Calcium ions replace sodium ions from the crystal lattice of the clay platelets, thus resulting in calcium-base clay. Due to the interparticle forces of calcium-base clay, the platelet aggregates.
As the ion exchange continues, the platelets collapse upon each other and lead to a state of aggregation. As a result of continuous flocculation and the aggregation of platelets, there is an overall reduction in solid volume, thus enabling the clay aggregates to move freely through the aqueous phase with the consequent lowering of the internal friction. From Fig. Exposure to high temperature for a long period of time caused degradation in the mud system thereby leading to particles repulsion towards one another.
The three muds experienced particles dispersion at the same temperature with different yield points. Due to the high yield point of ferrobar, we can conclude that it increases the carrying capacity of the mud which aids hole clearing although it may not be necessary in high weight muds to insure good cutting carrying capacity. The temperature at which a very rapid decrease in gel strength occurs indicates the onset of deflocculating. During a circulation stop, the drilling mud cools down to a very low temperature and gives rise to a gel.
Recirculation after such a rest period demands a pressure surge to break the gel. Figure 3 shows that as temperature increases, there is progressive fluid loss into the formation. Barite mud which is generally used for drilling operation experienced higher fluid loss into the formation at high temperature than other muds which indicates that barite mud has the tendency to experience differential sticking as the temperature increases before other two muds, while ferrobar mud provides satisfactory rheological properties required for optimum performance in oil well drilling at elevated temperatures.
Figure 5 shows the plastic viscosity against temperature. Plot of yield point against temperatures on three different mud samples before salt contamination. Figure 6 above shows that with the magnesium saltwater influx, there is progressive decline in the performance of barite and hematite muds which indicates that saltwater affects the hydration, dispersion and flocculation behavior of the viscosifier and weighting agent causing particles dispersion and increasing the number of individual platelets in suspension which renders it ineffective for cutting lifting while ferrobar mud shows that cutting suspensions are maintained with the influx of magnesium saltwater at elevated temperature.
However, ferrobar and hematite experienced thermal degradation as temperature increases. This indicates that the muds are not likely to be good weighting and cutting suspender with saltwater influx. Figure 9 shows the effects of magnesium saltwater influx on the ES in the mud samples.
From the plot, it is discovered that an increase in temperature augments the ionic activity of any electrolyte and the solubility of any partially soluble salt that may be present in the muds. This alters the balance between the interparticle attractive and repulsive forces and the degree of dispersion and flocculation of the mud systems which deeply affect the emulsion stability of oil base muds. Figure 10 shows effect of plastic viscosity against temperature.
It is very important to know precisely the temperature evolution of the drilling mud during the different drilling and circulation stop. From the research carried out, it was observed that increase in temperature reduces the stability and viability of drilling fluid.
Al-Marhoun MA, Rahman SS Optimizing the properties of water-based polymer drilling fluids for penetrating formations with electrolyte influx, Erdol Erdgas, pp — Annis MR High temperature flow properties of water-base drilling fluids.
J Petrol Technol — Article Google Scholar. Burkhardt JA Wellbore pressure surge produced by pipe movement. Trans AIME — Google Scholar. Transaction AIME. J Phys Chem — Street N Viscosity of clay suspensions. World Oil — What brand and weight of oil should I use in my What weight motor oil should i use if a car normal Should I switch to a heavier weight oil when I am What weight crankcase oil does an 83 Nighthawk use?
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What engine oil weight should I use in a GM engine The rheological properties of drilling fluids can be controlled by employing viscosifiers that should have exceptional stability in downhole environments. Identical drilling fluid formulations were designed for comparison using MSils and a commercial viscosifier. Owing to strong covalent linkages, drilling fluids that were formulated with MSils showed a The higher yield point and lower apparent viscosity are known to facilitate and increased drilling rate of penetration of the fluids and an enhanced equivalent circulation density ECD , the dynamic density condition, for efficient oil and gas wells drilling procedures.
The properties of drilling fluids govern the successful completion of oil and gas well drilling operations. It has been well established that the non-productive time NPT , owing to the deteriorating performance of drilling fluids, has largely amplified the cost of drilling operations and delayed the production of oil and gas from the reservoirs 1. The principal functions of drilling fluids are 1 , 2 , 3 , 4 i suspending and transporting formation cuttings from the bottom of the wellbore to the surface, ii suspending formation cuttings during the shutdown of drilling operations, iii counter balance the formation pressures to prevent in-flow of gas, oil or water from rocks, iv forming a filter cake on the formation surface to improve wellbore stability, and v lubricating the drilling tools and drill pipes.
There are mainly two types of drilling fluids employed in field operations, oil-based drilling fluids and water-based drilling fluids 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , Water-based drilling fluids WBMs are often known for their environmentally benign characteristics, albeit unfavorably high viscosity and lack of stability under high temperature conditions have restricted their applications to certain hydrocarbon reservoirs 7 , 8.
Oil-based drilling fluids, also known as oil-based muds OBMs or as invert emulsion fluids IEF , have demonstrated wide acceptance in oil and gas drilling operations on account of their stability under extreme rock and reservoir conditions, e.
The water-in-oil invert emulsions in OBMs have shown low to moderate viscosity that reduce the energy requirement to pump the fluids and significantly improve the rate of penetration. The key merits of OBMs over water-based drilling fluids are their abilities to perform in soluble salt, water sensitive formations, and offers low frictions 1. Drilling fluid formulations are composed of several additives, e. These complex mixtures of additives in fluids address the stability of OBMs under the desired wellbore conditions and provide efficient drilling operations of oil and gas wells.
One of the most vital among these additives is the viscosifier, because it preserves the viscosity of the fluids over wide range of temperatures.
Numerous viscosifiers have been developed in last five decades and the majority of these viscosifiers are based on organically modified natural layered materials, also known as organoclays 1. The historical developments in the area of various viscosifiers that have been employed as additives in drilling fluids are summarized in Scheme 1 a. Organoclays have been employed as a viscosifying additive in drilling fluid formulations since the s. Organoclays are produced through an ion-exchange reaction between cationic clays and quaternary ammonium salts The resulting organophilic clays can easily be dispersed in an oil- or diesel-based medium that imparts viscosity to the drilling fluids.
Since organoclays have been synthesized from naturally abundant clay minerals, they are relatively low cost viscosifiers to manufacture. The refining of crude oil into value-added chemicals and polymers in the early s has allowed for additional development in the area of modified polymers, which can also generate viscosity in the base fluid medium.
However, the high cost and thermal degradation of polymers have restricted their wide scale deployment as a fiscally favorable additive in drilling fluid formulations. Researchers in the upstream petroleum sectors established techniques to control the particle size of organoclays to obtain nanoclays in the beginning of twenty-first century. The size reduction of organoclays allow for better dispersion of their nanometer-thick alumino-silicate platelets in the organic phase, however, the electrostatic interaction of organic moieties with layered materials remains as one of the unresolved characteristics.
We have developed the next generation of viscosifiers to overcome the disadvantages associated with the current clay-based and polymeric viscosifying additives.
Development of viscosifiers and their shortcomings. The organic functionalities in organoclays and nanoclays are attached through electrostatic bonding on the surface of layered materials Scheme 1 b. The organic functionalities are isolated from the layered materials, thereby losing their ability to contribute to the viscosifying properties in drilling fluids. Therefore, it is very important to have strong linkages between the layered materials and organic functionalities to preserve the rheological properties of the drilling fluids.
We have designed and synthesized layered materials that have covalently-linked organic functionalities. The synthesis of MSil without organic functionality MSil-OH was also demonstrated in order to compare the structural changes upon organic functionalization.
The formation of layered structures was evaluated by X-ray diffraction and covalent bonding of organic moieties with nanometer-thick magnesium silicates was revealed by infrared spectroscopic analyses. The thermal stabilities of MSils were studied by thermogravimetric analysis.
MSil-C16 and MSil-Ph were incorporated in the drilling fluids to demonstrate the effect of covalently-linked organic moieties. We have also compared the rheological properties of drilling fluids with commercial organoclay under identical conditions to establish the unique characteristics of MSils. Commercial drilling fluid additives were obtained from Schlumberger, USA. All chemicals were used as received. The storage modulus and loss modulus of the fluids were recorded at different temperatures under 3.
The angular frequency was varied between 0. The couette coaxial cylinder rotational viscometers Model 35 Rheometer and iX77 Rheometer, Fann Instrument Company were used to simulate wellbore conditions for studying the rheological properties of the OBMs. These rheometers offer a true simulation of the most significant flow process conditions encountered during drilling operations. Gel strength of the OBMs were measured after holding the OBMs at 10 s and 10 min, followed by applying 3 rpm rotation in the rheometer.
The dial readings were recorded and represented as gel strength of the drilling fluids. Organically modified synthetic magnesium silicates were prepared according to the reported technique with minor modifications 15 , 16 , Detailed syntheses of MSils are given in Supplementary Information. Briefly, 0. Subsequently, 0. The reaction mixtures were cooled to room temperature, followed by filtrations and washing with de-ionized water.
It is very important to follow the time and order of mixing for each additive to formulate the OBMs. A facile synthetic approach has applied for the preparation of organically modified magnesium silicates MSils.
The architectures of these layered materials were created from the combination of precipitation and sol—gel techniques Scheme 2. The seed crystals of the brucite layers act as structure directing agents and resulting in nanometer-thick magnesium silicate platelets.
Pendant groups of organosilanes also facilitate the formation of lamellar structures, due to the hydrophobic nature of the organic functionalities Synthesis and structural characteristics of MSils. Layered magnesium silicates and organic functional groups show characteristic vibration signals that confirmed the generation of the desired materials Fig. Stretching bands at 3,—3, cm —1 , cm —1 , and 1, cm —1 in MSil-Ph are attributed to C—H aromatic stretch, C—C stretch in the aromatic rings, and Si—H 5 C 6 , respectively.
The organic moieties attached with layered materials can be identified from the vibrational band of the alkyl or aromatic functional groups. Hydroxyl groups in the magnesium silicates show characteristic broad signals around 3,—3, cm —1.
Formation of covalently-linked MSils. Magnesium silicates are the most common class of phyllosilicate mineral. In these minerals, Mg in octahedral coordination with O—H that are bound to two sheets of Si in tetrahedral coordination with O atoms.
Since one of the O atoms is replaced by organic functionalities in organosilanes, it is expected to form Si tetrahedral with Si—C covalent linkages in layered magnesium silicates. If such a surface suffers a small scratch, the paint will flow a little and effectively self-heal the scratch.
Another coating that protects steel is to use a metal that is further down the activity series, a metal that does not oxidize in the air.
The ideal metals are gold, silver and copper, which are towards the bottom of the activity series. Galvanized buckets and dustbins that used to be commonplace did not rust even though they were made from steel. The metal surface of these containers appears to have irregular shiny crystals. Galvanizing is the process by which a metal surface is given a coating of zinc. The process of galvanizing does seem to work; it is more expensive than conventional paint protection but is finding increasing use in the motor industry.
Where does zinc come in our activity series? We have argued that to coat steel with a metal that does not oxidize in air makes sense, so it seems odd to use a metal that oxidizes even more readily than does iron.
Zinc, like aluminium, oxidizes easily. It also has an oxide that clings well to the metal and is not porous to water or oxygen. So the surface of the steel is protected by zinc metal overlain with zinc oxide. But there is a further advantage to using zinc. If the zinc coating is damaged and iron exposed, one might expect the iron to rust just as if a protective paint surface had been damaged. However, as zinc is more easily oxidized than iron, zinc is oxidized in preference and the iron remains in the metallic form as we can see here.
Representation of the protection of a galvanized surface. For such large structures, it would not be practical to provide a covering of zinc. What is done is to attach a block of an easily oxidized metal magnesium is often used to the structure by a steel cable.
The electrons produced can flow along the steel cable and give the oil rig a small negative charge. This makes it difficult for iron in the structure to oxidize and form positively charged ions as this would add even more electrons to what is an already negatively charged structure and the steel rig remains intact. In time, the block of magnesium is eaten away and has to be replaced. This is much easier and cheaper than carrying out repairs on the structure of the rig. Modifying metals The resistance to corrosion of a metal can be changed by providing a surface coating of paint or other metal, but there is another way of changing the properties of the metallic elements that has been known for thousands of years.
Bronze is an alloy of copper and tin, and like copper, its major component, it is resistant to corrosion.
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