CA2027504A1 - Compositions for oil-base drilling fluids - Google Patents

Abstract

IMPROVED COMPOSITIONS
FOR
OIL-BASE DRILLING FLUIDS

ABSTRACT OF THE INVENTION

An improved oil-base drilling fluid comprising a continuous oil phase and a dispersed internal phase using aqueous non-halide salt solutions is described. Prefer-ably, the non-halide salt is potassium acetate, calcium acetate, sodium proprionate or combinations thereof, however, citrate, tartrate, or gluconate salts may also be used. Emulsifiers, wetting agents, and other chemicals may be added in varying concentrations to achieve desired characteristics for the drilling fluid.
The composition has suitable rheological properties, stability, and hole cleaning abilities for use as a drilling fluid; and it is more compatible with environmentally acceptable land disposal methods than conventional oil-base drilling fluids used in land drilling applications.

Description

-` 2 ~ ~ 7 i~ O ~ MIDR:440 IMPROVED COMPOSITIONS
FOR
OIL-BASE DRILLING FLUIDS ~

,-The invention relates to an improved oil-base drilling fluid. The improved drilli~g ~l~id has the stability, rheological properties, and hole cleaning abilities required for drilling fluid applications; but it i5 less toxic than known oil-base drilling fluids and exhibits greater environmental compatibility with land disposal methods than current oil-base drilling fluids. ; More particularly, ~he improved drilling fluid incorporates novel compounds into the solution used to form the internal ~ ;
water phase. Also, the use of low aromatic content oils for the continuous oil phase in the preferred embodiment -;
further reduces the toxicity and improves the environmental compatibility of the drilling fluid.

2~5 ~ Drilling fluids or muds are an important component of petroleum exploration and production. ~hese fluids, which are made with a variety of components, are used to clean ~ -drill~bits, remove cuttings from holes, and maintain drilling pressure~. The rheological properties of a 30~ dril1ing~flu1d;~ar-~;Gr1t1cal because the fluid must exhibit ~ ;
certain~ properties to accomplish these tasks and must maintain these~properties during continued use at well conditions. `~

Drilling fluids may be either water-base or oil-base.
Typically, wa~er-base drilling fluids are used for drilling operations, but they suffer from disadvantages related to the ~nature of water as used in drilling applications.
Specifically, water migrates from the drilling fluid into -~
. , ; ., - -2- 2~750~ ~

surrounding clay or shale formations and causes disintegration or alteration of the clay or shale forma-tion. Further, the water will dissolve salts in the clay or shale formation, interfere with the flow of gas or oil through the formation, and corrode iron in the drilling equipment.

Oil-base drilling fluids, on the other hand, do not affect clay or shale formations or soluble salts in the formations, because oil is nativé to these formations.
Further, oil-base drilling fluids provide several advan-tages over water-base drilling fluids such as better lubricating qualities, higher boiling points, and lower freezing points. Because oil-base drilling fluids cost more than water-base drilling fluids, they are used in applications where they provide superior performance under particular conditions.
.
Oil-base drilling fluids typically contain some amount of water. This water may occur in concentrations less than approximately 5 percent as an emulsified contaminant in oil-base drilling fluids. In other oil-base drilling ~ `
fluids, water is intentionally added along with an effective emulsifier to produce a water-in-oil or invert emulsion. An emulsifier is necessary to prevent over thickening of the-drilling fluid which typically occurs when higher concentrations (> 5%) of water are used in oil-base~ drilling fluids. These emulsions use water as a suspending agent for various components of the drilling ~ lf1u1d, and typically contain 10 to 60 percent water.

Oil-base invert-emulsion drilling fluids include two phases: (1) A continuous phase containing oil (typically No. 2 Diesel Fuel), surfactants, and wetting agents; and (2) a dispersed internal water phase which is often a water-based solution of calcium chloride.

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The water in the internal phase of an invert emulsion drilling fluid may act just as the water in a water-based drilling fluid and migrate into surrounding clay or shale formations with negative effects on the ~ormation. This migration is primarily due to the thermodynamic properties of the water. For example, the thermodynamic activity of a pure water internal phase in a drilling fluid is higher than the thermodynamic activity of water in clay or shale formations which contain dissolved salts. Consequently, there is a tendency for the thermodynamic activities of the water in the drilling fluid and the water in the clay or shale formation to equilibrate. This occurs by the transfer of pure water into the clay or shale formation and the associated transfer of dissolved salts into the pure water of the drilling fluid. The transfer of water from the drilling fluid to the clay or shale formation may cause the formation to swell and crack.
'`~'' ' The thermodynamic tendency of the water in a drilling fluid to migrate into the surrounding formation can be measured as a vapor pressure, and is commonly referred to as the water activity. The water activity is referenced as the tendency that the solution will migrate relative to pure water under the same conditions. Solutions, especi-ally chloride solutions, are used in the internal phase inknown oil-base drilling fluids to minimize the water activity of the internal phase. Solutions are used instead of pure water to decrease the migration of water from the drilling fluid into surrounding formations because the 30 ldissolved salt decreases the water activity. Chloride salts such as calcium chloride are often used in known drilling fluids as the dissolved salt in the internal phase for the purpose of controlling the water activity of the internal phase.

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It should be appreciated that by accurately measuri~g the water activity of the water in surrou~ding ~ormations, the water activity of the internal phase in an invert emulsion drilling fluid may be adjusted by the proper addition of salt to match the water activity in the surrounding formation. This prevents the transfer of water between the drilling fluid and the surrounding formation, and avoids adverse effects on the surrounding formation.
Generally, sufficient calcium chloride is added to balance the lowest water activity of surrounding formations and the emulsified water of the drilling fluid.

Unfortunately, calcium chloride solutions and other halide salt solutions are toxic to life, especially plant d 15 life. Problems associated with environmental contamination and oil-base drilling fluid disposal are well documented.
(See, for example, George R. Gray and H.C.H. Darley, Composition and Properties of Oil Well Drillina Fluids, Fourth Edition, Gulf Publishing Company at page 585).
Concern has been expressed by environmentalists and others with the possibility of polluting underground water supplies, damaging soil productivity and diminishing surface water quality. In a conference sponsored by the Environmental Protection Agency in May of 1975 in Houston, Texas, the effects of both techniques and chemicals used in drilIing fluids and their impact on the environment were ~ discussed. The outlook for landfill disposal of oil-base ;~ drilling fluids was not good. Such muds were thought to be toxic and the effects long-term. The toxic effect of oil-base muds on the soil was thought to be inherent in the chemicals used. Thus, known oil-base drilling fluids using a calcium chloride internal phase have adverse environmental consequences when used for land drilling operations.
Preferably, land farming could be used to dispose of both drilling fluida and the cuttings produced at a land The OCR engine was not able to convert this image.

` -6- 2027~01 The invention relates to an improved oil-base drilling fluid having enhanced environmental compatibility with land disposal methods and comprising a continuous oil phase and a dispersed internal water phase which uses non-halide compounds to control the water activity of the drilling fluid and minimize the environmental impact of the drilling fluid. These salts of organic acids have been identified as being particularly useful. These compounds are calcium acetate (Ca(OAc)2), potassium acetate (KOAc), and sodium proprionate (NaOaCaH3). Each compound has specific advantages, and mixtures of these salts are normally recommended. Additionally, a low aromatic content oil may be used for the continuous oil phase to further minimize the environmental impact of the drilling fluid. An effective amount of an emulsifying agent is included to ensure proper dispersal of the internal water phase in the continuous oil phase. Surfactants, wetting agents, and other additives may also be included to vary the fluid's rheology, HTHP (high temperature, high pressure) fluid loss, and other properties.

The surprising results of applicant's unique oil-base drilling fluid have resurrected the possibility that oil-base drilling fluids might be environmentally compatible with disposal in landfills and by land farming. The compositions of the invention have lower toxicities than known oil-base drilling fluids due to the use Or acetates, proprionates or other non-halide salts to control the water activity of the internal phase. The toxicity of the Icomposition can be further reduced by using a low aromatic content oil for the continuous oil phase. The use of the compositions of the invention enables the drilling fluid and cuttings from a well to be disposed of in an acceptable environmental manner.
Essentially, the compositions of the invention comprise an invert-emulsion, oil-base, drilling fluid made 2 0 ~7 J 0 ~

from a continuous oil phase and a dispersed internal phase that can be used for land drilling operations in a manner environmentally compatible with land disposal methods. For purposes of this application, the phrase "environmentally compatible with land disposal methods" will be understood to refer to the chemical characteristics of applicant's unique muds that permit their disposal in landfills and land farms without long-term toxicity to soil productivity or similar adverse characteristics.
' ''' The dispersed internal phase is made with novel solutions that have reduced toxicity as compared to known internal phases in drilling fluids. The preferred method for the novel solution formulation is to use a mixture of calcium acetate with either sodium proprionate or potassium acetate. The calcium acetate lends emulsion stability and is used from 4-10% by weight. The other salts are used for further adjustment of the internal phase activity. The potassium acetate concentration in the solution can range from 3% by weight to the saturation concentration of potassium acetate. A potassium acetate solution is saturated at 69 wt.% under normal conditions. The sodium proprionate is used for concentrations of up to 28% by wt.
Although sodium proprionate is not as soluble as potassium acetate, and solutions saturate approximately 28% by weight, its use is preferred in solutions needing an activity from 1.00 to 0.58 because of better environmental compatibility and better economics. When activities of below 0.58 are needed or when an inhibitive X~ ion would !qive added stability, KOAc is the salt used with Ca(OAc)2 in the internal phase. These salts serve as a substitute for the calcium chloride in known solutions used for invert emulsions. Other acetate salts can ~e used such as sodium acetate. Further, other compounds such as the citrate, tartrate, gluconate, and proprionate salts of alkali metals may be used.
'' -8- 20~7J~-~

Preferably, a low aromatic content mineral oil, such as Exxon~s Escaid 90 product ( < 0.5 wt.% aromatic), is used for the continuous oil phase. Other low aromatic oils can also be used such as Exxon's Escaid 110, Conoco's LVT
200, and Shell~s Shellsol DMA. Generally, any low aromatic content mineral oil will improve the environmental compatibility of the drilling fluid for land disposal methods. It should be appreciated that conventional mineral and diesel oils may also be used with the compositions of the inventionf but they will not achieve as favorable environmental compatibility as is achieved with low aromatic content mineral oil. ~he oil-phase/water-phase ratio of the drilling fluid can vary from 20:1 to 1:2 by volume.
A known emulsifier is added in an effective amount to ensure the dispersal of the internal water phase in the continuous oil pha~e. For example, M-I Drilling Fluids' VersaMul can be used as an emulsifier. Other commercially available emulsifiers known in the art may also be used.

Other additives known in the art can be included as necessary to modify the characteristics of the drilling fluid. For example, the following additives may be included to achieve particular characteristics:

Additive Exam~le Emulsifying Agent VersaCoat l Wetting Agent VersaWet Wettihg Agent VersaSWA
Gelling Agent VG-69, VersaGel Viscosifying Agent VersaHRP
Viscosifying Agent Ver~aMod Weighting Agent Barite Neutralizing Agent Lime ,:

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These additives are used as necessary over a range of concentrations. Other commercially available additives can also be used to modify the rheology and other properties of the drilling fluid. The stability of the improved compositions over a wide range of formulations affords great flexibility in tailoring their properties to specific drilling applications.
,, ;

Preparation of the compositions of the invention requires some care. Particularly, the addition of the internal phase acetate solution may destabilize the invert emulsion. This can be avoided by adding the emulsifier and other liquid agents which modify the fluid's rheology to the oil before adding the internal phase. Initially, the ;--~ ;
invert emulsion will be thinner than expected. The -r application of shear, typically two circulations through a drill bit, will cause the drilling fluid to thicken to an appropriate viscosity and stabilize.
- -'';"-''-~
Rheoloqv and Stability -The fluid properties of the improved compositions have been measured for a range of formulations. See Examples 1 and 2, and Tables 1 and 2. The data indicates that the compositions have rheological properties and stabilities acceptable for use as oil-base drilling fluids. The invert emulsion formed by the oil and acetate solution i8 stable over a wide range of potassium acetate concentrations (3 -wt% to 69 wt%). Moreover, the rheology can be easily ~modified;by the addition of gelling or thickening agents -~
such as VersaMul or VG-69 to increase viscosity and lower the HTHP fluid lo~s, or the addition of a emulsifying agent such as VersaCoat to lower the viscosity. One advantage of this system is its stability in high solution concentrations.

-` -lO- 20~7~ 04 The effects of commonly encountered drilling contam-inants on the rheology and other properties of the improved composition were measured. See Example 3, Table 3. Only modest rheological changes were observed for exposure to drill solids, anhydrite (CaSO4), sodium chloride ~NaCl), and Class H wet cement in high concentrations. Thus, the improved compositions retain their desired fluid properties upon exposure to contaminants commonly encountered in drilling.
'' '' ' The rheological properties of one composition of the invention were measured as a function of exposure to cold temperatures. See Example 4, Table 4. This experiment, which represents worst case conditions due to a high water activity in the internal phase, a high concentration of barite and drill solids, and exposure to -32-F for 48 hours, indicates there was little change in the rheological properties due to cold temperatures.

Water Activity The water activity of the internal phase made with a potassium acetate solution can be varied from 1.0 (pure water) to 0.225 (saturated potassium acetate solution).
Thus the range of water activities attainable with this system is even greater than that for calcium chloride, which has an activity of 0.295 at saturation. Most calcium chloride solutions are used at a water activity near 0.75 -25 wt.% calcium chloride). This same activity can be lachieved with a potassium acetate concentration of 23% by weight. Use of sodium proprionate will restrict the range of water activity from 1.00 - 0.520, at saturation common salt effect of calcium acetate mixtures seem to give little change in overall activity or solubility when calcium acetate is 10% by wt. or less.
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Environmental Im~act .: .
Referring to Examples 1, 4, and 5, the environmental impact of the improved compositions were measured using a ~icrotox analysis. This method measures the effect of a water soluble extract from a drilling fluid composition on the emission of fluorescent light from bioluminescent marine bacteria. Results are reported as an "EC-50", or effective concentration of water soluble extract which causes a 50% reduction in light transmitted by the bacteria. The higher the EC-50, the less toxic the composition.

The toxicity of an invert emulsion drilling fluid is dependent on the oil, additives, and internal phase solution that are used as components. Oil has a signifi-cant effect on toxicity. Tests on neat oil samples show three "levels" of toxicity. In a procedure involving extraction into deionized water for two hours, EC-50's of 2.4-3.6 are observed for diesel oils, 7.3-13.9 for conven-tional mineral oils ( 4-5% aromatic), and 80.0 - 115.6 for low aromatic mineral oils (Escaid 90 and 110, ~ 0.5 wt%
aromatic). It appears that toxicity of aromatic hydrocarbons is greater than toxicity for non-aromatic hydrocarbons such as aliphatic hydrocarbons because oil solubility in water generally increases with the aromatic content of the oil. Consequently, the tendency of a high aromatic content oil to leach into a water phase whose toxicity is measured by a Microtox analysis is greater.
! ~ ' 30 The internal water phase in an invert emulsion drilling fluid can affect toxicity in two ways. First, an increase in the salt concentration of the water phase decreases toxicity by decreasing the water activity with a subsequent decrease in the water soluble toxins leached from the oil phase. Thus, an improved EC-50 i9 observed .

-12- ~0~7.~ 0!1 in a typical drilling fluid when the potassium acetate concentration is increased from 4% to 19.5% by weight.

The salt dissolved in the internal water phase also contributes to toxicity. For example, the EC-50 for a 29 wt% potassium acetate solution is twice as good as that of a 25 wt% calcium chloride solution (same water activity); that is, its toxicity is half that of the calcium-chloride solution. Generally, the use of a potassium acetate internal pXase improves the EC-50 of a drilling fluid as compared to the same drilling fluid made with a calcium chloride internal phase regardless of the oil used. see Example 5, Table 5. Thus, the compositions of the invention are a major improvement over conventional invert emulsion drilling fluids.

Additives which associate with and stabilize the oil phase appear to decrease toxicity by decreasing leeching into the aqueous phase. Likewise, additives which decrease HTHP fluid loss will decrease toxicity. However, a "saturation" effect in which no additional effect on HTHP
fluid ~loss is measured can be observed with these additives. Additional additives beyond this point may increase toxicity if the additives themselves are leeching z5 into the aqueous phase and contributing to the toxicity.

Oil retention on simulated cuttings has been measured by~ retort analy~is ~or a range of oil-phase/water-phase ratios and acetate concentrations. See Example 1, Table 1.
~ILow oill retention facilitates the disposal of these cuttings by landfill or land farm methods. Cutting oil retentions as low as 7.7 wt.% have been observed with the compoiitions of the invention. Oil-base drilling fluids ~;~ with~a high water content generally yield greatly reduced oil retention on the cuttings.
- , .,- ., -13- ~ 3 0 Examples Preparation of Samples The appropriate amount of base oil was weighed out.
The predetermined amount of liquid ingredients li.e.
VersaMul, VersaCoat, VersaWet) were then weighed into the ~ ;
oil and sheared for 10-15 minutes. Next, VersaGel was added, and the mixture was sheared for an additional 15 minutes. Lime was then adde~ and the mixture was sheared for an additional 10 minutes. The solution of the internal phase was added while stirring, and the mixture was sheared for 20 minutes at the highest possible shear rate (7000-8000 rpm). Drill solids, a mixture of 50:50 bentonite and Rev Dust, were then added, and the mixture was sheared for ; , -an additional 15 minutes. Finally, Versa~od was added, and the mixture was sheared for an additional 30 minutes. ~

Example 1 ~ ~ `
~ ~ -Twelve formulations of various compositions were ' :
prepared using the procedure described above. All samples were aged at 150'F for 16 hours. Approximately 15 ppb of lime and 50 ppb of drill solids were added to each ~
formulation. ; ~ ;

one barrel equivalent of each sample formulation was treated with 35 grams of cuttings of a size that would pass through a 12 mesh screen but be retained on a 20 mesh 0 iscreen. The fluid and cuttings were hot rolled for one hour at 150'F, and the fluid was filtered over a 40 mesh screen for 2 minutei using medium agitation. The cuttings were weighed into a retort and the oil distilled from the solid. The oil retention values were calculated from the weight difference. Likewise, a Microtox EC-50 is reported for each formulation.

-14- 20~730~ `

Rheological properties at a variety of conditions along with other fluid properties are reported. Referring to Table 1, the numbers corresponding to 600 rpm, 300 rpm, etc. represent the Fann~ rotational viscometer readings at those rpm settings. Plastic viscosity is the difference between the 600 rpm and 300 rpm readings from the Fann~
rotational viscometer. Yiêld psint is the difference between the 300 rpm reading and the plastics viscosity.
The Os, lOs, and lOm Gel represent the FannO viscometer reading at 3 rpm after 0 séconds, 10 seconds, and 10 minutes. HTHP fluid losses were corrected for area and at 175-F and 500 psi differential pressure. These rheological properties are likewise reported in Tables 2, 3, 4, and the tables of the appendix.
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-17~ 7 3 0 Example 2 Eighteen compositions using different salts in the internal phase were prepared according to the procedure described above. Each composition had a density of lo ppg and an oil-phase/water-phase ratio of 4/1. The base oil for each formulation was Escaid 90. The base formulation of each composition was:

VersaCoat3.0 ppb VersaMul5.0 ppb VersaModl.5 ppb VG-696.0 ppb Lime 15.0 ppb Drill Solids 55.0 ppb The samples were heat aged for 16 hours at 180-F.

The rheological properties, other fluid properties and Microtox EC-50 analysis for each composition are reported in Table 2. ~ - --18-202730~

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Example 3 Six sample~ were prepared with the following contam-inants: drill solids (18.6 and 37.3 ppb), anhydrite (CaSo4) (18.6 ppb), salt (NaCl) (18.6 and 55.9 ppb), and Class H wet cement (8~ by volume). Only modest ' rheological changes were observed after aging for 3 hours at 150'F. In the worst case (NaCl at 55.9 ppb), 10 second/10 minute gel strengths increased from 12/13 to 26/14 (lbs/100 ft2), HTHP (at''176'F) increased from 9.6 to 11.6 mL/30 minutes, and the electrical stability decreased form 525 to 470 volts. These results are reported in Table 3.

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, Example 4 A composition was prepared in the manner described above with the following formulation:
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Escaid 90 Oil (bbl eq) 0.667 Potassium Acetate Solution 3% at (bbl eq) 0.170 VersaMul (ppb) 3.50 versacoat (ppb) l.oo VG-69 (ppb) 6.00 VersaMod (ppb) 2.00 Lime (ppb) 15.00 Drill Solids (ppb) 50.00 M-I Barrite (ppb) 122.11 Final Mud Weight 10.47 ppg Solids (% vol) LGS: 8.13 HGS: 8.13 -a ~ . ~
The composition was aged at 150-F for 42 hours, and then tested at progressively lower temperatures, until the rheological properties were not measurable. The ~ -fluid was then warmed to 115-F and measured again. The :~
: results of this experiment are reported in Table 4. ....
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-26- 20~7~ o~

Exam~le 5 Ten different fluids were prepared according to the ~
procedure described above using four different mineral -oils and a diesel oil for the continuous phase and two solutions made with different salts for the internal phase: a 25 wt% calcium chloride (CaCl2~ solution and a 29 wt% potassium acetate (K02C2H5~ solution. The concentra-tion of additives, the oil/water ratio, and the mud weight were all held constant. Thé component concentrations of the water soluble fraction were determined by atomic absorption. The results of these studies are reported in Table 5. ;~

The formulations in the examples described above and in the Appendix are illustrative of the invention, and other variations and modifications may be made without departing from the scope of the invention. The details described above are to be interpreted as explanatory and -not in a limiting sense.

Tables 6 through 13 are attached as an Appendix.
They report the results on further experiments determining the rheological and other properties of ~-various formulations and under various-conditions. - -~ ' ~
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-28- 20~7~ 0~ :

Example 6 - -, ''' .' '' ,' Seed Germination Tests Drilling Fluid Preparation This part of the project was undertaken to assess ~ -~
the environmental impact of drilling fluid waste on plant ' germination and growth beyond the 2-leaf stage of development.

Five different drilling fluids were prepared on a ~
18.50 barrel equivalent scale. The fluid were designed ~ - -to have similar components and properties using five different internal phases.

The com~o~tion of fluids are listed below.
Oil u~ed - Esca~d 110 from Exxon USA
Denslty ~i 0.7939 g/ml O/W Ratio 70:30 Fluid i~ 1 2 3 4 5 ~alt uaed CaC12 KOAc Ca(OAc)2 Na(OPr) XlCa-OAc -conc (wt%) 23~ 23% 23~ 23~ 8~/15~ ~ `
den~$ty 1.2242 1.1370 1.1186 1.0999 1.1299 , volume exp. 1.0851 1.1422 1.1257 1.1808 1.1495 All starting formatlon~ contained: -VERSACOAT 2.0 ppb VERSAMUL 2.5 ppb Lime 4.0 ppb VG-69 3.5 ppb ~-VERSAMOD 0.75 ppb I Drill Solids 30.00 ppb 50:50 mixture of M-I
GEL/Re~ Dust ~:; '' ' ' ' ;'' Oil(g) 3,152.0 3,092,3 3,092.4 3,035.4 3,070.0 Bar~g) 1,662.7 1,848.4 1,949.4 1,912.6 1,853.6 Brine(ml) 1,847.5 1,907.9 1,879.4 1,934.9 1,905.3 . -; , . . .

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2~7~04 Mud No. 1 2 3 4 5 CaC12 = Calcium chloride KOAc = Pota~ium acetate Ca(OAc)2 = Calcium Acetate NaOPr = Sodium proprionate K/Ca-OAc = Mixture of pota~ium & calcium acetate The drilling fluids were prepared by weighing the mineral oil out into 2 gallon buckets. Next, the VERSAMUL AND
VERSACOAT were weighed into the bucket and the solution stirred on a dispersator mixer. After a homogenous solution was obtained, the correct amount of VG-69 and lime were weighed and added to the stirring solution. The slurry was allowed to mix for 30 minutes. At this point the previously prepared internal phase was measured out by volume and added to the fluid. The dispersator speed was increased to a `
.20 maximum level which still kept the components in the bucket.
The drilling fluid was stirred 30 additional minutes, then the M-I BAR and drill solids were weighed and added. Finally, the VERSAMOD was added by dropper and measured by weight loss of the dropper/container unit. The fluid was stirred another 30 ~- 25 minutes before being sealed and stored for treatment by the -flow loop -To better simulate a drilling fluid that had been ~ -c~irculated on a well, each fluid was then sheared on a flow loop. The flow is passed from approximatley 6 liter reservoir through a pump and into steel pipe approximately 3/8-1/2" id.
Th-~fluid is heated in the pipe and then passed through a shear value at about 275-F under approximately 800 psi. It -then passed through a heat exchanger and cooling coils before being returned to the reservoir. Samples were collected every - 45 minutes (2-1/2 circulations and P~ and rheology measured. ~t~ ;~
Ad~us~tments were made as needed to give a fluid having a 4-8 #flOo ft2 yield point, at least a ~5 lb/100 ft2 yield point, ;
at least a t5 lb/100 ft2 10 minute] gel and a P~ of 0.5 -0.9 mL H2SO~(O.lN). $he additional additives are shown: -~

:,-:

-30~ 7~ 0 1 '- :','" ' Mud # 1 2 3 4 5 tppb) VG-69 1.5 3.0 0 3.25 0 - -~ppb) Llrn~ 0 2.75 0 1.5 0 ,, ,,, ~
Compulation of the above data gives the final formulations listed below. ---All fluids have a 70:30 oil:water ratio. Fluid properties were also taken and are below.

Mud No. 1 2 3 4 5 Brine salt C~Clz K02CC113 C~(o2ccH3)2 NA2CCZ~5 X~C~ 2CC~3)11~2Y1 r- y - 1.3n % Wt salt 23% 23% 23% 23% 23%
Escaid 110 (bbl eq) 0.613 0.599 0.602 0.590 0.597 VERSACOAT (ppb)2.00 2.00 2.00 2.00 2.00 :: !' ,' ' VERSAMUL (ppb)2.50 2.S0 2.50 2.50 2.50 VG-69 (ppb) 5.00 6.50 3.50 6.75 3.50 --::-Lime (ppb) 4.00 6.75 4.00 5.50 4.00 Brine (bbl eq)0.285 0.293 0.290 0.2g9 0.294 Drill solids (ppb) 30.00 30.0030.00 30.00 30.00 ~ar (ppb) 122.2 116.7105.4 103.4 100.2 : :~
VERSAMOD (ppb)0.75 0.750.75 0.75 0.75 Properties~
Mud Weight 9.90 9.889.80 9.80 9.93 : "
600 RPM 28 25 27 35 29 ~ :-300 RPM 17 15 16 20 17 ~-100 RPM 9 8 8 12 10 :
6 RP~ 5 5 5 7 5 3 RPM 4 4 4 6 5 :
PV (cps) 11 10 11 15 12 YP (lbs/100 ft2) 6 5 5 5 5 10"/10" gel 5/6 ~/8 5/7 7/10 5/8 - :
10 /30 gel 8/l0 11/11 11/12 11/11 11/11 ES (volts) 4i5 361 438 345 420 i :
Pom (mL H2SO;) 0.45 0.60 0.s5 0.60 0.55 Cl (mg/L) 53,500 100 100 100 100 HTHP (300/500)11.4 20.8 12.8 22.8 24.4 ~::
~ ~o in filtr~t- -- (3.2~ __ (2.3) __ :' :

~: ' -31- 2~7S04 Germination Tests The seed tested was a sorghum grain. The procedure used was approved by the UsAOSA. Each drilling fluid was run in quadruplicate. A sample of 1000 g of soil (obtained from Texas ~ept. Agriculture) was placed in a plastic container. Then the drilling fluid was trickled over the top of soil in 3~ by weight (30 g). It was then spooned into the soil and shaken until a homogenous mixture was obtained. At this point the samples were turned over to the Seed Lab of the Texas Department of Agriculture. They then hand planted 100 seeds in each box. Thus 400 seeds were tested for each run. The containers were watered and the open containers were placed into a greenhouse. They were watered twice daily, once in the morning and once at night. The test was run for 28 total days. Results are shown below.

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Claims (20)

1. An improved oil-base drilling fluid, said drilling fluid being environmentally compatible with land disposal methods, comprising:
a continuous oil phase, an internal phase, said internal phase comprising a solution of a non-halide compound dissolved in water, and an emulsifier, said emulsifier being present in an amount effective to disperse said internal phase in said continuous phase.

2. The improved oil-base drilling fluid of claim 1 in which the non-halide compound dissolves in water and is selected from the group consisting of: acetates, proprionates, tartrates, gluconates, citrates and combinations or salts thereof.

3. The improved oil-base drilling fluid of claim 1 in which the non-halide compound is selected from the group consisting of: potassium acetate, calcium acetate, sodium proprionate or combinations thereof.

4. The improved oil-base drilling fluid of claim 3 in which said non-halide compounds are present in said internal phase at a concentration of from about 3.0 percent by weight to saturation.

5. The improved oil-base drilling fluid of claim 1 in which said oil-base continuous phase comprises less than about 1.0 percent by weight of aromatic hydrocarbons.

6 The improved oil-base drilling fluid of claim 1 wherein said oil-base continuous phase is present in a volume ratio to said internal phase of from about 1:2 to 20:1.

7. The improved oil-base drilling fluid of claim 1 in which said oil-base continuous phase comprises in major portion a petroleum oil selected from the group consisting of: diesel oil, mineral oil, kerosene, fuel oil, white oil, crude oil, and combinations thereof.

8. The improved oil-base drilling fluid of claim 1 in which the emulsifier is selected from the group consisting of: alkali and alkaline earth metal salts of fatty acids, rosin acids, tall oil acids, alkyl aromatic sulfonates, oxidized tall oils, carboxylated 2-alkyl imidazolines, imadazole salts, alkanolamides, alkyl amidoamines and combinations thereof.

9. An improved oil-base drilling fluid, said drilling fluid being environmentally compatible with land disposal methods, comprising:

an oil-base continuous phase comprising in major portion a petroleum oil selected from the group consisting of: diesel oil, mineral oil, kerosene, fuel oil, white oil, crude oil and combinations thereof;

a water-base internal phase, said internal phase comprising a solution of a non-halide compound dissolved in water, said non-halide compound being selected from the group consisting of:
acetates, proprionates, tartrates, gluconates, citrates and combinations or salts thereof; and an emulsifier, said emulsifier being present in an amount effective to disperse said internal phase in said continuous phase.

10. The improved oil-base drilling fluid of claim 9 in which the non-halide compound is selected from the group consisting of: potassium acetate, calcium acetate, sodium proprionate or combinations thereof.

11. The improved oil-base drilling fluid of claim 10 in which said non-halide compounds are present in the internal phase at a concentration ranging from about 3.0 percent by weight to saturation.

12. The improved oil-base drilling fluid of claim 9 in which the oil-base continuous phase comprises less than about 1.0 percent by weight of aromatic hydrocarbons.

13. The improved oil-base drilling fluid of claim 9 in which the oil-base continuous phase is present in a volume ratio to said internal phase of from 1:2 to 20:1.

14. The improved oil-base drilling fluid of claim 9 in which the emulsifier is selected from the group consisting of: alkali and alkaline earth metal salts of fatty acids, rosin acids, tall oil acids, alkyl aromatic sulfonates, oxidized tall oils, carboxylated 2-alkyl imidazolines, imadazole salts alkanolamides, alkyl amidoamines and combinations thereof.

15. An improved oil-base-drilling fluid, said drilling fluid being environmentally compatible with land disposal, comprising:

an oil-base continuous phase, said oil-base continuous phase comprising in major portion a petroleum oil selected from the group consisting of: diesel oil, mineral oil, kerosene, fuel oil, white oil, crude oil and combinations thereof;

an internal phase dispersed in the continuous phase, said internal phase comprising an aqueous solution of a non-halide compound selected from the group consisting of: potassium acetate, calcium acetate, sodium proprionate and combina-tions thereof, said non-halide compound being present in said internal phase at a concentration of from 3.0 percent to saturation, said oil-base continuous phase being present in a volume ratio of from 1:2 to 20:1 to said internal phase; and an emulsifier, the emulsifier being present in an amount effective to disperse the internal phase in the continuous phase, said emulsifier being selected from the group consisting of alkali and alkaline earth metal salts of fatty acids, rosin acids, tall oil acids, alkyl aromatic sulfonates, oxidized tall oils, carboxylated 2-alkyl imidazolines, imadazole salts alkanolamides, alkyl amidoamines and combinations thereof.

16. In a process for drilling a well through a subterranean formation comprising circulating in said well an oil-based liquid drilling fluid, the improvement comprising:

using as said drilling fluid an internal phase dispersed in an oil-based continuous phase, said internal phase including a solution of a non-halide compound dissolved in water; and disposing of drilling cuttings in a land-farming operation, said cuttings being at least partially coated with said drilling fluid.

17. The process of claim 16 wherein said internal phase further includes an emulsifier present in an amount effective to disperse said internal phase in said oil-based continuous phase.

18. The process of claim 16 in which said non-halide compound is selected from the group consisting of acetates, proprionates, tartrates, gluconates, citrates and combinations or salts thereof.

19. The process of claim 16 in which said non-halide compound is selected from the group consisting of potas-sium acetate, calcium acetate, sodium proprionate or combinations thereof.

20. The process of claim 16 in which said non-halide compounds are present in said internal phase at a concen-tration of from about 3.0 percent by weight to saturation.