A New Mechanism For Integrating Long Term Reservoir Predictions And Short Term Topsides/Compressor Performance To Predictions And Short Term Topsides/Compressor Performance To Produce Accurate Gas Production Forecasts Produce Accurate Gas Production Forecasts 23161

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Abstract

North Sea gas sales contracts are defined in such a way that a seller for the decline years of a gas supply must, on an annual basis, nominate expected short term production levels to his gas purchaser. Failure to meet production levels to his gas purchaser. Failure to meet these production targets can result in severe financial penalties. On the other hand, under nominating is penalties. On the other hand, under nominating is detrimental to project economics. Reservoir models alone can be too coarse a tool to provide the necessary accuracy when looking forward only one or two years. Process systems and compressor performance also Process systems and compressor performance also need to be modelled in order to more accurately define short term production potential. This paper describes a novel way of integrating long term reservoir predictions and short term topsides performance characteristics so as to provide an accurate nomination of gas production rate.

Introduction

There are many aspects of gas production operations that are much more straightforward than oil production. In the southern North Sea where the majority of gas reservoirs are found, reservoir depletion mechanisms are more simplistic, and there is less of a need for ancillary systems such as water injection and artificial lift. In one area, however, gas production is more problematic. Unlike oil production, where sales is on problematic. Unlike oil production, where sales is on a best endeavours basis - gas sales are tied to contracted quantity.

In the United Kingdom, sale of gas to the National Supply Grid is normally based on a fixed plateau production for a number of years after which the production for a number of years after which the producer "nominates" his annual gas production producer "nominates" his annual gas production sometimes as much as 1 or 2 years in advance. Failure to meet these targets results in financial penalties in addition to loss of revenue resulting from penalties in addition to loss of revenue resulting from shortfall. Deliberately under-nominating in order to avoid penalties results in unnecessarily deferred revenues and below optimum project economics.

On face value the prediction of production rates only a few years ahead and from relatively simple reservoirs, appears straightforward. It is important, however, to correctly relate reservoir productivity with the performance of topside equipment. Modelling performance of topside equipment. Modelling pressure drops in process systems and pipelines is pressure drops in process systems and pipelines is relatively straightforward although increased liquid loadings can lead to inaccuracies. The most difficult topside system to model, however, is the gas compression facility. It is an unfortunate coincidence that a gas development coming off plateau normally coincides with the early years of use of gas compression.

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