Alternative Approachto Multi-Rate Testing

Abstract

In Nigeria it is a statutory requirement to frequently perform multi-rate test (MRT) on gas wells to update well deliverability and for optimal reservoir management. Analysis of MRT test data provides information on well potential, average reservoir pressure, flow correction, skin factors, condensate and water rate. This information is useful when calibrating well models and in reservoir management. Allthisinformation when not properly estimated can have a huge impact in reserve estimation as well as production forecasting. Traditionally, MRT testing is done using a mobile tester. The inability to conduct MRT tests frequently using themobile tester is due to budget constraints and associated deferment or flaring affectingobligation to meet gas sale agreement. Other demerits associated with the traditional approach to MRT include large personnel exposure, mobilization of heavy equipment, high environmental footprint, inability to flow well to potential due to flare limitation and difficulty in reconciling test rates with actual rates. Due to these limitations, an alternative testing method is proposed. The proposed approach makes frequent MRT's possible and attractive from both economic and HSSE standpoint. The proposed method discussesusing existing gas central processing facility to conduct MRT. This new method offers a major advantage over the former since it requires little or no equipment mobilization, no flaring nor deferment, reduced number of personnel exposure, no test rate limitation nor rate reconciliation, all of which can be achieved at a significantly lower cost, reduced HSSE exposure and testing duration. Pilot tests were successfully carried out on well X, well Y & well Z. In each case there were zero incidents, zero deferment and zero production loss. This method saved $2.34M and gained some volume of gas which would have been lost to flaring if testing was done using the traditionalmobile tester. These three pilot examples demonstrate that MRT's can be performed more frequently using an existing gas central processing facility provided all of the metering equipment are installed and that the activities is meticulously planned to capture all of the required data.