Interstitial Water Determination by an Evaporation Method
- E.S. Messer (Continental Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- October 1951
- Document Type
- Journal Paper
- 269 - 274
- 1951. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 5.5.2 Core Analysis, 2.4.3 Sand/Solids Control, 5.1 Reservoir Characterisation, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.1.1 Exploration, Development, Structural Geology, 4.3.4 Scale, 5.8.5 Oil Sand, Oil Shale, Bitumen
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A knowledge of the magnitude of the irreducible interstitial water in aporous medium is so important to petroleum engineering that its determinationhas become routine in core analyses.
The method of determination, being a production problem, should encompassthe basic requirements of simplicity in technique and calculations, withreproducible results obtainable in a short interval of time. The results of theevaluation tests outlined in this report indicate that the evaporation methodfor determining the irreducible water is a technique which meets therequirements.
The procedure consists, as the name implies, of permitting the saturant inthe pore spaces to evaporate until only an irreducible volume remains. Thedetermination of this volume can be made either graphically or by amathematical comparison of fluid flows; the time required for eachdetermination being dependent on the fluid used.
When fluids other than those having reservoir characteristics were used, avolume factor had to be calculated which was based on the relative volume ofvarious liquids adsorbed on grain surfaces and retained in pores. This factormade possible the calculation of an irreducible water volume when more volatilefluids such as toluene and benzene were used as the saturants.
Also presented is the theoretical discussion necessary for the calculationof the capillary pressure as determined from the evaporation curve. Acomparison is made between the calculated values and those obtained byexperimental means.
In all geological formations there exists, in the pore spaces of the rockstructure, water that is held in a state of equilibrium between capillary andhydrostatic forces. "Interstitial water" is the term given to thiswater and is defined as that water coexisting in the pore space with the oilprior to exploitation. The term "connate water" has often been usedsynonymously with this term; however, this can be true only by a specificdefinition since, geologically, it means the water in place at the time therock structure was formed.
The quantity of the interstitial water is a variable factor in anyformation, since it depends on the hydrostatic forces present in anymultiple-phase system. These forces may become unbalanced by the introductionof an extraneous force such as the raising or lowering of the "watertable" or the migration of oil into a water-filled formation. Anyunbalanced force results in a change in the interstitial water.
There exists, however, an irreducible interstitial water, for a particularsand, that is the fraction of the pore space occupied by water when thecapillary pressure at the particular point in question is at an equilibriumwith the hydrostatic head of the oil sand in the reservoir. For this discussionthe term "irreducible water saturation" will be used in place of"irreducible interstitial water saturation" for the sake of brevity;however, they are understood to be identical.
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