective of this operation was to return the well to production. The integrated system using a new cleanout fluid product was recommended to address the challenges of this well. This system is a combination of several technologies, fluid chemistry, a specifically optimized downhole tool system, a surface solids monitoring system, and application methodologies supported with design and execution software.3 The novel fluid's shear thinning capability acts similarly to high-performance friction reducers. This fluid, which is a bipolymer gel, has considerably longer solids carrying capabilities than xanthan and guar based fluids. It can be modeled in the job design software, along with all conventional cleanout fluids. This paper describes how the integrated cleanout system efficiently addressed the cleanout challenges of the West Sak Well to bring the well back to post-drilling production.