PREDICTION OF RESERVES AND PRODUCTION PERFORMANCE BY SIMULATION: HALIBUT FIELD

Abstract

Production from Halibut began in 1970 and after seven years 44.7 megatonnes (354 million barrels) of oil have been produced from initial Halibut reserves estimated at 82.1 megatonnes (653 million barrels). Thus the field is 54% depleted and approaching the point where oil production rates will start to decline rapidly due to increasing production of formation water. The accurate prediction of this decline point in time is of critical importance in scheduling the installation of artificial lift facilities. As a result of a 1974 reservoir engineering study, which formed part of the basis for a 53% increase in estimated Halibut reserves, predictions of near term performance have proved to be reasonably accurate and substantiated a decision in 1974 to program installation of artificial lift facilities for a 1978 start-up.

A significant part of the 1974 study was the comparison of reservoir performance data obtained through regular reservoir surveillance and specialized well testing programs with predictions of reservoir performance from a three-dimensional, two-phase simulation model of the field. Reservoir description parameters used in the model were varied until its performance matched actual history for the period in hand. In achieving a history match, the model was adjusted: firstly, to reflect permeabilities estimated by in situ pressure build-up and pulse tests (these values being more than twice as high as those measured in recovered core material); secondly, to simulate restricted areas of vertical communication as defined by pulse testing between different sand units; and thirdly, to match water contact rises indicated by TDT logging. Once the model was calibrated by this method it was used to predict field performance over the whole life of the field and to schedule and size additional production facility needs.

Since completion of the study, two years of additional reservoir behaviour history have become available. Performance predictions made after achieving a satisfactory history match have been in good agreement with actual performance over the past two years and work is well along on facilities design and implementation.