Abstract

Natural gas is generally produced by depletion drive and the rate declines to economically productive limits. The rate of production depends on the contract sales volume which in turn is determined by the reservoir characteristics.

To enter into a gas sales contract, reservoir performance must be predicted. Many factors are important in predicting gas reservoir performance, including reservoir drive mechanism, flow capacity, size, and heterogeneity. In a new gas field these factors are often known with only limited precision. Unfortunately, sales contracts are usually required to justify gas field development, so the contract volumes are often based on limited knowledge. In many instances the best method to predict reservoir performance and assess sensitivity to the unknown factors is reservoir simulation, however, simulation is expensive, time consuming, and it is only as good as the input data.

A new method has been developed for making gas reservoir performance predictions using personal computer spreadsheet programs such as SUPERCALC, LOTUS 123 or QUATTRO. This method is easy to use, and it is cheaper and faster than reservoir simulation. It uses simple equations and it can be used quickly and easily by management to decide on the feasibility of developing a new gas field.

Pertamina UEP-III Cirebon has used this method for over three years to assist in the development of several new gas reservoirs.