Process for preparing effluent water-based drilling fluid

Abstract

A process for preparing an effluent water based drilling fluid is provided. The process comprises treating effluent water with a pre-determined amount of sodium carbonate and bactericide to obtain a base fluid. The effluent water is obtained by treating produced water generated during oil well drilling or by treating a drill site wastewater. The amount of sodium carbonate and bactericide added to the effluent water is determined based on an elemental analysis of the effluent water. The process further comprises adding one or more additives to the base fluid to obtain the effluent water-based drilling fluid.

Description

PROCESS FOR PREPARING EFFLUENT WATER-BASED DRILLING FLUIDField of the invention

[0001] The present invention in general relates to the field of drilling fluids. More particularly, the present invention relates to a process for preparing a drilling fluid using effluent water as base fluid.Background of the invention

[0002] There is a growing trend towards developing more intricate drilling techniques in order to improve oil and gas extraction. A key component of drilling operation is use of a circulating fluid, commonly referred to as drilling fluid or drilling mud. Drilling fluid is introduced into a wellbore through drill pipes during rotary drilling operations carried out under high-temperature conditions. Typically, drilling fluid comprises a base fluid and various chemical additives. Drilling fluids are crucial in ensuring the safety and efficiency of oil and gas well operations. Drilling fluids play an essential role in the drilling process, by mitigating friction and facilitating removal of drilling residues from wellbore's depths to the surface.

[0003] Drilling fluids, depending on the base fluid, are classified into water-based drilling fluids and oil-based drilling fluids. Due to environmental concerns, water-based drilling fluids are commonly used in drilling operations in the oil and gas industry. The base of a water-based fluid is usually fresh water. Chemical additives used in water-based drilling fluids are, typically, caustic soda, various salts, wetting agent, polymers, etc.

[0004] Fresh water used for preparing drilling fluids must be free of contaminants to ensure it does not compromise effectiveness of drilling fluids. Substantial volumes of fresh water are drawn from underground aquifers or surfacefreshwater reservoirs for the preparation of drilling fluids.Use of fresh water in the drilling fluid preparation process adds to overall expenses associated with hydrocarbon recovery. In addition to the financial aspect, environmental repercussions of freshwater use in drilling fluid preparation result in a depletion of fresh water. Consequently, it is imperative to prioritize strategies that minimize both cost and environmental consequences associated with preparation of water-based drilling fluids using fresh water.

[0005] The term "produced water" in an oil and gas industry refers to an aqueous byproduct that is generated along with the oil and gas. Produced water constitutes one of the largest undesirable byproducts generated during oil wellbore drilling as it contains high levels of heavy metals, organic compounds, and other toxic pollutants. Produced water can have detrimental effects on the environment and is required to be treated before disposal. After treatment, a part of treated water can be used for extended oil recovery and in brine preparation. The remaining quantity of the treated prepared water is required to be pumped underground beyond the ground water table in specially drilled Effluent Disposal (ED) wells to prevent environmental pollution that may be caused by treated prepared water. Injection of treated prepared water into ED wells consumes extensive quantity of energy.

[0006] Therefore, conventional methods of preparing drilling fluids are fraught with, inter alia, two significant challenges. Firstly, there is a cost and environmental impact linked to extensive use of fresh water in drilling fluid preparations. Secondly, there is water pollution stemming from surface disposal of treated effluent water.

[0007] In light of the above-mentioned drawbacks, there is a need for a process for preparing effluent water-based drilling fluid. There is a need for a process to effectively treatproduced water and repurpose it as a base for preparing waterbased drilling fluids .Summary of the invention

[0008] In various embodiments of the present invention, there is provided a process of preparing effluent water-based drilling fluid. The effluent water is obtained by treating prepared water or drill site wastewater. The process comprises treating effluent water with a pre-determined amount of sodium carbonate and bactericide to obtain a base fluid. In an embodiment of the present invention, the amount of sodium carbonate and bactericide added for treating effluent water is determined based on an elemental analysis of the effluent water. The process further comprises of adding one or more additives to the base fluid to obtain the effluent water-based drilling fluid.Brief description of the drawings

[0009] The present invention is described by way of embodiments illustrated in the accompanying drawings herein:

[0010] Fig.l illustrates result of dispersion study conducted with effluent water-based drilling fluid, in accordance with an embodiment of the present invention; and

[0011] Fig. 2 illustrates inhibitive properties of drilling fluid prepared with treated effluent water compared to drilling fluids prepared with water from different ONGC oil fields, in accordance with an embodiment of the present invention .

[0012] In accordance with various embodiments of the present invention, a process for preparing an effluent water-based drilling fluid is provided. The process comprises the steps of treating effluent water and reusing the treated effluent water as a base fluid to prepare water-based drilling fluids. The process concurrently addresses issues of disposal of effluent water and consumption of fresh water for preparing drilling fluid preparation.

[0013] 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 are 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.

[0014] In various embodiments of the present invention, a process for preparing effluent water-based drilling fluid is provided. In an embodiment of the present invention, the process comprises treating effluent water with a predetermined amount of sodium carbonate and a bactericide to obtain a base fluid. In an embodiment, the amount of sodium carbonate and bactericide added to the effluent water is determined based on an elemental analysis of the effluent water. The process further comprises of adding one or moreadditives to the base fluid to obtain the effluent water-based drilling fluid.

[0015] In an embodiment of the present invention, effluent water is obtained by subjecting a produced water from oil reservoirs to a treatment process. In an embodiment of the present invention, the produced water is obtained along with oil and gas during exploration of hydrocarbons. The mixture of oil, gas and produced water is further subjected to heating and a demulsification process in a separator which separates the oil, gas and produced water. In an exemplary embodiment of the present invention, pH of the produced water is in a range from 6.5 to 8.5. In an embodiment of the present invention, treatment of the produced water is carried out by treating produced water with polyelectrolyte and polyaluminium chloride to obtain the effluent water. In an exemplary embodiment of the present invention, pH of the effluent water obtained by treating produced water is in a range from 7.0 to 8.0.

[0016] In another embodiment of the present invention, effluent water is obtained by subjecting a drill site wastewater to a treatment process. In an embodiment of the present invention, the pH of the drill site wastewater is in a range from 8.0 to 8.5. In an embodiment of the present invention, drill site wastewater is treated by polyelectrolyte and alum to obtain the effluent water. In an exemplary embodiment of the present invention, pH of the effluent water obtained by treating the drill site wastewater in a range from 6.5 to 7.0.

[0017] In an embodiment of the present invention, the effluent water obtained (by treating prepared water and drill site wastewater) is subjected to elemental analysis. In an embodiment of the present invention, elemental analysis of the effluent water is performed to determine the basic constituents of effluent water. In an embodiment of thepresent invention, the elemental analysis of the effluent water is performed by using different methods known in the art, but not limited to, Integrated Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) , ion chromatograph, water quality analyzer, Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) with titration.

[0018] In an embodiment of the present invention, after elemental analysis, the effluent water is treated with sodium carbonate. In an embodiment, the amount of sodium bicarbonate added to the effluent water depends on the elemental analysis of the effluent water. In an exemplary embodiment, if the hardness of effluent water is high, dosage of sodium carbonate is increased. In an embodiment, treatment of the effluent water with sodium carbonate is carried out by adding 0.1-0.2% (w / v) of sodium carbonate to effluent water. Subsequently, the effluent water and sodium carbonate is stirred for a duration of 5 minutes for a homogeneous mixing. The treatment of effluent water with sodium carbonate facilitates removal of hardness of effluent water along with neutralization of bicarbonates and other trace calcium and magnesium elements in the effluent water. This increases the efficiency of polymeric additives in drilling fluid.

[0019] In an embodiment of the present invention, the effluent water may comprise significant concentration of Sulfur Reducing Bacteria (SRB) that enhances the tendency of degradation of polymeric additives. Further, SRB produces hydrogen sulphide that reacts with iron and steel (in borewell pipelines) to form ferrous sulphide and subsequently leads to corrosion. In addition, hydrogen sulphide is also a health hazard. In an embodiment of the present invention, after the treatment of effluent water with sodium carbonate, the effluent water is further treated with a bactericide. In an exemplary embodiment the bactericide is selected from a group comprising of formaldehyde and paraformaldehyde. In anembodiment of the present invention, the amount of bactericide added to the effluent water depends on the elemental analysis of the effluent water. In an exemplary embodiment of the present invention, the amount of bactericide added to the effluent water is in a range from 0.1 to 0.2% (w / v) . In an exemplary embodiment of the present invention, bactericide can be added to the effluent water prior to treatment with sodium carbonate .

[0020] The effluent water obtained by treating produced water or drill site wastewater forms a base fluid for preparing the drilling fluid. In an exemplary embodiment of the present invention, pH of the base fluid is in a range from 6.5 to 8.0.

[0021] In an embodiment of the present invention, the process further comprises of adding one or more additives to the base fluid. In an exemplary embodiment of the present invention, the dosage and choice of additives added to the base fluid depends on the desired type of drilling fluid. In an exemplary embodiment, the additives added to the base fluid are selected from a group comprising of clay, viscosifiers , filtration loss control additive, wellbore strengthening materials, clay swelling inhibitors, rheology modifiers, weighing material, and alkalis. In an embodiment of the present invention, the choice of additives added to the base fluid determines the type of drilling fluid.

[0022] Different types of drilling fluids are used for different sections of wellbore. In an exemplary embodiment of the present invention, the types of water-based drilling fluids include gel-polymer drilling fluid, KCl-PHPA-Polyamine- Polyol (KPPP) drilling fluid, saturated salt based drilling fluid, lignite based drilling fluid etc.

[0023] In an embodiment of the present invention, the base fluid is used to prepare the gel-polymer drilling fluid. Table1 below provides the additives added to the base fluid to prepare the gel-polymer based drilling fluid .Table 1

[0024] In another embodiment of the pres ent invention , the bas e fluid is used to prepare the KPPP drilling fluid . Table 2 below provides the additives added to the base fluid to prepare the KPPP drilling fluid .Table 2

[0025] In yet another embodiment of the present invention, the bas e fluid is used to prepare saturated s alt based drilling fluid . Table 3 below provides the additives added to the base fluid to prepare the saturated salt based drilling fluid .Table 3

[0026] In another embodiment of the pres ent invention , the bas e fluid is used to prepare lignite based drilling fluid . Table 4 below provides the additives added to the base fluid to prepare the lignite based drilling fluid .Table 4

[0027] In an embodiment of the present invention, pH of the effluent water-based drilling fluid is in a range from 8.5 to 10.0. The pH is maintained by adding a specific amount of caustic soda or caustic potash. In an embodiment of the present invention, density of the effluent water-based drilling fluid is in a range from 1.06 g / cc to 1.85 g / cc, to encounter subsurface pressure and well bore instability issues .

[0028] In an exemplary embodiment of the present invention, the effluent water-based drilling fluid has a plastic viscosity of 17-46. Plastic viscosity indicates the mechanical interactions in drilling fluids. In an exemplary embodiment, as drilling fluid weight / solid concentration increases in drilling fluid, plastic viscosity increases. The plastic viscosity of the effluent water-based drilling fluid prepared by the process of the present invention is less than the conventional fresh water-based drilling fluid. In an exemplary embodiment of the present invention, the drilling fluid has a yield point of 19-32. Yield Point indicates the electrostatic interactions between drilling fluid particles, whichfacilitates cutting lifting. An optimum yield point is required in drilling fluids for better well bore cleaning. In an exemplary embodiment of the present invention, the drilling fluid exhibits thermal stability up to 180°C.

[0029] Rheological properties of drilling fluid represent the behavior of drilling fluid under pressure. Optimum rheological properties are required for better well bore cleaning and wellbore stabilization. In accordance with various embodiments of the present invention, the drilling fluid obtained from effluent water is found to be optimum for all the drilling fluid systems, as illustrated in the working examples provided below.

[0030] Filtration loss is loss of drilling fluid filtrate in the formation due to pressure difference between pore pressure and Hydrostatic head of drilling fluid. Ideally, filtration loss is maintained at minimum to keep the wellbore stable. The higher the fluid loss, more filtrates will be available to react with formation thereby increasing complications during wellbore drilling. In accordance with various embodiments of the present invention, the drilling fluid obtained from effluent water had minimum filtration loss, as illustrated in the working examples provided below.

[0031] In various embodiment of the present invention, the effluent water-based drilling fluid prepared in accordance with an embodiment of the present invention is suitable for drilling operation in complete range of temperature and pressures, ranging from, low pressure low temperature (LPLT) to high pressure high temperature (HPHT) conditions. Advantageously, the process of the present invention is economical by eliminating use of fresh water and achieves effective treatment of effluent water by reusing effluent water to prepare water-based drilling fluids without the need for fresh water as base for drilling fluids .

[0032] The disclosure provided herein illustrates exemplary embodiments in accordance with an 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 ExamplesPreparation Of Effluent Water from Treated Produced Water

[0033] The crude oil emulsion received from oil well was passed through a heater treater and treated with demulsifier where produced water was separated from emulsion. This produced water was transferred to a wash tank and treated with ~10 ppm of de-oiler and oil skimming process was carried out in TPI / CPI. Subsequently, in flash mixer the produced water was treated with 75-125 ppm of poly-aluminium chloride. The produced water was subsequently passed to an induced gas flotation (IGF) unit sand filters and ultra filtration unit, and further transferred to a conditioning tank. In the conditioning tank, produced water was treated with a mixture of Hydroxyethylidene diphosphonic acid (HEDP) (~10ppm) , corrosion inhibitor (~10ppm) , sodium hypochlorite (~20ppm) and sodium sulphite (~30-40ppm) . The treated produced water is referred to as effluent water and was further used for preparation of drilling fluid.Preparation Of Effluent Water From Treated Drill-SiteWastewater

[0034] Drill-site wastewater from a drilling well was collected at a common collection pit and pumped up to a girth chamber for screening and removal of coarse suspended solids. Subsequently the drill site wastewater was treated with ferricalum (~150 ppm) , poly-aluminium chloride (~75-120 ppm) and lime (~2 ppm) for neutralization and demulsification. The drill site wastewater and chemicals were mixed vigorously in a flash mixer where the destabilized colloidal particles were flocculated in a solid media base. The suspended colloidal particles were separated using chevron settler and oil coalescer. Subsequently, using a multi-media filter, fine suspended matter from the treated drill site wastewater was removed. The treated drill site wastewater is used for drilling fluid.sis Of Effluent Water

[0035] The elemental analysis of effluent water obtained from produced water / drill site wastewater was carried out using water quality analyzer to measure the properties such as turbidity, pH, Total Dissolved Solids (TDS) , conductivity etc. Other parameters such as carbonates, bicarbonates, Biological Oxygen Demand (BOD) , Combined Oxygen Demand (COD) and salinity were measured using ICP-OES and Ion Chromatograph via various titrimetric analysis. The data of elemental analysis of effluent water from various locations is provided in table 5 below.Table 5Preparation Of Base Fluid

[0036] Subsequently, the effluent water was treated with sodium carbonate by adding 0.1-0.2% (w / v) of sodium carbonate to the effluent water and stirred for a duration of 5 minutes for a homogeneous mixing. Further, the effluent water was treated with a bactericide by adding 0.1 to 0.2% (w / v) of a bactericide to the effluent water. The effluent water treated with sodium carbonate and bactericide formed the base fluid for preparation of effluent water based drilling fluid.Preparation Of Gel-Polymer Drilling Fluid

[0037] Base fluid prepared in accordance with above example was mixed with the composition in table 1 to obtain gel- polymer drilling fluid. Gel-polymer drilling fluid thus prepared was poured in aging cells and hot rolled at 100°C for16 hrs. After 16 hrs of hot rolling the drilling fluid was cooled and agitated for 15 minutes. Rheological properties of gel-polymer drilling fluid were evaluated at 50±l°C using viscometer to assess gel strength. Filtration properties of gel-polymer drilling fluid were also assessed on low pressure low temperature (LPLT) filter press.

[0038] The gel-polymer drilling fluid prepared with effluent water from different locations (Assam, Rajahmundry & Ankleshwar) exhibited good yield point (15-24) , gelations (10 sec gel, 10 minute gel and 30 minute gel) and low PV (16-28) . The fluid loss was observed to be 3.6 - 8.0 mL which is optimum for gel-polymer drilling fluids since it is used in upper sections of the wellbore.Rheological Properties

[0039] Plastic Viscosity (PV) and Yield Point of a drilling fluid are two major rheological parameters to be measured. PV can be defined as the mechanical interaction between the soild-soild, solid-liquid and liquid-liquid particles and layers so PV signifies the amount of solid present in drilling fluid system. YP on the other hand can be defined as the electrochemical interactions between solid particles present in the drilling fluid and it signifies the cutting lifting capacity of the fluid, which is essential for hole cleaning, a primary function of drilling fluid.

[0040] Rheological properties of the gel-polymer drilling fluid were determined before and after hot roll conditions at 50±l°C as per API guidelines. Uniformly mixed drilling fluid was kept in a thermostatic cup and placed in viscometer. After achieving the 50±l°C the dial values were noted at different RPM speed of viscometer i.e. 600, 300, 200, 100, 6 and 3 RPM. The plastic viscosity (PV) of DF was calculated as follows. PV = Dial reading at 600 RPM - Dial reading at 300 RPMx .Similarly Yield point (YP) is calculated as follows: YP = Dial reading at 300 RPM - PV.

[0041] Gel values (0, 10 and 30) of the gel-polymer drilling fluid were noted by checking maximum deflection of the dial at 3 RPM after keeping drilling fluid static for 10 sec, 10 min and 30 min respectively.Filtration Study

[0042] The gel-polymer drilling fluid was placed in a filter press under low pressure (low temperature (LPLT) and high pressure high temperature (HPHT) conditions) and a sieve for 30 minutes time which simulated the formation. Under LPLT filtration 100 psi pressure was applied under ambient temperature. The HPHT filtration was done at 500 psi differential pressure and the desired temperature as per bottom hole temperature (BHT) . The filtrate volume after application of pressure was reported in mL .

[0043] Table 6 herein provides rheological and filtration study data of gel-polymer drilling fluid prepared with base fluid having effluent water from Assam.Table 6

[0044] Table 7 herein provides rheological and filtration study data of gel-polymer drilling fluid prepared with base fluid having effluent water from Raj ahmundry .Table 7

[0045] Table 8 herein provides rheological and filtration study data of the gel-polymer drilling fluid prepared with bas e fluid having effluent water from Ankleshwar .Table 8Preparation Of KPPP Drilling Fluid

[0046] The KPPP drilling fluid was prepared as per the formulations given in table 2. The prepared KPPP-drilling fluid was then poured in aging cells and hot rolled at 130°C for 16 hrs. After 16 hrs of hot rolling the drilling fluid was cooled and agitated for 15 minutes. Later rheological properties of KPPP drilling fluid were evaluated at 50±l°C using Viscometer. Further, filtration properties of KPPP drilling fluid were evaluated at low pressure low temperature (LPLT) filter press and high pressure high temperature (HPHT) filter press at 100°C and 500 psi differential pressure.

[0047] The KPPP drilling fluids were prepared with effluent water from different locations (Assam, Rajahmundry & Ankleshwar) exhibited good yield point (20-46) , gelations (10 sec gel, 10 minute gel and 30 minute gel) and low PV (23-63) . The range of yield point and PV values is wide as density of drilling fluids are different. The PV and yield point value increases with an increase in drilling fluid density. The LPLT fluid loss was observed as 2.8 - 4.8 mL . The HPHT fluid loss values are 16-20.Rheological Properties

[0048] Rheological properties of the KPPP drilling fluid were determined before and after hot roll conditions at 50±l°C as per API guidelines. Uniformly mixed KPPP drilling fluid was kept in a thermostatic cup and placed in viscometer. After achieving the 50±l°C the dial values were noted at different RPM speed of viscometer i.e. 600, 300, 200, 100, 6 and 3 RPM. The plastic viscosity (PV) of DF was calculated as follows: PV = Dial reading at 600 RPM - Dial reading at 300 RPM. Similarly Yield point (YP) is calculated as follows: YP = Dial reading at 300 RPM - PV.

[0049] Gel values (0, 10 and 30) of the KPPP drilling fluid were noted by checking maximum deflection of the dial at 3 RPM after keeping KPPP drilling fluid static for 10 sec, 10 min and 30 min respectively.Filtration Study

[0050] The KPPP drilling fluid was placed in a filter press under low pressure (low temperature (LPLT) and high pressure high temperature (HPHT) conditions) and a sieve for 30 minutes time which simulated the formation. Under LPLT filtration 100 psi pressure was applied under ambient temperature. The HPHT filtration was done at 500 psi differential pressure and the desired temperature as per bottom hole temperature (BHT) . The filtrate volume after application of pressure was reported in mL .

[0051] Table 9 herein provides rheological and filtration study data of KPPP drilling fluid prepared with base fluid having effluent water from Assam.Table 9

[0052] Table 10 herein provides rheological and filtration study data of the KPPP drilling fluid prepared with base fluid having ef fluent water from Raj ahmundry .Table 10

[0053] Table 11 herein provides rheological and filtration study data of the KPPP drilling fluid prepared with base fluid having ef fluent water from Ankleshwar .Table 11Preparation Of Lignite Based Drilling Fluid

[0054] The Lignite based drilling fluid was prepared as per formulation given in Table 4. The prepared Drilling fluid was then poured in aging cells and hot rolled at 180°C for 16 hrs. After 16 hrs of hot rolling the drilling fluid was cooled and agitated for 15 minutes. Later rheological properties of Lignite based drilling fluid were evaluated at 65±1°C using Viscometer. Further, filtration properties of Lignite based KPPP drilling fluid were evaluated at low pressure low temperature (LPLT) filter press and high pressure high temperature (HPHT) filter press at 150°C and 500 psi differential pressure.

[0055] The Lignite based drilling fluid was prepared with effluent water from Rajahmundry, exhibited good yield point (32) , gelations (10 sec gel, 10 minute gel and 30 minute gel) and low PV (46) . The LPLT fluid loss was observed 3.8 mL and HPHT fluid loss was 10.0 mL .Rheological Properties

[0056] Rheological properties of the Lignite based drilling fluid were determined before and after hot roll conditions at 65±1°C as per API guidelines. Uniformly mixed Lignite based drilling fluid was kept in a thermostatic cup and placed in viscometer. After achieving the 65±1°C the dial values were noted at different RPM speed of viscometer i.e. 600, 300, 200, 100, 6 and 3 RPM. The plastic viscosity (PV) of DF wascalculated as follows: PV = Dial reading at 600 RPM - Dial reading at 300 RPM. Similarly Yield point (YP) is calculated as follows: YP = Dial reading at 300 RPM - PV.

[0057] Gel values (0, 10 and 30) of the Lignite based drilling fluid were noted by checking maximum deflection of the dial at 3 RPM after keeping Lignite Based drilling fluid static for 10 sec, 10 min and 30 min respectively.Filtration Study

[0058] The Lignite based drilling fluid was placed in a filter press under low pressure (low temperature (LPLT) and high pressure high temperature (HPHT) conditions) and a sieve for 30 minutes time which simulated the formation. Under LPLT filtration 100 psi pressure was applied under ambient temperature. The HPHT filtration was done at 500 psi differential pressure and 150°C temperature as per Bottom Hole Temperature (BHT) . The filtrate volume after application of Pressure was reported in mL .

[0059] Table 12 Herein provides Rheological and Filtration study data of Lignite based drilling fluid prepared with base fluid having effluent water from Rajahmundry.Table 12Linear Swell Meter (LSM)

[0060] The inhibitive properties of drilling fluids of the present invention were determined by LSM apparatus. The drilling fluid was hot rolled at maximum bottom hole temperature for 16-18 hrs for a particular phase of the well condition and temperature up to which the particular drilling fluid system is stable. It was cooled and agitated for 10-15 minutes to make a homogenous solution. 20g powdered sample of formation was placed in a cylindrical die and compressed hydraulically using compactor at 10000 psi for 30 minutes which simulates the formation compactness in presence of pressure. The pellet was put in the test assembly and submerged in drilling fluid the test was carried out for 4-6 hrs. The same test was also carried out with water to compare the inhibitive properties of the drilling fluid.

[0061] Table 13 provides data of comparative LSM study conducted with (a) KPPP drilling fluid prepared with base fluid having effluent water from Assam and (b) drilling fluid prepared with fresh water.Table 13

[0062] Table 14 provides data of comparative LSM study conducted with (a) KPPP drilling fluid prepared with basefluid having effluent water from Rajahmundry and (b) drilling fluid prepared with fresh water.Table 14

[0063] Table 15 provides data of comparative LSM study conducted with (a) KPPP drilling fluid prepared with base fluid having effluent water from Ankleshwar and (b) drilling fluid prepared with fresh water.Table 15

[0064] The formation swelling percentage of the drilling fluid was observed to be low as compared to fresh water based drilling fluid which shows better inhibitive properties of effluent water based drilling fluid.on test was carried out using bentonite cutting. 10g Bentonite cutting sample was poured in the drilling fluid and hot rolled for 16-18 hours at desired temperature. After hot rolling drilling fluid was poured on 44 mesh sieve. The cutting samples retained on 44 mesh wereweighted after drying. The percentage recovery of cuttings was calculated subsequently.

[0066] Fig.l (A) illustrates a bentonite cutting sample passed by a 6 mesh sieve and retained on 16 mesh sieve which is used for dispersion studies of the drilling fluid of the present invention, in accordance with an exemplary embodiment of the present invention. Fig.l (B) illustrates recovery of bentonite cuttings after hot roll in presence of KPPP drilling fluid, in accordance with another embodiment of the present invention. The cutting recovery observed was 98.2%. Fig.l (C) illustrates the amount of bentonite cuttings recovered after hot roll in presence of water, in accordance with yet another embodiment of the present invention. The cutting recovery percentage was 13.1%.Inhibition Studies

[0067] Inhibition study was conducted on LSM apparatus. Fig. 2 illustrates inhibitive properties of drilling fluid prepared compared to mobile effluent treated water from different ONGC oil fields, in accordance with an embodiment of the present invention. The percentage of swelling of a pellet in mobile effluent treated water was observed to be 7.2%. The percentage of swelling of pellets in drilling fluids prepared with treated effluent water was observed to 2.8%, 1.6% and 2.4% respectively. Therefore, the drilling fluid of the present invention reduced the formation swelling by more than 60%.

[0068] 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 process of preparing effluent water-based drilling fluid, the process comprising the steps of: treating effluent water with a pre-determined amount of sodium carbonate and bactericide to obtain a base fluid, wherein the pre-determined amount of sodium carbonate and bactericide added to the effluent water is determined based on an elemental analysis of the effluent water; and adding one or more additives to the base fluid to obtain the effluent water-based drilling fluid.2) The process as claimed in claim 1, wherein the effluent water is obtained by treating produced water generated during oil well drilling.3) The process as claimed in claim 1, wherein the effluent water is treated drill site wastewater.4) The process as claimed in claim 1, wherein the bactericide is selected from a group comprising of formaldehyde and paraformaldehyde .5) The process as claimed in claim 1, wherein amount of the bactericide added to the effluent water is in a range from 0.1% to 0.2% (W / V) .6) The process as claimed in claim 1, wherein amount of the sodium carbonate added to the effluent water is in a range from 0.1% to 0.2% (W / V) .7) The process as claimed in claim 1, wherein the process is carried out at a temperature in a range from 90°C to 185°C.8) The process as claimed in claim 1, wherein the one or more additives added to the base fluid are selected from a groupcomprising of clay, viscosifiers , filtration loss control additive, water softeners, bactericides, wellbore strengthening materials, clay swelling inhibitors, rheology modifiers, lubricants, weighing material, and alkalis.9) The process as claimed in claim 1, wherein a gel polymer based drilling fluid comprises the additives selected from a group comprising of pre hydrated bentonite suspension, soda ash, caustic soda, PAC (LV) , drilling detergent and XC polymer .10) The process as claimed in claim 1, wherein a KPPP based drilling fluid comprises the additives selected from a group comprising of soda ash, biocide, caustic soda, potassium chloride, polyamine, PAC (LV) , XC Polymer, PHPA, sulphonated asphalt, polyol grade II, HPEP Lube, MCC, NIF additive, and barite .11) The process as claimed in claim 1, wherein a lignite based drilling fluid comprises the additives selected from a group comprising of pre-hydrated bentonite suspension, sodium carbonate, biocide, caustic soda, sodium sulphite, potassium chloride, HT Fluid Loss Reducer-I, HT Fluid Loss Reducer-II, polyol grade II, HT deflocculant, resinated lignite, HPEP lube, sulphonated asphalt and barite.12) The process as claimed in claim 1, wherein a saturated salt based drilling fluid comprises the additives selected from a group comprising of soda ash, biocide, caustic soda, sodium chloride, PAC (LV) , XC polymer, PHPA, polyamine, polyol grade II, NIF additive, MCC, HPEP lube and barite.