Abstract

The study of reservoir, fluid and capillary pressures can be very rewarding to the explorationist as well as to the engineer. This paper discusses the concepts of formation pressures and their relationship to geology, and the application of pressure data towards accurately defining hydrocarbon accumulations and aid exploration for new fields.

Pressure gradients, capillary pressure, relative permeabilities and water chemistry under hydrostatic and hydrodynamic conditions are reviewed. In a hydrodynamic environment, fluid movement occurs in response to potential energy differentials; flow is from regions of high to low energy, commonly involving meteoric water influx at topographically elevated intake or recharge regions. The significant topographical relief and high rainfall in the Indonesian Archipelago favor such hydrodynamic mechanisms.

Common effects of hydrodynamic pressure gradients include tilted oil-water contacts, flushed structural or stratigraphic traps, and structurally offset hydrocarbon accumulations, as well as pools with no apparent trap.

The influence of hydrodynamics on traps – whether they be stratigraphic, fault or unconformity – as well as on the lateral and vertical continuity of accumulations is also discussed.

Further exploration applications of pressure data include identification of:

a. Field boundaries by determination of fluid contacts.

b. Hydrocarbon pools that may be in different pressure regimes, and are therefore separate accumulations, though correlatable on the basis of log character.

c. Migration paths.

d. Cellar oil.

Techniques using pressure – depth plots and maps of potentiometric surfaces are described.

A combination of hydrodynamic studies with the standard geological and geophysical exploration techniques may result in a substantial reduction in the finding cost of oil in Indonesia.