Berea sandstone adsorption

Experimental results include adsorption data for systems containing surfactant, cosurfactant, brine, and Berea sandstone. Adsorption values of pure surfactant (Texas 1) and commercially available petroleum sulfonates (TRS 10-80) are reported and the retention of surfactants in the Berea rock is related to a surfactant solubility limit in the brine. 

This value seems to be on the higher side of the typical values of surfactant adsorption on Berea sandstone cores Green and Willhite (1998) summarized... 

Hanna, H.S., Somasundaran, P, 1977. Physico-chemical aspects of adsorption at solid/liquid interfaces, 11 Mahogany sulfonate/Berea sandstone, kaolinite. In Shah, D.O., Schechter, R.S. (Eds.), Improved Oil Recovery by Surfactant and Polymer Flooding. Academic Press, pp. 253-274. 

In equilibrium adsorption experiments, however, one must work with much smaller surfactant concentrations and those dilute surfactant solutions behave differently than concentrated ones. This was made evident in a dramatic way in two different experiments. In the first case, when a 6 inch column of crushed Berea sandstone was cation exchanged with 1.0 N NaCl, a slug of solution containing more than 200 ppm Ca+2 (measured by atomic absorption) and about 0.5 pore volumes wide issued from the column. The peak Ca concentration was about 1500 ppm. When a small amount of this solution was added to an approximately one wt.% SDBS solution, a copious white precipitate formed. In another experiment, a solution of SDBS in 1.0 wt.% NaCl was added to a sample of... 

Experimental Materials and Procedure The equilibrium adsorption of sodium dodecylbenzene sulfonate (SDBS), and deoiled TRS 10-410 (a commercial petroleum sulfonate with an equivalent weight of 418) on silica gel (Davison Grade 62), and crushed Berea sandstone was measured at 30°C at two brine concentrations (0 and 1 wt.% NaCl). 

Adsorption on Berea Sandstone. Berea sandstone was reported by Malmberg and Smith (20) to consist of approximately 91 wt.% sand and 9 wt. % clay. The adsorption measurements reported here are for the crushed sandstone but it should be noted that essentially all of the adsorption occurred on the clay fraction. In a separate experiment the clay fraction was separated from the sand and the adsorption of SDBS measured on both fractions. No adsorption on the sand could be detected while strong adsorption on the clay was found. Moreover, the adsorption on the clay agreed very well with that found on the original crushed sandstone when converted to a common basis. 

Adsorption of anionic surfactants on crushed Berea sandstone occurs on the clay only and adsorption maxima are observed. The addition of one wt.% NaCl to the surfactant solution results in greatly increased adsorption but in no significant change in the shape of the adsorption isotherm. 

Fig. 4.3. Adsorption isotherms of Mahogany sulfonate AA on two ground Berea sandstone samples and one crushed Berea sandstone sample.

Figure 11. The dependence of surfactant adsorption on temperature, measured in Berea sandstone or silica sand. Adsorption levels were obtained using the surface excess model (1—10).

An increase in electrolyte concentration reduces the solubility of anionic surfactants in the aqueous phase and increases their tendency to accumulate at the solid—liquid interface. An increase in temperature offsets the loss in solubility to some degree For the DPES—AOS on Berea sandstone, the slopes of the lines in Figure 13a decrease as the temperature increases, and this finding lends support to the hypothesis that surfactant adsorption is related to surfactant solubility. Adsorption of surfactants that are less salt-tolerant than the DPES—AOS, such as the AOS and the IOS, increases much more steeply with salinity. Both surfactants adsorb negligibly at salinities of 0.5 mass % NaCl, but adsorb similarly to the DPES—AOS at a salinity of 2.3 mass %. At moderate salinities (on the order of 3 mass %), these surfactants precipitate, which severely limits their applicability to foam-flooding in many reservoirs that are currently being flooded with hydrocarbon solvents. 

Clays are considered detrimental to EOR processes that are based on the injection of chemicals, such as foam-forming surfactants, because clays provide a large amount of surface area for adsorption. Table VII shows a comparison of specific surface areas of some clays (97, 117, 118) and of the solids used in the adsorption experiments of Figure 15 (12, 119, 120). Figure 15 allows comparison of adsorption levels in Berea sandstone, which consists mainly of quartz and 6-8% clays, with adsorption on clean quartz sand. 

When normalized to unit surface area, the adsorption density of the anionic surfactant is higher on quartz than on Berea sandstone because quartz carries a more positive surface charge than the clays (The clays provide most of the surface area for adsorption in Berea sandstone). If it is assumed that the betaine adsorbs on sandstone at least in part by its cationic group, then the lower adsorption density of the betaine on quartz than on Berea sandstone can also be attributed to electrostatic interactions. Matrix grains of the size encountered in typical reservoir rocks have low specific surface areas. Accordingly, the absolute amount of surfactant adsorbed or the amount adsorbed per unit mass of rock is lower for a clean sand than for a sand containing clays (12, 34, 82). Therefore, the... 

Figure 16. The effect of solid surface charge on adsorption of anionic and amphoteric surfactants. Key SS, Berea sandstone LS, Indiana limestone and Dolo, Baker dolomite. (Reproduced with permission from reference 12. Copyright 1992 Elsevier Science Publishers.)...

Limited studies of copolymer retention (9) in a consolidated silica, berea sandstone, were done with copolymers AC, AA, and BB. Firm conclusions about adsorption of copolymer from solution can not be gained from this data since the fluid was flowed through the porous rock. Occlusion and filtration phenomena may therefore produce a major portion of the retention seen in the tests. With the distinction established that retention is not equivalent to adsorption, the data show that adding a methyl group to the amide unit decreases copolymer retention while adding a 1-methylethyl unit (isopropyl) to the amide increases copolymer retention. These data are shown in Figure 6. 

Drainage and imbibition relative permeabilities of brine and Soltrol 160 were determined in a water-wet Berea sandstone sample and in one treated with 2.5% Dri-Film Solution in hexane. Drainage relative permeabilities were also measured in two other Berea sandstone samples, one treated with 1% and the other with 0.02% Dri-Film solution. The Penn State method was used throughout. The dye adsorption capacity of the sample as a function of increasing brine saturation was also determined in every test. A water-wet sample, initially saturated with brine, was oil-flooded, and then water-flooded two samples, one treated with 5% and the other with 0.02% Dri-Film solution, were initially saturated with Soltrol and then water flooded. 

Holbrook and Bernard (3) showed that Berea sandstone cores and 250-mesh sand adsorbed about 0.4-0.7 mg dye/gm core and 0.45 mg dye/ gm core, respectively, of methylene blue from 0.01 percent dye solutions, whereas the amount of adsorption was nil when the cores, or the sand, were treated with 5 percent Dri-Film SC-87 solution in hexane, oven dried and saturated with Soltrol. One of the untreated sandstone samples which was first saturated with water, driven to irreducible water with oil and then flooded to residual oil saturation with the dye solution adsorbed the same amount of dye as the untreated sample not containing oil, thereby indicating that in the process of water-flooding a water-wet core, the entire pore surface is contacted by the flood water. 

The dye adsorption capacity of water-wet Berea sandstone cores was determined by saturating two samples with brine and then flooding them with about 700 pore volumes of 0.1% solution of dye in brine. The values obtained were 1.59 mg dye/gm core and 1.47 mg dye/gm core. In two other tests, water-wet samples were driven down to irreducible brine saturation with Soltrol and then flooded with 0.1% solution of dye in brine. The adsorption capacities obtained in these tests were 1.59 mg dye/gm core and 1.60 mg dye/gm core, in excellent agreement with the first two results reported above. Hence there can be little doubt that the dye adsorption... 

The fourth part includes experimental results on adsorption of pure surfactant and petroleum sulfonates on Berea sandstone. Retention of surfactants is related to their solubility limits in the brine. 

Suffridge (12) concluded from studies of elution of adsorbed petroleum sulfonates that there are substantial differences in adsorption behavior of monosulfonates and disulfonates. Trogus et al. (13) attempted to explain maxima in adsorption isotherms using theory based upon the assumption of two surfactants with different critical micelle concentrations in the solution. Gale and Sandvik (4) showed that higher molecular weight sulfonates were adsorbed preferentially on the Berea sandstone, while Somasundaran (11)... 

The error in the surface excess is, of course, substantially larger because adsorption levels are quite low and concentration changes due to adsorption are therefore small. An example of uncertainties in the measurements of surface excess for surfactant systems caused by errors in analytical procedures is shown in Figure 7. This error analysis shows clearly that batch methods should not be used for measuring surfactant adsorption on Berea sandstone for surfactant concentrations above 1% unless extremely accurate analytical procedures are developed. 

A most noticeable feature is the maximum in both adsorption isotherms. Since the maximum is present even in the isotherm for the pure surfactant it can be explained only by accepting the idea of declining selectivity with increasing surfactant concentration. Selectivity values for TRS 10-80 surfactant, calculated from Equation (10) with monolayer values determined from cross-sectional areas of surfactant (22A ) and water (8.3A ) molecules, are shown in Figure 10. The specific area for Berea sandstone was assumed to be 1 m /g. 

Fig. 9. Adsorption isotherm for 1/10 Texas 1/sec-butylalcohol in 1% NaCl brine on Berea sandstone at 22°C.

An adsorption medium often considered typical of reservoir solids is sandstone. Sandstone is an agglomeration of individual minerals, but the primary component is usually quartz. Other minerals comprising sandstone include chert, feldspar, mica, illite, kaolinite and calcium carbonate. A common type of sandstone used in adsorption research is Berea sandstone [JO, JJj. 

There are two additional types of chemical flooding systems that involve surfactants which are briefly mentioned here. One of these systems utilizes surfactant-polymer mixtures. One such study was presented by Osterloh et al. [72] which examined anionic PO/EO surfactant microemulsions containing polyethylene glycol additives adsorbed onto clay. The second type of chemical flood involves the use of sodium bicarbonate. The aim of the research was to demonstrate that the effectiveness of sodium bicarbonate in oil recovery could be enhanced with the addition of surfactant. The surfactant adsorption was conducted in batch studies using kaolinite and Berea sandstone [73]. It was determined that the presence of a low concentration of surfactant was effective in maintaining the alkalinity even after long exposures to reservoir minerals. Also, the presence of the sodium bicarbonate is capable of reducing surfactant adsorption. 

Anionic Surfactant Blend and Amphoteric Surfactants onto Berea Sandstone, Indiana Limestone, Baker Dolomite, and Quartz. The first study to be presented examined the adsorption behavior of two amphoteric surfactants, a betaine (Empigen BT) and a sulfobetaine (Varion CAS) and a 50 50 blend of a Cio diphenyl ether disulfonate (DOWFAX 3B2), and a Ci4 i6 ot-olefm sulfonate [11]. The anionic surfactant blend was designated as DOW XS84321.05. The Cio diphenyl ether disulfonate surfactant is one isomer in a suite of surfactants which differ in their degree of alkylation and sulfonation and in their chain lengths. This suite consists of monoalkyl disulfonates (MADS), dialkyl disulfonates (DADS), monoalkyl monosulfonates (MAMS), and... 

The adsorption studies were conducted on core samples of Berea sandstone, Indiana limestone, Baker dolomite, and quartz sand from three brines (a sodium chloride solution of 2.32% and two synthetic reservoir brines with total dissolved solids of 2.1 and 10.5%). Conclusions were based on the maximum or plateau adsorption values obtained, and these values are shown in Table 1. 

The Berea sandstone had been split into clay and quartz fractions, but the Berea whole rock was still more negative relative to the other core listed for this study. Even though the trend was the same for both brines, the divalent cations in the 2.1% TDS brine produced less negatively charged surfaces than did the NaCl brine. This behavior was attributed to adsorption of these ions into the Stem layer or, in the case of earbonates, to preferential dissolution of CO over Ca or Mg in the presenee of excess divalent cations in the aqueous phase. It was also noted that adsorption of metal hydroxide ions or mineral transformation reaetions at the solid surface may play a role. 

The adsorption of ionic surfactants on a like-charged substrate is less understood, but can occur via hydrogen bonding or dispersive forces [43]. In the experimental work reported by Alveskog et al. [44], the wettability alteration of Berea sandstone, containing negatively charged minerd surfaces, with an anionic surfactant appeared consistent with the stated mechanisms. Details are provided in die Laboratory and Field Studies section of this chapter. 

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