A Review of Laboratory Experiments

Transcription

1 w A Review of Laboratory Experiments On Wetting Agents for Water Flooding 11 By J. C. Calhoun,* C. D. Stahl,* F. W. Prestan,* and R. F. Nielsen* Introduction Among the methods which have been proposed to reduce the amount of residual oil by water flooding, the use of wetting agents or additive chemicals has been prorninent, and a considerable amount of experimental wrok has been devoted toward the problem by these laboratories, commencing about The reported general conclusion has been that the use of a wetting agent was not economically feasible, although it would produce additional oil. The principal feature cited in arguments against the economic use of wetting agents has been excessive adsorption. The argument is based on the premise that al1 the rock surface must be saturated with adsorbed wetting agent. This argument ignores the desorption characteristics of a wetting agent and the possibility of moving the adsorbed material through the rock, possibilities which are inherent within the adsorption process, as a review of the adsorption literaturel has shown. If the use of a wetting agent will reduce residual oil, it should be recognized as a physicd fact to be considered in understanding the entire process of oil recovery. Thus viewed, the reduction of oil residuals by wetting agents should serve as a guide to methods of further reducing oil residual. Also, an understanding of the means by which a wetting agent lowers residual oil may lead to improvements which will bring the operation into practica1 reach. With these thoughts in mind it was deemed desirable to review the experimentation that has been reported in past progress reports from this laboratory, particularly re-examining the reports in light of concepts more recently developed. It is also hoped that the summarization of that work at this time will serve as a guide to others who are attempting experimental work in the same direction. It is emphasizied that this paper is a review of existing reports, some fully published, and others not. The credit for the work goes to the original experimenters who worked in these laboratories in past years, chiefly under the direction of Dr. S. T. Yuster. *Dept. of Petroleum & Natural Gas Engineering, Sehool of Mineral Industnes, The Pennsylvania State College, State College, Pa. Presented at the Fifteenth Teehnical Conferenee on Petroleiim Produetion, The Pennsylvania State College, State College, Pa., October 24-26, Criteria of Analysis Severa1 questions need to be answered. These are: (1) Can residual oil be lowered, by flooding with a wetting agent solution, below that' normally resulting from a water flood? (2) If so, by what means does the wetting agent perform its action? (3) What relation, if any, exists between the amount of wetting agent employed and the lowering of oil residual? and (4) How important is adsorption of the PRODUCING WATER-OIL RATlO Figure 1 - lnfluence of oleo-glyceryl sulphate solution on water flood recovery. wetting agent and how can it be overcome? These questions are, of course, interrelated. The answers are no more than touched upon by the present review. The material at hand will be analyzed, however, with these questions in mind. The key to the entire problem is item (21, which concerns the means by which a wetting agent performs its action. It is not definite that there is a single action by which these agents could lower oil residual. In fact, it was early recognized that the agent should be considered not only for its ability to lower interfacial tension but also for its ability to render the rock surface water wet. In addition one should also consider a wetting agent for its ability to act as an emulsifier..experiments Relative to Oil Recovery As early as 1934 this laboratory reported that the use of wetting agents in flooding tests resulted in residual oil saturations lower by 15% than those attained by ordinary water floods. Such agents as sodium sulfo-resinoleate, oleoglyceryl-sulfates, Gardinol WA, Maprom01 Special and Igepon T were used. Figure 1 shows some of the reported results of such flooding tests? These were performed on radial samples of Bradford sand which contained both oil and gas as initial saturants. In 1936 there is a report made of oil recovery by use of wetting agent solutions when no oil could be produced upon normal water flooding of field core samples. The agent was Igepon T and the recovery with the agent is reported as 4% of the pore space.ls During 1937 there were reported further oil recovery tests using a wetting agent called Ninol #555, a cation-active condensation product of the fatty acids and the ethanol amines. These recovery tests were run with radial flood pots using Bradford sand cores and crude oil. Initial conditions were 100% oil saturation. Figure 2 is a reproduced graph showing oil recovery on four cores when flooded with distilled water, 0.01% solution of the agent and 0.1% solution of the agent.$ In examining these results it is to be noted that flooding pressures were 200 mm Hg. On the cores of lower permeability, therefore, it is to be expected that the recovery figures given are not true recoveries. It is felt that the two higher permeability cores show true recoveries because the flooding pressure is sufficient to overcome boundary capillary effects. In 1942 wetting agents were being studied as a means of increasing the conductivities of flood waters in low permeability ~ands.~ The procedure was to saturate a Bradford core with oil and then water flood until no more oil was produced and the water rate was constant. The water flood was then followed 80 W 3 70 YL : ac z O - O a0 so 40 o.o1 WEIGHT % NINOL 555 r 9. A DlSTlLLED WATER T OIL-SOLUTION INTERFACIAL TENSION I I I PERMEABILITY, md Figure 2-lnfluence of permeability and agent concentration upon oil recovery by water flood.

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