Xina Xie

Prospects of improved oil recovery related to wettability and brine composition

Although attention is given to the composition of the injected brine in a waterflood with respect to compatibility with the formation, tests are not usually made to determine its effect on oil recovery. This study shows that the wettability and laboratory waterflood recoveries of crude oil/brine/rock (COBR) ensembles can be strongly dependent on brine composition and on related COBR interactions. The sensitivity of these interactions to temperature and crude oil composition is also demonstrated.

Contact angle hysteresis and the stability of wetting changes induced by adsorption from crude oil

The dynamic Wilhelmy plate technique was used to investigate contact angle hysteresis and the stability of wetting changes induced on quartz surfaces by adsorption from crude oil. Some degree of contact angle hysteresis was always observed on surfaces that were first equilibrated with brine, then exposed to crude oil at elevated temperature. The extent to which hysteresis persisted through repeated cycles of advancing and receding of the probe fluids was different for different crude oil compositions. Regardless of whether or not the surface was dried, and whether the measurements began with the surface in brine or decane, quartz surfaces aged in asphaltic crude oils having more basic than acidic character showed large and reproducible contact angle hysteresis. For quartz surfaces aged in less asphaltic crude oils that are below their wax appearance temperatures (WAT) at room conditions, receding contact angles were usually reproduced but advancing angles tended to decrease with each wetting cycle.

Application of the dynamic Wilhelmy plate to identification of slippage at a liquid-liquid-solid three-phase line of contact

The dynamic Wilhelmy plate provides force-distance records that result from the plate passing through an interface at slow constant speed. The form of these force-distance records is determined by a combination of buoyancy and capillary forces. In the present work, wetting behavior of liquid-liquid-solid systems is investigated with changes in wetting properties of silica or glass substrates induced by crude oil. Two initial plate positions are analyzed. In the first, the plate is initially suspended in air above a vessel containing brine overlain by oil. The plate is then lowered through the air-oil and oil-brine interfaces. In the second, the plate is initially immersed in brine and then raised into the oil phase. In each case, the direction of plate motion is reversed during the course of measurement. Oil-brine-solid systems commonly exhibit contact angle hysteresis. Idealized force-distance records have been calculated for which receding and advancing contact angles are constant and the three-phase line of contact remains pinned during contact angle transitions that result from reversing the direction of motion of the plate. Comparison of experimental results with the idealized behavior shows that stabilized wetting conditions are not always achieved. It was often observed that slippage of the three-phase line of contact caused the distance of plate motion over which contact angle transitions occur to be much longer than that predicted by theory.

Spontaneous imbibition for mixed-wettability states in sandstones induced by adsorption from crude oil

Abstract Wettability control by methods that are of practical relevance to oil recovery is an ongoing problem in wettability research. The preparation of mixed-wettability cores by adsorption from an asphaltic crude oil at elevated temperature and pressure has been investigated. After aging, crude oil was displaced by flow of decalin, an intermediate solvent that was compatible with the crude oil with respect to asphaltene precipitation but not likely to cause undue desorption of polar components of crude oil from pore walls. The decalin was in turn removed by flow of refined oil. In tests of the stability of the induced wetting states obtained by this approach, imbibition measurements were repeated for up to six cycles of imbibition and drainage. In most cases, wettability changed slightly towards water wetness after the first cycle, but there was comparatively little or no change for further cycles of spontaneous imbibition and forced drainage. Factors in preparation of mixed-wet cores such as the volume of decalin used to flush crude oil from the core and the temperature of flushing were investigated during the course of development of the experimental procedures. Once established, the induced wetting states were stable with respect to further flushing with decalin and also to flushing with toluene, a stronger solvent for asphaltenes. In experiments on displacement of brine by high viscosity refined oils, the initial water saturation of mixed wet cores could be readily reduced to much lower values than the water saturation that was present at the time of aging. However, in contrast to the drastic reduction in imbibition rate for cores aged at low water saturation, low initial water saturation obtained by this means had very little effect on subsequent spontaneous imbibition. This observation is consistent with the concept of mixed wettability postulated by Salathiel (1973) [JPT (1973) 12616] that the distribution of water at the time of aging controls the distribution of adsorbed components of crude oil.

Contact angles on quartz induced by adsorption of heteropolar hydrocarbons

The wetting behavior induced by the adsorption of crude oil components onto mineral substrates initially covered with brine is of special importance to petroleum engineering. The wettability of reservoir rock is a controlling factor in the efficiency of oil recovery from the swept zone of a waterflood. The effect of the adsorption of polar components from crude oil on the wetting properties of quartz plates was investigated by the dynamic Wilhelmy plate technique. Force-distance relationships were measured for treated quartz plates passing through oleic-aqueous interfaces. Water receding and advancing contact angles under dynamic conditions were obtained. Changes in the wetting of the quartz plate from a completely water-wet state were induced by adsorption from crude oil or solutions of its components. Different wetting states were developed by varying the oil composition, aqueous phase pH. temperature, time of adsorption, the solvents used to remove excess crude oil, and the probe oil used in contact angle measurements. Some important features of wetting, contact angle hysteresis and slippage of the three-phase contact line, are presented. Organic films adsorbed from the crude oil were examined by atomic force microscopy.

A statistical model of apparent pore size distribution and drainage capillary pressure

Abstract Apparent pore size distributions of porous media are commonly obtained from capillary pressure measurements. Drainage capillary pressure curves depend on the penetration pressures of pore necks and the interconnectivity of pore space that determines access to the necks. In this paper, a probability distribution function is proposed to describe the apparent pore size distributions of porous media. The distribution function can be integrated directly to obtain the related mathematical model of capillary pressure versus wetting phase saturation. The model parameters, related to entry pressure, pore size sorting factor, characteristic pore neck radius, and retained wetting phase saturation, can be obtained by fitting the model to experimental capillary pressure curves. Examples of determining model parameters from measured data are presented. The physical significance of each parameter is demonstrated by its effect on apparent pore size distributions and capillary pressure drainage curves. The model provides a dimensionless capillary pressure function that corresponds to a generalized form of the Leverett J-function.

Permeability Modification Using a Reactive Alkaline-Soluble Biopolymer

Polymer injection has been used in reservoirs to alleviate contrasting permeability zones to enhance oil recovery (EOR). Polymer technology relies mainly on the use of polyacrylamides cross-linked by a hazardous metal or organic. Contemporary polymer plugging has investigated the stimulation of in-situ microorganisms to produce polymers (Jenneman et. al., 2000) and the use of biocatalysts to trigger gelling (Bailey et. al., 2000). The use of biological polymers are advantageous in that they can block high permeability areas, are environmentally friendly, and have potential to form reversible gels without the use of hazardous cross-linkers. Recent efforts have produced a reactive alkaline-soluble biopolymer from Agrobacterium species ATCC # 31749 that gels upon decreasing the pH of the polymeric solution. Microbial polymers are of interest due to their potential cost savings, compared to conventional use of synthetic chemical polymers. Numerous microorganisms are known to produce extracellular polysaccharides. One microbiological polymer of interest is curdlan, â - (1, 3) glucan, which has demonstrated gelling properties by a reduction in pH. The focus of this study was to determine the impact an alkaline-soluble biopolymer can have on sandstone permeability.

ASPECTS OF COALBED NATURAL GAS WATER AND OIL RECOVERY 1

The application of coalbed natural gas (CBNG) water injection to improved oil recovery is being investigated. Such application can be permitted as Class II injection. This is more advantageous economically than Class V injection. Therefore CBNG water injection for improved oil recovery is value- added disposal. Use of CBNG water for oil recovery will also reduce the depletion of fresh water aquifers currently used in Wyoming as a source of injection water. The potential for application of low salinity flooding to a specific reservoir requires tests on cores and crude oil obtained from that reservoir. Information will be presented on the Tensleep reservoir rock from the Teapot Dome field that was selected for laboratory tests of CBNG water injection in Wyoming oil reservoirs.