US 2660550 A
Description (OCR text may contain errors)
Patented Nov. .24, 1953 UNITED STATES PATENT OFFICE SECONDARY RECOWJRY OF PETROLEUM OEL BY DESULFOVIBRIO No Drawing. Application August 27, 1949,
' Serial No. 112,836
4 Claims. 1
This invention relates to recovery of petroleum oil from oil-bearing earth formations and relates more particularly to secondary recovery of petroleum oil from these formations.
Petroleum oil is generally recovered from oilbearing earth formations initially as a result of gas pressure, rock pressure, or natural water drive forcing the oil from the formation through the poducing well to the surface. As oil production continues, the reservoir energy gradually decreases and finally becomes insumcient to iorce the oil to the surface, although a major portion of the original quantity of the oil in the formation still remains therein. To increase the ultimate recovery of the oil, pumping is then employed but when the rate of recovery by pumping falls to an uneconomically low level, a further increase in the ultimate recovery of the oil may still be economically effected by the employment of secondary recovery methods such as gas drive or water flooding.
It has recently been proposed to facilitate or increase the recovery of petroleum oil from an oil bearing earth formation by subjecting the formation to the action of oil-releasing bacteria. Apparently, the facilitation or increase in the recovery of petroleum oil by these bacteria, which are sulfate reducers, is the result of a number of factors such as production of acids which dissolve the formation and increase its porosity, production of carbon dioxide which increases gas pressure in the formation, production of detergents or surface-active substances which effect release of adsorbed oil and reduce surface tension, and conversion of high molecular weight hydrocarbons to lower molecular weight hydrocarbons with consequent reduction in viscosity of the oil. The oil-releasing, sulfate-reducing bacteria are able to utilize as nutrients, or sources of energy, the petroleum hydrocarbons having a molecular weight greater than decane present in oil-bearing earth formations, and thereby are able to remain active and to multiply within oilbearing formations. However, petroleum oil as a source of energy for oil-releasing bacteria provides for only slow and limited multiplication and low activity, with the result that release of oil from the oil-bearing formation is slow and incomplete.
It is an object of this invention to provide a method for secondary recovery of petroleum oil from oil-bearing earth formations. It is another object of this invention to increase the rate and extent of recovery of petroleum voil from oilbearing earth formations subject to the action of oil-releasing bacteria. It is another object of this invention to increase the multiplication and activity of oilereleasing bacteria in an oilbcaring earth formation. It is another object of this invention to increase the extent of recovery of petroleum oil from an oil-bearing earth formation by water flooding. These and other objects of the invention will become apparent from the following description thereof.
In accordance with our invention, secondary recovery of petroleum oil from an oil-bearing formation subject to the action of oil-releasing bacteria is effected by driving therethrough water containing a nutrient comprising molasses for the oil-releasing bacteria.
The oil-releasing bacteria known to facilitate and increase the recovery of petroleum oil from an oil-bearing earth formation are the hydrocarbon-oxidizing species of the genus Desu-lfo- Vibrio, namely, Desulfovibrio hydrocarbonoclasticus and Desulfouibm'o halohydrocarbonoclasticus. The Desulfom'brio halohydrocarbcnoclasticus species distinguish from the Des-ulfouihrio hydrocarbonoclasticus species in their ability to be active and to multiply in the presence of salt water of high concentration, for example, solutions containing as high as 300,090 parts per million of salt. Both species are anaerobic and require water for their multiplication and activity. In addition to water, they require a number of dissolved mineral elements including phosphorus (as phosphate ion) sulfur (as sulfate ion), nitrogen (as ammonium or nitrate ion) and iodine, potassium, calcium, and ferrous iron ions. Carbon is also required and they may utilize carbon dioxide or organic matter, such as petroleum oil, as the source of carbon. These bacteria are active and multiply in an aqueous medium but the pH of the medium must be above 5.5 and not greater than 9.0, with an optimum pH between 6.0 and 8.5, and the temperature must not exceed about 180 F.
The hydrocarbon-oxidizing bacteria species of the genus Desulfov-ibrio are obtainable from many natural sources. They are found in marine sediments and in oil well waters. Desulfovibrio halohydrocarbonoclast'icus has been isolated from oil well brines and marine muds and Desulfovibrio hydrocarbonoclasticus has been isolated from muds obtained from the bottoms of fresh water lakes and rivers. We have found that Desalinoz'brio haZohg drocarbonoclasticus and Decal ooibrio hydrocarbonoclasticus are present in many oil-bearing earth formations although they are not active in every formation in which they are present most likely because of lack of nutrients or the presence of inhibitory substances such as high concentrations of hydrogen sulfide.
In recovering petroleum oil from an oil-bearing earth formation by water flooding, either fresh l;
or saline water is injected under pressure into one or more input wells leading to the earth formation. The water migrates through the formation, forcing the oil contained in the formation before it and along with it, to an output well or wells leading from the formation. The oil is then recovered from the output, or production, wells.
In the practice of our invention, a nutrient comprising molasses is admixed with the water injected into the input well in quantities sufficient to provide for the growth, multiplication, and activity or oil-releasing bacteria whereby the effectiveness of the water drive in recovering petroleum oil from the oil-bearing formation is enhanced by the bacterial activity. Where the oil-bearing formation does not contain oil-releasing bacteria, a culture of hydrocarbon-oxidizing bacteria of the genus Desulfovibrio is admixed with the water containing the molasses. On the other hand, where the formation contains the oil-releasing bacteria, whether or not in active state, inoculation of the formation with the oil-releasing bacteria by admixture of a culture thereof with the injection water may not be necessary.
By molasses, we mean the uncrystallizable syrup obtained during boiling down of raw cane sugar or raw beet sugar. The commercial product may contain between about 50 and 75% by weight of carbohydrates and the commerical product may be used in the practice of our invention. The use of molasses as a nutrient for oil-releasing bacteria is particularly advantageous in that molasses, in addition to containing carbohydrate in large quantities assimilable by bacteria, also contains proteinaceous nutrients as Well as growth factors, or vitamins, and mineral constituents which are stimulating to the growth and multiplication of bacteria. In this connection, molasses is commercially available in several grades, the grades differing from each other with respect to their degree of refinement. The cruder grades of molasses, having been subjected to a lesser degree of refinement, contain larger quantities of growth factors and mineral constituents and, therefore, are preferred to the more highly refined grades of molasses.
The molasses may be added to the injection water in various quantities. We have found that the addition of about 100 to 2,000 parts of molasses to one million parts of water effects more rapid multiplication and more rapid and complete release of petroleum oil from oil-bearing earth materials than can be achieved in the absence of such added nutrient. However, larger or smaller amounts of molasses may be added to the injection water as desired particularly in view of the fact that the carbohydrate concentration of the molasses may vary. Preferably, the quantity of molasses employed should be equivalent to at least 50 parts of carbohydrate to one million parts of injection water. Quantities of molasses may be employed equivalent to more than 1,000 parts of carbohydrate per million parts of injection water, but ordinarily there is no particular advantage in using these larger quantities. The molasses may be added continuously to the injection water so that the injection water as it enters the input well will con tain the desired concentration of molasses. However, the molasses may be added intermittently to the injection water, as, for example, once every hour or other suitable time interval, the amount being added intermittently being sufficient, of course, to obtain, on the average, the desired concentration with respect to the amount of water injected into the well.
As previously mentioned, Desulfooibrio halohydrocarbonoclasticus and Desuljooibn'o hydrocarbonoclastz'cus require, in addition to a nutrient, various mineral elements. Many of these elements are found in natural water sources or in oil-bearing earth formations and, accordingly, fresh water or salt water obtained from natural sources and employed in water flooding will supply the mineral elements required for growth, multiplication, and activity of these bacteria, or the elements will be supplied when the water reaches the oil-bearing formation. However, where neither the water supply nor the formation will supply the necessary mineral elements, they may be admixed with the injection water as part of the nutrient. Additionally, as previously stated, Desulfovibrio halohydrocarbonoclasticus and Desulfooibr'io hydrocarbonoclasticus require an equeous medium having a pH above 5.5 and not greater than 9.0. The pH of natural waters will generally be about 7.5 and are therefore satisfactory as a medium for these bacteria. Further, most oil-bearing earth formations contain calcium carbonate which will maintain water injected into the formation at a proper pH for bacterial growth and activity. However, the oil-releasing bacteria, through reduction of sulfate and assimilation of the molasses, may produce acids reducing the pH of the aqueous medium to a point where growth and activity of the bacteria are inhibited. It is accordingly necessary, where the formation does not contain calcium carbonate or other alkaline material in sufficient quantity to react with the produced acids and maintain the injection water at proper pH, to add a buffer or buffers, such as phosphates or carbonates, to the injection water in addition to the molasses and in addition to the other mineral elements, if addition of other mineral elements is necessary. The injection water, after injection into the formation, should preferably contain the following, as mineral elements required by the bacteria:
5. Where the oil releasing bacteria are Desulfovibrio halohydrocarbonoclasticus, the injection water, after injection into the formation, should contain, in addition to the above, sodium chloride in a concentration at least as high as 20,000 parts per million.
The desired mineral elements and buffers may be added to the injection water prior to injection into the oil-bearing earth formation. However, as previously stated, natural waters contain many or all of these mineral elements and where natural waters are employed, they may first be analyzed to determine the kind and concentration of mineral elements contained therein and, thereafter, the mineral elements in which they are deficient for bacterial growth and activity, as determined by the analysis, added thereto. Further, from knowledge of the chemical composition of the oil-bearing earth formation, it can be determined whether the injection water, after injection into the formation, will dissolve from the formation any of the mineral elements or bufiers desired, and these mineral elements and buffers need not be added to the water prior to injection.
If mineral elements and buifers are added to the injection water, they may be added in admixture with the molasses or added separately. Further, they may be added continuously or intermittently to the injection water, and, where added intermittently, the amount, of course, must be suiiicient to obtain, on the average, the desired concentration with respect to the amount of water injected into the formation.
[is mentioned hereinbefore, where the oilbearing earth formation does not contain Desalfooibrio haZohg/drocarbonoclasticus or Desulfovibrz'o lig/drocarbonoclasticus, a culture of either of these bacteria is admixed with the injection water. Cultures of these bacteria may be prepared in various ways. As an example, a culture of Desulfovibrio hydrocarbonoclasticus may be prepared by adding a bacterial source material such as water from a subterranean earth formation or a mud from the bottom of a fresh water lake or river to a sterile aqueous solution containing the following:
Parts per million Magnesium sulfate 500 Sodium carbonate 100 Monopotassium phosphate 100 Ammonium sulfate 1,000 Ferrous sulfate (FeSOMI-IzO) 50 Molasses 500 and incubating for a suitable period of time which may be between three and nine days. The temperature of incubation may be between 70 F. and 180 F., and should be the same temperature as the temperature of the oil-bearing earth formation to be treated, in order to obtain bacteria acclimatized to the formation temperature. The culture thus obtained, termed an enrichment culture, is admixed with the injection water. An enrichment culture of Desuljovibrio halohydrocarbonoclasticus is prepared, for example, by adding a bacterial source material obtained from an oil well brine or a salt water marine mud to a sterile aqueous solution similar to the solution previously mentioned but containing 20,000 parts per million of sodium chloride, and incubating for a suitable period of time preferably at the temperature of the earth formation to be treated.
We have discovered that, while molasses provides a suitable nutrient for Desuljom'brio halohydrocarbonoclasticus and Desulfovibrio hydrocarbonoclasticus, these bacteria utilize the molassee more readily in the presence of a symbiont. By symbiont, we mean a dissimilar species of bacteria living in intimate association with the desired oil-releasing bacteria, and the association is advantageous to both of the bacteria. Enrichment cultures prepared through the use of natural bacterial source materials such as formation waters or salt or fresh water muds will contain symbionts for the oil-releasing bacteria. Further, the oil-releasing bacteria in oil-bearing earth formations will contain symbionts. However, where pure cultures of Desulfovibrz'o halohydrocarbonoclasticus or Desulfovibrio hydrocarbonoclasticus are employed, symbionts may be provided by admixing with the pure culture, a culture of bacteria obtained from a natural source such as natural formation water, marine mud, or ordinary garden soil,
The following example will be illustrative of the results to be obtained by our invention:
A petroleum oil-bearing sand from which the oil was not flowing by natural means was subjected to water flooding until no further removal of oil could be effected. Approximately 50% of the oil originally contained in the sand was removed by this procedure. The sand was then flooded with a natural water containing a culture of Desulfovibrio haZohydrocarbonoclasticus and 100 parts per million by weight of molasses. The mineral content of the water in parts per million was as follows: phosphate-70, ammonium-270, sulphatel,147, iodide3, magnesium100, potassium-29, ferrous ir0nl0, calmum-75, and sodium carbonate-100. By this second procedure, approximately 35% of the oil remaining in the sand was removed.
By the procedure of our invention, a greatly increased recovery of petroleum oil from an oilbearing sand can be effected. Further, oil-bearing earth formations from which oil can no longer be recovered by water drive can be treated by the procedure of our invention to effect a substantial recovery of the remaining oil.
Having thus described our invention, it is to be understood that such description has been given by way of illustration and example only and not by way of limitation, reference for the latter purpose being had to the appended claims.
1. In the method for the recovery of petroleum oil from an oil-bearing earth formation by the injection of water through an input well to said formation, the improvement comprising admixing with said water prior to injection to said formation a culture of bacteria of the hydrocarhon-oxidizing species of the genus Desulfovibrio and a nutrient for said bacteria comprising molasses.
2. In the method for the recovery of petroleum oil from an oil-bearing earth formation by the injection of water through an input well to said formation, the improvement comprising admixing with said water prior to injection to said formation a culture of bacteria of the species Desulfovibrio halohydrocarbonoclasticus and a nutrient for said bacteria comprising molasses.
3. In the method for the recovery of petroleum oil from an oil-bearing earth formation by the injection of water through an input well to said formation, the improvement comprising admixing with said water prior to injection to said formation a culture of bacteria of the species Desulfom'brio hydrocarbonocldsticus and a 7 nutrient for said bacteria comprising molasses. 4. In the method for the recovery of petroleum oil from an oil-bearing earth formation by the injection of water through an input well to said formation, the improvement comprising admixing with said water prior to injection to said formation a culture of bacteria of the hydrocarbon oxidizing species of the genus Desulfovibrio a culture of a symbiont bacteria, and a nutrient for said bacteria comprising molasses.
DAVID M. UPDEGRAFF.
GLORIA B. WHEN.
8 References Cited in the file of this patent UNITED STATES PATENTS 2,485,385 OTHER REFERENCES Zobell, Bacterial Release of Oil, World Oil, August 25, 1947, pages 36, 39-40, 42, 44, 47.