Porous Plate Method Research Articles

Determination of Oil/Water Saturation Functions of Chalk Core Plugs From Two-Phase Flow Experiments

Summary A new procedure for obtaining oil/water saturation functions, i.e., capillary pressure and relative permeability, of tight core samples uses the pronounced end effect present in flooding experiments on such material. In core material with high capillary pressure, the end effect may allow determination of the saturation functions for a broad saturation interval. A complex coreflooding scheme provides the fluid distributions and production data from which the saturation functions are computed for both drainage and imbibition by a least-squares technique. A chemical shift NMR technique is used for fluid distribution determination. An undesirable interdependency of the saturation functions is avoided by their calculation from different data sets. Killough's method is employed to account for the scanning effect in hysteresis situations for both capillary pressure and relative permeability. The procedure is demonstrated on chalk samples from the North Sea. The experimental time is intermediate between the centrifuge and porous plate methods.

Resistivity index of fractional wettability porous media

The effects of fractional wettability on electrical resistivity index curves of porous media are investigated using pore network models. A bond percolation-and-fractal roughness model is used to simulate the oil/water drainage of the conventional porous plate method in pore networks composed of randomly distributed `strongly water-wet' and `strongly oil-wet' capillaries. Based on universal scaling laws of percolation quantities, effective medium approximation and fractal geometry, approximate analytic relationships are developed with respect to the dependence of the resistivity index, capillary pressure and saturation exponent on certain microstructural properties of the pore space and surface fractional wettability over the various water saturation regions. The simulated data are fitted to two-exponent power laws, which in turn are evaluated as macroscopic conceptual models of the resistivity index. At high water saturations, the saturation exponent becomes a strongly increasing function of the fraction of oil-wet pores when the value of this parameter exceeds the percolation threshold of the lattice network and oil percolates spontaneously through network joining clusters of oil-wet pores. At intermediate water saturations, the saturation exponent is a moderately increasing function of the fraction of oil-wet pores, whereas the slope of the capillary pressure curve remains almost unaltered to variations of wettability. At low water saturations, as the fraction of oil-wet pores becomes quite large, permanent trapping of water may occur with result that both the saturation exponent and the slope of the capillary pressure curve tend to infinity at the limit of irreducible water saturation. The exponents of the phenomenological models of the resistivity index change significantly with fractional wettability and are consistent with the values of the saturation exponent obtained with the approximate analytic relationships.

Pore Network Analysis of Resistivity Index for Water-Wet Porous Media

Pore network analysis is used to investigate the effects of microscopic parameters of the pore structure such as pore geometry, pore-size distribution, pore space topology and fractal roughness porosity on resistivity index curves of strongly water-wet porous media. The pore structure is represented by a three-dimensional network of lamellar capillary tubes with fractal roughness features along their pore-walls. Oil-water drainage (conventional porous plate method) is simulated with a bond percolation-and-fractal roughness model without trapping of wetting fluid. The resistivity index, saturation exponent and capillary pressure are expressed as approximate functions of the pore network parameters by adopting some simplifying assumptions and using effective medium approximation, universal scaling laws of percolation theory and fractal geometry. Some new phenomenological models of resistivity index curves of porous media are derived. Finally, the eventual changes of resistivity index caused by the permanent entrapment of wetting fluid in the pore network are also studied.

Threshold pressure as a measure of degree of rock wettability and diagenesis in consolidated Omani limestone cores

The pore-size distribution in a given rock is usually determined using a displacement process. In the process one fluid displaces another which originally filled the void spaces of the rock. This project involves a study of pore-size distribution for different Omani limestone cores using the concept of threshold pressure. Threshold pressures are obtained from capillary pressure curves for 17 Omani limestone cores. The drainage process “decreasing wetting phase” is carried out using the porous plate method. The degree of wettability can be determined from the shape of the capillary curve and the magnitude of the threshold pressure. Furthermore, additional concepts of tortuosity and cementation factor are investigated. Together with the degree of wettability, concept of property (porosity and permeability) degradation and diagenesis is also studied. A complete synergy of the above-mentioned factors can then lead to the appropriate well completion, stimulation, secondary and enhanced oil recovery (EOR) methods.

SURFACE FORCES IN FOAM FILMS FROM AN ABA TRIBLOCK COPOLYME

Foam films from aqueous solutions of an ABA triblock copolymer of polyethylene oxide and polypropylene oxide (M = 14,000) are studied. A narrow polymer concentration range located below the CMC is investigated at both low and high electrolyte (NaCI) concentrations. The dependence of the surface force on film thickness is monitored by two complementary techniques: the porous plate method and the dynamic method of Scheludko and Exerowa. When the film thickness decreases, the total surface force is initially negative and after a minimum gradually increases to positive values. A transition from electrostatic to polymeric stabilization is induced by increasing the NaCI concentration. Our data can be fitted reasonably well with a combination of the DLVO theory ( van der Waals attraction and double layer repulsion) and de Gennes' scaling theory of steric interaction between grafted polymer layers.

Gas-oil capillary pressure measurements at reservoir conditions: effect of interfacial tension and connate water saturation

Abstract This paper describes laboratory equipment and procedures aimed at determining drainage gas-oil capillary pressure functions under reservoir conditions. Two series of capillary drainage tests (porous plate method) were performed with sandstone core samples using binary mixtures of methane/ n -heptane at different equilibrium pressures, leading to very wide variations in the gas-liquid interfacial tension (IFT) values. Measurements were performed first without connate water (two-phase conditions) and then in the presence of connate water saturation (three-phase conditions). This study has shown that the gas-oil capillary pressures measured at different levels of IFT and without connate water can be transformed into one capillary pressure function, P c /IFT, down to IFT = 3.7 mN/m. Below this value, the capillary pressures measured were significantly lower than those estimated by the Young-Laplace equation. In the presence of connate water, the gas-oil capillary pressures were always higher than the ones measured without water saturation. The difference increased when gas saturation increased and gas-oil IFT decreased. Finally, this paper showed that it is not valid to deduce three-phase capillary pressure from two-phase measurements.

A Comparison Between Capillary Pressure Data and Saturation Exponent Obtained at Ambient Conditions and at Reservoir Conditions

Summary The porous plate method was used to determine capillary pressure curves and saturation exponents at ambient conditions and at full reservoir conditions (reservoir pressure, temperature, and fluid) on sandstone core plugs from a North Sea reservoir. The main objective of this study is to determine whether any difference exists between the capillary pressure curves and the saturation exponents obtained at ambient conditions and those obtained at reservoir conditions for a North Sea reservoir. Results show that the capillary pressure and electrical resistivity measurements performed at ambient conditions with nonreservoir fluid displacing water can give results different from measurements performed at conditions prevailing in the reservoir.

Effect of Overburden Pressure and the Nature and Microscopic Distribution of Fluids on Electrical Properties of Rock Samples

Summary Laboratory equipment aimed at determining the exact correlation between resistivity and water saturation under stress, pressure, and temperature conditions is described in the first part of this paper. The porous-plate method adapted to reservoir conditions is used to obtain different saturation values during both drainage and imbibition. With this equipment, the influence of the effective stress on the porosity and formation resistivity factor can be studied before the test. In the second part of this paper, the values of the formation resistivity factor and resistivity index are compared for water-wet samples from sandstone and carbonate reservoirs. These measurements indicate that the influence of the effective stress depends on the nature of the rock sample. In addition, the resistivity/water-saturation law depends on the direction of the saturation change (drainage or imbibition) and on the nature of the fluids (water/oil or water/gas).

Absorbency of Terry Towels: A Comparative Evaluation of Test Methods

Five test methods were compared on their potential for measuring the moisture absorhency ("thirstiness") of terry towels. The comparison was made by using both survey and laboratory techniques to determine the overall utility of each test for research applications. The results indicate that the Porous Plate and Sliding Block Methods have potential for measuring the moisture absorbency of towels. However, both tests have strengths and limitations, and the particular test chosen will depend on the researcher's needs.