Evaluation of Coriolis Meters and Gas Flow Computers for Well Testing

Abstract

Accurate and timely welltest data is critical to evaluate well performance and for effective reservoir management. In Kuwait Oil Company's Burgan South and East areas, the standard method of welltesting in the past has been through test separators and test tank. Because of the flow rate stabilization time and minimum volume required in the test tank for accurate reading of fluid level, welltest duration can range from 10 to 24 hours, especially for low volume wells. This is an operational challenge from the standpoint of acquiring accurate data and meet welltest frequency targets. In an effort to meet these goals, KOC has installed a new system of well testing with Coriolis meter and AGA Gas flow meters in its gathering centers (GCs). The coriolis meter, an online mass and density flow meter, can measure well flow rates with reasonable accuracy within 1–2 hours. This study has compared "simultaneous" well tests results of different categories of wells - high and low flow rate, dry and wet and high GOR using the Coriolis meter, GC test tank and portable test separator at the well. The performance and accuracy of this technology of well testing under different flow conditions are reported. Introduction Well testing is one of the most important data gathering activities that occur throughout the life of a field or a reservoir. The data collected impacts every aspect of work planned and performed in a field/reservoir. This data is a key component of the well surveillance program which effects capital and operational decisions in an oilfield. Therefore, every effort should be made to ensure that this data be accurate and is generated at regular intervals. For a well test to be considered accurate, the fluid rates (oil, water & gas), temperatures and pressures measured should reflect the normal flowing conditions of the well. It calls for appropriate metering equipment and methodology for well testing and correct reporting of the data in the database. Accurate analysis of field performance and timely remedial actions also necessitate data acquisition at appropriate frequencies. Frequent well tests are important in order to be able to identify well problems when they occur and to establish consistent production (oil, water & gas) trends. Any deviation from an established trend may indicate a well problem, which may require corrective measures. The desired frequency of well testing depends on the type of reservoir and maturity of the field. Early stage of development of a reservoir may require low well testing frequency, if minor changes are occurring in production rates, water cuts and GORs. However, with the field maturing, reservoir and production characteristics may change rapidly which will require higher testing frequency to better understand reservoir performance and changes as they occur. Thus, there is no general rule to define "appropriate" well test frequency as it depends upon multitude of factors prevailing in a field. In Kuwait Oil Company (KOC), the short term target for well test frequency has been fixed at 4 accurate well tests per string per year (1 welltest per string per quarter). The long term objective is to acquire one test per string per month.