TARDIS: A COMPUTER MODEL TO PREDICT FUTURE GAS SUPPLY

Abstract

Because much of South Australia's electricity is gas- generated the future supply of gas from the Cooper Basin is the central issue in the state's energy planning. Available proven reserves of gas are only sufficient to meet the state's demand until the early 1990s.

The TARDIS computer program has therefore been written to enable production scheduling of proved and probable gas reserves and, by using historically derived discovery- rate algorithms, to calculate the exploration- drilling effort necessary to meet future gas supply requirements.

The mandatory requirement was that the program should complete a simulation within several minutes. This necessitated the decomposition of complex engineering procedures to a simple level without unacceptable loss of accuracy.

TARDIS simulates a network of discovered and undiscovered fields which may be allocated to four zones. The fields supply a defined gas market via a processing plant. Appraisal drilling in zones one and three converts estimates of possible gas- in- place into the proved and probable category after allowance for risk. Exploration drilling in zones two and four predicts the discovery of additional reserves using an algorithm, calibrated by historical data, based on the observation that field size decreases as cumulative drilling effort increases.

Fields are scheduled in development priority and sufficient fields are brought on line to satisfy a defined gas market. The required number of on- line fields is determined by the cumulative field deliverability and the peak day gas demand. As each field comes on line development wells are drilled until the field is fully developed.

A processing plant is simulated to produce sales gas which is within the required specification for chemical composition. The quantity of each of the ancillary gaseous and liquid products is also computed.

Data entry and graphical display of results is processed with a spreadsheet and the program runs on a personal computer.

TARDIS enables an assessment of whether the current and forecast drilling effort is likely to discover sufficient reserves to satisfy the market. It has proved an invaluable tool in investigating future gas- supply options for South Australia.