A detailed study of a number of methods of relative permeability measurement has been made in a search for the technique most suited to routine analysis of cores taken from reservoir rock. It has been found from tests run on the same samples of core material by a number of techniques that the Penn State, Hassler, Hafford, and dispersed feed techniques all yield results which are felt to be reliable. Conditions under which the faster single core dynamic technique may be used are described. Further work on the calculation of relative permeabilities to oil from data obtained by the gas drive method is needed before this latter rapid method can be utilized.Correlations between theoretical studies and experimental results have been obtained in studies of the boundary effect, pressure distribution in two-phase flow, and gas expansion effects. Previous conclusions that the effects of the outflow boundary could be made negligibly small have been substantiated. Results of experimentally determined oil and gas pressure distributions along a core sample during flow are presented. Further studies of the effects of rate of flow in the measurement of relative permeability-saturation relations have shown that results are independent of the rate of flow as long as the flow rate is below the point where inertial effects commence. An analysis of the effects of a severalfold expansion of gas along the flow path indicates that while saturation gradients are induced in the test sample, the errors caused by this phenomenon in relative permeability measurements are ~mall.
This paper presents the results of laboratory measurements of relative permeabilities to oil and gas on small core samples of reservoir rock by five methods, and describes the influences of such factors as boundary effect, hysteresis, and rate upon these measurements. The five methods used were the "Penn State," the "single core dynamic," the "gas drive," the "stationary liquid," and the "Hassler" techniques.In those methods in which the results are subject to error because of the boundary effect, the error may be minimized by the use of high rates of flow. In order to avoid complexities introduced by hysteresis, it is necessary to approach each saturation unidirectionally. Observed deviations of relative permeabilities with rate can be explained as a manifestation of the boundary effect, and disappear as the boundary effect vanishes.The results indicate that all five methods yield essentially the same relative permeabilities to gas. Of the four methods applicable to the determination of relative permeability to oil, three, the Penn State, single core dynamic, and gas drive, gave relative permeabilities to oil which were in close agreement. The Hassler method gave relative permeabilities to oil which were consistently lower than the results obtained by the other methods.
The effect of C02 on carbonate rock during carbon dioxide flooding of petroleum reservoirs was investigated using dolomite cores. The studies were made at several pressure levels to determine the effects of pressure on the inter-action of C02 and dolomite. Fifteen cylindrical dolomite cores with lengths varying from 3 in. to 9 in. and with diameters of 2.25 inches were chosen for the study. The corE!S were saturated with 0.1 N KC1 lolution which was displaced with liquid CO.The tests were conducted at pressures varying from 1000 psig t:o 2500 psig, while the temper-ature of the system was maintained 80'F. The result!3 of the laboratory study showed that C02 would dissolve some of the rock around an injection well in a field application. The higher the injection pressure, the more pro-nounced would be this effect. Dissolved carbo-nate was found to be precipitated along the flow Path as the pressure dropped in the laboratory experiments. The precipitate reduced the permeability of the rock. The amount of carbonate precipitated was dependent on the magnitude of the pressure drop. The larger the pressure drop, the more the carbonate precipitation and the reduction in the permeability of the rock. References and illustrations at end of paper. INTRODUCTION The effic iency of a tertiary oil recovery process will be affected when the injected fluid(s) react chemically with the reservoir rock.1 Chemical reaction between the rock and the injected fluid could be in form of fluid adsorption on to the rock surfaces or rock dissolution by the injected fluid. In micro-emulsion fLooding, the efficiency of the process is affected by surfactant adsorption on to the rock surface . 1 Holm2 reported a study in which the permeability of a dolomite core increased threefold after about nine pore volumes of carbon dioxide slug and carbonated water was injected through the core. This is a case of rock dissolution by the injected fluid.Crawford et. al3 reported a case history in which the use of carbonated water as post-fracture treating fluid resulted in rapid and complete well clean up. Formation of stalactite and stalagmite in caverns show that, although carbon dioxide does dissolve carbonate rocks in the presence of water, the reaction is to some extent reversible in nature. This understanding can be extended to the reaction between C02 and the rock in C02 flooding of carbonate reservoirs. Since many carbonate reservoirs (mostly dolomite) are potential candidates for C02 flooding, there is a need for an in-depth study of the reaction
It is extremely desirable in the interpretation of resistivity measurements made on porous media containing saline water and hydrocarbons to have at hand a better knowledge of the geometry of the conducting salt water. One geometric characteristic is the tortuosity of the aqueous phase. A method was devised several years ago for the measurement of the tortuosity of completely brine‐saturated sands by the measurement of transit time of ions migrating through the aqueous phase under a potential gradient. This method has been improved and extended to the investigation of the tortuosity of sands containing both brine and oil. Results obtained to date on a group of sandstone samples containing water and oil indicate that there is a relation between the tortuosity of the aqueous phase, the brine content of the sand, the resistivity of the brine, and the resistivity of the gross sample. These results were used to relate the saturation exponent, n, which is customarily used in the interpretation of the electric log, to the tortuosity and apparent cross‐sectional area of the electrolyte through which electric current flows.
The effect of column length on C02-crude oil minimum mis-cibility pressure (MMP) has been investigated in linear porous media. Sandpacks were placed in a vertical position and crude oil was displaced from them by C02 at pressures ranging from 5.17 MPa to 12.41 MPa. A Co2 crude oil miscibility pressure was established in each of the sandpacks. A 34 0 API gravity (at 25.6 OC) Foster Crude Oil, and three 1.59 cm diameter sandpacks, 0.5 m, 1.5 m and 6 m long respec-tively, were used for the study. The investigation was conducted at 48.8 OC.The results of the tests showed that the C02-crude oil MMP was independent of the length of the sandpack in the range Of lengths used. The crude oil was miscibly displaced from each of the three sandpacks at 10.34 MPa. The hydrocarbon pore volume of CO, required to achieve similar oil recoveries (per cent oil-in-place from the sandpacks was higher for the shorter sandpack and lower for the longer sandpacks at corresponding flooding pressures. While the breakthrough oil recoveries (per cent oil-in-place from shorter columns were less than that from the longer ones. More oil was recovered from shorter than from longer columns after breakthrough at similar flooding Pressures-Introduction A major factor to be considered when planning C02 miscible flooding is the C02-crude oil miscibility pressure. Earlier reports(],2) have demonstrated that displacing crude oil by C02 will result in high oil recovery if carried out above the miscible pressure. The C02-crude oil MMP is usually determined (3-5) by performing C02-crude oil displacement tests at different pres-sures in the laboratory.Menzie and Nielsen(2) and Holm and Josendale(3) have studied the mechanism by which C02 generates miscibility with crude oil. They showed that the process is due to the ability Of C02 to extract hydrocarbons (C5 through C30) from crude oils. The study also demonstrated that, for a given crude oil, *Present address: Department of Chemical Engineering, Obafemi Awolowo University, ile-Ife, Nigeria. Keywords: C02-crude oil, Column length, Vertical sandpacks, Oil recovery, Flooding pressure, Foster crude oil. more hyd . rocarbons are extracted/vapourized as the flooding pressure is increased. The factors that affect C02-crude oil miscibility pressure have been described in the literature as tem-perature, crude oil composition, and the purity of carbon dioxide(4).Holm and Josendal(3) related the length of the C02-crude oil transition zone to the flooding pressure. Low flooding pressures (near the miscible pressure) are less efficient and will produce long transition zones while high flooding pressures (above the miscible pressure) are more efficient and win result in short transition zones. Adamson and Flock (6) reported that the length of the C02-crude oil transition zone (as in other miscible displace-ment processes) depends on the stability of the transition zone.The transition zone is stable if it is devoid of viscous fingers and if there is a gradual change in fluid properties from that of the in-place reservoi...
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