US3121460A - Solvent flood secondary recovery method - Google Patents

Description

3,121,460 Patented Feb. 18, 1964 3,121,460 SOLVENT FLOOD SECONDARY RECOVERY METHOD John B. Braunwarth and Le Roy W. Holm, Crystal Lake, 111., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Filed June 9, 1960, Ser. No. 34,861 6 Claims. (Cl. 166-9) This invention relates to the recovery of petroleum from subterranean reservoirs. More particularly, it relates to an improved process for recovering petroleum by means of displacement materials injected into the reservoir to displace petroleum and drive it towards produclng wells. The displacement materials are driven by the injection of floodwater.

Various secondary-recovery techniques have been proposed for the production of additional quantities of oil from reservoirs which have undergone primary depletion. These methods involve the injection of various materials into the formation to act upon the petroleum oil and drive the oil to producing wells from which it may be recovered. Water has been found to be an outstanding scavenging agent because it is a cheap, abundant, stable liquid having a mobility approximating that of most petroleum oils. Conventional water-flooding however, still leaves great quantities of oil in the formation when the flood has reached the stage where the ratio of waterto-oil being produced is so great that it is uneconomical to continue production. The prior art has discovered that improved recoveries may be obtained if the fluid which displaces the petroleum oil is miscible therewith. Since all known oil-miscible fluids are too expensive to be left in the reservoir, they must be displaced by a scavenging fluid, and water is usually preferred for this purpose. In order to achieve a smooth transition from oil to oil-soluble displacing fluid to scavenging Water, it is necessary that the oil-soluble fluid be soluble in the scavenging water. The prior art has accordingly suggested the use of various alcohols, ketones, aldehydes, etc., for use as miscible solvents which are injected into the formation prior to the injection of flood-Water. Typical of such prior art processes is the patent to Morse, No. 2,742,089. Such processes, while capable of giving excellent recoveries in laboratory experiments, have never been applied to actual petroleum reservoir treatment because there are in fact very few materials having the necessary solubility characteristics which will permit their use as a single-phase solvent. While a few materials such as amyl alcohol, tertiary butyl alcohol, and methyl ethyl ketone have been found to give outstanding results in laboratory secondary-recovery water-flood experiments, these materials are so expensive and must be used in such large quantities that the processes are economically unattractive, despite potential oil recoveries ranging as high as 90% of the oil in place in the reservoir at the time secondary recovery is undertaken.

It is an object of this invention to provide a method for producing relatively inexpensive solvents for use in conjunction with a water-flood process to enhance oil recoveries. Another object of this invention is to provide a method for producing a pair of mutually-miscible solvents which may be injected in sequence prior to Waterflood to thereby increase the quantities of oil recoverable. Still another object of this invention is to provide an improved process for the secondary recovery of petroleum. Yet another object of this invention is to provide a secondary recovery process by which virtually all of the petroleum oil in the reservoir can be produced at reasonable cost.

Briefly, the method of this invention, is directed to the treatment of crude oxygenated hydrocarbon products to render these products suitable for use as miscible solvents in secondary recovery of petroleum. The invention is further directed to minipulative steps involving the use of the treated crude oxygenated hydrocarbon products.

The prior art teaches processes for economically oxidizing low-molecular-weight hydrocarbons, or mixtures thereof, to produce a mixture comprising various partially oxidized hydrocarbons. The low-molecular-weight hydrocarbons are oxidized at temperatures of about 200 to 500 C. and pressures of about 100 to 2,500 p.s.i. Known oxidizing agents may be used, such as air, oxygen, or other oxygen-containing gases. Complete descriptions of suitable oxidation techniques are given in Petroleum Refiner, 35, No. 12, 172 (1956); Industrial and Engineering Chemistry, 26, 267 (1934); and Petroleum Engineer, 27, l3Cl4C (December 1955). The oxidation products produced by such processes may vary somewhat depending upon the conditions, catalysts, etc., employed, but typical product distributions approximate those set out in Table I for the partial oxidation of pentane, butane, and propane.

The crude oxidation product obtained by oxidizing light hydrocarbons is relatively inexpensive, but such a product tends to be excessively soluble in water and insoluble in oil, which detracts from its efficiency in secondaryrecovery processes. In accordance with this invention, an improved method has been devised for producing highly eflicient solvents for the secondary recovery of petroleum using crude, mixed, oxygenated hydrocarbon products. The novel process of this invention consists of preparing a solvent consisting of oxygen-containing compounds obtained by oxidizing one or more light hydrocarbons, treating a portion of this solvent with an esterification catalyst, such as a small amount of a strong acid, at esterification conditions to render the mixture preferentially oil soluble, injecting a quantity of preferentially-oil-soluble mixture into a petroleum reservoir, thereafter injecting a quantity of crude oxygenated mixture into said reservoir, and finally driving the sequentially-injected solvent banks through the reservoir toward producing wells by the injection of floodwater. Excellent recoveries of both petroleum and the injected solvent are thereby obtained. Since the methods for producing oxygen-containing compounds by oxidizing light hydrocarbons are well known, the starting material for the process of this invention may be considered to be either the raw products of these prior art oxidation methods or the low-molecular-weight hydrocarbons themselves. Since low-molecular-weight hydrocarbons are generally available in large amounts in oil fields, and since the value of such hydrocarbons at the oil fields is relatively low, it is preferred that these materials be used as the starting materials in the process and that they be converted to hydrocarbon oxidation mixtures by use of suitable prior art processes. The product distribution in the mixtures is similar to those set out in Table I, depending upon the proportions of the various low-molecular-weight hydrocarbons on the feed stock oxidized. Generally, the most economically attractive feed stock is an unseparated mixture of C to C hydrocarbons. Mixtures of liquefiable petroleum gases, commonly referred to as LPG, are suitable for use in the method of this invention and are preferred in oil fields where LPG is available in sufficient quantities. It should be understood that the crude product from the oxidation process contains small amounts of unconverted hydrocarbon feed, water, carbon monoxide, and carbon dioxide, and also contains nitrogen where the oxidizing medium is air. Any normally gaseous products, such as nitrogen and carbon monoxide, may be stripped from the product and discarded. In one embodiment of the process of this invention, the unreacted hydrocarbons are separated and recycled. In another embodiment of the process of this invention, the unreacted hydrocarbons are not separated, but are retained in admixture with the oxidation products.

In the preferred embodiment of the method of this invention, a portion of the oxidized product is contacted with a catalytic amount of a strong acid at esterification conditions. In this step, the alcohols present in the oxidized mixture combine with the acids present to form esters, while the aldehydes tend to polymerize. The resulting esters and aldehyde polymers tend to be preferentially soluble in oil as opposed to the preferential water solubility of the original oxidized mixture. However, the esterified product and the original raw oxidation product are mutually soluble. It is preferred that any acidity in the esterified product be neutralized by treatment with a base, such as sodium hydroxide, to prevent corrosion of piping and well casing, and to avoid possible plugging of the reservoir by the formation of insoluble salts therein. Moreover, neutralization of the acid followed by removal of a water phase which forms in the esterified product enhances the oil solubility of the esterified product. The amount of solvent injected into a petroleumcontaining reservoir in accordance with the method of this invention depends upon the characteristics of the reservoir and the crude oil contained therein, but in general it is preferred that 0.5 to 15.0% of the total pore volume of the reservoir be the amount chosen. In accordance with the preferred method of this invention, 0.5 to of the total pore volume of an esterified, neutralized, oxidation product is injected into the reservoir. Then 0.5 to 15 of the pore volume of crude oxygenated product is injected into the reservoir. The reservoir is then flooded by the injection of water, and petroleum oil is produced from the producing wells until the waterto-oil ratio at the producing wells becomes uneconomically high.

One distinct advantage of the method of this invention is that the oil is displaced from the reservoir without displacing large amounts of reservoir water. Consequently, the oil-to-water ratio in the fluids pumped from the producing wells is much higher than when prior art processes are used, and, when production pumping capacity is limited, more oil can be produced in a given amount of time than could be if conventional processes were used. Also, the use of this recovery technique achieves results superior to those achieved by prior art processes because a favorable mobility ratio is maintained between the driven and driving fluids in the reservoir, and this feature provides more favorable volumetric contact efficiency in the reservoir.

The following examples demonstrate the method of this invention and provide a comparison with the processes of the prior art.

EXAMPLE I A Berea sandstone core, one foot long and containing 0.63 pore volume of Dollarhide Devonian crude oil and 0.37 pore volume of water, was flooded with water in conventional fashion. When 0.5 pore volume of water had been injected, 45% of the oil in place had been recovered. No more oil was recovered during the injection of an other pore volume of water.

EXAMPLE II A Berea sandstone core, one foot long and containing 0.63 pore volume of Dollarhide Devonian crude oil and 0.37 pore volume of water, was flooded with 0.45 pore volume of a synthetic mixture of oxygen-containing hydrocarbons having the composition defined in Table I as typical of the products obtained by the partial oxidation of butane. Floodwater was then injected, and when 0.5 pore volume of water was passed into the core, 49% of the oil initially in place was recovered. This recovery increased to 58% during the injection of another pore volume of water. The oil solubility of the synthetic mixture representing butane oxidation products was tested, and it was determined that these products had a solubility of 40% in No. 3 white oil. Similar experiments were carried out on identical Berea sandstone cores using synthetic blends of hydrocarbon oxidation products corresponding to the pentane oxidation blend and propane oxidation blend of Table I. After 1.5 pore volumes of water had been injected, oil recoveries were 64% in the case of the pentane oxidation blend, and 54% in the case of the propane oxidation blend.

EXAMPLE III Into a ZOO-cc. round-bottom flask, equipped with a water-cooled reflux condenser, were placed cc. of a synthetic mixture of oxygen-containing hydrocarbons as set forth in Table I for the butane oxidation blend, 8 cc. of distilled water, and 0.5 cc. (0.8 weight percent) of concentrated sulfuric acid. The total equivalent of acid present was 0.26. After refluxing for 2 hours at 57 C., the total acid equivalent present was 0.15. The material was then 40% soluble in No. 3 white oil, indicating substantial increase in solubility. After refluxing for two additional hours, the total equivalent of free acid remaining was 0.12, and the material was 50% soluble in No. 3 white oil. The quantity of distilled water added to the synthetic butane oxidation products was equivalent to the water which would have been formed in an actual oxidation. No further treatment of the refluxed material was made prior to use in the secondaryrecovery experiment. 1

A l-foot Berea standstone core, containing 0.63 pore volume of Dollarhide Devonian crude oil and 0.37 pore volume of water, was flooded using 0.45 pore volume of the esterified product as an oil-soluble solvent bank ahead of the water flood. When 0.5 pore volume of water was injected, 68% of the oil initially in place was recovered; when 1.5 pore volumes of water were injected, 77% of the oil initially in place was recovered. These recoveries represent increases of 38% and 33% over the recoveries achieved with the original, raw, oxidized hydrocarbon mixture in Example II.

EXAMPLE IV The experiment of Example 3 was repeated using a synthetic oxidized mixture corresponding to the propane oxidation blend as set forth in Table I. A total oil recovery of 59% of the oil initially in place was obtained after 0.45 pore volume of the refluxed material was injected, followed by 1.5 pore volumes of water.

EXAilIPLE V A 500-cc. synthetic blend of oxygen-containing hydrocarbons, as set forth in Table I for the butane oxidation products, and 15 cc. (7 weight percent) of concentrated sulfuric acid were charged into a one-liter flask equipped with a reflux condenser. The total equivalents of acid present were 1.4.- After refluxing for 4 hours at 57 C., the total equivalent of acid present was 0.6. After refluxing for 15 additional hours, the total equivalent of free acid remained the same. A solubility check on this material showed it to be 50% soluble in No. 3 white oil. It will be observed that this is the same solubility as that obtained after refluxing for 4 hours after the addition of 0.8 weight percent of sulfuric acid, as set forth in Example 3. A 100-cc. portion of this material was made neutral by the addition of 5.84 grams of sodium hydroxide in cold water. The material was filtered to remove salt, and the water phase was separated. The organic upper phase was found to be 60% soluble in No. 3 white oil.

A l-foot Berea sandstone core containing 0.63 pore volume of Dollarhide Devonian crude oil was flooded by injecting 0.27 pore volume of the above material followed by 0.18 pore volume of raw butane oxidation products, as defined in Table I, and then injecting 1.5 pore volumes of water. After the injection of the first pore volume of water, 80% of the oil initially in place was recovered. After the injection of 1.5 pore volumes of water, 89% of the oil initially in place was recovered. lThese recoveries represented increases of 50% and 27% over the recoveries achieved when 0.45 pore volume of the synthetic oxidized product was followed directly by water, as in Example II, and represented increases of 78% and 100% over the recoveries achieved with only floodwater. They further represented increases of 18% and 16% over the recoveries achieved when the same total volume of an esterified oxidation product mixture only was used, as in Example III.

EXAMPLE VI A l-foot Berea sandstone core containing 0.63 pore volume of Dollarhide Devonian crude oil was flooded by injecting 0.27 pore volume of a fluid consisting of 25% by volume pentane and 75% by volume of the esterified, neutralized organic material produced in Experiment V. The total oil recovery after the injection of 0.27 pore volume of this fluid, followed by 0.18 pore volume of raw butane oxidation products (as set forth in Table I) and 1.5 pore volumes of Water, amounted to 91% by Weight of the oil initially in place. The 2575 mixture of pentane and esterified material was determined to be 80% soluble in No. 3 White oil.

It is evident that the oil recoveries achieved in Experiments V and VI are very high. The results of each example are given in Table II following.

identical conditions may be expected to give oil recoveries slightly higher, perhaps 1 or 2% higher, than those obtained in Experiments V and VI. It is evident that the method of this invention permits oil recoveries of a very high order using as solvents materials which are far less expensive than the pure chemicals suggested by the prior art, and which may readily be produced from raw materials available in oil fields.

When a crude oxygenated-hydrocarbon mixture: is produced using C to C hydrocarbons as a feed stock, it may be preferred not to separate and recycle the unconverted hydrocarbon feed, as taught by the prior art hydrocarbon oxidation methods, but to permit the unconverted hydrocarbon to remain in admixture with the oxidation products. The unconverted hydrocarbon will pass unaltered through the refluxing and neutralization steps, and will be present in the injected mixture to increase the oil solubility of the injected mixture and enhance oil recoveries. The failure to remove unconverted hydrocarbons will result in a final product approximating that obtained by the addition of hydrocarbon to the esterified, neutralized finished product as set out in Example VI.

The method of this invention contemplates an alternative process by which the crude oxygenated hydrocarbons may be treated. The crude oxidation products can be separated into a predominantly oil-soluble fraction and a predominantly water-soluble fraction by distillation. The higher-boiling fraction is first injected into the reservoir, and followed by the lower boiling-fraction. Floodwater is then injected to drive the two miscible solvents through the formation. The quantities of higher-boiling and lower-boiling fractions injected may be 0.5 to 15.0 pore volume percent. Where the hydrocarbon feed to the oxidation process has a lower boiling point than the temperature at which the oxidation products are fractionated, it is evident that the oil-soluble, unconverted hydrocarbon feed will condense with the lower-boiling, predominantly water-soluble materials, such as methanol. In such a case it is desirable to remove the unconverted hydrocarbon from the predominantly water-soluble fraction, and either recycle it through the oxidation step, or add it to the higher-boiling fraction to increase the oil solubility thereof.

TABLE H 011 Recoveries from Berea Sandstone Cares Oil Recovery (Percent of oil in place) Example Number Flooding System Solvent Slug (pore volume) With 0.5 With 1.5

pore volpore volume of umes of water water injected injected Conventional water flood 45 Butane oxidation products followed 49 58 by water. Estcrified butane oxidation prod- 08 77 ucts followed by water. Estcrified propane oxidation prod- 0.45

ucts followed by water. Esterified butane oxidation prod- 0.27 esterlfied -1 ucts, followed by unesterified 80 89 oxidation product, followed by 0.18 not cstcrified 1. water. VI 25/75 pentane and cstcrified butane 0.27 25/75 peutane and esterioxidation product, followed by fied product. 85 91 unesterified oxidation product, 0.18 uncsterified oxidized mix- I followed by water. ture.

As a specific example of this alternate method, a synthetic oxygenated hydrocarbon mixture corresponding to the pentane oxidation blend of Table I was distilled to produce a fraction boiling above 76 C., and a fraction boiling below 76 C. In a secondary-recovery experiment, 0.3 pore volume of said higher-boiling fraction and 0.2 pore volume of said lower-boiling fraction were inperiments V and VI. The use of amyl alcohol under jected into a 1-foot Berea sandstone core containing 0.62

pore volume of Dollarhide Devonian Crude oil and 0.38 pore volume of water. After the injection of 1.5 pore volumes of water, it was determined that 66% of the oil initially in place had been recovered.

A typical product distribution for a pentaue oxidation blend, distilled to remove the materials boiling below about 65 C., is as follows:

The oxidation products of C to C hydrocarbons are used, and it is preferred that the volumes of the higherboiling and lower-boiling fractions injected be equal, but since the volumes of the two fractions will seldom be equal, it may be more convenient to inject the fractions in the volume ratio at which they exist as produced.

In some cases, it may be desired to add a minor amount, 5 to 40% by volume, of a low-molecular-weight hydrocarbon to the first fluid injected, i.e., the predominantly oilsoluble fluid, to further increase the oil solubility thereof. In such cases, it is preferred that a mixture of hydrocarbons having about 4 to 8 carbon atoms per molecule be chosen.

The quantity of acid used as an esterification catalyst in the step of refluxing the crude oxygenated products is not critical, but it is preferred to use 0.5 to 10 weight percent of acid. The period of refluxing should be suflicient to substantially increase the oil solubility of the materials, and is usually about 4 hours. Catalysts other than sulfuric acid which may be used include hydrogen chloride, boron fluoride, and cation-exchange resins.

The embodiments of this invention in which a special property or privilege is claimed are defined as follows:

1. In the secondary recovery of petroleum from a subterranean reservoir by the injection of water through an input well into said reservoir, and the recovery of petroleum from said reservoir through a producing well, the improvement comprising injecting prior to the injection of water 0.5 to 15.0 percent of the total pore volume of a predominantly oil-soluble fluid, and then injecting 0.5 to 15.0 percent of the total pore volume of a predominantly water-soluble fluid, said water-soluble fluid comprising partial oxidation products of C to C hydrocarbons, and said oil-soluble fluid having been produced by refluxing the partial oxidation products of the C C hydrocarbons with a small amount of sulfuric acid for sufficient time to render the refluxed product mixture soluble in mineral oil to an extent not less than about 40% by volume.

2. A method according to claim 1 in which said oilsoluble fluid after refluxing is further treated by neutralizing any acidity with aqueous caustic, and separating a water phase and an organic phase from said oil soluble fluid.

3. A method according to claim 2 in which the amount of sulfuric acid used in the refluxing step is about 0.5 to 10.0 weight percent, and said oil soluble fluid is refluxed for about 4 hours.

4. A method according to claim 3 in which the oilsoluble fluid consists essentially of about 5 to 40 percent of hydrocarbons and to percent of neutralized, refluxed, oxygenated hydrocarbons.

5. In the secondary recovery of petroleum from a subterranean reservoir by the injection of water through an input well into said reservoir and the recovery of petroleum from said reservoir through a producing well, the improvement comprising injecting prior to the injection of water 0.5 to 15.0 percent of the total pore volume of a predominantly oil-soluble fluid, and then 0.5 to 15.0 percent of the total pore volume of a predominantly watersoluble fluid, said fluids being produced by fractionating the partial oxidation products of C to C hydrocarbons into a higher-boiling fraction boiling above about 76 C., and a lower-boiling fraction boiling below about 76 C., and separating unconverted hydrocarbons from said lower-boiling fraction, said higher-boiling fraction being said oil-soluble fluid, and the remaining portion of said lowerboiling fraction being said water-soluble fluid.

6. A method according to claim 5 wherein the unconverted hydrocarbons, separated from said lower boiling fractions, are combined with said higher boiling fractions to produce said predominantly oil-soluble fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,742,089 Morse et al Apr. 17, 1956 2,885,002 Jenks May 5, 1959 2,891,982 Brown June 23, 1959 2,897,894 Draper et al Aug. 4, 1959 2,934,487 Whitney Apr. 26, 1960

Claims (1)

1. IN THE SECONDARY RECOVERY OF PETROLEUM FROM A SUBTERRANEAN RESERVOIR BY THE INJECTION OF WATER THROUGH AN INPUT WELL INTO SAID RESERVOIR, AND THE RECOVERY OF PETROLEUM FROM SAID RESERVOIR THROUGH A PRODUCING WELL, THE IMPROVEMENT COMPRISING INJECTING PRIOR TO THE INJECTION OF WATER 0.5 TO 15.0 PERCENT OF THE TOTAL PORE VOLUME OF A PREDOMINANTLY OIL-SOLUBLE FLUID, AND THEN INJECTING 0.5 TO 15.0 PERCENT OF THE TOTAL PORE VOLUME OF A PREDOMINANTLY WATER-SOLUBLE FLUID, SAID WATER-SOLUBLE FLUID COMPRISING PARTIAL OXIDATION PRODUCTS OF C3 TO C8 HYDROCARBONS, AND SAID OIL-SOLUBLE FLUID HAVING BEEN PRODUCED BY REFLUXING THE PARTIAL OXIDATION PRODUCTS OF THE C3-C8 HYDROCARBONS WITH A SMALL AMOUNT OF SULFURIC ACID FOR SUFFICIENT TIME TO RENDER THE REFLUXED PRODUCT MIXTURE SOLUBLE IN MINERAL OIL TO AN EXTENT NOT LESS THAN ABOUT 40% BY VOLUME.