Abstract Some of the horizontal wells that were drilled in the Saladin field on Thevenard Island in Western Australia have produced below expectations or have experienced sharp production declines. The reasons for this were not known, although the following were suspected to be contributing factors:Reservoir quality could vary considerably.The horizontal sections were intentionally drilled in a sinusoidal shape and the low points could become traps for sand and heavy fluids.Formation damage may have occurred in some wells that were drilled with a water based mud and a high overbalance. A specialized well cleaning system, which consists of a specially designed jet pump run on concentric coiled tubing, was determined to be a better method than conventional coiled tubing to clean the horizontal sections and investigate the causes of the production problems. The tool can be operated in a fines removal mode or a fluid removal mode which provides a localised drawdown at every point in the wellbore. The localized drawdown allows the mud-damaged zones, gas, oil and water intervals to be identified. The well cleaning system has been successfully used to remove sand and drilling mud damage from horizontal wells in Canada, Venezuela and California. The well cleaning tool can be configured to work with different concentric coiled tubing sizes and a 1" inside 2" concentric string was designed for the Australia project. This paper reviews the design and mechanism of the well cleaning system and provides results on the first 3 wells that were cleaned in the Saladin field. Introduction Thevenard Island is located approximately 900 miles north of Perth and 15 miles from the coast (Figure 1). The fields on this island have been developed by the Joint Venture ChevronTexaco, ExxonMobil and Santos and operated by ChevronTexaco. The Saladin field has 12 producing horizontal wells, six on the island and 6 offshore (Figure 2). The producing formation is a layered glauconitic sandstone called the Mardie Greensand. The first horizontal well was drilled in 1994. Early wells were completed open hole but later wells had pre-drilled liners installed in the horizontal sections. Initial production was high, ranging from 1000 to 3000 barrels of oil per day, but declined steeply as reservoir pressure depleted. The wells are being produced with gas lift. Gas injection is currently being used to maintain reservoir pressure although water flooding is scheduled to begin in 2002 with some producers being converted into injectors. The field has experienced some problems and production anomalies. Two of the early wells that were completed with open hole horizontal sections endured hole collapse near the heel. Other wells with steep production declines were suspected to have blockage or debris buildup in the liners. Some wells were drilled with a water-based mud and a high overbalance so formation damage was suspected due to the nature of the glauconitic sandstone. A technical study was undertaken to investigate cleanout strategies for the Saladin wells. In particular, cleanouts using water and nitrogen with 1.25", 1.5" and 1.75" coiled tubing were compared to the well cleaning system. A 1" inside 2" concentric coiled tubing string could meet equipment requirements and provide the necessary performance. As a result of the investigation, the well cleaning system was chosen as the preferred cleanout method. Most of the Saladin wells are completed with 3.5" production tubing and 3.5" liners. Since the existing well cleaning tool outside diameter (OD) was 3.75", a smaller 2.5" OD tool had to be developed. In a period of 3 months, the new tool was designed, built and subjected to full scale testing in a 20 foot long, 5" inside diameter, flowloop.