MXPA98007587A - Perforation fluid thermally this - Google Patents

Abstract

A thermally stable drilling fluid system comprising a drilling fluid and an additive containing styrene-butadiene copolymers whose average molecular weight is greater than about 500,000 g / mol, in which said fluid system controls the fluid loss under conditions of temperature and elevated pressure

Description

DESCRIPTION The invention relates to drilling fluids and, more particularly, to a thermally stable drilling fluid comprising an additive which provides thermal stability and allows better control of fluid loss towards formation.

Drilling fluids are commonly used to drill holes in underground formations. Oil-based drilling fluids are known that are used both for the recovery of crude oil and gas. However, in industry the problem still persists, in general, that the thermal stability of commercial drilling fluids is not entirely satisfactory and, after being exposed to temperatures greater than about 300 ° F, they tend to lose their rheological properties, such as gel strength and yield point, also decreasing the control of fluid loss. In addition, known drilling fluids typically contain many ingredients, most of which are solid in nature, which make the drilling fluid more expensive. As in the course of drilling, large volumes of fluid are used, the various ingredients have a considerable economic effect on the entire drilling process. This type of additives present in conventional drilling fluids can cause formation damage during drilling.

It is clear, therefore, that a system of. a thermally stable fluid that can be used at temperatures greater than 350 ° F, maintain its rheological properties and control the loss of fluid at such high temperatures, be economical, and cause minimal damage to the formation.

Therefore, the main objective of the present invention is to provide a thermally stable drilling fluid containing an additive that improves thermal stability and maintains control of fluid loss at high temperatures.

It is also an object of the present invention to provide a thermally stable drilling fluid system in which fewer ingredients are used than is conventionally required to obtain an appropriate fluid.

Another object of the present invention is to provide a thermally stable drilling fluid system in which the solids content and the consequent potential to cause damage to the formation are reduced.

Below are other objects and advantages of the present invention.

SUMMARY OF THE INVENTION The above objects and advantages can be easily obtained in accordance with the present invention.

According to the invention, a fluid system is provided. thermally stable perforation comprising: a drilling fluid and an additive comprising a styrene-butadiene copolymer whose molecular weight is greater than 500,000 g / mol, in which the drilling fluid system controls the loss of fluid under temperature conditions and high pressure.

According to an embodiment of the invention, the drilling fluid preferably comprises oil and an organophilic clay, to which is added the additive comprising the styrene-butadiene copolymer.

According to another alternative embodiment, the drilling fluid comprises an emulsion, preferably an inverted water-in-oil emulsion, stabilized with a surfactant and the additive comprising the styrene-butadiene copolymer.

DETAILED DESCRIPTION The invention relates to a thermally stable drilling fluid system comprising an additive formed by a styrene-butadiene copolymer which serves to improve the thermal stability of the drilling fluid and to control the loss of fluid under conditions of high temperature and pressure. .

According to the invention, the drilling fluid systems exhibit thermal stability and excellent fluid loss control at temperatures exceeding 350 ° F, when an additive is incorporated into the drilling fluid system comprising styrene-styrene copolymers. butadiene whose average molecular weight is greater than about 500,000 g / mol.

According to the invention, the styrene-butadiene copolymer additive can be incorporated with utility into oil-base drilling fluids such as pure oil base drilling fluids, or inverted emulsion drilling fluids.

According to the invention, it is convenient to add the styrene-butadiene copolymer to the drilling fluid in an amount ranging from one (1) pound per barrel (lpb) to 6 lpb, measured per barrel of drilling fluid. The styrene-butadiene copolymer preferably has a styrene content of about 23% by weight. As indicated above, suitable styrene-butadiene copolymers preferably have an average molecular weight greater than 500,000 g / mol. Suitable examples include a hot-synthesized copolymer, such as the copolymer known as SBR 1012, and a cold-synthesized copolymer such as the copolymer known as SBR 8113. Mixtures or combinations of different copolymers, such as combinations of SBR 1012, could also be provided, as noted above, and another known copolymer SBR 1502, which has an average molecular weight of about 500,000 g / mol. As will be demonstrated in the following, the best results are obtained when the average molecular weight of the copolymer or copolymer mixture exceeds 500,000 g / mol according to the instructions of the present invention.

- - According to the invention, there is provided a drilling fluid system of the 100% oil type comprising, oil, an organophilic clay, the styrene-butadiene copolymer, and optionally a surfactant that acts as an emulsifier and wetting agent. Moreover, the drilling fluid system of the present invention can be provided in a densifying agent so as to adjust the density of the fluid to the desired level, for example, about 14 pounds per gallon (lpg), depending on the characteristics of the fluid. deposit and other factors.

According to the invention, gas oil is particularly suitable for use in a drilling fluid of the 100% oil type. Suitable oils include but are not limited to mineral oils of low aromatic content, synthetic oils, vegetable oils and their derivatives.

The organophilic clay which is used in pure oil drilling fluids is preferably a clay selected from the group consisting of hectorite, bentonite and mixtures thereof, more preferably bentonite. The organophilic clay is added to the drilling fluid system of the 100% oil type preferably in an amount ranging from about 1 lpb to about 8 lpb, depending on the weight of the mud.

Emulsifiers and convenience wetting agents include ionic surfactants such as fatty acids, amines, amides and organic sulfonates, mixtures of some of these with nonionic surfactants as ethoxylated surfactants.

The densifying agent, if desired, can be added to adjust the density of the drilling fluid system. Conventional densifying agents include calcium carbonate, barite, hematite, and mixtures thereof, as well as other well-known substances that can be used to adjust the density of the drilling fluid.

The inverted water-in-oil emulsion according to the present invention may preferably include an oil phase, a water phase, a surfactant, and the additive comprising the styrene-butadiene copolymer of the present invention.

As in drilling fluids of the 100% oil type, the oil can be diesel oil or any other oil that can be used properly as the base of the drilling fluid, such as mineral oils with low aromatic content, synthetic oils, vegetable oils and their derivatives.

Water, such as forming water or fresh or salt water from any source, can be added, and the oil-in-water phases are preferably provided in an inverted water-in-oil emulsion, whose water to oil ratio by volume ranges from 40: 60 and 5:95.

Suitable surfactants for preparing an inverted water-in-oil emulsion type drilling fluid comprise anionic surfactants, preferably of the alkyl aryl sulfonate type, more preferably calcium phenylsulfonate. The surfactant may be provided in a water-in-oil inverted emulsion drilling fluid system, preferably in an amount ranging from about 5 lpb to about 10 lpb.

Densifying agents such as calcium carbonate, barite, hematite and mixtures thereof can be conveniently added to the inverted emulsion drilling fluid system of the present invention so as to adjust the density thereof, as desired. Salts and electrolytes such as calcium chloride may also be included to maintain the osmotic pressure of the water in the emulsion and to prevent the migration of water into the formation. Suitable salts include potassium chloride, sodium chloride, potassium acetate and the like.

For the inverted emulsion drilling fluids of the present invention, additional additives such as viscosifiers and the like, and other conventional additives may be provided as necessary or convenient.

According to the present invention, it has been found that the addition of the styrene-butadiene copolymer, as noted above, improves the control of fluid loss, particularly at high temperatures, as well as the rheological properties of the drilling fluid. . In addition, drilling fluids are formulated using the additive of the present invention, which require fewer ingredients or additives than conventional drilling fluids, and include fewer solid ingredients, thus reducing the cost and possible damage to the formation caused by the use of fluids with a high solids content.

The following examples further illustrate the advantageous characteristics of the drilling fluids of the 100% oil and inverted water-in-oil emulsion type according to the present invention employing additives comprising the styrene-butadiene copolymer whose average molecular weight is greater than 500,000 g / mol.

Example 1 This example demonstrates the properties of a drilling fluid of the 100% oil type according to the invention, which employs a styrene-butadiene copolymer, whose average molecular weight is greater than 500,000 g / mol, and compared to a drilling fluid prepared using other copolymers as additives, according to the list in Table 1. Four (4) drilling fluids were prepared using the additives in the proportions shown in Table 2, and added in the order indicated. The drilling fluid number 1 is an example of a drilling fluid of the present invention. The polymers were dissolved in the oil for 16 hours before adding all the additives. After adding each additive, the resulting composition was mixed during the indicated mixing time, before adding the following additive.

Table 1 Polymer Average molecular weight (g / mol) (1) Random styrene-butadiene (Type SBR 1012) > 500,000 (2) Styrene-butadiene in 120,000 block (30% by weight of Styrene) (3) Styrene-butadiene at 500,000 random (Type SBR 1502) (4) Thermoplastic rubber of Styrene-butadiene Table 2 Additives Concentration Mixing time (minutes) Diesel fuel (barrels) 0.71 Copolymer (lpb) 3.00 Fluid loss control agent (Versatrol) (lpb) 15 30 VG-69 Bentonite, organophilic clay) (lpb) 6.00 15 Rheological modifier (Versa) HRP) (lpb) 3.00 10 Oil Moisturizing Agent (Versacoat) (lpb) 0.5 10 Cal (Ca (0H) 2) (lpb) 1 10 CaC03 (Lo- a e) (lpb) 25 25 Barite (lpb) (enough 330.8 30 to reach a density of 14 Lpg.) The drilling fluids will be allowed to age for 16 hours at 350 aF in a cell placed in a rotary roller kiln. After aging, the rheological properties were measured, in particular the plastic viscosity, yield point, and gel strength using a Fann 35A viscometer at 150aF and at atmospheric pressure, according to the API procedure. The control of fluid loss was measured in ATAP conditions at 500 psi and 350aF after aging, also according to the API procedure. The results appear in Table 3 below, in which the numbers of the drilling fluids correspond to the drilling fluids that were prepared using the polymeric additives of Table 1.

Table 3 Viscosity Fluid Point of L6 L3 Resistance Loss of Plastic perforation (cP) yield (*) (*) (*) of the ATAP fluid gel (IVO) (ml / 30 min) 1 61 12 6 5 11/50 8,4 2 36 5 4 3 9- / 38 98.2 3 58 .15. J7. .6. 12 / 47. 64 4 41 10 7 6 12/44 85.6 (*): pounds / 100 ft2. ATAP: High temperature - High pressure. (10"/ 10 '): Gel resistance at 10 seconds and 10 minutes It can be seen in Table 3 that the drilling fluid of the 100% oil type of the present invention, fluid number 1, presents the best results because it maintains its rheological properties and an effective control of the fluid loss at water conditions.

ATAP.

As is known to those skilled in the art, it is considered that a drilling fluid of the 100% oil type possesses good rheological properties when the. yield point is greater than 2 pounds / 100 ft2, the gel strength is equal to or greater than 2 lbs / 100 ft2, and the control of ATAP fluid loss is less than 10 ml / 30 min. As can be seen in Table 3, the drilling fluid (1) according to the invention is the only fluid of the tested that meets all the desired criteria, including control of fluid loss to ATAP.

Example 2 Five drilling fluids were prepared as shown in Table 4, varying the concentration of the polymer. The initial rheological properties were measured. Except where otherwise indicated, the samples were aged at 350aF for 16 hours, and then the rheological properties were measured at atmospheric pressure and at a temperature of 150ßF ± 2aF in a Fann 35A viscometer.

Table 4 Ingredient Mixing time (minutes) Gasoil (barrels) 0.75 Polymer (lpb) (4.5; 4.3) previously dissolved in diesel Moisturizing agents (lpb) 6 10 Cal (Ca (0H) 2) (lpb) 4 15 Organophilic clay (lpb 3)) 6 30 Barita ** 30 (**) Sufficient to reach the desired density (141 ppg) The results are shown in Table 5.

Table 5 Concentration Fluid Viscosity Resistance Point Loss of plastic perforation (cP) gel yield of fluid gel ATAP polymer ration (I / DE) (*) (10 ') (*) (10") ( *) (ml / 30 min) 1 4,5 60/73 13/28 3/7 5/10 5,0 2 ** 4.5 73/37 13/18 3/2 5/2 3 3 38/40 7/6 3/4 7/12 5,6 4 4 48/56 11/9 4/5 7/13 5,6 *** 4 47/42 11/6 4/4 7/21 10 I / DR: Initial / After aging. *: pounds / 100 ft2. ** Properties measured in Fann viscosimeter 70 to 350"F and 10,800 psi *** Aged at 400aF for 16 hours.

This example demonstrates that the rheological properties and fluid loss control of the pure oil drilling fluid of the present invention remain stable when the polymer concentration is reduced and subjected to a temperature of 400aF.

Example 3 Four formulations of commercial drilling fluids were prepared according to the procedure established for each one in the corresponding tables that appear below. For comparison purposes, drilling fluids were also prepared according to the scope of the present invention. The properties of each sample were measured before and after aging. The rheological properties were measured at 150aF, with a Fann 35A viscometer, and at atmospheric pressure, according to the API procedure. ATAP fluid loss control at 500 psi and 350aF was measured.

A commercial fluid was prepared, the drilling fluid "Versacore" from MI, Drilling Fluids, density: 14 lpg and 15 lpg according to the procedure indicated in Tables 6 and 7. The process for preparing a fluid according to the invention it is also shown in Table 7.

Table 6 Ingredient Vßrsacora Vßrsacorß Time d? Rforfor 350 aP mixed mixed (minutes) Gasoil (barrels) 0, 70 0, 61 previously Polymer (lpb) 0 0 dissolved in diesel Versatrol-HT (lpb) 15 25 30 Lorte Tech (lpb) 25 30 25 Organophilic clay based on bentonite brand VG-69 10 15 (lpb) Rheological modifier 10 Versa-HRP (lpb) Oil moisturizing agent 0.5 10 brand Versacoat (lpb) Cal (Ca (OH) 2) (lpb) 10 Barite (lpb) (**) (**) 30 (**) Sufficient to obtain the desired density. (14 lpg or 15 lpg) lpb: pounds per barrel - D - Table 7 Time of Ingredient Vers - Mixed invention core (minutes) M- Inven Gasoil (barrels) 0.61 0.75 previously Polymer (lpb) 0 4.5 dissolved in diesel Versatrol-HT (lpb) 15 0 20 Lorte Tech (lpb) 25 0 30 Organophilic clay based on bentonite brand VG-69 15 15 (lpb) Versa-HRP (lpb) 3 0 15 Oil moisturizing agent 0,5 0.5 10 10 brand Versacoat (lpb) Cal (Ca (0H) 2) (lpb) 1 1 15 10 Barite (lpb) (**) (**) 30 30 (**) Sufficient to obtain the desired density, lpb: pounds per barrel The results of the test are shown in Table 8.

Table 8 Versacore versacore Versacore Reformulated Invention 350 «F (Iniclal-DR) (Initial-DE) (Initial-DB) (Initial-DE) Plastic viscosity 31-28 22-22 73-56 60-73 (cP) Transfer point 37-3 23-4 87-12 13-28 (*) L6 (*) 25-1 23-4 60-8 4-8 L3 (*) 24-0 20-3 58-7 3-6 Resistance-gel 33 / 37-2 / 27 25 / 36-3 / 31 78 / 92-14 / 3 / 5-7 / 10 (10"/ 10 ') 54 Loss of fluid ATAP - / (**) - / 90 - / 2,2 - / 4,7 (ml / 30min) (*): pounds / 100 ft2 (**) Uncontrolled ATAP: High temperature - High pressure (10"/ 10 '): Gel resistance at 10 seconds and 10 minutes. DE: after aging.

As noted, the comparison of the drilling fluid of the present invention with respect to all other fluids yields results in its favor. Unlike the Versacone fluid, the fluid of the present invention does not possess progressive gels, which makes it more suitable for drilling.

The "Carbocore" drilling fluid preparation method of Baker-Hughes / Inteq (BHI) is shown in Table 9. The prepared mud has a density of 14 lpg.

- - Table 9 Mixed time of mixed entry (minutes) Gasoil (bbl), 75 Carbotec (lpb) 4 10 Cal (lpb) 4 10 Carbovis (lpb) 8 15"Carbotrol-HT (lpb) 14 10 Barite (lpb) (**) 30 (bbl): barrels (lpb): pounds per barrel (lpg): pounds per gallon (**) Sufficient to obtain the desired density of 14 ppg.

Two drilling fluids according to the present invention were also prepared at different concentrations, as illustrated in Table 10.

Table 10 Time of Ingredient Invention Mixed invention (1) (2) (minutes) Diesel (bbl) 0.75 0.75 Polymer (bbl) 3.0 4.0 Previously dissolved in the diesel Carbotrol-HT (lpb) 0 0 Carbotec (lpb) 6.0 6.0 10 Cal (lpb) 4.0 4.0 15 Carbovis (lpb) 6.0 6.0 30 Barite (lpb) (**) (**) 30 (**) Sufficient to obtain the desired density of 14 lpg.

The results of the comparative tests can be seen in Table 11. Table 11 BBI Invention Invention (1) (2) (Initial-DB) (Initial-DB) (Initial-DB) Plastic viscosity (CP) 27 29 41 41 48 56 Delivery point (*) 11 1 7 10 11 9 L6 (*) 7 3 4 5 4 4 L3 (*) 6 2 3 4 3 3 Gel strength (10- / 10 ') 7/22 3/15 4/8 5/14 4/7 5/13 Loss of ATAP fluid (ml / 30min) 2.2-4.4 4.0 (*): pounds / 100 ft2. (**) Out of control. ATAP: High temperature - High pressure. (10"/ 10 '): Resistance of the gel at 10 seconds and 10 minutes DE: after aging.

This example shows that the drilling fluid of the present invention has good rheological properties, presents a better yield point and maintains control of fluid loss at high temperature, while using fewer additives than those used in the commercial drilling fluids.

Example 4 A drilling fluid was prepared as in Example 3, Table 10, Invention (1), and allowed to react at 350aF and 400aF for 16 hours. The results of the test are shown in Table 12.

Table 12 Invention Invention (1) Invention (1) (1) After After Initial aging to age at 350 > F 400 * F Viscosity plastic 55 72 42 (CP) Transfer point 12 22 6 (*) L6 (*) 4 10 3 L3 (*) 3 9 2 Resistance / gel 4/10 14/28 4/21 (10 ' / 10 ') (*) Fluid loss 3.0 to 350 * F 9.6 to 400 * ATAP (ml / 30min) F This example demonstrates that the rheological properties and fluid loss control of the drilling fluid of the present invention are maintained after aging at temperatures up to 400 aF, despite containing fewer additives than other formulations; while commercial fluids such as Versacore from M-I drilling fluids and Baker Hughes Inteq's Carbocore lose their properties at 350 aF, as demonstrated in Example 3.

Example 5 This example demonstrates the advantages of the water-in-oil reverse emulsion type drilling fluid of the present invention. Three commercial reverse emulsion drilling fluids were prepared according to the procedures provided by the respective service companies. The ingredients were added and mixed as indicated in Tables 13, 14 and 15. Table 13 Ingredient Emulsion Reverse Time of M-I mixed drilling fluid (minutes) Gasoil (barrels) 0.62 Emulsifier Versamul 10 (lpb) Cal (lpb) 8 30 (a) Organophilic clay with base 2 10 of bentonite VG-69 (lpb) Versatrol (lpb) 10 (filter controller) Moisturizing agent Versacoat 10 (lpb) Barite (lpb) (**) 10 (**) Sufficient to obtain a density of 15 pounds per gallon, (a) 230,000 ppm of brine are mixed simultaneously with the lime.

Table 14 Time of Ingredient REVERSE mixed emulsion (minutes) BAKER HUOES INTEQ Gasoil (barrels) 0,62 Emulsifier Carbotec 5 10 (lpb) Cal (lpb) 6 30 (a) Organophilic clay Carbboo- 2 10 Gel (lpb) Filter controller 5 10 Carbo-Trol (lpb) Carboo brand emulsifier - 5 10 Mul Barite (**) 10 (**) Sufficient to obtain a density of 15 pounds per gallon, (a) 230,000 ppm of brine are mixed simultaneously with the lime.

Table 15 Emulsion Time of Baroid mixed inverse ingredient (minutes) Gasoil (barrels) 0.62 Emulsifier Invermul 5 10 (lpb) Cal (lpb) 8 30 (a) Organophilic clay marccaa 2 10 Geltone II (lpb) Duratone 10 fluid loss controller (lpb) EZ-MUL emulsifier (lpb) 10 Barita (**) 10 (**) Sufficient to obtain a density of 15 pounds per gallon, (a) 230,000 ppm of brine are mixed simultaneously with the lime.

Table 16 shows the results of commercial drilling fluids found in the market.

Table 16 Reverse Emulsion Emulsion Reverse Reverse Emulsion of H-I Drilling Baker Hughes Baroid Fluid Inteaj (Initial / Final) (Initial / Final) (Initial / Final) Plastic Viscosity 31-45 25/27 25/28 (CP) Transfer point 10/0 9/8 7/0 (*) Resistance / gel 10"(*) 14/5 4/3 6/3 10 '(*) 22/4 5/4 7/5 Density (lpg) 15/15 15/15 15/15 Fluid loss 44/12 6/6 53/70 ATAP (ml / 30 min.) (*): Pounds / 100 ft2. ATAP: High temperature - High pressure. (10"/ 10 '): Gel resistance at 10 seconds and 10 minutes.

Seven drilling fluids were prepared according to the invention with different concentrations of polymer, surfactant and water / oil ratio, as indicated in Table 17. They were allowed to age at different temperatures, and the results are shown in Tables 18 and 19 Table 17 Ratio of Polymer Fluid Surfactant Proportion Perforation Concentration Oil / Water Concentration (FP) (lpb) (lpb) FP1 2 10 85/15 FP2 3 10 85/15 FP3 2 15 85/15 FP4 3 15 85/15 FP5 3 10 70/30 FP6 3 10 95 / 5 FP7 3 7.5 85/15 Table 18 FP1 to 300 * F FP2 to 350 * F FP3 to 300 «F FP4 to 350 * F (Initial / Final) (Initial / Final) (Initial / Final) (Initial / Final) Plastic viscosity 74/28 96/68 nm / 42 nm / 81 (CP) Cedencia (*) 57/8 55/27 nm / 9 nm / 17 L6 (*) 13/3 15/8 39/4 52/7 L3 (*) 5/3 12/6 27/3 52/5 Resistance / gel (10 *) (*) 12/3 12/7 12/3 12/7 (10 ') (*) 22/8 17/15 22/8 17/15 Loss of fluid ATAP - / 3.6 - / 6.8 - / 5.6 - / 12 (ml / 30 rain) nm: not measurable (*): pounds / 100 ft2.

Table 19 FP5 to 350 «F FP6 to 350 * F FP7 to 350« F (Initial / Final) (Initial / Final) (Initial / Final) Plastic viscosity (cP) nm / 67 87/31 90/45 End point (*) nm / 43 57/0 42/7 L6 (*) 47/17 9/1 12/3 L3 (*) 40/14 6/0 9/2 Resistance / gel (10") (*) 40/15 8/12 10/16 (10 ') (*) 52/19 1/1 3/5 Loss of ATAP fluid (ml / 30 min) - / 2.4 - / 12.4 - / 4.4 nm: not measurable (*): pounds / 100 ft2.

As shown, the water-in-oil reverse emulsion drilling fluid of the present invention is stable under ATAP conditions.

Therefore, a thermally stable drilling fluid is provided which has excellent fluid loss control and comprises a reduced fraction of solids compared to conventional fluids, which reduces the possibility of formation damage being caused, as the cost of the fluid.

This invention can be carried out in other ways or carried out in other forms without leaving aside the spirit or the essential characteristics thereof. Therefore, the present embodiment should be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated in the appended claims, in which it is intended to cover all changes that fit in their meaning. and range of equivalences.

Claims (1)

1. RE I V I N D I CA C I O N E S. A thermally stable drilling fluid system comprising a drilling fluid and an additive comprising styrene-butadiene copolymers whose average molecular weight is greater than 500,000 g / mol, in which said fluid system exhibits fluid loss control in conditions of temperature and high pressure. A system of a drilling fluid according to claim 1, wherein said additive has a styrene content of about 23% by weight. A system of a drilling fluid according to claim 1, wherein said additive is present in an amount ranging from 1 lpb to 6 lpb. A drilling fluid system according to claim 1, wherein said drilling fluid comprises oil and an organophilic clay. A system of a drilling fluid according to claim 4, wherein said oil is diesel. A drilling fluid system according to claim 4, wherein said clay is selected from the group consisting of hectorite, bentonite and mixtures thereof. A system of a drilling fluid according to claim 4, wherein said clay is bentonite. A system of a drilling fluid according to claim 4, wherein said clay is present in an amount ranging from 1 lpb to 8 lpb. A drilling fluid system according to claim 4, wherein said drilling fluid comprises at least one additional additive selected from the group consisting of emulsifiers, wetting agents and mixtures thereof. A drilling fluid system according to claim 9, wherein said additive is an emulsifier selected from the group consisting of ionic surfactants, and mixtures of ionic and nonionic surfactants. A system of a drilling fluid according to Xa claim 4, wherein said drilling fluid comprises a densifying agent to provide the system with the desired density. A system of a drilling fluid according to claim 11, wherein said densifying agent is selected from the group consisting of calcium carbonate, barite, hematite and mixtures thereof. A drilling fluid system according to claim 4, wherein said system consists essentially of said oil, said organophilic clay and said styrene-butadiene copolymer. A drilling fluid system according to claim 1, wherein said drilling fluid comprises a water-in-oil emulsion, and a surfactant. A drilling fluid system according to claim 14, wherein said water and said oil are present in a volume ratio of said water to said oil between 40:60 and 5:95. A system of a drilling fluid according to claim 14, wherein said surfactant is an anionic surfactant. A system of a drilling fluid according to claim 14, wherein said surfactant is an alkyl aryl sulfonate. A system of a drilling fluid according to claim 14, wherein said surfactant is calcium phenylsulfonate. A system of a drilling fluid according to claim 14, wherein said surfactant is present in an amount between 5 lpb and 10 lpb. - A system of a drilling fluid according to claim 14, wherein said system is constituted essentially of said water-in-oil emulsion, said surfactant and said styrene-butadiene copolymer.