Chapter 27 Mobility of CO and Surfactant Adsorption in Porous Rocks Downloaded by KTH ROYAL INST OF TECHNOLOGY on December 18, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch027
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Hae Ok Lee and John P. Heller New Mexico Petroleum Recovery Research Center, New Mexico Institute of Mining and Technology, Socorro, N M 87801
High pressure equipment has been designed to measure foam m o b i l i t i e s i n porous rocks. Simultaneous flow of dense C O and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CO2-foam mobility measure ments were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sand stone to study the e f f e c t of rock permeability. Also, other dependent variables associated with CO2foam mobility measurements, such as surfactant concentrations and CO2-foam fractions have been investigated as well. The surfactants incorporated in t h i s experiment were c a r e f u l l y chosen from the information obtained during the surfactant screening test which was developed i n the laboratory. In addition to the mobility measurements, the dynamic adsorption experiment was performed with Baker dolomite. The amount of surfactant adsorbed per gram of rock and the chromatographic time delay factor were studied as a function of surfactant concentra t i o n at d i f f e r e n t flow rates. 2
For a miscible displacement at the required reservoir conditions, carbon dioxide must exist as a dense f l u i d ( i n the range 0.5 to 0.8g/cc). Unfortunately, the v i s c o s i t y of even dense CO2 i s i n the range of 0.03 to 0.08 cp, no more than one twentieth that of crude o i l . When CO2 i s used d i r e c t l y to displace the crude, the un favorable v i s c o s i t y r a t i o produces i n e f f i c i e n t o i l displacement by causing fingering of the CO2, due to f r o n t a l i n s t a b i l i t y . In addition, the unfavorable mobility r a t i o accentuates flow non0097-6156/89/0396-0502$06.00/0 o 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by KTH ROYAL INST OF TECHNOLOGY on December 18, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch027
27. LEE AND HELLER
Mobility of C0 and Surf octant Adsorption 2
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uniformities due to permeability s t r a t i f i c a t i o n or other hetero geneities. The mobility of CO2 i n porous rock can be decreased by containing i t i n a foam-like dispersion. Such CO2-foams have been proposed as a useful i n j e c t i o n f l u i d i n enhanced o i l recovery ( 1 , 2 ) . A c r i t i c a l l i t e r a t u r e review on general foam rheology i s given elsewhere (3). The foam flooding method modifies the flow mechanism by changing the structure of the displacing f l u i d at the pore l e v e l . This method of decreasing the mobility of a lowv i s c o s i t y f l u i d i n a porous rock requires the use of a surfactant to s t a b i l i z e a population of bubble films or lamellae within the porespace of the rock (4). However, the degree of thickening achieved apparently depends to a great extent on the properties of the rock i t s e l f . These properties probably include both the distance scale of the pore space and the w e t t a b i l i t y , and so can be expected to d i f f e r from reservoir to reservoir, as well as to some extent within a given f i e l d . Laboratory measurements of CC^-foam mobility as well as studies involving mobility control of C02/surfactant i n core flooding have been investigated by several r e searchers recently (5-7). Special e f f o r t s have been made to investigate the reservoir application of mobility control foams i n CO2 floods (8), and the influence of reservoir depth on enhanced o i l recovery by CO2 flooding (9). Furthermore, the economic model of mobility methods for CO2 flooding has been taken into con sideration to determine the p r o f i t a b i l i t y of carbon dioxide flooding i n non-waterflooded f i e l d s , and of the use of thickening agents for mobility control ( 1 0 ) . Also, an actual f i e l d test was conducted with (X^-foam. The r e s u l t s of the f i e l d test of CO2 mobility control at Rock Creek have been published (11). In order to understand the nature and mechanisms of foam flow in the reservoir, some investigators have examined the generation of foam i n glass bead packs ( 1 2 ) . Porous micromodels have also been used to represent actual porous rock i n which the flow behavior of bubble-films or lamellae have been observed (13,14). Furthermore, since foaming agents often exhibit pseudo-plastic behavior i n a flow s i t u a t i o n , the flow of non-Newtonian f l u i d i n porous media has been examined from a mathematical standpoint. However, representa t i o n of such flow i n mathematical models has been reported to be s t i l l inadequate (15). Theoretical approaches, with the goal of computing the mobility of foam i n a porous medium modelled by a bead or sand pack, have been attempted as well (16,17). The use of surfactant as a foaming agent to s t a b i l i z e the CO2foam motivated addtional subresearch areas related to foam flood ing. Over the past years, continous e f f o r t s and a great deal of time were invested to f i n d the most suitable surfactant f o r CO2 flooding (18,19). In addition to research to f i n d the most e f f e c t i v e surface active agents, the use of surfactant causes concern that, due to the inherent amphipatic nature of t h i s type of molecule, adsorption on the rock surfaces would reduce t h e i r concentration to such an extent that the process would not be successful. Consequently there has been much c a r e f u l analysis of adsorption, and several independent experiments have been carried out to study t h i s question ( 2 0 - 2 2 ) . The purpose of t h i s paper i s to present the r e s u l t of two
In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
OIL-FIELD CHEMISTRY
Downloaded by KTH ROYAL INST OF TECHNOLOGY on December 18, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch027
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kinds of relevant laboratory measurement. The f i r s t kind measures the mobility of CC^-foam at d i f f e r e n t flow rates, carrying out steady-state experiments using r e a l rock samples as the porous media. The second experiment deals with the dynamic adsorption of surfactant on porous rock. The mobility of CC^-foam i s greatly dependent on the size of the porespace, as expressed i n the single-phase permeability of the rock sample. This i s shown by comparison of mobility measurements made with Baker dolomite and with Berea sandstone. This r e s u l t was supported by the previous work with Rock Creek and Berea sandstones. Also the adsorption results indicate that indeed additional surfactant i s required due to the permanent adsorption, and that the chromatographic delay associated during the flow of surfactant through the core sample cannot be ignored. In addition to presenting the results of these measurements, the operation of the apparatus and the conduct of both experiments are discussed. Measurements of CC^-Foam Mobility In t h i s section the laboratory measurements of CC^-foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown i n the order of the e f f e c t s of surfac tant concentration, CC^-foam f r a c t i o n , and rock permeability. The preparation of the surfactant solution i s b r i e f l y mentioned i n the E f f e c t of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfac tant Enordet X2001 (AEGS) from S h e l l were used f o r t h i s experimen t a l study. Experimental. A s i m p l i f i e d representaion of the basic elements of the flow system i s shown i n Figure 1 and the schematic of the C02" foam mobility measurement experiment i s presented i n Figure 2. The CO2 flows through the c a p i l l a r y tube and the pressure drop across the tube i s measured by a Validyne d i f f e r e n t i a l pressure transduc er. An Isco pump i s used to pressurize the brine/surfactant solution, which also flows through the foam generator and the core. The foams are generated inside the short core used as a foam gener ator, where the mixing between CO2 and surfactant solution occurs. The mixed CC^-foam flows through the core. The pressure drop across the core i s recorded by a second Validyne d i f f e r e n t i a l pressure transducer. Two f i n e tapered needle valves i n series are used to regulate the output flow rate of the mixture of surfactant solution and dense CO2. In addition to the d i g i t a l readout of the values of pressure drop across the c a p i l l a r y and across the core, a two-pen recorder i s used to record these simultaneous measurements. Both of these measurements are subject to rapid short-term v a r i a tions of f a i r l y small magnitude, that seem to be indicative of the mechanism of foam flow. A l l calculations were performed with steady-state values that were averaged over these short-term variations. In t h i s experiment, the measured variables are APcap and APcore. Knowing the APcap, the flow rate of pure CO2 into the core i s computed by using a c a l i b r a t i o n constant obtained by measuring the flow of dense CO2 through the c a p i l l a r y tube. The
In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Mobility ofCO and Surfactant Adsorption
27. LEE AND HELLER
rAPcap-.
Downloaded by KTH ROYAL INST OF TECHNOLOGY on December 18, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch027
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Figure 1. Basic flow system f o r mobility measurements.
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