IL27759A - Process of secondary recovery of petroleum from substerranean formations by a water-flooding method - Google Patents

Description

/ 27759/2 1 1> PATENTS FORM No.3 PATENTS AND DESIGNS ORDINANCE SP EC IFIC ATION PROCESS OF SECONDARY RECOVERY OF PETROLEUM FROM SUBTERRANEAN FORMATIONS BY A WATER - FLOODING METHOD yd! 'ypnp-nn p^aaao w ΐη log; s? n»3s?o n>ap - ^nn We. GENERAL ANILINE & FILM CORPORATION, a corporation organized under the laws of the State of Delaware, United States of America, of 140 West 51st Street, New York, New York, United States of America, DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed, to be particularly ascertained in and by the following The present invention relates to a new and improved method for the recovery of oil from subterranean oil reservoirs by the water-flooding technique and, more particularly, is concerned with an improved and outstanding process whereby the fluid employed is modified to increase the amount of oil recovery from the oil reservoirs.

It is conventional practice in the petroleum industry when an underground oil reservoir lacks sufficient jiitixtbJL/ recoverable by primary recovery methods hhlli to produce an economically constant flow of oil from the underground reservoir to employ a fluid to displace the oil which is present in the underground reservoir by injecting such fluid and thereby forcing the oil which is present in the reservoir, to the surface* It has been common practice for some time to inject either a gas or water for 3uch pur- 0 poses. This general technique of obtaining oil which is not readily available under its own pressure, is known as secondary oil recovery. Where water is used as the injected fluid or driving medium, the technique is specifically known as water-flooding, or just flooding.

The oil which is desired to be recovered by such flooding techniques is, as pointed out above, oil which exists as "fixed" oil and is held by absorption or adsorption on the particles of the surrounding underground earth strata and which is usually a sand, or sand clay, or shale formation.

This oil is termed "fixed oil" because it will not naturally flow from the underground earth strata to the surface. In addition to fixed oil there is also present as normally unrecoverable oil, free oil which is located in the voids of the sand, the sand clay mixtures and the shale strata of earth. Both free oil and fixed oil are recoverable to a ./ their economic feasibility.

The major deficiency of the heretofore employed water-flooding techniques derives from the fact that water mediums will hydrate the subterranean soil formation and par-ticularly the clay iitlh/ therein, to render such formations completely impermeable to the drivin force of the water and eventually the entire formation becomes "plugged". When "plugging" results, the practice has been heretofore to abandon such formation since no amount of driving force acting through the injected fluid will result in any further oil recovery. In the main, water-flooding techniques have been employed and such techniques are the primary ones used for secondary oil recovery, particularly because of the ready availability of suitable waters for such purposes. It has been suggested to employ non-aqueous fluid media as the driving force but usually the economics of employing such other fluids does not render these techniques feasible.

Another solution to the problem of clay hydration has been to employ inhibited fluids containing high concentra-tions of salt materials. While this technique has obviated the hydration of the clay, it has not, however, overcome the problem of plugging due to the fact that highly inhibited fluids as have been suggested and used cause the clayey materials to disintegrate to "fines". In this state the clay is, physically, very much like a fine sand, and while plugging does not occur due to the swelling of the clay, nevertheless plugging of the formation occurs as a result of the filling of the voids therein by the sand-like finely divided clay particles.

Since it has been found that only approximately 50 secondary recovery methods for obtaining most of the oil out of the ground is evident.

In order to improve the mechanics of water-flooding procedures most efforts in this area have been directed towards increasing the viscosity of the driving fluid or driving water relative to the oil to be recovered. Many materials have been suggested for this purpose and the general class of substances which have been used may be characterized as thickening agents. Among the various thickening agents, numerous natural gums and synthetic polymers have been employed. While the water-flooding operation is improved by increasing the viscosity of the injected water, the major defect which has been . described above, namely, the plugging of the formation due to hydration of the clay materials still remains with such viscosity fluids.

The new process for secondary oil recovery of the invention substantially obviates plugging of the subterranean formations due to the hydration of the clay materials con tained therein. It also results in outstanding and improved yields of oil recovery. The physical condition of the earth strata so treated is substantially unchanged and thereby permits a more complete recovery of the oil present in the reservoir.

. It has now been discovered that in secondary oil recovery processes, and primarily where such processes are employed in recovering oil not normally recoverable by primary techniques from clay-containing subterranean reservoirs, the clay-containing formations can be made to yield substantially all of the free and fixed oil contained therein by using a water-flooding technique if the water contains a specific It has now been discovered that a combination of the specific copolymer substances hereinafter to be described together with a critical concentration of salt materials, produces a stabilizing condition within the subterranean clay-containing oil reservoir. The flow of water and the subsequent displacement of the oil in the reservoir is substantially unimpeded and the oil thereby readily recoverable.

The addition of the critical amount of the salt materials substantially reduces the viscosity of the driving fluid. · Notwithstanding this factor, there is obtained an improvement in the amount of oil which can be recovered.

While the particular mechanism is not fully understood, it is believed that the process of the present invention acts to stabilize clay-containing substances and, particularly, soils so that they remain pervious, i.e., their pore structure remains unchanged, thereby permitting the fluids to flow unimpeded. As will be demonstrated below, the amount of salt materials employed is especially critical. Too large an amount, while resulting in an inhibition of clay hydration, produces a plugging of the well or the subterranean formation due to the complete disintegration of the clay particles to an almost microscopic size. It is only by virtue of the use of a combination of the specific copolymer to be described and the critical amount of salt materials to be shown, that there results a unique equilibrium condition which produces a remarkable stabilizing effect on the subterranean clay-containing soils.

The particular copolymer which is employed in the present invention is a copolymer of an alkyl vinyl ether and maleic anhydride, and particularly lower alkyl vinyl ethers. γ Generally, such copolymers contain each of the aforementioned chemical moieties in equimolar amounts. For the purposes of this invention, such, moieties may be present in the copolymer not only in equimolar amounts but in ratios ranging from about 5 :4 to 4 : 5. The molecular weights of the copolymer may vary considerably, depending upon the general techniques employed in the polymerization process. For the purposes of this invention, any copolymer with an average molecular weight from about 500, 000 to upwards of several million may be used. In terms of viscosity, which is often used to define the molecular weight of high polymer materials, the copolymers which may be employed are those which have specific viscosities from about 1.3 to about 10.0. The determination of specific viscosity and the inter-related viscosity, intrinsic viscosity and relative viscosity, is readily made from well known equations, on empirical determinations resulting from viscosity measurements usually employing one gram of copolymer dissolved i 100 ml. of a suitable solvent, e.g., 2-butanone at 25°C.

Salts which may be used and which are essential and critical in the present invention, may be any water-soluble inorganic or organic salts with the proviso, however, that there be present in the composition a minor amount of a multivalent cation. The preferred multl-valent cations are calcium and magnesium, with the former being particularly preferred. From an economic point of view, it is preferred to employ inorganic salts, particularly inorganic sodium and potassium salts such as sodium chloride, potassium chloride, sodium nitrate, potassium nitrate, sodium bicarbonate, and, as a general class, the alkali metal halides. usually extremely small and ranges from about 0.001$ to about 1$ by weight thereof based on the weight of the total aqueous composition. A preferred range is from 0.05$ to 0. 5$. The total salt concentration should range from about 0.2$ to about 1.5$. More precisely, it has been determined that the salt concentration should be such that thec¾^/&¾¾¾^y|^y of the aqueous fluid lies between about 0. 3 and about 1 ohm"1. With these aforementioned limitations of salt concentrations and resistivity one may select any combination of water soluble salts noting, however, that there should be present an amount of multi-valent cation material (e.g., calcium or magnesium) in an amount from about 0.0025$ to about 0.25$. Again, within this broad range it is preferred to use from about 0.0075$ to about 0.125$. The remaining Inorganic salts comprise the major portion of the total salt content and any combination of concentration within the limits above-defined may be used. The preferred salt is sodium chloride in an amount ranging from about 0.1 to about 1$ with about 0.5$ being the most preferred concentration.

In the preferred embodiment of the present invention., there should also be present a small amount of bicarbonate anion. The preferred salt of this ion is sodium bicarbonate and the concentration thereof which may be used may range from about 0.02 to about 1$.

The following examples will serve to illustrate the present invention. In these examples, where parts are used, these should be parts by weight unless otherwise indicated.

Example I In this example, flow rates through a clay core sample are determined, using the following parts and technique: pulverized field samples, 2 cm. of 80-100 mesh sand, with the remainder in the tube glass wool. Other such tubes are prepared and separately there is passed through the tubes the following composition: (A) Water (B) Vfo sodium chloride solution in water (C) a water solution containing 1% sodium chloride, 0.2 sodium bicarbonate, 0.025 calcium chloride, and 0.1% of a copolymer (1 :1 ratio of monomers) of maleic anhydride with methyl vinyl ether characterized by a specific viscosity of 1.9 ( * s 1, 300, 000 ) These solutions are then passed through the filled glass tubes of mercury under a pressure of 190 cm./ and the amount of fluid passing through the tubes is collected. Composition (A) which is untreated water, almost immediately clogs the tube and after 30 minutes only about 2 cc. of water is collected. Solution (B), after 20 minutes passage, yields a flow through of about 70 cc, and Solution (C) a flow through of about 85 cc. This example demonstrates the superiority of the copolymer salt combination vis-a-vis water alone and a salt solution alone insofar as flow through rates are concerned.

While there has been satisfactory flow through using 1% sodium chloride solution, the clay sample has begun to disintegrate after 20 minutes and shortly thereafter no flow through is obtained. This is in contrast to the results obtained with Solution (C) where excellent flow through rates persist long after Solution (B) has ceased to flow.

Example II As a further illustration of the superiority of the specific composition of the present invention in stabilizing clay soils in secondary oil recovery processes, the following experiment is carried out: The following four solutions are prepared: A. tap water B. 0.1$ sodium chloride, 0.025$ calcium chloride in tap water C. Solution B to which there are further added 0.1$ of the copolymer employed in Example I, and 0.2$ sodium bicarbonate D. 1$ sodium chloride and 0.1$ calcium chloride To each of four 8 oz. wide-mouth jars, each containing 25 gr. of graded 10-30 mesh Mojave clay, there is slowly added separately 150 cc. of the four solutions described above. Each jar is capped, inverted gently and permitted to stand for 16 hours at room temperature. Each jar is then inverted five times to loosen the clay and the contents poured directly on to a 30 mesh sieve which is mounted over a 60 mesh sieve. The sieve residues are dried to constant weight and per cent distribution and recovery determined. The results are as follows : With plain tap water 5.2$ of the clay is retained on the 30 mesh sieve and 1.4$ on the 60 mesh sieve with total recovery of 6.6$. With Solution B, 19$ is retained on the mesh sieve and 44$ on the 60 mesh sieve, giving a total recovery of 63$. Solution C results in 44. 5$ retention on the 30 mesh sieve and 31$ retention on the 60 mesh sieve for a total recovery of 75. 5$. Solution D gives a recovery retention of 10$ on the 30 mesh sieve, 22$ on the 60 mesh sieve and a total recovery therefore of 32$ of the clay. only 5.2$ of all of the clay particles present are large enough to be retained on a 30 mesh sieve. Using the salts, Solution B results in a much higher recovery of total clay but significantly, only 19$ is retained on the 30 mesh sieve. Thus, somewhat over 80 of the clay present has disintegrated to a size retainable on a 60 mesh sieve or smaller. With higher salt concentrations as demonstrated, using Solution D, only 32$ of total clay is recoverable indicating that almost 70$ thereof has disintegrated to a size smaller than can be retained on a 60 mesh sieve and only 10$ is still retainable on the 30 mesh sieve. Solution C demonstrates the highest weight recoverabillty, namely, 75.5$ with almost 1/2 (44.5$) of all of the clay originally present being substantially unchanged in particle size and almost 1/3 of all of the clay originally present still retainable in the 60 mesh sieve.

This example demonstrates the remarkable stabilizing effect on clay particles of Solution C vis-a-vis the other three solutions.

Example III Example I is repeated except that Solution C contains as the copolymer a (1:1) methyl vinyl ether-maleic anhydride copolymer of specific viscosity = 2.63 (¾ s 1* 390,000). The flow through of this solution is 120 cc. after 20 minutes.

Example IV Example 1 is again repeated using the indicated copolymers of .1:1 methyl vinyl ether-maleic anhydride and the flow through rates obtained after 20 minutes are: Flow Through A. sp. vis. = 3-6 (Mw = 2, 340,000) 2 0 cc.

Example V The general procedure of Example I is again repeated except that the glass tubes which are used are 30 mm. internal diameter and 12 in. long. The clay employed is a screened a bentonitic clay used in the commercial Mohave Rogers Lake clay (&/ j /t ftt-ftflWW WW irW ' preparation of drilling mud I4l£†l) the particle size of which is 10 mesh and larger. The tubes are filled by first plugging the bottom with glass wool, then filling with 2 inches of 80 mesh sand.

This is followed with 50 g. of the screened clay described above and then another additional 2 inches of sand. Pour tubes are prepared in this manner.

Each of the four tubes is then treated with 1 pour volume of 4 different solutions. The first is treated with a 1. $ sodium chloride solution (Solution A) the second with a 1.5 sodium chloride solution containing also 0.2 of a copolymer similar to the one used in Example I (Solution B); the third with a solution similar to Solution B but using as the copolymer the one used in Example III (Solution C); and finally, the fourth with a solution similar to B and C but the copolymer differs in that it has an = 2,600,000 (Solution D). After permitting these solutions to remain in the tubes for several hours, there is passed through each of the tubes a 1.5$ sodium chloride solution to determine the flow-through characteristics of the treated clay samples. After 30 minutes, Solution A has yielded a flow-through of 20 cc. and the rate has deteriorated to 0 after 30 minutes. Solution B yields a steady 15 cc. per minute and after 30 minutes, 0 cc. have been passed through. Solution C flows at a steady rate of cc. per minute and after 30 minutes, there has been col- lec ed 750 cc. Solution D flows at a steady rate of 70 cc.

This example demonstrates the stabilizing effect of the salt-polymer combination on the clay and the improvement which is manifested by using a polymer of high molecular weight. To illustrate further, the effect of a multi-valent ion, tube 3 (through which Solution C was passed), is treated after the 30 minute test period described above with 100 cc. of a dilute calcium chloride solution. Plain water is then passed through the tube and the flow rate determined.

Initially, the rate of flow of the plain water is 35 cc. per minute (contrasted with 2 cc. per minute during the first 30 minute test) which rises to about 60 cc. per minute and. then gradually falls off with flow ceasing after 18 minutes. The total water which has been collected is 750 cc. Tube which has previously passed 2100 cc. of the salt solution in 30 minutes is subjected to the passage of plain water and while this tube demonstrated good clay stabilization, only 250 cc. of water are collected in 6 minutes, at which time shut-off of the flow occurs.

The combination of the polymer-salt treatment plus calcium ion has thus resulted in a most remarkable stabilization of the clay, i.e., even to the extent of substantial insensitivity to pure water for a considerable period of time, as contrasted with the other treatments.

Example VI Example V is repeated using a tube which is aged as in Example V but with a solution as used in Example III (i.e., salt copolymer-inorganic salt-calcium Aj W) . Using the 1. $ sodium chloride solution gives a flow rate of 50 cc. per minute which is steady for 30 minutes. After this time, the salt solution is replaced by plain water and the rate continues at 50 cc. advantage of using the composition of Example III as a pre-treat ent for the clay and stabilization thereof over the sequential treatment shown in Example V.

In addition to the outstanding flow rate character-istics which are achieved by the compositions for use in the process of the invention, and in addition to the remarkable degree of clay stabilization afforded thereby, the process of the present invention and the compositions used therein has still another outstanding and unexpected advantage. This resides in the ability of the herein-disclosed composition not only to stabilize clay-containing soils to the remarkable degree indicated above, but further, by stabilizing the clay materials, to achieve a condition and characteristic of the clay particles which manifests itself even after subsequent treatments are carried out with plain or untreated water, as shown above, or with brine solutions. Having made one or several passes through the clay-containing soils with the compositions for use in the process of the present invention, it becomes possible to continue water-flooding operations with ordinary, untreated water or brine without disturbing the original characteristics of the subterranean clay-containing strata. This of course is an extremely valuable and unexpected result since secondary oil recovery operations can then proceed under the most advantageous economic outlook with optimum oil recovery occurring.

Still another outstanding effect resulting from the use of the process of the invention lies in the discovery that the stabilization of the clayey materials achieved, makes it possible to employ subsequently various materials, and euti afce active particularly cationic/substances, to obtain the optimum of the present invention and the techniques described herein, it has been found that such formations have become much less surface active substantive to various materials, and particularly cationic/ substances which are often employed in conjunction with, or in sequential treatment with, water-flooding operations. surface active Among the outstanding cation /substances which are employed in water-flooding operations are the cationic quaternary ammonium compounds which are used for their germicidal, and in general, their biocidal activity to cut down and/or elimi-nate undesirable plant and animal growth within the formation. Heretofore, tremendous quantities of such quaternary ammonium compounds have been necessary in view of the fact that a major portion thereof becomes lost or inactivated by adsorption and/or the physical and/or chemical effect on the clay in the formation. The use of the process of the invention prevents to a major extent this deterioration of the biocidal action of the quaternary ammonium compounds by the clayey substances in the oil formations.

Claims (8)

27759/ 3

1. A method for the secondary recovery of petroleum oil from subterranean formations containing clay by water flooding characterized by adding to the water injected into the formation through an input well, a composition com prising A. A copolymer of an alkyl-vinyl ether and maleic acid and B. from 0. 2 to 1. 5% by weight of a mixture of alkali metal inorganic or organic salts and including from 0. 0025 to 0. 25% of the weight of the solution of salts of divalent cations preferably calcium and or magnesium, the amount of salt added being sufficient to give the solution an electrical conductance between 0. 3 and lOHM"1 '.

2. A method as claimed in claim 1, wherein the composition also contains from 0. 2 to 1. 0% by weight of an alkali metal bicarbonate.

3. The process claimed in claim 1, wherein the copolymer has a specific viscosity within the range of from about 1. 3 to 10. 0.

4. The process claimed in claiml, wherein the salt is an alkyl metal halide in an amount from 0. 1 to 1% by weight based on the total weight of the composition.

5. The process claimed in claim 4, wherein the amount of copolymer is from about 0. 001 to about 1% by weight based on the total, weight of the composition.

6. The process claimed in claims 1 and 2, wherein the composition contains: 0. 1% copolymer 0. 2 & sodium bicarbonate 1. 0% sodium chloride and 0. 25% calcium chloride.

7. The process claimed in claim 1, wherein the composition com rises co ol mer and salt in a ratio of co ol mer to salt 9·/

8. composition adaptable in an aqueous medium for use in the secondary recovery of petroleum from subterranean clayey formations by a water-flooding technique comprising: (a) A copolymer of methyl vinyl ether and maleic anhydride having a specific viscosity within the range of from about 1. 3 to 10. 0, and (b) an inorganic salt, including a multi-valent cation salt, the ratio of copolymer to salt varying from 20:1 to 1:1500 and the ratio of multi-valem t cation salt to inorganic salt ranging from about 5:1 to 1:600. 0 · ^OK S. HOROWITZ & CO. AGENTS FOR APPLICANTS