Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-09-14
2003-08-19
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S129000, C507S135000, C507S145000, C507S239000, C507S244000, C507S259000, C507S277000, C507S921000
Reexamination Certificate
active
06608006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved methods of drilling well bores using invertible oil external-water internal emulsion drilling fluids.
2. Description of the Prior Art
Invertible oil external-water internal emulsion drilling fluids have been utilized heretofore for drilling well bores penetrating one or more crude oil producing zones. Such emulsion drilling fluids lubricate the drill bit and reduce the overall time required for drilling well bores. The oil external-water internal emulsion drilling fluids have heretofore been stabilized with nonionic amine emulsifiers and the emulsions have a high pH which insures that the emulsifier retains a non-ionic oil wetting character during drilling.
When a well bore has reached total depth and penetrated one or more oil producing zones, the oil external-water internal emulsion drilling fluid is contacted with an acid which protonates the nonionic amine emulsifier causing it to take on a cationic charge and increase in water solubility. The resulting water soluble emulsifier has water wetting properties, and as a result, the oil and water phases in the emulsion invert whereby a water external-oil internal emulsion of lower viscosity is formed in the well bore.
The inverted low viscosity water external-oil internal emulsion water wets the producing formations which increases oil production. In addition, the water external-oil internal emulsion fluid is easier to clean up whereby subsequent operations such as cementing or stimulation can be accomplished.
The acid utilized for contacting the oil external-water internal emulsion drilling fluid and causing it to invert is generally in the form of an aqueous acid solution. In order to prevent the formation of aqueous acid solution-crude oil emulsions and crude oil sludging, the aqueous acid solutions used have heretofore contained anionic sulfonate surfactants. While the anionic sulfonate surfactants function well in preventing the formation of aqueous acid-crude oil emulsions and prevent oil sludging from taking place, it has been discovered that the anionic sulfonate surfactants react with the amine emulsifier after it is protonated by acid. The result of the reaction is that the emulsifier does not become water soluble and does not invert the oil external-water internal emulsion to a water external-oil internal emulsion. This not only prevents water wetting and faster clean up, but the aqueous acid solution utilized adds to the internal water phase of the emulsion which results in the emulsion significantly increasing in viscosity. The highly viscous oil external-water internal emulsion formed is difficult to remove and can cause damage to the crude oil producing zones penetrated by the well bore.
Thus, there are needs for improved methods of drilling well bores penetrating crude oil producing zones using invertible oil external-water internal emulsion drilling fluids whereby problems related to the non-inversion of the emulsion drilling fluids do not take place.
SUMMARY OF THE INVENTION
The present invention provides improved methods of drilling well bores using invertible oil external-water internal drilling fluids which meet the needs described above and overcome the deficiencies of the prior art. That is, in accordance with the present invention, improved methods of drilling well bores penetrating one or more crude oil producing zones using an invertible oil external-water internal emulsion drilling fluid stabilized with a nonionic amine emulsifier and then inverting the drilling fluid to a water external-oil internal emulsion are provided. In accordance with the methods, a well bore is drilled using an oil external-water internal emulsion drilling fluid. An aqueous acid solution comprised of water, an acid, an anionic sulfonate surfactant for preventing the formation of aqueous acid solution-crude oil emulsions and crude oil sludging and a chemical for preventing the anionic sulfonate surfactant from reacting with the nonionic emulsifier is prepared. The oil external-water internal emulsion drilling fluid is next contacted with the aqueous acid solution to thereby invert the emulsion and the inverted water external-oil internal emulsion is removed from the well bore.
It is, therefore, a general object of the present invention to provide improved methods of drilling well bores using invertible oil external-water internal drilling fluids.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
Well bores have heretofore been drilled into one or more crude oil producing zones using invertible oil external-water internal emulsion drilling fluids stabilized with high pH nonionic emulsifiers. When the well bore reaches total depth, the oil external-water internal emulsion is contacted with an aqueous acid solution to invert the emulsion, i.e., to form a lower viscosity water external-oil internal emulsion which water wets the formation surfaces in the well bore and facilitates the clean up of the well bore.
In accordance with the present invention, the oil external-water internal emulsion drilling fluid is contacted with an aqueous acid solution comprised of water, an acid, an anionic sulfonate surfactant for preventing the formation of aqueous acid solution-crude oil emulsions and crude oil sludging and a chemical for preventing the anionic sulfonate surfactant from reacting with the nonionic emulsifier after the emulsifier is made cationic by the acid. After the drilling fluid has been inverted to a water external-oil internal emulsion, the emulsion is removed from the well bore.
The chemical for preventing a reaction between the anionic sulfonate surfactant and the cationic emulsifier is preferably selected from the group of ethoxylated rosin amines and ethoxylated alkyl amines. The term “rosin amines” is used herein to mean hydroabietylamines. The term “alkyl amine” is used herein to mean alkylamines having from about 8 to about 20 or more carbons.
The oil used for forming the invertible oil external-water internal emulsion drilling fluid includes, but is not limited to, olefins, kerosene, diesel oil, gas oil (also known as gas condensates), fuel oil and certain mixtures of crude oil. Of these, a mixture of internal olefins having in the range of from about 8 to about 24 carbon atoms is preferred. The water utilized in the emulsion can be fresh water or salt water, with calcium-containing brine being preferred. As mentioned, the emulsion is stabilized with a nonionic amine emulsifier, preferably an ethoxylated soya amine emulsifier. Other components of the emulsion generally include lime for producing a high pH, various surfactants, and weighting materials. The various components of oil external-water internal emulsion drilling fluids are well known to those skilled in the art as are the techniques for forming the emulsion drilling fluids.
As mentioned above, upon the completion of drilling a well bore with the oil external-water internal emulsion drilling fluid, the drilling fluid is contacted with an aqueous acid solution which causes it to invert to a water external-oil internal emulsion. The aqueous acid solutions utilized have heretofore included strongly anionic sulfonate surfactants for preventing the formation of aqueous acid solution-crude oil emulsions in the well bore and crude oil sludging therein. Examples of such strongly anionic sulfonate surfactants include, but are not limited to, linear or branched alkylbenzyl sulfonates, alkyl diphenyloxide disulfonates, alpha-olefin sulfonates and sulfosuccinates. While the anionic sulfonate surfactants successfully prevent the formation of aqueous acid solution-crude oil emulsions and crude oil sludging, it has been discovered that they often also prevent an oil external-water internal emulsion drilling fluid from inverting whereby the emulsion increases in viscosity making it extremely dif
Arnold Suzanne
Gardner Tommy R.
King Karen L.
Taylor Robert S.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Kent Robert A.
Tucker Philip
LandOfFree
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