Preserving oil gravity

Abstract

Volatile organics in newly produced oil and gas, and/or condensates and distillates from produced oil and gas, are treated to depress vapor pressure to preserve light hydrocarbons in them when they are in storage vessels. The loss of volatile organics during storage of high gravity oil is minimized by forming a flowable or pumpable gel in the high gravity oil, (and/or condensates and distillates), as they are introduced to a storage vessel. The gel-former may comprise a phosphate ester of one or more low molecular weight alcohols, and a crosslinker including a source of iron or aluminum. Although the gels are flowable and pumpable, they can be broken for transportation from the production site or at another desirable time, returning the hydrocarbon product to its original properties.

Description

TECHNICAL FIELD

The invention relates to the conservation of volatile organics in oil and gas, and/or condensates and distillates from produced oil and gas, in storage vessels generally, but most usefully as they are recovered from the earth. The loss of volatile organics during storage of high gravity oil is minimized by forming a flowable or pumpable gel in the high gravity oil, (and/or condensates and distillates), as they are introduced to a storage vessel. The gel-former may comprise a phosphate ester of one or more low molecular weight alcohols, and a crosslinker including a source of iron or aluminum. Although the gels are flowable and pumpable, they can be broken after transportation from the production site or at another desirable time, returning the hydrocarbon product to its original properties.

BACKGROUND OF THE INVENTION

The American Petroleum Institute's system of classifying crude oils includes designations by gravity, relating the oil to the density of water. By this system, a high gravity oil is one which contains a high concentration of volatile, low molecular weight hydrocarbons, and a lower gravity oil will contain fewer such components.

When a high gravity oil is recovered from the ground and placed in a tank or other vessel not equipped with a special seal or vent designed to contain or minimize vapor emissions, substantial losses of light hydrocarbons can be incurred simply from evaporation and volatilization. This not only represents an economic loss but also is environmentally undesirable; moreover, some of the volatile components—for example, benzene, toluene and xylene in the atmosphere—could be hazardous for nearby workers.

Liquid storage is also commonly provided for liquid components removed from natural gas, sometimes known as “condensates and distillates.” Although in the liquid phase at the time of removal from the produced gas, they tend to include significant concentrations of readily volatilized light hydrocarbons, which are especially vulnerable to loss.

Some tanks and other storage vessels are equipped with special seals, pressure controls, or vents made to suppress emissions not only during static storage conditions, but also when the tanks are being filled or when the contents are being removed, and otherwise when there may be a degree of turbulence in them. Variations in head space when the vessels are low or near filled are of course important factors in volatilization, as are variations in temperature, which affect vapor pressures. Numerous storage tanks in the field—in the vicinity of producing wells—are not equipped with the expensive vents necessary to adjust to such variations. A simple way of inhibiting volatilization in such storage vessels is needed.

SUMMARY OF THE INVENTION

Although this invention is applicable to lower gravity oils, it is most useful for high gravity oils, designated 33° API or higher, and is well suited for oils in the range of 40-45° API. Perhaps the most beneficial use is with respect to “condensates and distillates,” typically produced with natural gas, and sometimes described as “natural gas liquids,” having API gravities of 45° to 60°. For my purposes in this application, a high gravity oil is defined as one having a gravity of 33° API or higher, including an API value higher than 60°, regardless of whether it is a crude oil or is derived from natural gas; for example, a condensate (I consider “condensate” and “distillate” to be interchangeable for my purposes) from natural gas.

I are able to preserve the high gravity rating of high gravity oils and condensates in storage by forming a weak gel in the high gravity oil or condensate as it is conducted from the producing well to the storage tank, it being understood that other steps, such as filtration, may be practiced also during transport. By a weak gel I mean one which is flowable and pumpable, so that the normal passage from well to storage, including whatever equipment or treatment steps are between, will not be unduly retarded by a suddenly induced high viscosity. A strong gel is not necessary to retard emissions in storage, and would require further treatment to remove from the storage vessel. My weak gel is substantially formed in the conduit prior to introduction to the storage vessel.

Hydrocarbon gels are commonly used for fracturing fluids, the gelling agents having been found to be excellent aids for suspending propping agents. Virtually any gelling agent useful in a hydrocarbon fracturing fluid may be used in my invention. Well known gelling agents have two basic components—a phosphorous-containing gelling agent, and a crosslinking agent including a source of polyvalent metal; by a polyvalent metal, I mean iron or aluminum.

DETAILED DESCRIPTION OF THE INVENTION

I may use any known gelling agent for hydrocarbons used in fracturing fluids.

Generally I may use any of the combinations of phosphorous-containing gelling agents and crosslinkers containing a source of polyvalent metal described in the following patents, all of which are incorporated herein specifically in their entirety:

• • Monroe U.S. Pat. No. 3,505,374, describing gels made with a reaction product of Fe₃O₄ and an alkyl oleyl diester of orthophosphoric acid. Other diesters of phosphoric acid may be used.
  • Crawford U.S. Pat. No. 3,757,864 uses aluminum salts of alkyl aliphatic orthophosphate diesters as friction reducers in flowing hydrocarbons.
  • Griffin, in U.S. Pat. No. 4,153,649, lists, in just a few lines of column 1, eighteen US patents said to describe organic phosphoric acid esters used to thicken organic liquids, and summarizes his invention in claim 1 as an organic phosphate ester composition having as a property the ability to increase the viscosity of kerosene when admixed in kerosene with sodium aluminate, said composition being prepared by the process which comprises the reaction of: [A] a pentavalent phosphorus compound selected from the group consisting of P₂O₅ and a mixture of P₂O₅ with polyphosphoric acid; [B]. a hydroxy ether of the formula ROR₁OH wherein R is a C₁ to C₆ alkyl group, R₁ is a C₂ or C₃ alkylene group and the total carbon atoms of R and R₁ range from 3 to about 8; and [C]. when the total carbon atoms of R and R₁ and is 3 or 4, a long chain substantially unsubstituted monohydric aliphatic alcohol containing at least 5 carbon atoms, but when the total carbon atoms of R and R₁ is 5 to 8, an alcohol selected from the group consisting of a long chain substantially unsubstituted monohydric aliphatic alcohol containing at least 5 carbon atoms, a short chain substantially unsubstituted monohydric aliphatic alcohol containing from 1 to 4 carbon atoms and a mixture of said alcohols, the individual mole ratios of the hydroxy ether, the long chain alcohol and the short chain alcohol to total P₂O₅ being within the ranges of 0.4:1 to 4.5:1; 0:1 to 4.0:1 and 0:1 to 5.0:1 respectively, said reaction being conducted at temperature ranging from about 70.degree. to about 90.degree. C. for a period of time of from about 1.5 to about 6 hours, and said pentavalent phosphorus compound, hydroxy ether, and alcohol or alcohols being provided in molar ratios and admixed in a sequence effective to provide a reaction product suitable for use in increasing the viscosity of kerosene. See also Griffin's U.S. Pat. Nos. 4,174,2283 and 4,152,289 disclosing additional aluminum salts of phosphate esters useful for gelling fracturing fluids.

In U.S. Pat. No. 4,316,810; Burnham uses the term “pumpable” as desirable for gelled fracturing fluids. He describes a class of aluminum oxaalkyl phosphates useful for the purpose.

As indicated in Smith & Persinski U.S. Pat. No. 5,571,315 and related patents, a common orthophosphate diester may be expresses as HPO₄RR′ where R is a straight or branched chain alkyl, aryl, alkoxy, or alkaryl group having about 6 to about 18 carbon atoms and R′ is hydrogen or an aryl, alkaryl, alkoxy, or alkyl group having up to about 18 carbon atoms. These phosphates are combined with ferric aluminum citrate to make gels in hydrocarbon based fracturing fluids.

More complicated phosphorous-containing gelling agents are described by Jones et al in U.S. Pat. No. 5,990,053 and U.S. Pat. No. 6,147,034. Generally, they are two-component systems, one providing a phosphorous-containing gelling agent and the other providing a polyvalent metal, typically aluminum or iron. But see also Taylor et al U.S. Pat. No. 7,534,745, who utilize as the phosphorous-containing gelling agent various organophosphonic acid esters and organophosphinic acid esters, again together with a polyvalent metal.

For my purposes, while any orthophosphate diester of the formula HPO₄RR′ where R is a straight or branched chain alkyl, aryl, alkoxy, or alkaryl group having about 6 to about 18 carbon atoms and R′ is hydrogen or an aryl, alkaryl, alkoxy, or alkyl group having up to about 18 carbon atoms may be used as the phosphorous-containing material, I can use a product of the reaction of orthophosphoric acid (PO₄) with an excess of a mixture of C₂ to C₆ alcohols to maximize the formation of diesters.

For the crosslinker, while any known aluminum crosslinker may be used, such as sodium aluminate or polyaluminum chloride, any of the iron crosslinkers mentioned in the above patents or used commercially in formation fracturing may be applied. For example, I may use an iron solution such as ferric sulfate dispersed with a mixture of imidazolines, amides and alkanolamides derived from primarily vegetable oils and dimethylaminopropylamine and diethanolamine. Vegetable oils include but are not limited to, coconut, palm kernel, palm, soya, safflower, sunflower, linseed, tall oil, rapeseed(high and low euric), and blown versions of the above, or oxidized oil versions. Other non vegetable oils, as tallow of swine, sheep(including lanolin), and beef or other mammals, as well as aquatic species of fish, mammals, encompassing many water living species.

The crosslinking composition may contain a coconut(food grade) diethanolamide. The properties of this well known emulsifier in the cosmetic and detergent-market is also used in the oilfield, typically having a TAV of about 137 from diethanolamine, as the amine equivalent weight of the amide is infinity. Stabilizers for the crosslinking composition can be cellosolves, glycerin and/or ethanols.

If the storage vessel is discharged into a sales line, transmission line, or other pipeline of some length, the user may wish to break the gel just prior to beginning discharge in order not to unnecessarily consume energy in pumping because of the viscosity of the gel, even though it is a weak gel. If the storage vessel is discharged into a truck, it may be more efficient to wait until the truck arrives at its destination; the benefits of high gravity preservation will thereby be obtained while the truck holds the weakly gelled hydrocarbons. The gel can be broken in either case by adding a small amount of aminoalcohols, and especially in the form of hexahydro triazines, aminoalcohol(reactions of glycidyl ethers and secondary amines). Addition of the gel breaker can be made either to the holding vessel or truck or directly to a pipe or other conduit. Addition can be “batch” or substantially continuous if the material is flowing, and may be coordinated with a stabilizer or other system where light ends are deliberately separated.

While viscosity is objectively measurable and useful in evaluating my gels, it should be observed that our invention is not simply a matter of increasing the viscosity of the stored hydrocarbons, since it is normally desirable to break the gel on termination of storage. In other words, I do not use polymeric viscosifiers that cannot be readily broken down to restore the original viscosity of the hydrocarbons. Moreover, crosslinked gels are more efficient at suppressing emissions than are linear polymers because they inhibit the formation of bubbles below the surface of the stored hydrocarbons, while linear polymers may only temporarily divert the ascent of small bubbles to the surface. A crosslinked network on or near the liquid surface also physically alters the phase interface, resulting in vapor pressure effects favorable to retention of the lighter components of the stored material. My gels containing butanes, pentanes, and other C5s to C8s exhibit Reid Vapor pressure of <2 psi, while ungelled hydrocarbon liquids and vapors have Reid vapor pressures of 3 to 8 psi or even higher. My method will frequently provide a Reid vapor pressure is a hydrocarbon storage vessel at least two Reid vapor pressure units lower than it would be without my invention.

My invention includes inhibiting volatilization of light hydrocarbons from a liquid mixture of hydrocarbons in a storage vessel comprising, (1) prior to placing said liquid mixture of hydrocarbons in said storage vessel, adding to said liquid mixture (a) a phosphorous-containing gel former and (b) a source of polyvalent metal crosslinking agent in an amount effective to form a pumpable gel comprising said liquid mixture of hydrocarbons, and (b) pumping said pumpable gel into said storage vessel.

My invention also includes a method of storing and transporting newly produced high gravity oil comprising (a) converting said high gravity oil to a weak gel, (b) placing said weak gel in a storage vessel, (c) storing said weal gel in said storage vessel, (d) breaking said weak gel to render said high gravity oil substantially free of said weak gel, and (e) transporting said high gravity oil to a new location.

In another aspect, my invention includes a method of storing newly produced high gravity oil to inhibit a reduction in its high gravity by vapor loss comprising (a) adding to said newly produced high gravity oil 0.001 to 0.02 parts by volume phosphate ester of C₂-C₆ alcohol per cubic meter of high gravity oil, (2) adding to said newly produced high gravity oil containing said phosphate ester 0.001 to 0.02 parts by volume of a crosslinker for said phosphate, thereby forming a pumpable gel, and (c) introducing said newly produced high gravity oil in the form of said pumpable gel to a storage vessel.

Claims

1. Method of inhibiting volatilization of light hydrocarbons from a liquid mixture of hydrocarbons in a storage vessel comprising, (1) prior to placing said liquid mixture of hydrocarbons in said storage vessel, adding to said liquid mixture (a) a phosphorous-containing gel former and (b) a source of polyvalent metal crosslinking agent in an amount effective to form a pumpable gel comprising said liquid mixture of hydrocarbons, and (b) pumping said pumpable gel into said storage vessel.

2. Method of claim 1 wherein said liquid mixture of hydrocarbons is a newly produced mixture of hydrocarbons from a producing oil well.

3. Method of claim 1 wherein said liquid mixture of hydrocarbons is a newly produced mixture of hydrocarbons from a producing gas well.

4. Method of claim 1 wherein said pumpable gel has a Reid vapor pressure in said storage vessel at lest two pounds per square inch lower than said liquid mixture of hydrocarbons would have had without said gel former and said crosslinking agent.

5. Method of claim 1 wherein said source of multivalent metal crosslinking agent comprises a source of aluminum.

6. Method of claim 3 wherein said mixture of hydrocarbons from a producing gas well comprises condensates from produced gas.

7. Method of storing and transporting newly produced high gravity oil comprising (a) converting said high gravity oil to a weak gel, (b) placing said weak gel in a storage vessel, (c) storing said weal gel in said storage vessel, (d) breaking said weak gel to render said high gravity oil substantially free of said weak gel, and (e) transporting said high gravity oil to a new location.

8. Method of claim 7 wherein said transporting in step (e) is conducted in a pipeline.

9. Method of claim 7 wherein said weak gel stored in step (c) has a Reid vapor pressure no greater than 2 psi.

10. Method of claim 7 wherein said weak gel is broken in step (d) by adding at least one aminoalcohol in an amount effective to break said weak gel.

11. Method of storing newly produced high gravity oil to inhibit a reduction in its high gravity by vapor loss comprising (a) adding to said newly produced high gravity oil 0.001 to 0.02 parts by volume phosphate ester of C2-C6 alcohol per cubic meter of high gravity oil, (2) adding to said newly produced high gravity oil containing said phosphate ester 0.001 to 0.02 parts by volume of a crosslinker for said phosphate, thereby forming a pumpable gel, and (c) introducing said newly produced high gravity oil in the form of said pumpable gel to a storage vessel.

12. Method of claim 11 wherein said newly produced high gravity oil has a Reid vapor pressure in said storage vessel in step (c) no greater than 2 pounds per square inch.

13. Method of claim 11 wherein said high gravity oil has an API gravity of 33° or higher.

14. Method of claim 11 wherein said high gravity oil is a condensate from natural gas.

15. Method of claim 11 wherein said newly produced high gravity oil flows substantially continuously from a producing well to said storage vessel and the additions of steps (a) and (b) are made into said substantially continuously flowing high gravity oil.

16. Method of claim 15 wherein the adding of phosphate ester in step (a) is conducted by adding said phosphate ester to said newly produced high gravity oil as said oil flows from said producing well to said storage vessel.

17. Method of claim 16 wherein said adding of said crosslinker of step (b) is conducted after said phosphate is added in step (a) and before said oil reaches said vessel in step (c).

18. Method of claim 11 wherein said phosphate ester is predominantly a diester.

19. Method of claim 11 wherein said crosslinker contains iron.

20. Method of claim 11 wherein said crosslinker includes a nitrogen-containing compound selected from amines, amides, and imidazlines, and an oil selected from animal and vegetable oils.