Determination of Chemical Requirements and Applicability Of Wettability Alteration Flooding
- H.R. Froning (Pan American Petroleum Corp.) | R.O. Leach (Pan American Petroleum Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1967
- Document Type
- Journal Paper
- 839 - 843
- 1967. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.6.4 Drillstem/Well Testing, 5.4.1 Waterflooding, 4.1.5 Processing Equipment, 5.3.2 Multiphase Flow, 6.5.2 Water use, produced water discharge and disposal, 1.6.9 Coring, Fishing, 5.6.5 Tracers, 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating, 5.8.7 Carbonate Reservoir
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In wettability alteration flooding, a chemical agent is moved through areservoir by the flood water to increase oil recovery by decreasing the degreeof wetting of the rock by the oil. Substantial amounts of the chemical may belost during movement through the reservoir. The extent of the loss, andtherefore the economics of the process, depends in some cases on factors whichare difficult to reproduce in the laboratory. Therefore, a short-duration,low-cost field test method is needed to permit evaluation of chemicalrequirements under actual field conditions. This paper describes a small scaletest conducted at a single well for measuring chemical requirements, therebygiving a more reliable evaluation of this important factor in the applicabilityand economics of the process. In the test a small water slug containing thechemical agent and a nonadsorbed tracer is displaced into the reservoir by aknown volume of water. The well is then placed on production. Chemical loss perbarrel of pore volume contacted is calculated from the fractional recoveries ofthe agent tested and the nonadsorbed tracer. The method has been used todetermine within the actual reservoirs the chemical requirements for both asandstone and a dolomite reservoir. Several chemical agents are potentiallyavailable for wettability alteration flooding, although none is universallyapplicable. For some applications of the method, chemical costs per barrel ofadditional oil recovered can be substantially less than one dollar.
Wettability alteration flooding provides a means of increasing oil recoveryfrom reservoirs by decreasing the degree of wetting of the rock by the oil andincreasing the displacement efficiency of the flood water. Earlier studiesdemonstrated a relationship between oil recovery during waterflooding and thedegree of wetting of a rock surface by an oil. The application of wettabilityalteration flooding to the Harrisburg field of Nebraska provided a field testof this recovery process. Subsequently, additional laboratory and field testshave developed additional procedures for evaluating wettability alterationflooding, and have indicated where the process may be applicable. Applicabilityof this process to specific reservoirs is determined by a progression of teststo determine susceptibility of the reservoir to alteration of its wettability,to indicate the degree of recovery improvement and to estimate the amount ofchemical required to process the reservoir. The economics of applying improvedoil recovery processes depends not only upon the degree of improvement in oilrecovery achievable by the process, but also upon the process costs and thetiming of the income and the investment. Emphasis in this paper is on theexpenditure aspects of the process. The work reported in this paper indicatesthat the chemical investments required for wettability alteration flooding aresubstantial. For evaluating the economics of a potential flooding applicationit is imperative that a sound estimate of the chemical requirements be made forthe reservoir. Generally, true reservoir conditions are not adequatelysimulated in laboratory chemical propagation tests. Because of wide wellspacings, many years might be required to obtain chemical propagation data fromconventional pilots or inter-well tests. Consequently, a short-duration,low-cost method is needed to determine chemical requirements in the field. Thepotential applicability of wettability alteration flooding is discussed, aswell as the economics of wettability alteration with respect to the inherentand imposed restrictions on the timing of income and investments.
DETERMINATION OF CHEMICAL REQUIREMENTS
In the process of moving a chemical bank through reservoir rock, some of thechemical agent lags too far behind the flood front to be effective or isotherwise lost to the reservoir system. The extent to which these losses occurovershadows the reductions in chemical concentration due to diffusion and tomixing with the reservoir fluids. Experience indicates that almost withoutexception, chemicals which induce a wetting change undergo either sorptionreactions or chemical reactions with mineral constituents of the pore surfaces.Other reactions may occur between the added chemical and the reservoir oil andwater. Even in limiting consideration to reactions of the relativelyinexpensive inorganic salts, bases and acids, the reactions may be exceedinglycomplex. Reservoir pore surfaces consist of more than silica in sandstonereservoirs, and more than calcite or dolomite in carbonate reservoirs. Manymineral species are present, each exhibiting specific tendencies to react withan injected chemical. The reactions which occur can consume enough of the agentto have an important effect on economics.
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