LABORATORY TESTING FOR RESERVOIR ENGINEERS AND GEOLOGISTS—BE A DRIVER, NOT A PASSENGER!

Abstract

A detailed review by Santos of all its laboratory activities has revealed that nearly all laboratory work must be very closely tailored to the needs of the reservoir in question in order to produce meaningful results. The practice of just ticking a few items from the laboratory catalogue as if one were ordering breakfast in a hotel is fatal. Instead intensive preparation of procedures is required—this may involve months of discussion with the laboratory, development of new procedures tuned to the particular reservoir, testing of these procedures and modification, etc. Often the preparation for the laboratory work will begin long before the rock or liquid samples arrive at the laboratory.

Nearly all of Santos' Eromanga Basin oil reservoirs are thin (typically 30 to 40 ft gross column), have no gascap, and lie in the transition region of the capillary pressure curves. However the cores were traditionally analysed by the laboratories assuming the reservoirs extended far beyond the transition zone. This led to major inconsistencies in the results, and difficulties in comparing core results to log analysis. Procedures were developed appropriate to transitional reservoirs. Experiments were run with the new procedures. These experiments have revealed many of the hitherto unappreciated properties of transitional reservoirs, leading to a better understanding of end point saturations, log analysis, reservoir seals and how to treat reservoirs which have leaked. Low invasion coring appears to be particularly well suited to transitional reservoirs.

The new laboratory procedures imply that most of our oil reservoirs are being very well swept, at least on a microscopic scale. This may have significant implications for EOR.

After realising the effort that is required to keep core analysis on track Santos then extended this thinking to all laboratory work. This has led to improvements in our ability to analyse oils, waters, muds, clays and in our ability to conduct 'multi-disciplinary experiments', i.e. experiments extending across more than one laboratory. At the end of the day we are achieving better log analysis, better estimates of original hydrocarbons in place and better estimates of oil remaining after primary production.