High-Water Cut: Experience and Assessment in PDO

摘要

A study from PDO indicated that the allocation andreconciliation factors of Nimr field had shown a deteriorationtrend since 1999. The suggested possible cause of thisdeterioration was the increase of net oil calculation uncertaintyas water cuts approaches 80% and above. On the individualwell basis, about 20% of all the wells produce at greater than95% water cut but contribute to about 8% of production. Theoverall water cut of the Nimr asset is currently 87% and isforecast to increase to 90% over the next ten years causingfurther deterioration of the reconciliation factor.Inaccurate water cut measurements causes failure to optimizewells production within the capacity constrains of productionfacilities. As such, PDO has been on the lookout for a solutionfor high accuracy water cut meter for the high water cut wells.A market search was done in 2001 as the first phase ofidentifying the water cut meters that could be considered forNimr application. The main criterion used in the marketsearch was to list down those meters with quoted absoluteerror lower than +/- 0.5% as the water cut approaches 80% andabove. Four meters were proposed for loop test i.e., Red Eyefrom Premier Instruments (USA), Phase Dynamics (USA),H2Oil from Honeywell (USA) and Haimo (China).All the four vendors were invited to participate in the accuracytest. Phase Dynamics declined to participate, while the otherthree vendors accepted to participate in the proposed test.The objective of the test was to evaluate the consistency of thequoted specifications and performance of the proposed water cut meters under a simulated field conditions with live crude,gas and water.The test was carried out at the DOD Multiphase Flow Facilityin Daqing Oilfield, Daqing City, China (DOD). The facilityuses live crude coming directly from the Daqing oil wells.The test was carried out during the period of 22nd January to26th January 2002. During the test, the Honeywell metercould not be operated due to problems with the hardware ofthe meter. Another test was then arranged to test theHoneywell meter separately during the period of 11th Marchto 13th March 2002 in the same facility.During the test, the accuracy of the three meters were assessedfor different water cut. The Red Eye meter proved to workwith an accuracy of within +/- 1% absolute for water cuthigher than 85% in oil/water flow. The meter exhibited largeerror (+/-2% absolute to +/-6% absolute) for water cut lowerthan 85% in oil/water flow. For three phase flow (GVF <25%), the accuracy of the meter was +/-2% absolute for watercut higher than 85% and +/-8% absolute for water cut lowerthan 85%.The Haimo meter has proved to work well within fulloperating range 0 to 100% water cut with an accuracy within+/-1.5% absolute for oil/water flow. For three phase flow(GVF < 25%), the accuracy of the meter was found to bewithin +/- 2% absolute.The Honeywell meter has proved to work within accuracy of+/- 1.5% absolute for water cut higher than 70% and +/- 0.5%absolute for water cut less than 30%. In the transition region(WC from 30% to 70%), the accuracy of the meter was +/- 5%absolute. The test has also shown that the accuracy of themeter deteriorates when gas is applied to the flow.