Sandstone, Berea

Initial surfactant concentration was 0.50% wt in pH 8.5 solution. 50 g of test solution was placed over 100.0 g crushed Berea sandstone. The sample bottle was sealed and shaken continuously for 24 h at 75°C. The mixed indicator titration technique was used to determine active surfactant concentration before and after exposure of the test solution to crushed Berea sandstone. AS HAS, alkene.hydroxyalkanemonosulfonate ratio. D.I. water, deionized water. ND, not determined. 

The x-ray diffraction analysis of the crushed Berea sandstone indicated the following mineralogy ... 

The surface area of the crushed Berea sandstone was 1.50 m2/g. b% branching of parent olefin. cAverage value average deviation. 

The effect of alkaline preflush was also studied under two different conditions. All of the oil-recovery experiments were conducted under optimal conditions with a viscous, nonacidic oil and with Berea sandstone cores. 

The D-T2 experiments were performed [51] for a Berea sandstone sample at a proton Larmor frequency of 1.74 MHz and a static gradient of 13 G cm-1. The sample was first vacuum saturated with brine, then centrifuged when immersed in oil resulting in a saturated mixture of oil and water. A D-T2 map was obtained using FLI, shown in Figure 2.7.5. The T2 and D distributions were obtained by... 

Fig. 2.7.5 Two-dimensional D—T2 map for Berea sandstone saturated with a mixture of water and mineral oil. Figures on the top and the right-hand side show the projections of f(D, T2) along the diffusion and relaxation dimensions, respectively. In these projections, the contributions from oil and water are marked. The sum is shown as a black line. In the 2D map, the white dashed line indicates the molecular diffusion coefficient of water,...

In addition, mercury intrusion porosimetry results are shown together with the pore size distribution in Figure 3.7.3(B). The overlay of the two sets of data provides a direct comparison of the two aspects of the pore geometry that are vital to fluid flow in porous media. In short, conventional mercury porosimetry measures the distribution of pore throat sizes. On the other hand, DDIF measures both the pore body and pore throat. The overlay of the two data sets immediately identify which part of the pore space is the pore body and which is the throat, thus obtaining a model of the pore space. In the case of Berea sandstone, it is clear from Figure 3.7.3(B) that the pore space consists of a large cavity of about 85 pm and they are connected via 15-pm channels or throats. 

Fig. 3.7.3 (A) DDIF (circles) and reference (squares) data for a Berea sandstone sample. Measurements were performed at a proton Larmor frequency of 85.1 MHz. te = 100 ps. Signal-to-noise ratio is approximately 103.

Fig. 3.7.4 (A) CRMI results of pressure versus volume on the Berea sandstone sample with a porosity of 20% and permeability 0.2 darcy. The two lines are raw CRMI data and the corrected data by a calibration run. Transducer noise was also filtered. The amount of the correction is fairly small and the two data sets overlap. (B) CRMI pore body volume distribution showing a predominant peak at around 20 nL. Figure from Ref. [57] with permis-...

DDIF has been applied to understand two-phase flow (air and water) in a Berea sandstone sample and the relationship to the pore geometry [65], Several different states of saturation were studied full saturation and partial saturation by three methods, i.e., centrifugation, co-current imbibition and counter-current imbibition. Imbibition is a process in which a porous sample absorbs the wetting fluid through capillary force. In the case of co-current imbibition, the bottom of the rock sample was kept in contact with water, so the water is imbibed into the rock and the water and air flowed in the same direction. For counter-current imbibition, the whole sample was immersed and the water was drawn into the center of the rock as, the air was forced out in this case, the water and air flowed in opposite directions. 

Procedure. Core floods were carried out in horizontally mounted Berea sandstone cores of length 61 cm and diameter 5 cm. Porosity varied from 18 to 25% and brine permeability from 100 to 800 Jim2. The cores were coated with a thin layer of epoxy and cast in stainless steel core holders using molten Cerrobend alloy (melting point 70°C). The ends of the cores were machined flush with the core holder and flanges were bolted on. Pore volume was determined by vacuum followed by imbibition of brine. Absolute permeability and porosity were determined. The cores were initially saturated with brine (2% NaCl). An oil flood was then started at a rate of lOm/day until an irreducible water saturation (26-38%) was established. 

Figure 9 compares Equation 20 with the recent pressure drop flow rate data of Friedmann, Chen, and Gauglitz (5) for a 1 wt% commercial sodium alkyl sulfonate dimer (Chaser SD-1000) stabilized foam in a Berea sandstone. These data are particularly useful because they have been corrected for foam blockage and therefore correctly reflect the flowing bubble regime. The solid line in Figure 9 is best fit according to Equation 20. Unfortunately, neither of the parameters c or 6 is available. Two sets of estimates are shown in Figure 9. When e - 0 (i.e., no surfactant effect) the bubble size is about 30% of a grain diameter. When — 0.1 mm (i.e., a value characteristic of those in Figure 8) the bubble size is about 10 grain diameters. We assert that Equation 20 not only predicts the correct velocity behavior of foam but it does so with reasonable parameter values (23).

Figure 9. Experimental data for the effective viscosity of the foam bubble regime in Berea sandstone as a function of the foam superficial velocity. The solid line is drawn according to the scaling theory with values of the two sets of parameters e and 6 listed.

High pressure equipment has been designed to measure foam mobilities in porous rocks. Simultaneous flow of dense C02 and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CC -foam mobility measurements were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2-foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sandstone to study the effect of rock permeability. 

The Effect of Surfactant Concentrations, The effect of surfactant concentrations on CC -foam mobility is plotted on a log-log scale in Figure 3. The presented data points are the average mobility values obtained from a superficial velocity range of 2-10 ft/day, with the CC -foam fraction was kept constant around 80%. With Berea sandstone, ZS and AEGS surfactants were used. The measured average permeability of the Berea sandstone with 1% brine was 305 md. With Baker dolomite, AEGS was used to make comparison with Berea sandstone. The permeability of the Baker dolomite was 6.09 md measured with 1% brine solution. 

Effect of Rock Permeability. The effect of rock permeability has been investigated by comparison of mobility measurements made with Baker dolomite and Berea sandstone. Mobility measurements carried out with Rock Creek sandstone (from the Big Injun formation in Roane County, W.Va) is also reported. Rock Creek sandstone has a permeability of 14.8 md. A direct comparison was made with Berea sandstone and Baker dolomite measured with 0.1% AEGS. As mentioned in an earlier section, the permeability of Baker dolomite (a quarried carbonate rock of rather uniform texture with microscopic vugs distributed throughout) was 6.09 md, and of Berea sandstone was 305 md. The single phase permeabilities were measured with 1% brine solution. 

Another series of experiments used sandstone cores previously injected with starved bacteria to investigate the ability of the bacteria to grow within rock cores when given a suitable nutrient Berea sandstone cores of 200 and 400 millidarcy (md) permeabilities were used as they were considered to be more representative of reservoir conditions than the glass bead cores. The sandstone cores were injected with 300 to 450 pore volumes of 10 /ml starved bacteria until the cores contained an even distribution of bacteria (Fig. 3A B) and the core permeabilities were between 13% and 18%. SCM nutrient was injected through the cores (Fig. 3C) until the core permeability fell to 0.1%, this required 360 pore volumes of SCM. 

In this paper we report on a detailed experimental and theoretical investigation of the influence of acoustic waves on laminar liquid flow through the Berea sandstone. We focus our investigation on Berea sandstone, which is representative for the sandstone of an oil reservoir, with permeability 100 to 300 mD and on acoustic frequencies below the critical frequency [3],... 

The experiments were carried out in the set-up shown in Fig. 1. The cores that were used for the experiments were cylindrically shaped Berea sandstone samples. The length of the cores was 20 cm and the diameter 7.62 cm. The porosity was about 0.25. The initial permeability was 100-300 mD for all samples. During an experiment a core was placed in a rubber sleeve to keep it fixed during the experiment. It was then placed in a steel vessel in which downhole reservoir conditions of up to 150 bars and 100°C were simulated. An acoustic horn was placed at one end of the core (see Fig. 1). The high pressure in the vessel made it possible to avoid cavitation. For pressures lower than 100 bars the influence of cavitation becomes noticeable. The space between the vessel and sleeve, which was filled with water, was pressurized to 180 bars to make the rubber sleeve completely seal off. 

Agrawal, D.L., Cook, N.G.W. and Myer, L.R. (1991) The effect of percolating structures on the petrophysical properties of Berea sandstone. In Rock Mechanics as a Multidisciplinary Science, Balkema, pp. 345-354... 

Figure 11.7 Photomicrograph of gelled-foam lamellae (see arrow) stretching across a pore in Berea sandstone rock, showing films, rods, and intermediate structures. From Schramm and Kutay [71] Copyright 2004, The Petroleum Society.

In the following section we present results of our foam-enhanced oil recovery experiments in Berea Sandstone cores to assess the performance of the three a-olefin sulfonates discussed above. 

Our foam-enhanced oil recovery experiments in Berea Sandstones showed for the first time a striking correlation between basic foam... 

The stability of emulsion and foam films have also been found dependent upon the micellar microstructure within the film. Electrolyte concentration, and surfactant type and concentration have been shown to directly influence this microstructure stabilizing mechanism. The effect of oil solubilization has also been discussed. The preceding stabilizing/destabilizing mechanisms for three phase foam systems have been shown to predict the effectiveness of aqueous foam systems for displacing oil in enhanced oil recovery experiments in Berea Sandstone cores. 

Figure 5 shows the results of a typical surfactant transport study in a 2 ft long Berea sandstone core. The AEGS 25-12 surfactant, injected at 0.05 wt%, had a low loss on Berea sandstone of 0.008 meq/100 gm rock compared to -0.05 meq/100 gm for typical petroleum sulfonates used in chemical flooding. Surfactant breakthrough occurred at 0.62 PV (Sorw =0.38 PV). The surfactant concentration is consistent with about 10% transport with the brine front. Surfactant loss and transport were monitored using the hyamine titration technique. 

Final laboratory testing of CO2 foam was performed in Shell s CT facility (11-12L Tertiary miscible and immiscible CO2 corefloods, with and without foam mobility control, were scanned during flow at reservoir conditions. The cores were horizontally mounted continuous cylinders of Berea sandstone. Table I lists pertinent core and fluid data. 

Effect of Surfactant Concentrations. The effect of the surfactant concentration on foam mobility has been studied extensively. The surfactant under investigation for this effect was Varion CAS, a zwitterionic surfactant from Sherex. The rock under study was Berea sandstone which has a permeability of 308 9 md measured by using 1% brine solution. The permeability using N2 gas at atmospheric pressure was 1000 6.2 md. 

Rock type Berea Sandstone Permeability of the rock 308 9 md Inlet pressure of the pumps 1615 5 psia Temperature of the COj in Ruska pump 25.0 0.2 C... 

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