GAS FIELD DELIVERABILITY PREDICTIONS AND DEVELOPMENT ECONOMICS

Abstract

Forecast of well deliverabilities are an absolute necessity for the realistic planning of the production, transmission and reticulation of natural gas.

Gas well deliverability is a function of both natural and artificial limitations and both must be considered in a deliverability forecast.

The direct prediction of the decline in wellhead deliverability during the life of a well is a relatively recent development and uses a wellhead relationship analogous to the formation open flow formula. This relationship, combined with the material balance pressure decline equation and the formula relating bottom-hole to wellhead conditions, forms the basis for deliverability forecasts.

Compression is added to provide maximum well deliverability and wells may be drilled during the life of a project to maintain deliverability. New wells should meet certain minimum economic criteria before they can be justified. Suggested Criteria are:

The net revenue to be earned by the new well must be a pre-selected multiple of the investment required,

The present worth of the net revenue discounted at a pre-selected rate must be greater than the investment required.

A computer programme has been written to carry out the tedious, repetitive and time-consuming calculations which are necessary for the solution to the problem of deliverability forecasting. This programme calculates the annual production and availability of pipeline gas as well as the number of welJs required to deplete the reserves efficiently. The average reservoir pressure and shut-in and flowing wellhead pressures are forecast and the amount of compression required is calculated. The computer output includes all the production data required for a complete economic analysis of a project involving the depletion of a gas field.