NO172757B - TENSID MIXTURE AND PROCEDURE FOR TERTIAS OIL TRANSPORT - Google Patents

Description

The present invention relates to a method for tertiary transport of petroleum, as well as surfactant mixtures for use therein.

It is known that when extracting oil from oil-bearing reservoirs, only a small part of the originally present oil can be transported by primary and secondary extraction processes.

An increase in the oil yield is achieved by tertiary processes. By this is meant a method by which either the oil's viscosity is reduced or the viscosity of the post-flotation water is increased, or it is a matter of tension flotation processes which are primarily based on a strong lowering of the interfacial tension between oil and reservoir water or formation rock.

An overview of the previously used most important surface-active compounds can be found in the literature source: "Tenside fiir die Tertiårforderung von Erdol im hochsalinaren System", Tenside Detergents 17 (1980), 2.K. Oppenlånder, M.K: Akstinat, M.I. Murtarda.

Among the surfactants mentioned there, the sulphonates are especially important for the present purpose. According to European patent application 0047369, active surfactants based on carboxy methyl ether are described. However, a particularly strong absorption to the rock in contrast to the sulphonates seems to make application difficult. In addition, carboxymethyl ether near the inversion temperature point, at which the surfactant is used and is effective, causes a strong thickening of the oil, and this leads, even with relatively highly permeable artificial formations,

to pressure differences of more than 40 bar/m and when transferred in the field to pressures well above the petrostatic pressure (H.

Murtarda, M. Kurkowsky, Erdol Erdga's Zeitschrift 93_; 303

(1977).

Oil-mobilizing surfactants are therefore above all organic sulphonates such as alkyl, alkylaryl or petroleum sulphonates. These have a very low tolerance limit to the salt content of the reservoir water. Salt concentrations on

0.1% with special sensitivity to divalent ions is considered

here already as problematic. Since, however, many reservoir waters have a salt content of up to 25%, such as e.g. in northern Germany, the sulphonates cannot be used alone. According to Canadian patent 1,02 6,666 and US patent 3,811,505, an attempt has therefore been made to reduce this electrolyte depletion by adding co-surfactant agents such as alcohols, which however reduces the degree of effectiveness.

Finally, the use of alkylaryl polyglycol ether sulfonates was known only for secondary transport. In contrast to the alkyl sulfonates, the alkyl or alkylarylpolyglycol ether sulfonates showed a good tolerance with high salt contents, but the sensitivity of the sulfate group to hydrolysis in acidic media at the higher temperature that occurs in most reservoirs, however, severely limits their applicability.

Therefore, the previously known surfactants or surfactant mixtures could not work satisfactorily with regard to oil extraction effect, durability and tolerance at high salt contents.

Consequently, the task was to produce a method and a surfactant mixture that allows a high oil recovery from the reservoirs with good salt tolerance.

It has now surprisingly been found that this can be achieved with surfactant mixtures containing as essential components

a) an anionic surfactant with formula

in which

R<1> is a straight-chain or branched alkyl group with 8 more

15, preferably 8 to 12 carbon atoms,

R<2> hydrogen or methyl, and

x the numbers 1 to 2, preferably 1,

b) a nonionic surfactant with the formula

in which

R<1> means a straight-chain or branched alkyl group

with 8 to 15 carbon atoms,

R<2> means hydrogen or methyl,

y the numbers 3 to 16,

and wherein the weight ratio a:b is 4:1 to 1:10.

With aqueous solutions of the surfactant mixture according to the invention, high oil recovery rates of up to 97% can be achieved.

The glycol ether sulfonate, which is only partially soluble in saline solution, is brought into solution with the alkyl polyglycol ether, and the mixture is also remarkably stable at high temperatures in formation water with a high salt content. With 8 x 10~<3> mN/m, the new surfactant system has a very low interfacial tension in relation to crude oil, and this is an important prerequisite for good oil recovery (M. Burkowsky, C. Marx; Erdol - Erdgaszeitschrift, 95. Jg., January 1979). At the same time, however, the system shows a certain desired lability towards the hydrocarbon. When crude oil is added, a microemulsion is formed which consists of surfactant, hydrocarbons and salt water. According to common opinion, the formation of a microemulsion is a prerequisite for good oil mobilization. This property is tested in "phase tests", during which the same amount of crude oil and surfactant mixture is shaken and then stored at a higher temperature. The formation of a black opalescent, easily mobile intermediate phase is a prerequisite for an active product, in particular the mixture according to the invention of dodecylphenyl monoglycol ether sulfonate/monylphenol octaethoxylate (25 ml, 6% in formation water) with crude oil (25 ml) at 40°C forms 7 ml of a such intermediate phase.

The present invention provides an improved method for extracting oil.

According to this method, 1 to 20 percent by weight solutions of a aforementioned surfactant mixture are pressed into an underground reservoir whose formation water has a high total salt content with subsequent injection of formation water which is possibly thickened with biopolymers such as xanthans or cellulose derivatives such as hydroxyethyl cellulose.

The anionic/non-anionic surfactant mixture according to the invention has the advantage compared to the compounds with 'formula

which is described in Canadian Patent No. 1,086,046 and connection with formula

or

which is described in DT no. 2,558,548, in which the anionic and the non-ionic components are united in the same molecule, next to the generally improved oil extraction effect, that only by changing the proportion and nature of the non-ionic component can adapted to the often varying reservoir conditions (temperature, pressure, salt content of the reservoir water, crude oil composition, porosity and capacity of the rock formations, etc.). It is a particular advantage of the invention that the equilibrium is easy to set with regard to the hydrophobicity and hydrophilicity of the components.

In deltaj, the tensiftIotation is carried out analogously to what is described in DE 25 58 548, to which reference is hereby made.

The effectiveness of the new surfactant mixtures can be seen in the following examples. The procedure is as follows: The ethoxylates to be used are prepared according to known methods by reacting alcohol or the alkylphenols with the desired amount of ethylene oxide and alkaline catalysis (0.5% KOH) at 120°C in an autoclave. To prepare the sulfonates, 1 mol of alkylphenol is reacted according to known methods with 1 mol of C1SO3H or SO3 at 20 to 50°C. The sulphonic acid that is formed is neutralized with 50% NaOH. After addition of 5 mol% NaOH, the aqueous solution is reacted at 120°C in an autoclave with 1 to 2 mol of ethylene oxide. The excess of NaOH is neutralized after reaction with HC1.

The flotation with the surfactant solution to be used according to the invention can be pressed in either continuously or in the form of slugs, i.e. a narrowly limited volume of 0.02 to 0.5 times the pore volume of the reservoir rock, drill core or sand packing. The size of surfactant slugs depends on the surfactant concentration and economics. The concentration is usually 5% with a usage quantity of 0.1 x the pore volume. As a linear laboratory model for the reservoir, drill cores (100 - 300 mm long, 20 - 30 mm cross section) of Bendheimer sandstone, embedded in synthetic resin or lead, are used for testing. At the same time, the tests are carried out on sand packs (grain size 0.03 - 0.15 mm, porosity: 40%, permeability: 3900 mD, residual water: 15%) in thermostabilized pressure pipes of 25 or 100 cm length and 20 mm cross section.

The sample material is preferably floated with synthetic formation water with the following composition: 8.4% by weight NaCl, 2.9% by weight CaCl2, 0.9% by weight MgCl2, pH = 6. The pore space of the drill core or sand pile, prepared with a shaking test, is filled with the formation water as if with crude oil again up to 15% is displaced. Such oil-saturated material is then floated with formation water at the test temperature of 40°C for so long at a speed of 1.5m/d, that a dewatering degree of 99-100% is achieved after passage of 2 times the pore volume, which corresponds to secondary water flotation. It is achieved as oil extraction approx. 70%. The remaining oil is available for the subsequent tensifdIotation and is estimated as residual oil saturation Sq^- 100%. After the surfactant layer, a polymer slug is suitably injected both for mobility control and for protection of the surfactant solution before penetrating formation water. For this purpose, a polymer or polymer mixture is dissolved in such a concentration in the formation water that the viscosity is at least as high as that of the oil. As polymers, biopolymers come into consideration here, e.g. that sold by Pfitzer under the trade names "Flocon", Biopolymer 4800, polysaccharides or cellulose derivatives such as hydroxyethyl cellulose, e.g. "Natrosol" HH250 from Hercules Powder, or synthetic polymers based on copolymers, polyacrylamides and - acrylates.

Samples from sand packs confirmed on short drill cores: To CA 1.086.046 and DT 2.558.548

Test method: Slug flotation with 0.1 pore volumes, 5% surfactant solution, so that 2.5% surfactant in relation to the oil to be moved is available, post-flotation with 0.4% hydroxyethyl cellulose for approx. 12% salt water.

SQR = residual oil reduction as a percentage of the amount of oil available for testing.

Claims (3)

1. Procedure for tertiary transport of petroleum, characterized by A) in a first step pressing a 1 to 20% by weight aqueous solution of a surfactant mixture into the petroleum reservoir, which contains as essential components a) an anionic surfactant with formula in which R<1> means a straight-chain or branched alkyl group with 8 to 15 carbon atoms, R<2> hydrogen or methyl and x the numbers 1 to 2, b) a nonionic surfactant with formula in which R<1> means a straight-chain or branched alkyl group with 8 to 15 carbon atoms, R<2> means hydrogen or methyl, y the numbers 3 to 16, and wherein the weight ratio a:b is 4:1 to 1:10, and B) in a second step in a manner known per se repressurizes the formation water thickened with a polymer and recovers additional amounts of crude oil that can no longer be recovered with primary and secondary transport methods. 2. Surfactant mixture for tertiary transport of petroleum, characterized in that it contains as essential components a) an anionic surfactant with the formula in which R<1> means a straight-chain or branched alkyl group with 8 to 15 carbon atoms, R<2> hydrogen or methyl, and x the numbers 1 to 2, b) a non-ionic surfactant with the formula in which R<1> means a straight-chain or branched alkyl group with 8 to 15 carbon atoms, R<2> means hydrogen or methyl, y the numbers 3 to 16 and where the weight ratio a:b is 4:1 to 1:10. 3. Surfactant mixture according to claim 2, characterized in that the weight ratio of surfactant (a) to (b) is 2:1 to 1:9.