Description:Field of the invention

[0001] The present invention relates to the field of drilling fluids. More particularly, the present invention relates to a water-based drilling fluid composition which is capable of resisting pH fluctuations to ensure stability and optimal performance.

Background of the invention

[0002] Drilling fluids, commonly referred to as Drilling muds, are essential to the oil and gas industry, for performing drilling operations. Drilling fluids are primarily classified into three types, i.e., oil-based, water-based and aerated/foam-based, depending on the base fluid used. Water-based drilling fluids are commonly used for their cost-effectiveness, environmental compatibility, and ease of handling. Maintaining the water-based drilling fluids at an optimal pH, typically between 8.5 and 10.5, is key to their performance. The pH level of drilling fluids has a significant influence on their stability, rheological properties, and the efficiency of other additives in the drilling fluid. Further, the pH of the drilling fluid also plays a major role in protection of surface and downhole equipment from corrosion.

[0003] However, maintaining stable pH levels under variable conditions encountered during drilling operation remains a significant challenge. Further, the pH of drilling fluids tends to fluctuate over time due to high downhole temperatures, contamination from formation fluids, and the production of acidic gases such as hydrogen sulphide (H₂S), carbon di oxide (CO2). Any decrease in pH may result in decrease of the alkalinity of the drilling fluid, which accelerates the corrosion rate of surface and downhole equipment, potentially leading to equipment failure, costly operational delays, and increased maintenance requirements. This pH instability undermines the performance of the drilling fluid and compromises wellbore stability.

[0004] Decrease in pH levels may also cause degradation of other additives added to drilling fluid. This degradation reduces effectiveness of additives in stabilising the wellbore, controlling fluid loss, and optimising rheological properties, thereby reducing the performance of the drilling fluid. Furthermore, entry of degraded drilling fluid into surrounding formations can result in groundwater contamination, thereby posing environmental risks.

[0005] Currently available water-based drilling fluids lack sufficient resistance in pH fluctuations due to contamination from acidic gases, presence of any cement slurry in wellbore, wellbore temperature etc. Traditional methods of pH control rely on well-known alkalinity agents. However, these agents fail to offer long-term pH stability and sometimes result in undesirable chemical interactions within the fluid. Their effectiveness is further limited by the variability in fluid composition and external conditions, often requiring frequent adjustments and leading to overuse or insufficient treatment.
[0006] The operational consequences of inadequate pH control are considerable. Frequent pH adjustments increase material and labour costs, while inconsistent additive performance can result in overcompensation and overdosing which further escalates expenses. pH instability and its associated issues such as equipment corrosion, additive degradation, and fluid destabilisation, often result in increased non-productive time (NPT), operational interruptions, and higher overall well costs.

[0007] In light of the above drawbacks, there is a need for a water-based drilling fluid capable of resisting pH fluctuations for ensuring optimal performance across diverse operational conditions. There is a need for water-based drilling fluid which is capable of resisting pH fluctuations over extended periods and under a wide range of operational conditions.

Summary of the invention

[0008] In various embodiments of the present invention, a drilling fluid composition capable of resisting pH fluctuations to ensure stability and optimal performance is provided. The drilling fluid composition comprises a base fluid and at least one pH buffering agent selected from a group consisting of ammonium carbonate or Tris(hydroxymethyl) aminomethane hydrochloride in an amount ranging from 0.6 to 0.8 %W/V. The pH buffering agent is capable of resisting pH fluctuations and maintaining the pH of drilling fluid in a range from 8.5 to 10.0.

[0009] In an embodiment of the present invention, the base fluid is fresh water. The one or more additives are selected from a group comprising of, bentonite, soda ash, potassium chloride, XC polymer, poly anionic cellulose, caustic potash, caustic soda, micronized calcium carbonate, barite and at least one biocide.

[0010] In an embodiment of the present invention, the amount of bentonite is in a range from 2.0 to 3.0 %w/v, the amount of soda ash is 0.1 %w/v, the amount of potassium chloride is 5.0 %w/v, the amount of XC polymer is a range from 0.25 to 0.45 %w/v, the amount of poly anionic cellulose is in a range from 1.2 to 1.5 % w/v, the amount of caustic potash 0.1 to 0.2 %w/v, the amount of caustic soda is in a range from 0.1 to 0.2 %w/v, the amount of micronized calcium carbonate is in a range from 5.0 to 6.0 %w/v, and the amount of biocide is in a range from 0.1 to 0.2 %w/v.

Detailed description of the invention

[0011] The present invention provides a water-based drilling fluid capable of resisting pH fluctuations for ensuring optimal performance across diverse operational conditions. The drilling fluid of the present invention resists pH fluctuations caused by various factors such as contaminants, high temperatures, encountering acidic gases while drilling the well. The water-based drilling fluid maintains the pH within recommended range, thereby enhancing drilling efficiency, reducing equipment corrosion, and mitigating environmental risks. The water-based drilling fluid of the present invention also enhances stability, safety, and environmental sustainability in the oil and gas industry.
[0012] 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 persons skilled in the 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.

[0013] In an embodiment of the present invention, a water-based drilling fluid composition is provided. The composition comprises a base fluid, one or more additives, and at least one pH buffering agent in an amount ranging from 0.6 to 0.8 %W/V. The pH buffering agent is capable of resisting pH fluctuations and maintaining the pH of drilling fluid in a range from 8.5 to 10.0.

Base Fluid

[0014] In an embodiment of the present invention, the water-based drilling fluid comprises water as base fluid. In an exemplary embodiment, the water may be fresh water. The use of water as the base fluid provides a medium for the dispersion of various additives and acts as a bulk fluid. Water-based drilling fluids are characterized by their ability to hydrate certain clays, which increases the viscosity of the drilling fluid and enhances the carrying capacity. Water also facilitates the formation of a thin, low-permeability filter cake on the wellbore walls, thereby minimizing fluid loss to the formation and maintaining wellbore stability.

[0015] The use of water as base fluid in drilling fluid offers several advantages, including lower cost, reduced environmental impact, and ease of handling compared to oil-based systems. Water also supports the addition of other additives thereby ensuring that the drilling fluid maintains its desired properties under a range of downhole conditions. The water-based drilling fluids provides effective cooling and lubrication of the drill equipment, supports wellbore integrity, and enables efficient cuttings transport throughout the drilling process.

Additives

[0016] In an embodiment of the present invention, the water-based drilling fluid comprises one or more additives for effective functioning of the drilling fluid. The additives may be selected from a group comprising of bentonite, soda ash, potassium chloride, XC polymer, polyanionic cellulose, caustic soda and caustic potash, micronized calcium carbonate, barite and a biocide. In an exemplary embodiment of the present invention, the amount of additives varies depending on the type of drilling fluid.

[0017] In an embodiment of the present invention, the additive bentonite is in the form of pre-hydrated bentonite suspension. In an exemplary embodiment of the present invention, the amount of bentonite is in a range from 2.0 to 3.0% w/v. Bentonite also influences the viscosity of drilling fluid which is essential for suspending and transporting drill cuttings to the surface, thereby preventing their accumulation at the bottom of the wellbore. The gel structure formed by the bentonite also helps in forming a thin, low-permeability filter cake on the walls of wellbore, which minimises the loss of drilling fluid into the surrounding rock formations. Additionally, bentonite aids in stabilizing the wellbore which is crucial for maintaining wellbore integrity. Bentonite’s swelling properties also help seal micro-fractures and pores, thereby reducing the risk of formation damage and fluid invasion. The presence of bentonite also enhances the lubricity of the drilling fluid, thereby reducing friction between the drill equipment and the wellbore.

[0018] In an embodiment of the present invention, the additive soda ash in the drilling fluid helps to soften the base fluid, i.e., water, by precipitating calcium and magnesium ions, which are common in fresh water. These ions can interfere with the performance of other drilling fluid additives, particularly polymers and clays, by causing unwanted reactions or reducing their effectiveness. By removing hardness, soda ash ensures that the drilling fluid maintains its desired properties. Furthermore, soda ash also helps in maintaining the alkalinity of the drilling fluid, which is important for the stability and corrosion control. Due to the alkaline environment created by soda ash the growth of undesirable bacteria is also prevented. The use of soda ash thus contributes to the overall stability and longevity of the drilling fluid system. In an exemplary embodiment of the present invention, the amount of soda ash in the water-based drilling fluid is 0.1% w/v.

[0019] In an embodiment of the present invention, the additive potassium chloride (KCl) functions as a clay inhibitor. In an exemplary embodiment of the present invention, the amount of potassium chloride (KCl) is 5.0% w/v. Subterranean formations contain reactive clays which can swell and disperse when exposed to base fluid (water) in the drilling fluids. The potassium ions from KCl exchange with sodium ions in the clay structure, inhibit the clay’s tendency to swell and help maintain wellbore stability. By stabilising the formation, KCl allows for smoother drilling operations and minimizes non-productive time.

[0020] In an embodiment of the present invention, the additive XC polymer is a high molecular weight polymer that enhances the viscosity of drilling fluid, which is crucial for suspending and transporting drill cuttings. In an exemplary embodiment of the present invention, the amount of XC polymer is in a range from 0.25 to 0.45% w/v. The. The enhanced viscosity also improves hole cleaning efficiency and reduces the risk of stuck pipe. In addition, the XC polymer provides Low Shear Rate Viscosity (LSRV) and sheer thinning properties to drilling fluid.

[0021] In an embodiment of the present invention, the additive polyanionic cellulose is a water-soluble polymer which aids in controlling the filtration loss in drilling fluids. In an exemplary embodiment of the present invention, the amount of polyanionic cellulose is in a range from 1.2 to 1.5 % w/v. Polyanionic cellulose forms a thin layer on the wellbore wall, which acts as a barrier to prevent the invasion of drilling fluid into the formation. This minimises formation damage and helps maintain wellbore stability. The use of polyanionic cellulose also contributes to the viscosity of the drilling fluid, thereby aiding in the suspension and transport of cuttings. The use of polyanionic cellulose is particularly valuable in sensitive formations where fluid loss control is critical.

[0022] In an embodiment of the present invention, the additives caustic soda/caustic potash maintain an alkaline environment which is essential for the stability and performance of other additives, such as bentonite and polymers, and for inhibiting corrosion of wellbore equipment. Caustic soda and caustic potash facilitate neutralizing acidic contaminants that may be encountered during drilling. In an exemplary embodiment of the present invention, the amount of caustic soda (Sodium Hydroxide) is in a range from 0.1 to 0.2 %w/v and caustic potash (Potassium Hydroxide) is in a range from 0.1 to 0.2 %w/v.

[0023] In an embodiment of the present invention, the additive micronized calcium carbonate is a finely ground material that functions as a bridging agent in drilling fluids. Owing to its small particle size micronized calcium carbonate effectively seals micro-fractures and pores in the formation, thereby reducing fluid loss maintain wellbore integrity. In addition to its bridging properties, calcium carbonate enhances the overall performance and reliability of the drilling fluid, especially in challenging drilling environments. In an exemplary embodiment of the present invention, the amount of micronized calcium carbonate is in a range from 5.0 to 6.0% w/v.

[0024] In an embodiment of the present invention, the additive barite in the drilling fluid helps in increasing the density of drilling fluids, which is critical for controlling formation pressures. Further, the particle size of barite enables it to remain suspended in the drilling fluid, thereby contributing to the overall stability and effectiveness of the drilling fluid. Barite is crucial in deep or high-pressure wellbore where precise control of fluid density is required. In an embodiment of the present invention, the amount of barite varies depending on the desired density of drilling fluid. In an exemplary embodiment of the present invention, in KPP drilling fluid the amount of barite is approximately 23 %w/v, and in lignite-based drilling fluid the amount of barite is in approximately 148 %w/v.

[0025] In an embodiment of the invention, the additive biocide is added to the drilling fluid to prevent the growth of undesirable bacteria that can degrade other additives in the drilling fluid. Biocide also assists mitigating harmful bacteria such as sulphate-reducing bacteria, which poses safety and environmental risks. The biocide of the present invention helps maintain drilling fluid properties and reduces the risk of operational problems related to bacterial contamination. In an exemplary embodiment of the present invention, the amount of biocide is in a range from 0.1 to 0.2% w/v.

pH Buffering Agents

[0026] Maintaining pH of drilling fluids within an optimal range during drilling operations is critical to optimize the performance of additives in the drilling fluids. In an embodiment of the present invention, the drilling fluid comprises at least one pH buffering agent, to maintain the pH of drilling fluid in an optimal range. The pH buffering agent may be selected from a group consisting of ammonium carbonate or Tris(hydroxymethyl) amino methane hydrochloride (Tris hydrochloride). In an embodiment of the present invention, the amount of the pH buffering agent is in a range from 0.6 to 0.8 %W/V. In an embodiment of the present invention, the pH buffering agent of the present invention is capable of resisting pH fluctuations and maintain the pH of drilling fluid in a range from 8.5 to 10.0.

[0027] In an exemplary embodiment, the pH buffering agent is ammonium carbonate, which is capable of maintaining the pH of drilling fluid in a range from 9.0 to 10.0, thereby making it especially valuable in applications where precise pH control is critical. In a drilling fluid, the surprising ability of ammonium carbonate to dissociate into ammonium, carbonate and bicarbonate ions enables it to counteract both acidic and basic contaminants. In the presence of acids, carbonate and bicarbonate ions react with hydrogen ions to form less acidic byproducts, thereby mitigating reduction of pH. Conversely, in the presence of any basic contaminants, ammonium ions neutralize hydroxide ions by forming ammonia and water, thereby preventing any undesirable increase in pH. Advantageously, this dual-action buffering capacity ensures that the pH of drilling fluid remains stable even when subjected to significant acidic or basic conditions in drilling environments. The adaptable buffering action of ammonium carbonate not only enhances the operational stability of drilling fluids but also extends the functional lifespan and reliability of drilling fluid.

[0028] In an exemplary embodiment of the present invention, the drilling fluid comprises Tris hydrochloride as a buffering agent. Tris hydrochloride serves as an effective buffering agent due to its ability to maintain a stable pH environment within the range of approximately 7 to 9. Tris hydrochloride, being a zwitterionic compound exhibits low ionic strength, thereby minimizing interference with enzymatic activities and other sensitive biological contaminants. Tris hydrochloride is obtained by dissolving Tris hydrochloride in water and titrating with hydrochloric acid to achieve the desired pH, which offers both versatility and compatibility with water-based drilling fluids. In an embodiment of the present invention, the Tris hydrochloride neutralizes acid when encountered with an acidic contaminant during drilling. In another embodiment of the present invention, when encountered with a basic contaminant during drilling, the Tris hydrochloride releases H+ ion neutralizing the effect of Base.

[0029] In an embodiment of the present invention, the pH buffering agent such as ammonium carbonate or Tris hydrochloride effectively buffer drilling fluids in their capacity to maintain a stable pH during drilling operations. In an embodiment, when ammonium carbonate is used as a pH buffering agent it releases ammonia and carbon dioxide upon reaction, which provides a self-regulating pH environment particularly suitable for high-temperature and high-pressure downhole conditions. In another embodiment of the present invention, when Tris hydrochloride is used as a pH buffer, it maintains a non-volatile and thermally stable buffering system that operates efficiently in near neutral to slightly basic pH ranges. This reliable pH control preserves the functional properties of the drilling fluid, thereby resulting in improved drilling efficiency, reduced non-productive time, and greater wellbore stability.

[0030] In an embodiment of the present invention, the plastic viscosity of drilling fluid is in a range from 08 to 65. In an embodiment of the present invention, the yield point of drilling fluid is in a range from 09 to 47. In an advantageous embodiment, the plastic viscosity and yield point of the drilling fluid remained unchanged, indicating that the pH buffering agents are compatible with other additives of the drilling fluid.

[0031] Advantageously, the water-based drilling fluid of the present invention addresses issues related to corrosion that are prevalent in drilling operations. By maintaining the pH at optimal levels, the pH buffers significantly decrease the corrosion rate of surface and downhole equipment which helps extend equipment lifespan and lower maintenance expenses. In contrast to conventional pH agents that require frequent adjustments which may lead to inconsistent results, the pH buffers of present invention provide sustained pH stability with reduced additive usage. Further, advantageously the pH buffers of the present invention reduce environmental risks and supports the effectiveness of other fluid additives. The pH buffering agent reduces the reliance on conventionally used hazardous alkaline metal hydroxides, thereby improving safety during handling and use.

[0032] The disclosure herein provides for examples that illustrate various water-based drilling fluids prepared with ammonium carbonate or Tris hydrochloride as pH buffering agent in accordance with various embodiments 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, following examples should not be construed as limiting the scope of the embodiments herein.

Working Examples

[0033] Different types of water-based drilling fluids comprising the pH buffering agent of the present invention were evaluated for their pH buffering ability. Experiments were conducted on the following fluid types of drilling fluids (1) KCl-PHPA-Polyamine-Polyol drilling fluid, (2) Non-damaging drilling fluid, (3) Gel-polymer drilling fluid, and (4) Lignite-based HPHT drilling fluid to evaluate the effectiveness of ammonium carbonate and KCl-PHPA-Polyol Drilling Fluid for Tris hydrochloride
as pH buffer.

Experiment 1: Gel polymer drilling fluid

[0034] Gel polymer drilling fluid (F1) was prepared as per the components in Table 1 below.

Gel Polymer Drilling Fluid (F1)
S. No. Name of Additives Dosages % (w/v)
1. Pre-Hydrated Bentonite Suspension 3.0 (6 cp)
2. Soda Ash 0.1
3. Biocide 0.1
4. PAC – LVG 1.4
5. NaOH As per requirement
6. RL 1.5
7. Micronized Calcium Carbonate (MCC) 5.0
8. Barite Up to 1.20 SG
Table 1

[0035] In this experiment, out of the total volume, one set of the drilling fluid was kept as base drilling fluid (without pH buffer-F1), and the other set was treated with pH buffer (F1+ pH buffer). The set without pH buffer was again divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks). Similarly, the set with pH buffer (ammonium carbonate) was also divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks).

[0036] All the six sets (three with pH Buffer and three without pH Buffer) were evaluated for pH change after hot roll (AHR) for 24 hrs, 48 hrs and 120 hrs. After the hot roll, the drilling fluids were analysed for various properties, as shown below in Tables 2 and 3.

F1 F1 + Ammonium Carbonate (0.8%)
pH (A)
Base Fluid (B)
Citric Acid (0.2%) (C)
Cement (0.5%) (D)
Base Fluid (E)
Citric Acid (0.2%) (F)
Cement (0.5%)
BHR 11.64 9.2 11.9 9.25 8.99 9.30
AHR(24 hrs) 9.58 8.97 10.2 9.26 9.45 9.62
AHR(48 hrs) 9.19 8.77 9.49 9.39 9.53 9.59
AHR(120 hrs) 8.9 8.82 9.1 9.30 9.48 9.48
Table 2

F1 F1 + Ammonium Carbonate
24hrs 48hrs 120hrs 24hrs 48hrs 120hrs
Ɵ600 72 78 55 90 94 90
Ɵ300 47 54 36 56 57 61
Ɵ200 36 45 29 42 42 49
Ɵ100 25 35 21 27 26 32
Ɵ6 13 25 11 06 05 06
Ɵ3 12 22 10 05 04 05
Gel0/10/30 07/25 14/31 10/16 05/29 05/25 05/15
PV 25 24 19 34 37 29
YP 22 30 17 22 20 32
LPLT F/L (cc) 4.8 5.0 7.0 4.6 4.8 6.0
Table 3

[0037] Ammonium carbonate treated drilling fluid (F1) was found to be stable in a range from 9.25 to 9.39 as compared to the base fluid where pH was dropped from 11.64 to 8.9 after 120 hrs, as demonstrated in Table 2. Moreover, the ammonium carbonate was also found to be effective in case of acid and cement contamination as compared to the base fluid (F1). The rheological and filtration properties of gel-polymer drilling fluid was found to be not affected much after treatment with ammonium carbonate. In addition, relatively stable properties were observed after treatment for longer hours with ammonium carbonate treated drilling fluid, as demonstrated in Table no. 3.

Experiment 2: Non-Damaging Drilling Fluid

[0038] Non-damaging drilling fluid (F2) was prepared as per the components in Table 4 below.

Non-Damaging Drilling Fluid (F2)
S.No. Name of Additives Dosages % (w/v)
1. Technical Water As per requirement
2. Soda Ash 0.1
3. Potassium Chloride 5.0
4. XCP 0.45
5. PAC – LVG 1.2
6. PAC-RG 0.3
7. Micronized Calcium Carbonate (MCC) 6.0
8. KOH As per requirement
Table 4

[0039] In this experiment, out of the total volume, one set of the drilling fluid was kept as base drilling fluid (without pH buffer-F2) and the other set was treated with pH buffer (F2+ pH buffer). The set without pH buffer was again divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks). Similarly, the set with pH buffer (ammonium carbonate) was also divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks).

[0040] All the six sets (three with pH Buffer and three without pH Buffer) were evaluated for pH change after hot roll (AHR) for 24 hrs, 48 hrs and 120 hrs. After the hot roll the drilling fluids were analysed for various properties, as shown below in Tables 5 and 6.

F2 F2 + Ammonium Carbonate (0.8%)
pH (A)
Base Fluid (B)
Citric Acid (0.2%) (C)
Cement (0.5%) (D)
Base Fluid (E)
Citric Acid (0.2%) (F)
Cement (0.5%)
BHR 12.09 8.12 12.47 9.28 9.03 9.25
AHR(24 hrs) 10.12 8.5 9.8 9.25 9.09 9.36
AHR(48 hrs) 9.06 8.5 8.85 9.17 9.1 9.25
AHR(120 hrs) 8.60 8.53 8.42 9.08 9.03 9.2
Table 5

F2 F2 + Ammonium Carbonate
24hrs 48hrs 120hrs 24hrs 48hrs 120hrs
Ɵ600 80 53 35 50 33 25
Ɵ300 60 37 24 35 23 17
Ɵ200 49 29 16 29 18 12
Ɵ100 36 21 11 21 12 09
Ɵ6 11 07 06 06 02 05
Ɵ3 09 05 03 04 01 02
Gel0/10/30 10/14 05/08 03/05 05/06 02/03 02/03
PV 20 24 11 15 10 08
YP 40 30 13 20 13 09
LPLT F/L (cc) 4.5 5.0 8.0 4.8 5.2 8.0
Table 6

[0041] Ammonium carbonate treated drilling fluid (F2) was found to be stable in a range from 9.03 to 9.26 as compared to the base fluid where pH was dropped from 12.09 to 8.6 after 120 hrs of hot roll, as demonstrated in Table 5. Further, the ammonium carbonate buffer was also found to be effective in case of acid and cement contamination as compared to the base fluid. The rheological and filtration properties of the non-damaging drilling fluid was found to be not affected much after treatment with buffer as demonstrated in Table 6.

Experiment 3: KCl-PHPA-Polyol Drilling Fluid

[0042] KCl-PHPA-Polyol drilling fluid (F3) was prepared as per the components in Table 7 below.

KCl-PHPA-Polyol Drilling Fluid (F3)
S.No. Name of Additives Dosages % (w/v)
1. Technical Water As per requirement
2. Soda Ash 0.1
3. Biocide 0.1
4. Potassium Chloride 5.0
5. XCP 0.25
6. PAC – LVG 1.5
7. PHPA-HT 0.3
8. Polyol Gd II 5.0
9. Micronized Calcium Carbonate (MCC) 5.0
10. Sulphonated Asphalt 2.0
11. Barite Up to 1.40 SG
Table 7

[0043] In this experiment, out of the total volume, one set of the drilling fluid was kept as base drilling fluid (without pH buffer-F3) and the other set was treated with pH buffer (F3 + pH buffer). The set without pH buffer was again divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks). Similarly, the set with pH buffer (ammonium carbonate) was also divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks).

[0044] All the six sets (three with pH Buffer and three without pH Buffer) were evaluated for pH change after hot roll (AHR) for 24 hrs, 48 hrs and 120 hrs. After the hot roll, the drilling fluids were analysed for various properties, as shown below in Tables 8 and 9.

F3 F3 + Ammonium Carbonate (0.8%)
pH (A)
Base Fluid (B)
Citric Acid (0.2%) (C)
Cement (0.5%) (D)
Base Fluid (E)
Citric Acid (0.2%) (F)
Cement (0.5%)
BHR 9.6 8.73 9.93 9.11 8.9 9.16
AHR(24 hrs) 8.72 8.77 9.14 9.04 9.11 9.25
AHR(48 hrs) 8.58 8.70 8.82 9.06 9.24 9.32
AHR(120 hrs) 8.59 8.63 8.71 9.03 9.18 9.29
Table 8
F3 F3 + Ammonium Carbonate
24 hrs 48 hrs 120 hrs 24 hrs 48 hrs 120 hrs
Ɵ600 89 72 48 73 65 45
Ɵ300 56 46 30 47 40 28
Ɵ200 43 35 18 35 32 15
Ɵ100 28 21 14 23 18 12
Ɵ6 07 06 04 05 04 04
Ɵ3 06 04 03 04 03 02
Gel0/10 07/08 05/07 03/05 05/07 04/05 03/04
PV 33 26 18 26 25 17
YP 23 20 12 21 15 11
LPLT F/L (cc) 4.0 4.2 5.0 4.2 4.5 5.0
Table 9

[0045] Ammonium carbonates treated drilling fluid (F3) was found to be stable in a range from 8.9 to 9.32 as compared to the base fluid where pH was dropped from 9.6 to 8.59 after 120 hrs, as demonstrated in Table No. 8. Further, ammonium carbonate buffer was also found to be effective in case of acid and cement contamination as compared to the base drilling fluid. The rheological and filtration properties of drilling fluid (F3) was found to be not affected very much after treatment with buffer as demonstrated in Table no. 9.

Experiment 4: KCl - K-lignite Drilling Fluid

[0046] KCl-K-lignite drilling fluid (F4) was prepared as per the components in Table 10 below.

KCl - K-lignite Drilling Fluid (F4)
S.No. Name of Additives Dosages % (w/v)
1. Pre Hydrated Bentonite Suspension 2.0 (4 cp)
2. Oxygen Scavenger 0.1
3. Soda Ash 0.1
4. Biocide 0.2
5. Potassium Chloride 5.0
6. Micronized Calcium Carbonate (MCC) 5.0
7. Sulphonated Asphalt 2.0
8. K-lignite 3.0
9. High Temperature Fluid Loss Reducer 2.0
10. Barite Up to 1.85 SG
11. KOH As per requirement
Table 10

[0047] In this experiment, out of the total volume, one set of the drilling fluid was kept as base drilling fluid (without pH buffer-F4) and the other set was treated with pH buffer (F4 + pH buffer). The set without pH buffer was again divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks). Similarly, the set with pH buffer (ammonium carbonate) was also divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks).

[0048] All the six sets (three with pH Buffer and three without pH Buffer) were evaluated for pH change after hot roll (AHR) for 24 hrs, 48 hrs and 120 hrs. After the hot roll, the drilling fluids were analysed for various properties, as shown below in Tables 11 and 12.

F4 F4 + Ammonium Carbonate (0.8%)
pH (A)
Base Fluid (B)
Citric Acid (0.2%) (C)
Cement (0.5%) (D)
Base Fluid (E)
Citric Acid (0.2%) (F)
Cement (0.5%)
BHR 10.75 9.28 10.8 9.1 9.05 9.2
AHR(24 hrs) 9.23 8.84 9.34 9.52 9.47 9.70
AHR(48 hrs) 9.29 9.14 9.44 9.59 9.65 9.76
AHR(120 hrs) 9.28 9.23 9.46 9.69 9.67 9.77
Table 11
F4 F4 + Ammonium Carbonate
24 hrs 48 hrs 120 hrs 24 hrs 48 hrs 120 hrs
Ɵ600 153 140 98 165 146 104
Ɵ300 95 85 56 100 86 59
Ɵ200 76 65 40 82 62 43
Ɵ100 52 42 23 55 41 25
Ɵ6 20 18 03 22 17 03
Ɵ3 10 09 03 11 10 03
Gel0/10 12/15 10/14 04/08 13/17 10/15 04/10
PV 58 55 42 65 60 45
YP 37 30 14 35 26 14
LPLT F/L (cc) 3.0 3.2 3.8 2.8 3.2 3.6
Table 12

[0049] Ammonium carbonate treated drilling fluid (F4) was found to be stable in a range from 9.05 to 9.77 as compared to the base fluid where pH was dropped from 10.75 to 9.28 after 120 hrs, as demonstrated in Table 11. Further, ammonium carbonate buffer was also determined to be effective in case of acid and cement contamination as compared to the base fluid. A slight increasing trend of pH with time was observed in ammonium carbonate treated drilling fluid (f4) which is good as lignite-based drilling fluids are expected to have a pH range 9.5-10.5 and with time ammonium carbonate aids in maintaining the same pH range. The rheological and filtration properties of KCl-K-lignite drilling fluid was found to be not affected very much after treatment with buffer as demonstrated in, Table 12.

Experiment 5: KCl – PHPA – Polyol drilling fluid

[0050] KCl – PHPA – Polyol drilling fluid (F5) was prepared as per the components in Table 13 below.

KCl – PHPA – Polyol Drilling Fluid (F5)
S. No. Name of Additives Dosages % (w/v)
1. Technical Water As per requirement
2. Soda Ash 0.1
3. Biocide 0.1
4. Potassium Chloride 5.0
5. XCP 0.3
6. PAC – LVG 1.5
7. PHPA-HT 0.3
8. Polyol Gd II 5.0
9. Micronized Calcium Carbonate (MCC) 5.0
10. Sulphonated Asphalt 2.0
11. Barite Up to 1.40 SG
Table 13
[0051] In this experiment, out of the total volume, one set of the drilling fluid was kept as base drilling fluid (without pH buffer-F5) and the other set was treated with pH buffer (F5 + pH buffer). The set without pH buffer was again divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks). Similarly, the set with pH buffer (Tris Hydrochloride) was also divided into three parts: (a) without contaminant; (b) treated with acidic contaminant (citric acid); and (c) treated with basic contaminant (Powder of Set Cement Blocks).

[0052] All the six sets (three with pH Buffer and three without pH Buffer) were evaluated for pH change after hot roll (AHR) for 24 hrs, 48 hrs and 120 hrs. After the hot roll, the drilling fluids were analysed for various properties, as shown below in Tables 14 and 15.

F5 F5 + Tris Hydrochloride(0.6%)
pH (A)
Base Fluid (B)
Citric Acid (0.2%) (C)
Cement (0.5%) (D)
Base Fluid (E)
Citric Acid (0.2%) (F)
Cement (0.5%)
BHR 9.5 8.61 9.71 8.54 8.75 8.74
AHR(24 hrs) 8.57 8.24 8.82 8.60 8.67 8.78
AHR(48 hrs) 8.65 8.46 8.76 8.70 8.69 8.90
AHR(120 hrs) 8.64 8.43 8.61 8.58 8.53 8.75
Table 14

F5 F5 + Tris Hydrochloride
24hrs 48hrs 120hrs 24hrs 48hrs 120hrs
Ɵ600 117 97 61 105 96 59
Ɵ300 82 71 41 75 66 41
Ɵ200 66 57 30 60 50 31
Ɵ100 44 38 19 40 34 21
Ɵ6 12 10 04 10 10 05
Ɵ3 10 07 02 09 07 03
Gel0/10/30 10/11 07/08 03/03 10/11 07/08 04/05
PV 35 26 20 30 30 18
YP 47 45 21 45 36 23
LPLT F/L (cc) 3.0 3.2 6.0 3.5 3.6 6.4
Table 15

[0053] In the experiment, Tris hydrochloride treated drilling fluid (F5) was found to be stable in a range from 8.53 to 8.90 as compared to the base fluid where pH was dropped from 9.5 to 8.64 after 120 hrs, as demonstrated in Table 14. Further, Tris hydrochloride was also found to be effective in case of acid and cement contamination as compared to the base drilling fluid (F5). The rheological and filtration properties of KCl-PHPA-Polyol drilling fluid (F5) was not found to be affected much after treatment with buffer, as demonstrated in Table 15.

[0054] 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. A drilling fluid composition, comprising:
a base fluid;
one or more additives; and
at least one pH buffering agent selected from a group consisting of ammonium carbonate or Tris(hydroxymethyl) aminomethane hydrochloride in an amount ranging from 0.6 to 0.8 %W/V;
wherein the pH buffering agent is capable of resisting pH fluctuations and maintain the pH of drilling fluid in a range from 8.5 to 10.0.

2. The composition as claimed in claim 1, wherein the base fluid is fresh water.

3. The composition as claimed in claim 1, wherein the additives are selected from a group comprising of, bentonite, soda ash, potassium chloride, XC polymer, poly anionic cellulose, caustic potash, caustic soda, micronized calcium carbonate, barite and at least one biocide.

4. The composition as claimed in claim 1, wherein the amount of bentonite is in a range from 2.0 to 3.0 %w/v.

5. The composition as claimed in claim 1, wherein the amount of soda ash is 0.1 %w/v.

6. The composition as claimed in claim 1, wherein the amount of potassium chloride is 5.0 %w/v.

7. The composition as claimed in claim 1, wherein the amount of XC polymer is a range from 0.25 to 0.45 %w/v.

8. The composition as claimed in claim 1, wherein the amount of polyanionic cellulose is in a range from 1.2 to 1.5 % w/v.

9. The composition as claimed in claim 1, wherein the amount of caustic potash is 0.1 to 0.2 %w/v.

10. The composition as claimed in claim 1, wherein the amount of caustic soda is in a range from 0.1 to 0.2 %w/v

11. The composition as claimed in claim 1, wherein the amount of micronized calcium carbonate is in a range from 5.0 to 6.0 %w/v.

12. The composition as claimed in claim 1, wherein the amount of biocide is in a range from 0.1 to 0.2 %w/v.

13. The composition as claimed in claim 1, wherein the plastic viscosity of drilling fluid is in a range from 08 to 65.

14. The composition as claimed in claim 1, wherein the yield point of drilling fluid is in a range from 09 to 47.
Dated this 8th day of September, 2025

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