Description:Field of the invention

[0001] The present invention relates to the field of drilling fluids used in oil and gas industry. More specifically, the present invention relates to an oil-based drilling fluid composition for minimizing non-productive time associated with wellbore drilling.

Background of the invention

[0002] Drilling fluids, also known as drilling muds, are essential in the drilling of wellbores for the extraction of hydrocarbons. These fluids perform several critical functions during drilling of a wellbore including maintaining wellbore stability, cooling and lubricating the drill bit, carrying cuttings to the surface, and controlling formation pressures. Drilling fluids are broadly classified into two types based on continuous phase used viz., water-based drilling fluids and oil-based drilling fluids.

[0003] Water based drilling fluids has freshwater or saltwater as a medium, which makes it environmentally friendly. However, water-based drilling fluids induce clay swelling which reduce the wellbore stability. Oil-based drilling fluids on the other hand are based on mineral oils, diesel or synthetic oils in which the oil provides a continuous phase. Further, oil-based drilling fluid has advantages over water-based drilling fluid for drilling troublesome lithological formations which contains water sensitive shales and clays, water dissolved salt formation, anhydrite, carnallite and potash. Oil-based drilling fluid is a preferred choice across the world, particularly in challenging geological conditions that experiences high pressures and high temperatures. Oil-based drilling fluids are inert to the components of the geological formation, especially clay, thereby minimizing damage to the drill zone, and the fluid reduces friction better than water-based fluids.

[0004] Depending on the drilling conditions, particularly formation or wellbore pressure, the density of existing oil-based drilling fluid varies within an optimal range. To achieve optimum drilling fluid parameters, the existing oil-based drilling fluids often rely on expensive chemical additives, which can significantly increase operational costs.

[0005] In light of the above-mentioned drawbacks, there is a need for an improved oil-based drilling fluid composition which provides optimal drilling fluid properties without relying on expensive chemical additives. There is a need for an oil-based drilling fluid composition that has improved electrical stability for longer duration and has a minimum sag tendency.

Summary of the Invention

[0006] In various embodiments of the present invention, an oil-based drilling fluid composition is provided. The composition comprises a base oil in an amount ranging from 36.67 to 37.62 %w/w and an emulsifier. The composition also comprises lime in an amount ranging from 2.38 to 3.10 %w/w, a viscosifier in an amount ranging from 0.95 to 2.74 %w/w, a brine comprising calcium chloride and water, a fluid loss control additive in an amount ranging from 0.71 to 1.43 %w/w, calcium carbonate in an amount of 7.14 %w/w, and a weighing agent in an amount ranging from 18.57 to 20.24 %w/w. The ratio of base oil to water is 70:30. The oil-based drilling fluid composition exhibits a stable electrical stability for up to 5 days and a minimal sag tendency for a long duration, having a sag factor in a range from 0.50-0.53 for 120 hrs.

[0007] In an embodiment of the present invention, the emulsifier is either (a) an all-in-one emulsifier in an amount ranging from 2.38 to 3.57 %w/w, or (b) a combination of a primary emulsifier in an amount ranging from 0.95 to 1.43 %w/w, and a secondary emulsifier in an amount ranging from 1.90 to 2.38 %w/w.

[0008] In an embodiment of the present invention, the base oil is a low toxic mineral oil selected from a group comprising of n-Alkanes (C9-C17) having aromatics less than 1%.

[0009] In an embodiment of the present invention, the viscosifier is selected from a group comprising of amine treated bentonite or attapulgite.

[0010] In an embodiment of the present invention, the fluid loss additive is selected from a group comprising of organophilic lignites, gilsonite, or asphalt derivatives.

[0011] In an embodiment of the present invention, the weighing agent is barite.

[0012] In another embodiment of the present invention, the all-in-one emulsifier is selected from a group comprising of a blend of fatty acids or fatty acids derivatives, non-ionic surfactants, ionic surfactants.

[0013] In another embodiment of the present invention, the primary emulsifier is selected from a group comprising of fatty acids, and calcium soaps. In another embodiment of the present invention, the secondary emulsifier is selected from a group comprising of polyamides, alkanolamides, non-ionic surfactants (ethoxylated alcohols or amines), ionic surfactants (sulphonates or phosphates).

Detailed description of the invention

[0014] In an embodiment of the present invention, there is provided a composition for an oil-based drilling fluid which provides optimal drilling fluid properties without relying on expensive chemical additives. The oil-based drilling fluid, unexpectedly, demonstrates advantageous electrical stability for a long duration, resists the sagging of weighting agents and therefore has minimum sag tendency, and possesses a viscosity suitable for drilling operations.

[0015] The disclosure is provided to enable a person having ordinary skill in the art to practice the invention. Exemplary embodiments herein are provided only for illustrative purposes and various modifications will be readily apparent to a person skilled in art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. The terminology and phraseology used herein is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications, and equivalents consistent with the principles and features disclosed herein. For purposes of clarity, details relating to technical material that is known in the technical fields related to the invention have been briefly described or omitted so as not to unnecessarily obscure the present invention.

[0016] In an embodiment of the present invention, an oil-based drilling fluid composition is provided. The composition comprises a base oil in an amount ranging from 36.67 to 37.62 %w/w and an emulsifier, wherein the emulsifier is either (a) an all-in-one emulsifier in an amount ranging from 2.38 to 3.57 %w/w, or (b) a combination of a primary emulsifier in an amount ranging from 0.95 to 1.43 %w/w, and a secondary emulsifier in an amount ranging from 1.90 to 2.38 %w/w. The composition further comprise lime in an amount ranging from 2.38 to 3.10 %w/w, a viscosifier in an amount ranging from 0.95 to 2.74 %w/w, a brine comprising calcium chloride and water, a fluid loss control additive in an amount ranging from 0.71 to 1.43 %w/w, calcium carbonate in an amount of 7.14 %w/w, and a weighing agent in an amount ranging from 18.57 to 20.24 %w/w.

[0017] In an exemplary embodiment of the present invention, the ratio of base oil to water is 70:30. In an embodiment of the present invention, the water referred hereto is the water from brine. In various embodiments of the present invention, the oil-based drilling fluid composition exhibits excellent electrical stability for long duration i.e., 5 days. In an embodiment of the present invention, the drilling fluid also exhibited stable solids suspension capacity for 5 days, observed by way of a Sag test.

Base Oil

[0018] In an embodiment of the present invention, the base oil in the oil-based drilling fluid composition serves as a continuous phase in the drilling fluid providing a medium for carrying suspended particles and ensuring the fluid's stability under various temperatures and pressures. The base oil further provides chemical stability and compatibility with the other components of the composition. In an exemplary embodiment of the present invention, the base oil is a low toxic mineral oil selected from a group comprising n-Alkanes (C9-C17) having aromatics less than 1%. In an exemplary embodiment of the present invention, the composition comprises base oil in an amount ranging from 36.67 to 37.62 %w/w. In various embodiments of the invention, the specified amount of base oil ensures optimal lubrication, thermal stability, and compatibility with other components, creating a homogeneous fluid that maintains its properties throughout the drilling process under a wide range of temperatures.

Emulsifier

[0019] In an embodiment of the present invention, the composition comprises emulsifiers to reduce the surface tension between residual water and base oil. The emulsifiers play a crucial role in stabilizing the composition by being partially soluble in water and partially soluble in oil, which is essential for maintaining the integrity and performance of the drilling fluid. By stabilizing the composition, the emulsifiers contribute to the desired rheological properties of the drilling fluid. These rheological properties are important for effective hole cleaning and shale stability during drilling operations. The emulsifiers ensure that other components of the compositions are uniformly distributed within the drilling fluid. The emulsifiers prevent separation of the oil and water phases and facilitate dispersion of the water phase uniformly within the oil phase, even under high shear rates and varying temperatures. This is critical for maintaining consistency and effectiveness of the drilling fluid. Emulsifiers are selected for their compatibility with the base oil used in the drilling fluid.

[0020] In an exemplary embodiment of the present invention, the amount of all-in-one emulsifiers ranges from 2.38 to 3.57 %w/w. In an exemplary embodiment of the present invention, the all-in-one emulsifiers are selected from a group comprising of a blend of fatty acids or fatty acids derivatives, non-ionic surfactants (ethoxylated alcohols, amines), ionic surfactants (sulphonates, carboxylates). In various exemplary embodiments of the invention, the all-in-one emulsifier is a commercially available emulsifier selected from a group comprising of Good Mul A1 (AE1) and single shot emulsifier (AE2).

[0021] In an exemplary embodiment of the present invention, the primary emulsifier is in an amount ranging from 0.95 to 1.43 %w/w. The primary emulsifier is selected from a group comprising of fatty acids and calcium soaps (when combined with lime in-situ). In various exemplary embodiments of the invention, the primary emulsifier is a commercially available emulsifier selected from a group consisting Good Mul P (PE1), Core Mul P (PE2) and GS Mul P (PE3). These emulsifiers, such as fatty acids and calcium soaps (formed in-situ with lime) provide the basic stabilization needed to prevent the separation of the oil and water phases. They help to disperse the water phase uniformly within the oil phase, thereby creating a stable emulsion that is essential for the drilling fluid's performance. In an exemplary embodiment of the present invention, the secondary emulsifier is in an amount ranging from 1.90 to 2.38 %w/w. The secondary emulsifier is selected from a group comprising polyamides, alkanolamides, non-ionic surfactants (ethoxylated alcohols or amines), and ionic surfactants (sulphonates or phosphates). In various exemplary embodiments of the invention, the secondary emulsifier is a commercially available emulsifier selected from a group consisting Good Mul S (SE1), Core Mul S (SE2) and Gel Mul S (SE3).

[0022] The primary and secondary emulsifiers work synergistically to provide a more stable and robust emulsion of drilling fluid that can perform effectively over a wide range of conditions. This is particularly important in maintaining the emulsion under dynamic conditions, such as varying temperatures and pressures. Primary emulsifiers are responsible for the initial emulsion formation and basic stabilization of the emulsion, while secondary emulsifiers enhance and maintain this stability under more challenging conditions. Together, they ensure that the drilling fluid exhibits the necessary rheological properties and stability required for efficient drilling operations.

Lime

[0023] In an embodiment of the present invention, the composition comprises lime to maintain the alkalinity and enhance the stability of the drilling fluid. In an exemplary embodiment of the present invention, the amount of lime ranges from 2.38 to 3.10 %w/w. Lime plays a crucial role in maintaining the alkalinity of the drilling fluid by maintaining a stable pH which ensures the effectiveness of other chemical additives in the drilling fluid and helps to tackle acidic gases such as carbon dioxide and hydrogen sulphide, which are encountered during drilling.

[0024] Further, lime reacts with primary emulsifiers and forms calcium soaps, which creates a synergistic effect that enhances the overall performance of the drilling fluid to ensure that the oil and water phases remain mixed and effective throughout the drilling process. By maintaining the alkalinity and stabilizing the emulsion, lime also contributes to the desired rheological properties of the drilling fluid. This includes maintaining the appropriate viscosity and yield point, which are crucial for efficient drilling operations.

[0025] In addition, the alkaline nature of lime may help prevent corrosion of the drilling equipment by neutralizing acidic components in the drilling fluid. This extends the lifespan of the equipment and reduces maintenance costs. Further, lime also contributes to the fluid loss control properties of the drilling fluid by enhancing the stability of the emulsion and preventing excessive fluid loss to the formation.

Viscosifier

[0026] In an embodiment of the present invention, the composition comprises a viscosifier to control its viscosity and improve carrying capacity for cuttings. In an exemplary embodiment of the present invention, the viscosifier is selected from a group comprising amine-treated bentonite or attapulgite. The amount of viscosifier ranges from 0.95 to 2.74 %w/w. The viscosifier controls the viscosity of the drilling fluid, ensuring effective suspension and transport of cuttings. In various embodiments of the present invention, the choice and concentration of viscosifier ensures that the drilling fluid has the right balance of viscosity and yield point, thereby enhancing its ability to carry cuttings to the surface and maintain wellbore stability. In various exemplary embodiments of the present invention, the viscosifier is a commercially available viscosifier selected from a group comprising of VG-Plus (V1), VG-69 (V2), Organophilic clay (V3), GS Clay DP (V4) and Geltone-II (V5).

Brine

[0027] In an embodiment of the present invention, the composition comprises a brine solution. In an exemplary embodiment of the present invention, the brine comprises a mixture of calcium chloride and water. The amount of calcium chloride is 5.95 %w/w, and the amount of water ranges from 19.45 to 21.06 %w/w. The inclusion of brine comprising calcium chloride and water in the drilling fluid composition plays a critical role in enhancing the performance, stability, and effectiveness of the drilling fluid. Advantageously, the specified amount of the brine facilitates to achieve the desired density of the drilling fluid.

[0028] Further the brine helps in inhibition of shale swelling. It is possible that the interaction of drilling fluids with shale formations may cause shale to absorb water and swell, leading to wellbore instability. The presence of calcium ions in the brine helps to stabilize the shale by reducing its tendency to swell. By inhibiting shale swelling, the brine comprising calcium chloride and water helps to maintain wellbore stability, thereby reducing the risk of wellbore collapse and other related issues. Further advantageously, the brine also enables preventing the interaction of shale and water. In addition, the brine also contributes to the overall rheological properties of the drilling fluid under various operational conditions.

Fluid Loss Control Additive

[0029] In an embodiment of the present invention, the composition comprises a fluid loss control additive to minimize the loss of drilling fluid to the formation. In an exemplary embodiment of the present invention, the fluid loss additive is selected from a group comprising of organophilic lignites, gilsonite, or asphalt derivatives. In an exemplary embodiment of the present invention, the amount of fluid loss control additive ranges from 0.71 to 1.43 %w/w. The fluid loss additive forms a thin and low-permeable filter cake on the wellbore, which acts as a barrier, thereby controlling the loss of drilling fluid to the formation during drilling operations. In various exemplary embodiments of the invention, the fluid loss control additive is a commercially available additive selected from a group comprising of GS Trol (FLC 1) and Novatec F (FLC2).

Calcium Carbonate

[0030] In an embodiment of the present invention, the composition comprises calcium carbonate to provide bridging and sealing properties. In an exemplary embodiment of the present invention, the amount of calcium carbonate is 7.14 %w/w. Calcium carbonate plays a critical role, particularly in formations with fractures and vugs. In an embodiment of the present invention, calcium carbonate may act as a bridging material that helps to seal fractures and vugs within the formation. The specific concentration of calcium carbonate ensures that the calcium carbonate particles of right size effectively bridge the fractures. By forming a physical barrier, calcium carbonate helps to seal fractures and vugs, preventing the loss of drilling fluid into these voids. This sealing action is crucial for maintaining wellbore stability and preventing fluid loss. By enhancing wellbore stability and minimizing fluid loss, the precise amount of calcium carbonate helps to reduce non-productive time.

[0031] The presence of calcium carbonate in the drilling fluid helps to minimize the invasion of fluid into formation. This is particularly important in formations with fractures and vugs, where fluid loss can be significant. By minimizing fluid invasion and sealing fractures, calcium carbonate helps to prevent formation damage, which is essential for preserving the integrity of the formation and ensuring efficient hydrocarbon recovery.
Weighing Agent

[0032] In an embodiment of the present invention, the composition comprises weighing agent to increase the density of the drilling fluid. In an exemplary embodiment of the present invention, the weighing agent is barite, and the amount ranges from 18.57 to 20.24 %w/w. The concentration of the weighing agent in the composition is a critical factor that directly influences the density of the drilling fluid. The specific concentration of the weighing agent is critical to enhance the performance, stability, and effectiveness of the drilling fluid. The weighing agent increases the density of the drilling fluid, which is essential for maintaining wellbore stability and controlling formation pressures. A higher density drilling fluid can counteract formation pressures and prevent wellbore collapse. Further, the added weight from the weighing agent also contributes to the hydrostatic pressure exerted by the drilling fluid column. This pressure helps to balance the formation pressures and maintain wellbore stability.

[0033] In an embodiment of the present invention, the ratio of base oil to water is 70:30. The ratio of base oil to water ratio is a critical parameter that significantly influences the performance and stability of the drilling fluid. In an embodiment of the present invention, this ratio determines the emulsion type, rheological properties, and overall effectiveness of the drilling fluid in various operational conditions. The base oil to water ratio determines whether the drilling fluid forms an oil-in-water (O/W) or water-in-oil (W/O) emulsion. The higher base oil content results in a water-in-oil emulsion, which is preferred for its stability and performance in drilling operations. The ratio ensures that the emulsion remains stable, thereby preventing the separation of the oil and water phases. The ratio of base oil to water also directly affects the rheological properties of the drilling fluid. Compared to an all-oil based drilling fluid where water is not used, the drilling fluid of the present invention, having 70:30 oil to water ratio (invert emulsion), lowers the cost as the concentration of oil is low comparatively.

[0034] The ratio of base oil to water, in accordance with an embodiment of the present invention, is an optimal ratio to ensure that the drilling fluid has the right rheological properties at minimal cost. Further, the base oil provides lubrication to the drill bit and the wellbore, reducing friction and wear. A higher base oil content enhances the lubricating properties of the drilling fluid, which is essential for smooth drilling operations. In addition, a higher base oil content reduces the risk of water invasion into the formation, which can cause swelling and damage to the formation.

[0035] In various embodiments of the present invention, the specific concentration of each component in the oil-based drilling fluid composition is carefully selected to create a synergistic effect that enhances the overall performance, stability, and effectiveness of the drilling fluid. Each ingredient contributes to the fluid's properties in a specific way, and their combined effect ensures that the fluid performs optimally under various operational conditions. This synergy results in a drilling fluid that exhibits the necessary rheological properties, stability, and performance characteristics required for efficient and effective drilling operations.
[0036] Advantageously, in an embodiment of the present invention, the base oil in an amount ranging from 36.67 to 37.62 %w/w ensures optimal lubrication, thermal stability, and compatibility with other components, creating a homogeneous fluid that maintains its properties throughout the drilling process. The choice of emulsifiers in the specified range ensures that the emulsion remains stable under dynamic conditions, enhancing the fluid's rheological properties and improving cuttings transport and hole cleaning.

[0037] In an embodiment of the present invention, lime in an amount ranging from 2.38 to 3.10 %w/w maintains the alkalinity of the drilling fluid, enhancing emulsion stability and preventing corrosion. In an embodiment of the present invention, viscosifier in an amount ranging from 0.95 to 2.74 %w/w ensures that the fluid has the right balance of viscosity and yield point, enhancing its ability to carry cuttings to the surface and maintain wellbore stability. In an embodiment of the present invention, brine comprising calcium chloride in an amount of 5.95 %w/w and water in an amount ranging from 19.45 to 21.06 %w/w ensures inhibition of shale swelling and maintains wellbore integrity.

[0038] Further, advantageously, in an embodiment of the present invention, fluid loss control additive in an amount ranging from 0.71 to 1.43 %w/w minimizes the loss of drilling fluid to the formation while maintaining wellbore stability and preventing formation damage. In an embodiment of the present invention, calcium carbonate in an amount of 7.14 %w/w ensures that the fluid has the right balance of bridging and sealing properties while maintaining wellbore stability and preventing formation damage. In an embodiment of the present invention, weighing agent in an amount ranging from 18.57 to 20.24 %w/w, ensures that the fluid has the right density to counteract formation pressures, enhance cuttings transport, and maintain wellbore integrity.

[0039] Further advantageously, the oil-based drilling fluid composition exhibits a stable electrical stability for up to 5 days. Electrical stability (ES), also referred to as emulsion stability, is a critical parameter for evaluating the performance of oil-based drilling fluids. In oil-based drilling fluids, water is dispersed as fine droplets within a continuous oil phase, stabilized by emulsifiers. ES measures the voltage required to break down this emulsion and allow electrical current to pass, thereby indicating the strength and stability of the emulsion. A high ES value denotes a robust emulsion in which water remains dispersed and non-free which prevents interaction with the formation and preserving wellbore stability. Stable emulsions also contribute to effective filtration control, desirable rheological properties, reduced torque and drag and enhanced thermal stability under downhole conditions. Furthermore, strong emulsion stability ensures solids remain oil-wet, maintains a protective oil film on downhole equipment and minimizes corrosion, all of which are critical for efficient and reliable drilling performance.

[0040] Further advantageously, the oil-based drilling fluid composition exhibits minimal sag tendency for a long duration, having a sag factor in a range from 0.50-0.53 for 120 hrs. Sagging refers to the tendency of high-density solids to settle within a drilling fluid under both static and dynamic conditions. In oil-based drilling fluids, sagging typically occurs when solids are not adequately suspended, which may result from low rheological properties (weak gel strength or low yield point), inadequate emulsification, high wellbore inclination or insufficient annular velocity. The sag factor provides a quantitative measure of this tendency. An ideal sag factor generally lies within the range of 0.50 to 0.53, indicating stable suspension. Values within this range are considered acceptable. However, if the sag factor exceeds 0.53, it suggests that high-density solids are settling at the bottom of the fluid column, rendering the lower portion denser and the upper portion lighter. Such imbalance can lead to a range of wellbore complications, including well control issues, stuck pipe, and loss of wellbore stability.

[0041] Yet further, advantageously, in an embodiment of the present invention, the drilling fluid composition exhibits a density of 10ppg. In an exemplary embodiment of the present invention, the composition exhibits a plastic viscosity in a range from 23 to 37 cP. In an exemplary embodiment of the present invention, the composition exhibits yield point is in a range from 25 to 31 lbs/100ft2. In an exemplary embodiment of the present invention, the composition exhibits water phase salinity in a range from 172 to 189 g/L.

[0042] In an exemplary embodiment of the present invention, the composition exhibits emulsion stability in a range from 648 to 968 volts at 120±5oF. In an exemplary embodiment of the present invention, the gel strength of the composition is in a range from 13-30 lbs/100ft2. In an exemplary embodiment of the present invention, the weight of composition at 750F is 10.0±0.1 ppg. In an exemplary embodiment of the present invention, the low shear rate viscosity of the composition at 6RPM is in a range from 11-18. Low shear rate viscosity is a key indicator for the hole cleaning capability of the drilling fluid. In an exemplary embodiment of the present invention, the high-pressure high temperature filtration Loss of composition is in a range from 2.4 to 3.8.

[0043] In an embodiment of the present invention, a method of drilling a subterranean well is provided. The method comprising the step of operating a drill in a wellbore in the presence of an oil-based drilling fluid comprising: a base oil in an amount ranging from 36.67 to 37.62 %w/w; an emulsifier; lime in an amount ranging from 2.38 to 3.10 %w/w; a viscosifier in an amount ranging from 0.95 to 2.74 %w/w; a brine comprising calcium chloride and water; a fluid loss control additive in an amount ranging from 0.71 to 1.43 %w/w; calcium carbonate in an amount of 7.14 %w/w; and a weighing agent in an amount ranging from 18.57 to 20.24 %w/w. In an embodiment of the present invention, the ratio of base oil to water is 70:30. In an embodiment of the present invention, the temperature of wellbore is up to 120°C and the pressure regimes where the equivalent drilling fluid weight required to maintain wellbore stability and hydrostatic head in the well is up to 10 ppg.

[0044] In an embodiment of the present invention, a process for preparation of drilling fluid is provided. The method comprises the steps of adding emulsifiers, viscosifiers and lime to the base oil under stirring conditions at 6000rpm. Subsequently, brine, fluid loss additive, calcium carbonate and barite are added and mixed thoroughly. Further, the mixture is subjected to hot roll at 120°C and 100 psi pressure for 16 hours to obtain the drilling fluid of the present invention and to simulate down hole conditions. After hot rolling, the rheological properties of the drilling fluid are measured to ensure it meets the desired specifications.

[0045] The disclosure herein provides for examples of the oil-based drilling fluid in accordance with an exemplary embodiment of the present invention. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

Working Examples
Example 1

[0046] Drilling fluid compositions were prepared as per the components in table 1 below.

Viscosifier (V1)
Emulsifier PE2 + SE2 PE2 + SE2 PE1 + SE1 PE3 + SE3
Fluid Loss Additive FLC2 FLC1 FLC1 FLC1
Base Oil 36.90 36.90 36.90 36.90
Viscosifier 1.67 1.67 1.74 1.67
Lime 3.10 3.10 3.10 3.10
Primary Emulsifier 1.43 1.43 1.43 0.95
Secondary Emulsifier 2.38 2.38 1.90 1.90
Water 20.44 19.79 20.48 21.02
Calcium Chloride 5.95 5.95 5.95 5.95
Fluid Loss Additive 0.71 1.43 1.43 1.43
Calcium Carbonate 7.14 7.14 7.14 7.14
Barite 20.00 20.00 19.05 19.05
All values mentioned above are in (w/w) % for 1 lab bbl
Table 1
[0047] The drilling fluids prepared in accordance with Example 1 were hot rolled for 16 hrs at 120°C (248°F) temperature and 100 psi pressure in a pre-heated roller oven. After 16 hrs of hot rolling, heating was turned off and formulation was kept rolling for 30 minutes and then kept under stream of water for cooling. The compositions were allowed to retain the ambient temperature and the analysed for following properties of the drilling fluids such as weight, plastic viscosity, yield point, Gel0, Gel10, low shear rate viscosity, WPS (Cl-), emulsion stability, HPHT filtration loss were evaluated, as demonstrated below in table 2.

Viscosifier (V1)
Emulsifier PE2 + SE2 PE2 + SE2 PE1 + SE1 PE3 + SE3
Fluid Loss Additive FLC2 FLC1 FLC1 FLC1
DF Weight at 75±4 °F (BHR) 10.1 10.1 9.9 10
Plastic Viscosity, cP 35 23 24 25
Yield Point, lbs/100ft2 30 30 25 28
Gel0, lbs/100ft2 19 20 19 18
Gel10, lbs/100ft2 27 29 30 27
6 RPM LSRV, Dial reading 17 18 14 17
Oil to Water Ratio 70:30 70:30 70:30 70:30
WPS (Cl-), g/L 182 180 183 179
Emulsion Stability at 120 ±5 °F, Volts 705 940 873 726
HPHT Filtration Loss (30 min @ 300 °F/500psi as per API, all oil), mL 3.2 2.8 3.2 3.0
Table 2

Example 2

[0048] Drilling fluid compositions were prepared as per the components in table 3 below.

Viscosifier (V2)
Emulsifier PE3 + SE3 AE2
Fluid Loss Additive FLC1 FLC1
Base Oil 37.14 36.70
Viscosifier 1.90 2.14
Lime 3.10 3.10
All in One Emulsifier - 3.57
Primary Emulsifier 0.95 -
Secondary Emulsifier 1.90 -
Water 20.48 20.24
Calcium Chloride 5.95 5.95
Fluid Loss Additive 1.43 1.43
Calcium Carbonate 7.14 7.14
Barite 19.52 19.05
All values mentioned above are in (w/w) % for 1 lab bbl
Table 3

[0049] The drilling fluids prepared in accordance with Example 2 were hot rolled for 16 hrs at 120°C (248°F) temperature and 100 psi pressure in a pre-heated roller oven. After 16 hrs of hot rolling, heating was turned off and formulation was kept rolling for 30 minutes and then kept under stream of water for cooling. The formulation was allowed to retain the ambient temperature and the analysed for following properties of the drilling fluids such as weight, plastic viscosity, yield point, Gel0, Gel10, low shear rate viscosity, WPS (Cl-), emulsion stability, and HPHT filtration loss were evaluated, as demonstrated below in table 4.

Viscosifier (V2)
Emulsifier PE3 + SE3 AE2
Fluid Loss Additive FLC1 FLC1
DF Weight at 75±4 °F (BHR) 10 10
Plastic Viscosity, cP 28 30
Yield Point, lbs/100ft2 30 25
Gel0, lbs/100ft2 16 15
Gel10, lbs/100ft2 21 19
6 RPM LSRV, Dial reading 16 10
Oil to Water Ratio 70:30 70:30
WPS (Cl-), g/L 175 177
Emulsion Stability at 120 ±5 °F, Volts 648 907
HPHT Filtration Loss (30 min @ 300 °F/500psi as per API, all oil), mL 3.8 3.6
Table 4

Example 3

[0050] Drilling fluid compositions were prepared as per the components in table 5 below.

Viscosifier (V3)
Emulsifier PE2 + SE2 AE1 PE2 + SE2
Fluid Loss Additive FLC2 FLC1 FLC1
Base Oil 37.14 37.55 36.67
Viscosifier 0.95 1.67 0.95
Lime 3.10 3.10 3.10
All in One Emulsifier - 2.38 -
Primary Emulsifier 1.43 - 1.43
Secondary Emulsifier 2.38 - 2.38
Water 20.56 20.71 20.73
Calcium Chloride 5.95 5.95 5.95
Fluid Loss Additive 0.71 1.43 1.43
Calcium Carbonate 7.14 7.14 7.14
Barite 20.00 19.05 19.05
All values mentioned above are in (w/w) % for 1 lab bbl
Table 5

[0051] The drilling fluids prepared in accordance with Example 3 were hot rolled for 16 hrs at 120°C (248°F) temperature & 100 psi pressure in a pre-heated roller oven. After 16 hrs of hot rolling, heating was turned off and formulation was kept rolling for 30 minutes and then kept under stream of water for cooling. The formulation was allowed to retain the ambient temperature and the analysed for following properties of the drilling fluids such as weight, plastic viscosity, yield point, Gel0, Gel10, low shear rate viscosity, WPS (Cl-), emulsion stability, and HPHT filtration loss were evaluated, as demonstrated below in table 6.

Viscosifier (V3)
Emulsifier PE2 + SE2 AE1 PE2 + SE2
Fluid Loss Additive FLC2 FLC1 FLC1
DF Weight at 75±4 °F (BHR) 10.1 9.9 10
Plastic Viscosity, cP 37 23 32
Yield Point, lbs/100ft2 25 26 26
Gel0, lbs/100ft2 13 19 15
Gel10, lbs/100ft2 19 30 21
6 RPM LSRV, Dial reading 11 16 12
Oil to Water Ratio 70:30 70:30 70:30
WPS (Cl-), g/L 182 172 176
Emulsion Stability at 120 ±5 °F, Volts 707 968 686
HPHT Filtration Loss (30 min @ 300 °F/500psi as per API, all oil), mL 2.8 2.6 3.0
Table 6
Example 4

[0052] Drilling fluid compositions were prepared as per the components in table 7 below.
Viscosifier (V4)
Emulsifier PE3 + SE3 AE2
Fluid Loss Additive FLC1 FLC1
Base Oil 37.62 37.14
Viscosifier 2.74 2.74
Lime 3.10 3.10
All in One Emulsifier - 3.57
Primary Emulsifier 0.95 -
Secondary Emulsifier 1.90 -
Water 19.71 19.45
Calcium Chloride 5.95 5.95
Fluid Loss Additive 1.43 1.43
Calcium Carbonate 7.14 7.14
Barite 19.05 18.57
All values mentioned above are in (w/w) % for 1 lab bbl
Table 7

[0053] The drilling fluids prepared in accordance with Example 4 were hot rolled for 16 hrs at 120°C (248°F) temperature and 100 psi pressure in a pre-heated roller oven. After 16 hrs of hot rolling, heating was turned off and formulation was kept rolling for 30 minutes and then kept under stream of water for cooling. The compositions were allowed to retain the ambient temperature and the analysed for following properties of the drilling fluids such as weight, plastic viscosity, yield point, Gel0, Gel10, low shear rate viscosity, WPS (Cl-), emulsion stability, and HPHT filtration loss were evaluated, as demonstrated below in table 8.

Viscosifier (V4)
Emulsifier PE3 + SE3 AE2
Fluid Loss Additive FLC1 FLC1
DF Weight at
75±4 °F (BHR) 10 10
Plastic Viscosity, cP 28 27
Yield Point, lbs/100ft2 31 26
Gel0, lbs/100ft2 17 18
Gel10, lbs/100ft2 22 23
6 RPM LSRV, Dial reading 17 16
Oil to Water Ratio 70:30 70:30
WPS (Cl-), g/L 184 189
Emulsion Stability at
120 ±5 °F, Volts 814 711
HPHT Filtration Loss (30 min @ 300 °F/500psi as per API, all oil), mL 2.6 2.4
Table 8

Example 5

[0054] Drilling fluid compositions were prepared as per the components in table 9 below.

Viscosifier (V5)
Emulsifier AE1 PE2 + SE2 PE2 + SE2 PE1 + SE1
Fluid Loss Additive FLC1 FLC2 FLC1 FLC2
Base Oil 37.38 37.38 36.90 37.62
Viscosifier 1.67 1.67 1.67 1.74
Lime 2.38 2.38 2.38 2.38
All in One Emulsifier 2.86 - - -
Primary Emulsifier - 1.43 1.43 0.95
Secondary Emulsifier - 2.38 2.38 1.90
Water 20.76 20.11 20.34 21.06
Calcium Chloride 5.95 5.95 5.95 5.95
Fluid Loss Additive 1.43 0.71 1.43 0.71
Calcium Carbonate 7.14 7.14 7.14 7.14
Barite 20.00 20.24 19.05 19.05
All values mentioned above are in (w/w)% for 1 lab bbl
Table 9

[0055] The drilling fluids prepared in accordance with Example 5 were hot rolled for 16 hrs at 120°C (248°F) temperature and 100 psi pressure in a pre-heated roller oven. After 16 hrs of hot rolling, heating was turned off and formulation was kept rolling for 30 minutes and then kept under stream of water for cooling. The compositions were allowed to retain the ambient temperature and the analysed for following properties of the drilling fluids such as weight, plastic viscosity, yield point, Gel0, Gel10, low shear rate viscosity, WPS (Cl-), emulsion stability, and HPHT filtration loss were evaluated, as demonstrated below in table 10.

Viscosifier (V5)
Emulsifier AE1 PE2 + SE2 PE2 + SE2 PE1 + SE1
Fluid Loss Additive FLC1 FLC2 FLC1 FLC2
DF Weight at 75±4 °F (BHR) 10.1 10 10 10
Plastic Viscosity, cP 29 30 27 30
Yield Point, lbs/100ft2 25 25 26 29
Gel0, lbs/100ft2 18 14 16 20
Gel10, lbs/100ft2 28 24 26 27
6 RPM LSRV, Dial reading 15 13 12 16
Oil to Water Ratio 70:30 70:30 70:30 70:30
WPS (Cl-), g/L 182 178 183 176
Emulsion Stability at 120 ±5 °F, Volts 740 850 811 768
HPHT Filtration Loss (30 min @ 300 °F/500psi as per API, all oil), mL 3.0 3.2 2.8 2.8
Table 10

[0056] As demonstrated in the above working examples, the drilling fluid of the present invention surprisingly exhibited constant emulsion stability even after hot rolling it for 120 Hrs (5 Days). Only 5% variation was observed in emulsion stability over 5 days. Further, the drilling fluid of the present invention surprisingly exhibited a minimal sagging tendency (Sag factor) in a range from 0.50 to 0.53 for 120 hours.

[0057] While the exemplary embodiments of the present invention are described and illustrated herein, it will be appreciated that they are merely illustrative. It will be understood by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope of the invention.
, Claims:We Claim:

1) An oil-based drilling fluid composition, comprising:
a base oil in an amount ranging from 36.67 to 37.62 %w/w;
an emulsifier;
lime in an amount ranging from 2.38 to 3.10 %w/w;
a viscosifier in an amount ranging from 0.95 to 2.74 %w/w;
a brine comprising calcium chloride and water;
a fluid loss control additive in an amount ranging from 0.71 to 1.43 %w/w;
calcium carbonate in an amount of 7.14 %w/w; and
a weighing agent in an amount ranging from 18.57 to 20.24 %w/w,
wherein the ratio of base oil to water is 70:30, and wherein the oil-based drilling fluid composition exhibits an electrical stability for up to 5 days and a sag factor in a range from 0.50 to 0.53 for 120 hours.

2) The composition as claimed in claim 1, wherein the base oil is a low toxic mineral oil selected from a group comprising of n-Alkanes (C9-C17) having aromatics less than 1%.

3) The composition as claimed in claim 1, wherein the emulsifier is an all-in-one emulsifier in an amount ranging from 2.38 to 3.57 %w/w.

4) The composition as claimed in claim 1, wherein the emulsifier is a combination of a primary emulsifier in an amount ranging from 0.95 to 1.43 %w/w, and a secondary emulsifier in an amount ranging from 1.90 to 2.38 %w/w;

5) The composition as claimed in claim 3, wherein the all-in-one emulsifier is selected from a group comprising of blend of fatty acids or fatty acids derivatives, non-ionic surfactants, ionic surfactants.

6) The composition as claimed in claim 4, wherein the primary emulsifier is selected from a group comprising of fatty acids, and calcium soaps.

7) The composition as claimed in claim 4, wherein the secondary emulsifier is selected from a group comprising of polyamides, alkanolamides, non-ionic surfactants, and ionic surfactants.

8) The composition as claimed in claim 1, wherein the viscosifier is selected from a group comprising of amine treated bentonite or attapulgite.

9) The composition as claimed in claim 1, wherein amount of the calcium chloride is 5.95 % w/w.

10) The composition as claimed in claim 1, wherein amount of water is 19.45 to 21.06 % w/w.

11) The composition as claimed in claim 1, wherein the fluid loss additive is selected from a group comprising of organophilic lignites, gilsonite, or asphalt derivatives.

12) The composition as claimed in claim 1, wherein the weighing agent is barite.

13) The composition as claimed in claim 1, wherein plastic viscosity of the oil-based drilling fluid composition is in a range from 23 to 37 cP.

14) The composition as claimed claim 1, wherein yield point of the oil-based drilling fluid composition is in a range from 25 to 31 lbs/100ft2.

15) The composition as claimed in claim 1, wherein the water phase salinity is in a range from 172 to 189 g/L.

16) The composition as claimed in claim 1, wherein the emulsion stability at 120±5oF is in a range from 648 to 968 volts.

17) The composition as claimed in claim 1, wherein the gel strength is in a range from 13-30 lbs/100ft2.

18) The composition as claimed in claim 1, wherein the weight of drilling fluid at 750F is 10.0±0.1 ppg.

19) The composition as claimed in claim 1, wherein the low shear rate viscosity at 6RPM is in a range from 11-18.

20) The composition as claimed in claim 1, wherein the high pressure high temperature (HPHT) filtration Loss is in a range from 2.4 to 3.8.

Dated this 18th day of September, 2025

Oil and Natural Gas Corporation Limited
(Jogeshwar Mishra)
IN/PA - 2578
of Shardul Amarchand Mangaldas & Co.
Attorneys for the Applicant