Abstract
A significant portion of SE Asia's oil and gas reserves are found in marginal fields containing less than 30 million barrels (bbl) of recoverable oil. The cost of the typical infrastructure to develop these fields can be extremely large which results in some fields being too uneconomical to produce. Instead, some fields are tied-back to already existing infrastructure reducing the requirement for the additional expensive processing equipment. This results in larger production capabilities and more fields becoming economical. However, using this tie-back method requires the produced fluids to be measured and the correct volumes allocated back to the individual wells for both fiscal and ownership applications. As part of the industry standard Measurement Guidelines, the maximum allowable measurement uncertainty for these measurements is often ± 1% (k=2).
For marginal fields the production flowrate is often in the region of 2,000-8,000 bbl/day of oil with expected water cuts starting below 10% and rising to over 50% after several years of production. Owing to limitations in tie-back facilities there are situations where gas break-out in the metering stream can occur (due to insufficient static head). This can result in 3-phase flow through the measurement point which is known to increase the error and uncertainty of measurement. In order to meet the measurement uncertainty requirements a new method has been developed that corrects the mass flow based on live measurement data, PVT models and correction curves generated from a characterisation of the meters.
After a baseline calibration, the meter is then tested in 3-phase flow to give an indication of measurement accuracy and repeatability under these conditions. Correction curves are then generated to correct the meters performance with various quantities of gas and water present. From recent tests, the results from the baseline calibration of the meters showed excellent performance in terms of accuracy and repeatability. During the characterisation tests, large errors were present but these were found to be very repeatable for higher flowrates and corrections could easily be applied. At lower flowrates the Coriolis meters were less repeatable.
This paper will discuss the role of allocation meters in the development of marginal fields and provides a case study on a new method of using single phase flow meters under 3-phase conditions. To the author's knowledge, this method has not been used before and represents a novel use of commercial equipment. The paper will describe the measurement process and discuss the additional sources of uncertainty involved in the process. The paper will end with recommendations for future developments in the region to maximise production and lower costs associated with measurement equipment.
