Installation and Data Analysis of a Downhole, Fiber Optic Flowmeter at Mahogany Field, Offshore Trinidad

Abstract

Abstract In March, 2002, a downhole, fiber optic flowmeter was successfully installed in BP's Mahogany A-15 well, offshore Trinidad. The meter was installed at a measured depth of 12,114 ft and a deviation of 71°. The flowmeter is full bore, completely non-intrusive, contains no downhole electronics or moving parts, is electrically passive and was deployed with the production tubing string during completion of the well. It provides high quality measurements of temperature, pressure, gas flow rate, and oil flow rate directly to the platform SCADA system. In addition, data from the instrument is linked to BP's Wide Area Network through a network-accessible hard drive. The installation at Mahogany was a field trial of the flowmeter and represents a number of "firsts" for deployment of fiber optic flow metering technology, including the first application metering a downhole flowing gas phase and the first multiphase application. Performance of the flowmeter at Mahogany has exceeded expectations and demonstrates the value of real-time downhole production data. Data quality of the fundamental meter measurements of pressure, temperature, bulk velocity, and mixture sound speed from the first nine months of operation has been excellent and within specifications. The high deviation of the well at the meter location, along with a rapid increase in downhole free gas fraction, presented several interpretation challenges, including operation in complex flow regimes and slippage of the oil phase relative to the gas phase at the meter. This was resolved through development and implementation of a pseudo-three-phase slip model. The resulting downhole oil, gas, and water rates from the flowmeter are converted to surface rates using appropriate PVT data before being passed to the SCADA system. Thus far, rates from the downhole optical flowmeter agree with surface well test results to better than ±10%.