3,258,071 United States Patent Office Patented June 28, 1966 2 problems, referred to above, heretofore encountered in 3,258,071 the use of linear or chain sodium tripolyphosphate or SECONARY HYDRO CARBON RECOVERY Sodium hexametaphosphate. PROCESS Chung Yu Shea, Olivette, and Darwin A. Novak, Jr., It is, accordingly, one object of this invention to pro Overland, Mo., assignors to Monsano Company, a core 5 vide an inexpensive inorganic additive, not heretofore poration of Delaware Suggested for the purpose, for use in water flooding of No Drawing. Fied Sept. 19, 1962, Ser. No. 224,844 hydrocarbon formations for secondary recovery of hydro 10 Claims. (Ct. 66-9) carbons from such formations. It is another object of this invention to provide a rela The present invention relates to the art of the sec 0 tively inexpensive water flooding medium in oil bearing ondary recovery of petroleum or other hydrocarbons formations, which medium will aid in improving the yield from an underground hydrocarbon bearing formation by of oil recovered per unit of volume of water injected in a water flooding method, and it more particularly re the flooding operation. lates to a novel method and novel compositions useful It is a further object of this invention to provide a in practicing such art. water flooding medium in hydrocarbon bearing forma In recent years the practice of water flooding under tions, which medium enables one to alter the ability ground oil bearing formations to recover oil therefrom of the formation to be wetted by water and also enables in the form of a water-oil mixture, from which the one to inhibit or minimize precipitation of insoluble oil is Subsequently separated, has become quite com metal compounds in the medium. mon in the case of formations from which the oil can 20 Another object of this invention is to provide a novel no longer be recovered economically by primary re saline or brine water flooding composition. covery methods. However, many problems are en Still further objects and advantages of this invention countered with the water flooding technique. In most will become apparent from the following description. instances the oil bearing formation is of such a nature The present invention provides a novel saline or brine that the formation is preferentially wetted by the oil 25 Water flooding composition comprising natural saline and the water employed thus does not readily float away or brine water containing sodium salts such as sodium or remove the oil which is adsorbed on the surface of sulfate and/or sodium chloride dissolved therein, and the pores and/or contained in crevices of the forma which may or may not contain other dissolved metallic tion. salts or compounds, and an effective amount of an alkali Also, in some instances, the water available for water 30 trimetaphosphate, preferably sodium trimetaphosphate. flooding is moderately or highly saline (or of the nature The saline or brine water is one which occurs naturally of brine) and contains moderate to fairly high concen (in nature) and may be obtained from a river, lake, pond, trations of dissolved salts, particularly sodium sulfate the ocean or even from artesian wells or from some and/or sodium chloride. Saline water tends to suppress similar source. As such it may, and usually does, con the solubility of various compounds such as sodium tri 35 tain, in addition to a sodium salt, varying amounts of polyphosphate and sodium hexametaphosphate which have one or more dissolved hardness imparting metallic salts heretofore been suggested as additives to water floods or compounds such as calcium, magnesium, barium and to improve the yield of the oil recovered. This sup other metal ions which impart "hardness' to the water. pression of solubility decreases the effectiveness of such The term “hardness' refers to the presence of calcium additives. In addition, saline water often contains var 40 and magnesium salts, or similar acting salts, in water ious metallic compounds (e.g., metallic salts such as which cause incrustations in boilers and heater treaters, carbonates and bicarbonates in addition to chloride and and which form insoluble soap salts. The hardness of sulfate) and tends to suppress the solubility of calcium, water is usually expressed in parts per million of CaCO magnesium, iron and other metallic complexes of such in water, and for natural saline or brine waters this phosphate compounds with the result that such com 45 hardness may vary from about 20 up to about 30,000 plexes are often precipitated as finely divided particles parts of CaCO per million parts of water. However, or scales. These precipitates often cause restriction of in most instances the saline or brine water will have a flow and/or plugging of the input or injection well or hardness varying from about 50 up to about 4,000 parts the output or producing well, or of the oil bearing for per million. mation, or various combinations of these. This, in 50 Natural saline or brine water normally may be slightly turn, results in decreased volume of oil recovered per acid, neutral or from slightly alkaline to moderately unit of volume of water injected in the flooding opera alkaline, and may have a pH in the range of about 5 to 9. tion. More commonly, such water has a pH in the range of The water flooding technique also presents problems about 6 to 8 and this latter pH may be considered for in the case of relatively deep formations wherein the 55 most purposes to be neutral. Further, such water gen injection water may be heated by the ambient tempera erally contains a sufficient quantity of bicarbonate ions ture of the formation to temperatures as high as 100 to buffer the water which thus resists change in pH to 250 F. or possibly more. In such instances the even though some acid or alkali is added to it. linear or chain polyphosphate additives, such as sodium In general, the salt content of a natural saline water tripolyphosphate or sodium hexametaphosphate, degrade 60 may vary widely depending upon the source of the water, (hydrolyze) in a relatively short period of time, par and may contain from small amounts of salts up to, in ticularly when the water is recycled, to form orthophos cluding, and sometimes exceeding, the amount of salts in phates, and these form precipitates with calcium, magne a saturated solution of salts. In most instances the salt sium and iron ions. Such precipitates often cause the content (other than the trimetaphosphate content) may restriction of flow and plugging problems referred to 65 vary from about 0.5% by weight or less up to about 50% above. by weight, but more commonly will vary from about 1% In view of these circumstances, there has been a need by weight up to about 25% by weight. In the case of for an inexpensive inorganic additive to water employed natural brines, that is, natural water containing sodium in water floods, which additive will provide an increased 70 chloride dissolved therein, the sodium chloride content yield of oil per unit of volume of water injected, and may vary from about 1% by weight up to about 20% which will alleviate or eliminate at least some of the by weight, but is usually between about 1 and 10% by 3,258,071 3. 4. weight. One of the most likely available sources of water acid alkali tripolyphosphates which do act as sequestering flooding operations near coastal hydrocarbon bearing for or complexing agents, and other advantages (but not all mations is ocean or sea water which normally has a total of the disadvantages) attendant with the use of tripoly solids content of about 3.4 to 3.8% by weight, and a phosphates are obtained. Normally, the conversion or sodium chloride content of about 2.4 to 2.8% by weight. 5 hydrolysis proceeds at a relatively slow rate. This pro The preferred natural saline waters are those substan vides a definite and controlled amount of tripolyphosphate tially free of, or contain less than 5% (desirably less than in the media together with trimetaphosphate. The rate 1%) by weight of, suspended insoluble solids or com of conversion or hydrolysis of the trimetaphosphate to pounds. tripolyphosphates can be increased considerably to an The alkali trimetaphosphates employed in the novel O almost or essentially instantaneous rate by the presence saline water compositions or processes of this invention of alkalis in the flood water, the presence, for example, have the empirical formula: MPO, where at least one of two mols of NaOH per mol of trimetaphosphate giv M is an alkali metal or ammonium and the other M's are ing almost an instantaneous rate of hydrolysis and quan hydrogen or ammonium or alkali metal, prefereably the titative yield of tripolyphosphate, with lesser amounts of latter. In contrast to sodium tripolyphosphate or sodium alkali giving a fast rate initially but less complete instan hexametaphosphate which are chain phosphates (having taneous yield of tripolyphosphate. However, the addi 3 P atoms and an average of about 6 P atoms, respec tion of such alkali to the novel compositions of this in tively, in the chain), such alkali trimetaphosphate is a vention is not necessary, and in most instances it is prefer ring or cyclic compound which may be represented by the red to employ the trimetaphosphate in the water flood following general structure: 20 without, incorporating alkali other than that which may be present in the natural saline water that is used. Q-MP In other instances, however, and particularly when it 1N is beneficial to complex or sequester some of the "hard ness' producing cations in the water, the addition of some M-O-P=OQ o O=P-O-M9 alkali metal tripolyphosphate or alkali metal hexameta N o1 phosphate to the water flood media containing the tri metaphosphate may be beneficial, or this result can be where at least one M is an alkali metal (such as Na, K, achieved by adding small amounts of alkali, generally Li, Ce, etc.) or ammonium (NH4) and the other M's are about 0.05 to about 1 mol of alkali per mol of the trimeta hydrogen, ammonium and/or an alkali metal, preferably phosphate present in the water flood medium, thereby con an alkali metal.