High-Water Cut: Experience and Assessment in PDO
Authors: Khamis Busaidi , Haridas Bhaskaran 
Published: January 2008

A study from PDO indicated that the allocation and reconciliation factors of Nimr field had shown a deterioration trend since 1999. The suggested possible cause of this deterioration was the increase of net oil calculation uncertainty as water cuts approaches 80% and above. On the individual well basis, about 20% of all the wells produce at greater than 95% water cut but contribute to about 8% of production. The overall water cut of the Nimr asset is currently 87% and is forecast to increase to 90% over the next ten years causing further deterioration of the reconciliation factor.

Inaccurate water cut measurements causes failure to optimize wells production within the capacity constrains of production facilities. As such, PDO has been on the lookout for a solution for high accuracy water cut meter for the high water cut wells.

A market search was done in 2001 as the first phase of identifying the water cut meters that could be considered for Nimr application. The main criterion used in the market search was to list down those meters with quoted absolute error lower than +/− 0.5% as the water cut approaches 80% and above. Four meters were proposed for loop test i.e., Red Eye from Premier Instruments (USA), Phase Dynamics (USA), H2Oil from Honeywell (USA) and Haimo (China).

All the four vendors were invited to participate in the accuracy test. Phase Dynamics declined to participate, while the other three vendors accepted to participate in the proposed test.

The objective of the test was to evaluate the consistency of the quoted 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 Facility in Daqing Oilfield, Daqing City, China (DOD). The facility uses live crude coming directly from the Daqing oil wells. The test was carried out during the period of 22nd January to 26th January 2002. During the test, the Honeywell meter could not be operated due to problems with the hardware of the meter. Another test was then arranged to test the Honeywell meter separately during the period of 11th March to 13th March 2002 in the same facility.

During the test, the accuracy of the three meters were assessed for different water cut. The Red Eye meter proved to work with an accuracy of within +/− 1% absolute for water cut higher than 85% in oil/water flow. The meter exhibited large error (+/−2% absolute to +/−6% absolute) for water cut lower than 85% in oil/water flow. For three phase flow (GVF &lt; 25%), the accuracy of the meter was +/−2% absolute for water cut higher than 85% and +/−8% absolute for water cut lower than 85%.

The Haimo meter has proved to work well within full operating range 0 to 100% water cut with an accuracy within +/−1.5% absolute for oil/water flow. For three phase flow (GVF &lt; 25%), the accuracy of the meter was found to be within +/− 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 the meter deteriorates when gas is applied to the flow.