Over the years, the oil industries have avoided aromatic, naphthenic, and paraffinic oils as drilling mud base fluids principally because of their detrimental environmental issues on pelagic and benthic marine ecosystems as a result of their toxicity and nonbiodegradability coupled with the possible deterioration of the oil itself and the rubber parts of the drilling equipment because the aromatic hydrocarbons present in the oil have a tendency to dissolve/damage elastomers present in rubber. Hence, possible insights into how to chemically and/or physically produce synthetic base drilling fluids whose cuttings are nontoxic, readily biodegradable, environmentally friendly, and of nonpetroleum source become imperative. In this study, enzymatic interesterification of canola oil was done with ethanol by using enzyme lipase as catalyst under optimum conditions of temperature and pressure and the physicochemical properties of the produced ester were evaluated and compared with that of diesel and a synthetic hydrocarbon base fluid (SHBF). Results show that the specific gravity, kinematic viscosity, dynamic viscosity, and surface tension of canola oil were reduced by 5.50%, 94.74%, 95.03%, and 9.38%, respectively, upon enzymatic interesterification to conform to standard requirements. Similarly, increased |mud ability to pump fluids and possibility of cold temperature environment can be achieved with the reduction in pour point and cloud point, respectively, of the produced canola oil ester. Finally, the produced ester showed no aromatic content as confirmed from its FTIR analysis which indicates its nontoxicity, biodegradability, and environmental friendliness.
Drilling fluids are complex fluid mixtures which are principally formulated to carry cuttings from beneath the bit, transport them up the annulus and permit their separation at the surface, and prevent the inflow of formation fluids (oil, gas, and water) from the permeable rock that is being penetrated and to form a thin, low-permeability filter cake which seals pores and other openings in formations penetrated by the bit.
The oil industry started with water base fluids but because of formation clays that react, swell, or slough after exposure to water-based mud coupled with the need to penetrate a hole with high temperature, a shift to diesel-based mud began in 1960s [
Diesel is also harmful to the environment particularly marine environment during offshore drilling [
In many countries that are developing offshore oil and gas resources, cuttings discharge permits require performance of toxicity tests with drilling fluid ingredients and whole drilling fluids [
The most important fluid properties that may affect environmental impacts are toxicity and rate of biodegradation. Environmental impacts that may result from the discharge of drilling fluids and cuttings to the ocean are of two types: effects on water column (pelagic ecosystems) and effects on sea bottom (benthic ecosystems) [
The Norwegian regulatory authority defines a SBF as a drilling fluid where the base fluid consists of nonwater soluble organic compounds and where neither the base fluid nor the additives are of petroleum origin [
However, polymerized olefins such as linear alpha olefins (LAOs), poly alpha olefins (PAOs), and internal olefins (IOs) are the most frequently used synthetic hydrocarbons, and they have been reclassified as environmentally unacceptable and are no longer in use because they contain a benzene molecule which is aromatic and nonbiodegradable [
Synthetic-based muds (SBMs) were developed to replace OBMs in difficult drilling situation, and though SBMs are expensive than OBMs, they have superior environmental properties that may permit the cuttings to be discharged on-site [
Veil et al. [
All the SBF base chemicals evaluated by Norman [
Environmental authorities of the North Sea countries have hypothesized that rapid degradation will minimize the environmental impacts of SBF cuttings discharge and thus speeding ecosystem recovery [
Canola oil (Canada oil) is processed from the seed of
From the three main oil modification technologies (fractionation, hydrogenation, and interesterification), interesterification is by far the easiest process to understand and to control [
Interesterification is the process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. The reaction can also be accomplished with the help of enzymes (biocatalysts) particularly lipases:
Strong acids catalyze the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile, whereas bases catalyze the reaction by removing a proton from the alcohol, thus making it more nucleophilic. Esters with larger alkoxy groups can be made from methyl or ethyl esters in high purity by heating the mixture of ester, acid/base, and large alcohol and evaporating the small alcohol to drive equilibrium.
Six hundred milliliters of chemically degummed canola oil were measured and poured into a 1000 ml PYREX Erlenmeyer flask with rubber stopper. The degummed oil was then heated to a temperature of 60°C in an electric oven. This was followed by the addition of 120 ml of ethanol which was preheated to a temperature of 60°C with the aid of water bath. A 4% concentration of immobilized
The resulting filtrate was then taken to a rotary evaporator at 90°C (a temperature higher than the boiling point of ethanol (78.37°C)) in order to evaporate unreacted alcohol. Finally, the reaction mixture was placed in a separating funnel resulting in two distinct layers of upper ethyl ester and a lower layer of monoglyceride, diglyceride, glycerol, and other impurities. The produced ethyl ester was then bleached with 1.5% bleaching clay and deodorized, and its volume was measured in order to deduce its percentage yield:
After the synthesis of the ethyl esters, it is imperative to determine the physicochemical properties of the esters formed and those of the control sample fluids before any mud formulation can occur in order to compare with specified standards to know if there is marked deviation such as physicochemical properties including but not limited to fluid density, kinematic viscosity, dynamic viscosity, cloud point, pour point, flash point, fire point, and surface tension.
Experimental procedure is as follows: The density bottle was firstly dried to allow for accurate measurement of its mass as shown in Figure The cleaned and dried density bottle was weighed using a digital weighing balance to the nearest 0.0l g, and the weight was recorded. The density bottle was then filled completely with the fluid sample, and the stopper was inserted into the neck of the bottle resulting in spillage of the fluid outside the density bottle. This is necessary in order to avoid air being entrapped in the density bottle. The outside of the bottle was carefully dried using a soft tissue paper. The bottle and its content were weighed and the mass recorded. The liquid sample was poured out of the density bottle and the bottle was rinsed several times with distilled water and dried for subsequent samples weight determination. Water bath was then used to heat the fluid samples to the required temperatures prior to their weight measurement.
(a) A 50 ml density bottle. (b) Ostwald viscometer. (c) Seta cloud and pour point cryostat [
Deductions and calculations are as follows:
The viscometer (Figure The lower bulb of the viscometer was filled with the fluid sample to half of its capacity. Cold air was then blown into the viscometer so as to allow the fluid sample to travel up the viscometer at the other side of the upper mark of the bulb. The stop watch was switched on at the upper mark oil level, and it was stopped when the oil gets to the lower mark below the upper bulb. The two marks indicate a known volume and the time taken for the level of oil to pass between these marks is proportional to the kinematic viscosity. The time taken for the oil to travel to the lower bulb mark was recorded in seconds and it was converted to kinematic viscosity (in centistokes) using the viscometer size 200 constant of 0.1 cst/sec. The above steps were repeated for various oil samples at different temperatures.
Mathematically, the kinematic viscosity is obtained by using the following equation:
The dynamic viscosity (
The cloud point and pour point were measured by using the seta cloud and pour point cryostat shown in Figure
The following procedures were used in the course of the experiment: One of the three (3) compartments was filled with two liters of butyl glycol. The glass cups in each of the compartments were filled with different oil samples up to the upper mark. The glass cups were covered with the thermometer cork, and the thermometer was inserted into the oil sample in the glass cup through the cork. The outer black insulating gasket and disc were placed on the glassware, and this was placed in the cryostat compartment and the power corresponding to the compartment was switched on. The glass cups were brought out on periodic intervals to check the cloudiness of the oil samples. The temperature at which the oil sample becomes cloudy is its cloud point. After recording the cloud point, the thermometer was removed, and the glass cup was inserted into the compartment and the oil samples were allowed to freeze completely. The thermometer cork was removed, and the glass cup was placed tilted on a flat table with a thermometer in it. The temperature at which the first drop of oil is formed is the pour point of the oil samples.
Flash point of a flammable liquid is defined as the lowest temperature at which it can form an ignitable mixture in air while fire point is the temperature at which vapors of the flammable liquid continue to burn after being ignited even after the source of ignition is removed.
The following procedure was used to determine the flash point of each base fluid sample by using the equipment shown in Figure The gas supply was switched on from the gas canister filled with butane gas. The control valve on the gas canister was adjusted until the pilot jet flame is approximately 12 mm long. The test jet flame was also adjusted to 4 mm diameter by rotating the pinch valve, and the gas supply was then switched off. The flash point tester power was then switched on, and the test temperature was set by using the set temperature button. The tester sample cup was allowed to stabilize at the set temperature, and the syringe was loaded with the base fluid sample and injected into the sample cup through the filler orifice and the syringe was removed. The gas supply was then switched on, and a fire lighter was used to light and set the pilot and test jet flame at 4 mm. At the set test temperature, a warning beep sounds. The shutter was then opened and closed over a period of five seconds. A flash was detected at the flash point of the sample, and the temperature at which the flash occurred was recoded as the flash point of the fluid sample. After the flash point, the heating was continued, and the fire point was taken as the temperature at which the application of test flame causes the oil sample to burn for at least five seconds. The sample cup was allowed to cool to room temperature. The above steps were repeated for other samples.
The surface tension of a liquid can be experimentally measured by several methods such as the drop weight method (stallagmometer), Du Nouy ring method, Wilhelmy plate method, and the maximum bubble pressure method. However, the Du Nouy ring method is a rapid, simple, and most widely used method because it does not need to be calibrated using solutions of known surface tension [
Du Nouy ring method procedure for surface tension estimation is as follows: The measurement is performed by an instrument known as tensiometer as shown in Figure The weight of the circular ring to be immersed into the fluid sample was measured by weighing balance and recorded as The ring hanging from the hook of the balance was immersed into the fluid sample and then carefully pulled up by lowering the sample vessel. The force applied on the ring when it pulls through the air-liquid interface was continuously recorded by the microbalance. The above procedure was repeated for other fluid samples at designated temperature of 25°C.
Hence, the total force required to detach the ring is recorded as
Mathematically,
From (
Equation (
The results of the specific gravity of the base fluids are presented in Table
Base fluids’ specific gravity at different temperatures.
Temp (°C) | Canola oil | EICO | Diesel | SHBF |
---|---|---|---|---|
25 | 0.910 | 0.860 | 0.850 | 0.837 |
50 | 0.896 | 0.842 | 0.835 | 0.818 |
75 | 0.875 | 0.821 | 0.812 | 0.797 |
100 | 0.862 | 0.805 | 0.785 | 0.769 |
Specific gravity variation with temperature.
Base fluids’ weight in grams per 50 ml density bottle at different temperatures.
Temp (°C) | Canola oil | EICO | Diesel | SHBF |
---|---|---|---|---|
25 | 45.50 | 43.00 | 42.50 | 41.85 |
50 | 44.80 | 42.10 | 41.75 | 40.90 |
75 | 43.75 | 41.05 | 40.60 | 39.85 |
100 | 43.10 | 40.25 | 39.25 | 38.45 |
The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. During the course of evaluation, two types of viscosities were used to characterize the base fluids which are dynamic (shear) viscosity and kinematic viscosity. The dynamic viscosity expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different speeds while kinematic viscosity describes the resistance of a fluid to flow under gravity.
From the effluent time presented in Table
Ostwald viscometer (size 200) effluent time (seconds) of base fluid samples.
Temp (°C) | Canola oil | EICO | Diesel | SHBF |
---|---|---|---|---|
25 | 665 | 35 | 32 | 29 |
50 | 254 | 27 | 24 | 21 |
75 | 132 | 21 | 17 | 13 |
100 | 78 | 14 | 11 | 8 |
Similarly, from the results presented in Tables
Kinematic viscosity (cst) of base fluids at different temperatures.
Temp (°C) | Canola oil | EICO | Diesel | SHBF |
---|---|---|---|---|
25 | 66.5 | 3.5 | 3.2 | 2.9 |
50 | 25.4 | 2.7 | 2.4 | 2.1 |
75 | 13.2 | 2.1 | 1.7 | 1.3 |
100 | 7.8 | 1.4 | 1.1 | 0.8 |
Dynamic viscosity (cp) of base fluids at different temperatures.
Temp (°C) | Canola oil | EICO | Diesel | SHBF |
---|---|---|---|---|
25 | 60.52 | 3.01 | 2.72 | 2.43 |
50 | 22.76 | 2.27 | 2.00 | 1.72 |
75 | 11.55 | 1.72 | 1.38 | 1.04 |
100 | 6.72 | 1.13 | 0.86 | 0.62 |
Kinematic viscosity variation with temperature.
Dynamic viscosity variation with temperature.
Also, the viscosity reduces with the increase in temperature as shown in Figures
Drilling fluid surface tension measurement is very important in fluid characterization because high surface tensions decrease the ability of the drilling fluid to pass through a shale shaker screen, particularly fine screens with their small openings [
Similarly, the reduced surface tension of EICO base fluid as shown in Table
Surface tension of fluid samples at 25°C.
Base oil | Surface tension (N/m) |
---|---|
Canola | 0.032 |
EICO | 0.029 |
Diesel oil | 0.028 |
SHBF | 0.026 |
The pour point is the lowest temperature at which a liquid will begin to flow while the cloud point is the temperature at which wax crystals begin to form in a liquid as it is cooled.
From Table
Cloud and pour points of base fluid samples.
Base oil sample | Cloud point (°C) | Pour point (°C) |
---|---|---|
Canola oil | 8 | 2 |
EICO | 1 | −4 |
Diesel | 2 | −1 |
SHBF | 0 | −3 |
Similarly, knowing the cloud point is important for determining storage stability. Storing formulations at temperatures significantly higher than the cloud point may result in phase separation and instability. Hence, the EICO SBF has low cloud points and hence can be stored under lower temperature conditions.
The flash point is the lowest temperature at which a liquid can form an ignitable mixture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material. The fire point of a fuel is the lowest temperature at which the vapor of that fuel will continue to burn for at least 5 seconds after ignition by an open flame. At the flash point, a lower temperature, a substance will ignite briefly, but vapor might not be produced at a rate to sustain the fire. From Table
Flash point and fire point of base fluid samples.
Base oil sample | Flash point (°C) | Fire point (°C) |
---|---|---|
Canola oil | 284 | 315 |
EICO | 165 | 185 |
Diesel | 69 | 81 |
SHBF | 76 | 87 |
The relative degree of aromatic hydrocarbon present in a compound can be known through Fourier transform infrared spectroscopy (FTIR) spectra analysis. From FTIR spectra analysis, a well-defined absorption of one but typically two sets of bands in the region 1615 cm−1–1495 cm−1 for aromatic ring stretch and 3130 cm−1–3070 cm−1 for aromatic C–H stretch is consistent with aromatic compounds [
Diesel FTIR spectra.
SHBF FTIR spectra.
Canola oil FTIR spectra.
EICO FTIR spectra.
Hence, oils with zero aromatic content are the most desirable for use in drilling fluids in order to minimize damage to rubber equipment on the rig and to reduce death of marine organism when the cuttings are discharged.
The following conclusions were drawn: The EICO gave 94.74% reduction in kinematic viscosity to conform to the standard kinematic viscosity requirement of base fluids to be used. For SBMs, a kinematic viscosity of 2.0 to 3.6 cp is recommended according to API standard. The cloud point and pour point were considerably reduced in the enzymatically synthesized canola oil, so that an account of possible cold environment operation can be easily accommodated without the SMBs losing their excellent rheological and filtration properties. Because higher pour points can make a SBM to suffer from poor screening and excessive pressure surges in deep water wells or other operations that are subjected to low operation. Though the flash point and fire point were decreased after interesterification to a desirable level meaning that the fluids can still be worked with at higher temperatures without possible fair of ignition. Also, its transportation and storage ability will pose no threat. A reduction of 5.50% in specific gravity was achieved with the enzymatic interesterification which consequentially helps to formulate SBMs that are of moderate density because loss of circulation may result from excessive pressure due to mud that is too dense or heavy and thus reduces rate of penetration and increase drilling cost. The produced fluid has no aromatic compound as evaluated by its FTIR Spectra analysis and thus no environmental pollution can arise from its cuttings discharge and no deterioration of the rubber part of drilling equipment can occur during drilling.
The data used in this study were obtained from rigorous experimental research in the laboratory and not from any journal either in print or online. The authors declare that the data will be available for public use.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors are very grateful to the Chancellor of Covenant University and the University Management team for their support for Research and Development and the IR unit of University of Ibadan without which this research work would not have seen the light of the day.
Enzymatically interesterified canola oil
Fourier transform infrared spectroscopy
Oil-based fluid
Oil-based mud
Synthetic-based fluid
Synthetic-based mud
Synthetic hydrocarbon-based fluid
Water-based fluid
Water-based mud.