In-well fiber optic sensing systems offer the potential for continuous, high accuracy, high reliability data measurements. Over the past two years, permanent downhole fiber optic pressure and temperature monitoring has become an accepted new technology in the oil and gas industry. Northstar, on the North Slope of Alaska, represents the first multi-well, new field development to incorporate downhole fiber optic pressure and temperature monitoring. This paper will describe the fiber optic pressure and temperature systems being installed at Northstar. Data collection, data management, and data application will be discussed and examples of data from the first installations will be given. Northstar Project Overview The Northstar Pool is a discovery in the Ivishak formation, and is located approximately 6 miles offshore in the Beaufort Sea, north of the Prudhoe Bay Unit, as illustrated in Figs. 1 and 2. The Northstar Pool crosses from state waters into federal waters and lies beyond the barrier islands. The Northstar Pool was discovered in 1983 by Shell during the drilling of the Seal A-01 well and was appraised by Shell and Amerada Hess, who drilled a total of 5 wells to the target horizon. The exploration and appraisal wells were drilled from two gravel islands in approximately 40 ft of water. Amerada's Northstar Island was located over the northwest portion of the Northstar Pool, and Shell's Seal Island was located over the main southeast part of the Northstar Pool. Seal Island is located 6 miles offshore of the Point Storkerson area in the Alaskan Beaufort Sea. Both islands were abandoned and were washed away by winter storms following the initial appraisal of the field in the '80s. The Northstar project consists of a self-contained stand-alone production facility located on a 5-acre gravel island constructed over the remains of Seal Island. The facility provides full process and export facilities for 65,000 barrels per day (bpd) of oil, 600 million standard cubic feet per day (scfpd) of gas injection, and 30,000 bpd of produced water handling capacity. BP Exploration (Alaska), Inc. ("BP") and Murphy Exploration (Alaska), Inc. are the working interest owners of the field, with BP the Unit Operator. The pipeline system consists of a 10-inch crude export line that ties in to the Trans-Alaska Pipeline System ("TAPS") at Pump Station 1, and a 10-inch gas line for providing the import of make-up gas and fuel gas from Prudhoe Bay Unit for enhanced oil recovery ("EOR") at the Northstar project. Construction of the island and installation of the pipelines was completed early in 2000. The island includes slots for 37 wells, and the initial phase of development at the Northstar project calls for 16 production wells, 5 gas injection wells, and one Class I waste disposal well. Drilling began in December 2000. To date (February, 2002), BPXA has drilled the disposal well, one gas injection well, two pre-produced gas injection wells and three producing wells. Development drilling resumed following the facility startup in November 2001 and will continue into 2004. A permanent camp facility for up to 74 production and drilling personnel is installed on the island. Emergency power generation, seawater treatment and sewage facilities will be provided for the camp. Tankage for diesel fuel and water storage is also included. While drilling operations are underway, access to the island in the winter months is by ice road. During the summer open water period, routine access is barge or supply boat. At all other times, helicopters are used to travel to and from the island.

Summary In-well fiber-optic sensing systems offer the potential for continuous, highly accurate, highly reliable, real-time data measurements. During the past 3 years, permanent downhole fiber-optic pressure and temperature (P/T) transducers have become an accepted new technology in the oil and gas industry. Northstar, on the North Slope of Alaska, represents the first multiwell, new field development to incorporate fiber-optic P/T gauges. Real-time downhole pressure data are critical to managing the miscible-gas injection enhanced-recovery process at Northstar. Fiber-optic gauges were selected because of their reliability at high temperatures and their ability survive the severe shock and vibration conditions associated with post-installation perforating operations. As of publication, optical P/T gauges have been installed in 15 wells at Northstar. The data have proved valuable to the asset team in monitoring the perforating program, determining initial reservoir pressure, managing well drawdown, diagnosing completion problems, building wellbore-hydraulics and inflow-performance models, and providing pressure-buildup data, all without the need for well interventions and the resulting loss in production volume. Northstar Overview The Northstar pool is located in the Ivishak formation, approximately 6 miles offshore Alaska in the Beaufort Sea, as shown in Figs. 1 and 2. It was discovered in 1983 by Shell, and five appraisal wells were drilled to the target horizon by Shell and Amerada Hess in the mid-1980s. The Northstar development consists of a self-contained, stand-alone production facility located on a 5-acre gravel island. The facility provides full process and export facilities for 65,000 B/D of oil, 600 MMscf/D of gas injection, and 30,000 B/D of produced-water handling capacity. BP Exploration (Alaska) Inc. and Murphy Exploration (Alaska) Inc. are the working-interest owners of the field, and BP plc is the unit operator. Crude oil from Northstar is exported through a 10-in. pipeline that ties in to the Trans-Alaska Pipeline System, and a 10-in. gas line imports makeup and fuel gas from the Prudhoe Bay Unit for enhanced oil recovery (EOR). Island construction and pipeline installation were completed in early 2000. The island includes slots for 37 wells. The initial phase of development at Northstar includes 16 production wells, 5 gas-injection wells, and 1 waste-disposal well. Drilling began in December 2000 and will continue into 2004, with the reservoir accessed by directionally drilled wells. A typical well design is shown in Fig. 3. Northstar contains a volatile sweet crude. Oil gravities range from 43 to 45°API. The initial gas/oil ratio is approximately 2,200 scf/bbl, and the oil viscosity is approximately 0.14 cp. Reservoir temperature and initial pressure are at approximately 250°F and 5,200 psia, respectively. The field is being developed as a tertiary-recovery project using miscible-fluid displacement to increase recoverable oil reserves. The EOR project involves the initial injection of a large slug of miscible natural gas into the oil column of the Ivishak formation. This period of miscible-gas injection will last approximately 4 years and will be followed by injection of leaner chase gas through to the end of field life. Permanent downhole fiber-optic P/T gauges are being installed in the production wells at Northstar to provide real-time measurement of flowing pressure. Reservoir pressure in the Northstar reservoir is being carefully managed to:Ensure miscibility.Minimize oil loss caused by production at less than the bubblepoint.Minimize the possibility of oil loss because of overpressurization pushing oil into the aquifer.Achieve some aquifer influx to sweep the periphery and structurally low areas. The reservoir management strategy during the miscible phase of the project is to voidage replace 100% of total production to maintain reservoir pressure within 50 psia of the initial pressure at field startup, a State of Alaska requirement. Fiber-optic P/T gauges were selected for downhole pressure measurement because of their long-term reliability at Northstar reservoir temperatures and their ability to survive post-installation perforation operations. Permanent Monitoring at Northstar Northstar is different from other fields on the North Slope in that it produces a light, volatile crude and is being developed with a unique miscible-gas-displacement process. The process uses a combination of produced gas from Northstar and lean gas imported from Prudhoe Bay as the miscible injectant. This relatively lean injectant gas is miscible with Northstar's light, volatile crude. Other miscible gasfloods in Alaska (e.g., Prudhoe and Kuparuk) rely on liquids that are "spiked" into the injection-gas stream to attain miscibility. Reservoir pressure management is recognized as fundamental to the long-term efficient operation of this field. A significantly higher degree of control over the reservoir pressure is possible with real-time bottomhole-pressure-monitoring equipment installed in the Northstar producer completions than would be the case with conventional, intrusive measurement methods. Additional benefits include direct operating-cost savings from avoiding well interventions and optimizing well timing and placement for later wells, resulting from the early reservoir surveillance. These benefits will lead to additional oil reserves being produced. Avoiding the need to intentionally shut in flowing wells for pressure measurements will directly prevent deferral of oil production. Continuous, real-time monitoring of bottomhole P/T in the Northstar producers benefits the asset team by improving their knowledge and ability to manage production from the well and field. Applications of the data are numerous.