Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1998-12-08
2001-07-03
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S905000
Reexamination Certificate
active
06255256
ABSTRACT:
BACKGROUND
The present invention relates to wellbore fluids (especially, synthetic fluid-based drilling fluids) and systems and processes for using them in a subterranean formation in oil and gas recovery operations.
While drilling fluids employing synthetic fluids (such as polyalphaolefin- and ester-based drilling fluids) as the base fluid are capable of achieving 96 hour LC
50
Mysid shrimp (
Mysidopsis bahia
) bioassay test results greater than 100,000 ppm, their commercial use has been severely restricted because of the high cost of the synthetic fluids.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a drilling fluid which employs an inexpensive, non-toxic synthetic fluid as the base fluid. The present invention satisfies this need by providing a drilling fluid comprising (a) at least one drilling fluid additive (e.g., an emulsifier, a viscosifier, a weighting agent, and an oil-wetting agent) and (b) an inexpensive, non-toxic base fluid. In one embodiment of the invention, the base fluid is a synthetic fluid having a pour point greater than about −30° C. (−22° F.) and comprising (i) at least about 95 weight percent hydrocarbons containing 11 or more carbon atoms, (ii) greater than 5 weight percent hydrocarbons containing 18 or more carbon atoms, (iii) at least about 50 weight percent isoparaffins, (iv) at least about 90 weight percent total paraffins, (v) at least 2 hydrocarbons containing a consecutive number of carbon atoms, (vi) less than about 1 weight percent naphthenics, and (vii) less than about 0.1 volume percent aromatics. (This synthetic fluid is referred to hereinafter as the “isoparaffin synthetic fluid.”)
In another embodiment, the synthetic fluid comprises (1) at least about 95 weight percent hydrocarbons containing 10 or more carbon atoms and (2) at least about 90 weight percent n-paraffins. (This synthetic fluid is referred to hereinafter as the “n-paraffin synthetic fluid.”) The n-paraffins usually also contain (i) less than about 10 weight percent naphthenics and (ii) less than about 0.1 volume percent aromatics.
Typically, both the isoparaffin and n-paraffin synthetic fluids contain (i) less than about 1 weight percent sulfur, (ii) less than about 1 weight percent nitrogen, and (iii) less than about 1 weight percent oxygenated compounds.
The cost of the synthetic fluids employed in the present invention is comparable to that of diesel because the synthetic fluids are made by reacting inexpensive raw materials (e.g., H
2
and CO) on a massive scale designed to supply synthetic substitutes for gasoil and/or kerosene produced at conventional oil refineries. In contrast, polyalphaolefins and esters are made by polymerizing or reacting expensive raw materials on a small or moderate scale.
Because prior toxicity studies have shown that aromatics, sulfur, nitrogen, and oxygenated compounds can be toxic, the low or substantially non-existent concentrations of these materials in the synthetic fluids used in the present invention is very desirable. In addition, the fluids employed in the present invention which are in fact made synthetically are also desirable in view of anticipated environmental regulations which may restrict the off-shore discharge of non-aqueous-base drilling fluids to those drilling fluids using a synthetically produced base fluid.
A drilling system and a method for drilling a borehole are also provided by the invention. The drilling system comprises (a) at least on& subterranean formation, (b) a borehole penetrating a portion of at least one of the subterranean formations, (c) a drill bit suspended in the borehole, and (d) the above drilling fluid located in the borehole and proximate the drill bit. The drilling method comprises the steps of (a) rotating a drill bit at the bottom of the borehole and (b) introducing the aforesaid drilling fluid into the borehole (i) to pick up drill cuttings and (ii) to carry at least a portion of the drill cuttings out of the borehole.
DETAILED DESCRIPTION OF THE INVENTION
At least 95 weight percent of the isoparaffin synthetic drilling fluid is commonly composed of compounds containing 11 or more, and more commonly 12 or more, carbon atoms. Also, the isoparaffin synthetic fluid consists of greater than 5, typically greater than 10, more typically greater than 15, even more typically greater than 20, and most typically greater than 25, weight percent compounds containing more than 17 carbon atoms. In fact, compounds containing 18 or more carbon atoms can constitute about 30, 35, 40, 45, or even 50 or more weight percent of the isoparaffin synthetic fluid. In addition, the isoparaffin synthetic fluid can contain isoparaffin, naphthenic, aromatic, sulfur, nitrogen, oxygenate, and total paraffin compounds in concentrations independently set forth in the following Table I.
TABLE I
Isoparaffin Synthetic Fluid Composition
Iso-
Total
Normal
paraffin
a
,
Naphthenic
b
,
Aromatic
c
,
Sulfur
d
,
Nitrogen
e
,
Oxygenate
f
,
Paraffin
g
,
Paraffin
h
,
wt %
wt %
v %
wt %
wt %
wt %
wt %
wt %
≧50
≦1
≦0.1
≦1
≦1
≦1
≧90
≧5
≧55
≦0.5
≦0.05
≦0.5
≦0.5
≦0.5
≧91
≧10
≧60
≦0.1
≦0.01
≦0.1
≦0.1
≦0.1
≧92
≧15
≦65
≦0.05
≦0.005
≦0.05
≦0.05
≦0.05
≧93
≧20
≦70
≦0.01
≦0.001
≦0.01
≦0.01
≦0.01
≧94
≧25
≦75
≦0.005
≦0.0005
≦0.005
≦0.005
≦0.005
≧95
≧30
≦80
≦0.001
≦0.0001
≦0.001
≦0.001
≦0.001
≧96
≧35
≦85
≦0.0005
—
≦0.0005
≦0.0005
≦0.0005
≧97
≧40
≦90
≦0.0001
≦0.0001
≦0.0001
≦0.0001
≧98
≦45
≦95
≧99
≦50
≧99.5
a
As determined by UMT 407-90.
b
As determined by UTM 407-90.
c
As determined by ASTM D 5186.
d
As determined by ASTM D 2622.
e
As determined by ASTM D 4629.
f
As determined by UTM 484.
g
As determined by UMT 407-90.
h
As determined by UMT 407-90.
The pour point of the isoparaffin synthetic fluid (as determined by ASTM D 97) is commonly greater than about −30° C. (−22° F.), more commonly greater than about −25° C. (−13° F.), even more commonly greater than about −20° C. (−4° F.), and most commonly greater than about −15° C. (5° F.). Usually, the pour point of the isoparaffin synthetic fluid is less than about 6° C. (43° F.), preferably less than about 3° C. (37° F.), more preferably less than about 0° C. (32° F.), and most preferably less than about −3° C. (27° F.).
The flash point of the isoparaffin synthetic fluid (as determined by the Cleveland Open Cup method) is at least about 65.6° C. (150° F.), typically at least about 71.1° C. (160° F.), more typically about 76.7° C. (170° F.), even more typically at least about 82.2° C. (180° F.), and most typically at least about 85° C. (185° F.). Usually, the flash point of the isoparaffin synthetic fluid is less than about 121.1° C. (250° F.), lore typically about 118.3° C. (245° F.) or less, even more typically about 115.6° C. (240° F.) or less, and most about 112.8° C. (235° F.) or less.
As measured by ASTM D 93, the flash point of the isoparaffin synthetic fluid is at least about 65.6° C. (150° F.), typically at least about 71.1° C. (160° F.), more typically about 76.7° C. (170° F.), even more typically at least about 82.2° C. (180° F.), and most typically at least about 85° C. (185° F.), but usually less than about 115° C. (239° F.), more typically about 110° C. (230° F.) or less, even more typically about 105° C. (221° F.) or less, and most about 100° C. (212° F.) or less.
The isoparaffin synthetic fluid frequently has an initial boiling point (as determined by
Frieman Shlomo R.
Tucker Philip
Union Oil Company of California
Wirzbicki Gregory F.
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