Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Reexamination Certificate
1999-02-09
2001-02-27
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
C507S117000, C507S118000, C507S120000, C507S121000, C507S136000, C507S145000
Reexamination Certificate
active
06194355
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to brine-based drilling fluids used during petroleum recovery operations, and more particularly relates, in one embodiment,to using the use of aluminum chlorohydrate and alkoxylated surfactants in brine-based drilling fluids.
BACKGROUND OF THE INVENTION
Drilling fluids used in the drilling of subterranean oil and gas wells as well as other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply “muds”. The drilling fluid is expected to carry cuttings up from beneath the bit, transport them up the annulus, and allow their separation at the surface while at the same time the rotary bit is cooled and cleaned. A drilling mud is also intended to reduce friction between the drill string and the sides of the hole while maintaining the stability of uncased sections of the borehole. The drilling fluid is formulated to prevent unwanted influxes of formation fluids from permeable rocks penetrated and also often to form a thin, low permeability filter cake which temporarily seals pores, other openings and formations penetrated by the bit. The drilling fluid may also be used to collect and interpret information available from drill cuttings, cores and electrical logs. It will be appreciated that within the scope of the claimed invention herein, the term “drilling fluid” also encompasses “drill-in fluids”.
Drilling fluids are typically classified according to their base material. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water. Nonetheless, the water is the continuous phase. Oil-based muds are the opposite. Solid particles are suspended in oil and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds which are water-in-oil emulsions are also called invert emulsions. Brine-based drilling fluids, of course are a water-based mud in which the aqueous component is brine.
Polymers have been used in the past as viscosifiers in drilling fluids to carry or suspend cuttings, weighting agents and other solids in the brine-baseddrilling fluids. However, in the particularly harsh brine-based drilling fluidspresently in use, conventional polymers, such as PHPA, and other components undesirably precipitate out.
It is apparent to those selecting or using a drilling fluid for oil and/or gas exploration that an essential component of a selected fluid is that it be properly balanced to achieve all of the necessary characteristics for the specific end application. Because the drilling fluids are called upon to do a number of tasks simultaneously, this desirable balance is not always easy to achieve.
It would be desirable if compositions and methods could be devised to aid and improve the ability of drilling fluids to simultaneously accomplish these tasks.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide methods to give good viscoelasticity and suspension characteristics to harsh brine-based drilling fluids.
It is another object of the present invention to provide stable, viscoelastic brine-based drilling fluids.
Still another object of the invention is to provide a composition and method which give viscoelastic brine-based drilling fluids having the necessary gel strength for carrying solids.
In carrying out these and other objects of the invention, there is provided, in one form, a drilling fluid having from about 0.1 to 15 volume % of aluminum chlorohydrate as a viscosifying agent, from about 0.1 to 6 volume % of an alkoxylated surfactant, from about 0.1 to 6 lb/bbl (0.286-17.2 g/l) of an amphoteric polymer encapsulant, and a brine base fluid making up the balance, where the proportions are based on the brine base fluid.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a method of improving viscoelastic properties of a brine-based drilling fluid (which also includes drill-in fluids) by incorporating an alkoxylated surfactant and aluminum chlorohydrate. Incorporating both additives yields synergistic benefits in imparting a good gel structure necessary for solids suspension, such as bridging agents and/or weighting agents. As stand-alone additives, alkoxylated surfactants provide viscoelasticity to high density brines, particularly those based on calcium chloride and/or calcium bromide. However, gel strengths of these fluids tend to be low and flat. Aluminum chlorohydrate has been found to provide high gel strengths in brines; however, high dosage treatments (greater than about 5% by volume) are needed to produce sufficient gels for solids suspension. Also, the gels using aluminum chlorohydrate only tend to be stiff, thus requiring excessive pump energy to induce fluid flow. Another disadvantage when using excessive aluminum chlorohydrate is possible formation damage.
This invention has found that the use of both additives exhibits a synergy for yielding desirable flow properties with the necessary gel structure for solids carrying. Less of each component is required to suspend the same amount of solids, as compared to one or the other used separately. Suggested applications for this technology are for drilling and drill-in fluids, particularly in deep-water operations.
In a preferred embodiment of the invention, a brine-based drilling fluid having good gel strength and suspension characteristics for carrying solid particles, such as bridging agents, weighting agents, cuttings, is made using a brine base fluid, aluminum chlorohydrate as a viscosifying agent, an alkoxylated surfactant, and an amphoteric polymer encapsulant, all in a effective mounts to accomplish their stated purposes. Aluminum chlorohydrate, [Al
2
(OH)
5
Cl]
x
, has not previously been known to be useful as a viscosifying agent to help suspend solids in a brine-based drilling fluid. The aluminum chlorohydrate also provides excellent shale stabilization characteristics to the brine-based drilling fluids. In one embodiment of the invention, the aluminum chlorohydrate is present in the total brine-based drilling fluid in a proportion ranging from about 0.1 to about 15 volume %; in another embodiment from about 1 to about 10 volume %; preferably from about 2 to about 8 volume %; and most preferably from about 2.5 to about 5 volume %, all based on the brine base fluid.
The brine base fluid may be any brine, conventional or to be developed which serves as a suitable media for the various concentrate components. As a matter of convenience, the brine base fluid may be the brine available at the site used in the completion fluid, for a non-limiting example. In forming these high density brines, the salts employed include, but are not necessarily limited to calcium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium bromide, sodium bromide, potassium bromide, calcium nitrate, sodium formate, potassium formate, cesium formate and mixtures thereof. It is further anticipated that the drilling fluids of this invention are generally high density drilling fluids, which may be defined has having a density of about 8.4 to 19.4 lb/gal or more (1.01×10
3
to 2.30×10
3
kg/m
3
).
A surfactant is required to form a stable composition. Additionally, without a surfactant, so much aluminum chlorohydrate would have to be used that the fluid would be expensive, probably corrosive, and have shear thinning properties that may be acceptable, but which may not be as optimum as in the synergistic blend. Surfactants suitable for use in the present invention include, but are not necessarily limited to those having a hydrophilic/lipophilic balance of between about 12-19, preferably a HLB of between about 15-19. Such surfactants include, but are not necessarily limited to, ethoxylated fatty alcohols, such as oleyl alcohol ethoxylate; ethoxylated vegetable oils, such as ethoxylated castor oil; ethoxylated alcohols, such as ethoxylated isotridecyl alcohols; ethoxylated fatty
Gabrysch Allen
Jarrett Michael A.
Krause Harold R.
Potts Patricia
Welch John C.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
Tucker Philip
LandOfFree
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