Comprehensive Analysis of Water Based Emulsion Drilling Fluids in GHARRAF Oil Field in Southern Iraq: Properties, Specifications, and Practical Applications

During the last few years, oilfield technology has advanced significantly for making drilling operations more favorable, both on-land and offshore, in support of the world energy supply. In this aspect of oil and gas explorations, drilling fluids play a vital role and are considered as an important category of chemicals used [1]. They come in direct contact with the geology of the borehole and provide essential support for oilfield drilling operations by lubricating drilling bits, carrying drilling cuttings, and maintaining the stability of boreholes, the integrity of formations, and minimizing differential sticking—a problem in deviated cased wells. Moreover, they help in controlling downhole pressures, sealing permeable formations, and cooling and cleaning the drilling bit and the borehole [2]. It is obvious that without drilling fluids, the objectives of drilling an oilfield, which can lead to the largest and most important recoverable resource worldwide, would be impossible [3]. Water based muds (WBM) are environmentally favorable drilling fluids, and they are the most widely used drilling fluids. Significant advantages, which have made these fluids so popular, are: mud densities are easily kept in the range of 7–9.5 pounds per gallon (lb/gal) due to economic and environmental concerns; overall cost control is better than oil- and synthetic-based drilling fluids; it is usually simple to maintain WBM shale stability by means of wellbore stabilization; all additives can be readily mixed and halt; it is a basic requirement that additives should have equitable performance in hard water (20,000 ppm) conditions [4]. Furthermore, health and safety requirements are simple to fulfill. The use of WBM in domestic onshore fields has always been important. For environmental legislation, the commitment to WBM is second to none. They are often preferred for drilling protected environmental regions as the U.S. permits water to be the drilling fluid in environmentally sensitive coastal and inland waters [5].

The advancement of water based emulsion drilling fluid technology has generally been around acid, salt, or supplemented bentonite. The remarkable research work undertaken in this area has been presented. Comprehensive literature has been surveyed for gathering required information regarding the formulation, performance, field applications, advantages, and specifications of the water based emulsion drilling fluid. The work has been discussed and coordinated into analysis, presentation, formulation screening, and experimental investigation for laboratory development. With regard to performance in sum, the comprehensive investigation leading to laboratory development and field applications successfully indicates that the water based emulsion drilling fluid has significant potential for use in ready-to-use, cost-effective, and environmentally friendly drilling fluid systems. After the developments are carried out, several well tests have been undertaken to evaluate the performance of the water based emulsion drilling fluid in drilling operations. The field applications indicate that the water based emulsion drilling fluid can not only effectively lubricate the drill bit but also prevent lost circulation, easily wash the rock cuttings as showed Figure 1, and stabilize the borehole wall. The emulsion could be prepared either by mechanical agitation or mixing and high-shearing. The emulsification of water in oil takes place with the reduction of the droplet size under high energy. Mechanical emulsification requires large machines, while the latter is practically widely used in the preparation of laboratory formulations. Continuous mixers can be thought of as high-shear devices with narrow piping configurations, where the energy input is between centrifugal and peristaltic types of mixers. Quality control of petrolatum emulsions is important for the application; control value is the sabotage of drill pipes due to the formation of tarry deposits. The drilling fluid viscosity is divided into the useful and the monomeric viscosity; the latter is very important for the preparation of stable emulsions. The diluted dynamic viscosity is recommended as the raw emulsion is prepared first, and it is then diluted with diesel oil to the required ratio and viscosity. Commercial water based emulsions are adjusted to address operational difficulties. Surfactants having a high valence are capable of forming thermodynamically stable emulsions, oil emulsification occurs, and specific gravities of emulsions are higher than that of water.

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Figure 1. Flowchart showing the different type of drilling mud based on the type of base fluid [6]

1.1 Background and significance

During drilling operations, cooling, cuttings removal, suspending and lubrication of the bit, cleaning, and transportation of the rocks to the surface take place. In order to achieve these goals, the drilling fluid should have suitable properties. The fluids used in drilling operations are classified according to their basic functions as flushing, protective, and suspending fluids and as water based and oil-based [7]. Water fluids have the undesirable feature of swelling clays and blocking pore channels, creating high filtration pressures, reducing the well-bores' stabilities, and reducing the fluid holding capabilities of the fluid. However, the most widely used drilling fluid in the world is a type of water based drilling fluids that are usually prepared from natural clays [8]. These clays are used for cooling lubricant fluids at the top of the drill pipes, adding weight to the well bore, containing the circulation pressure, facilitating the waste removal from the well-bore, and preventing the eruption and caving of the pipes.

The point is that the components of unwanted water fluids are replaced by water based substances with a structure similar to betonies. It has presented different water based mud systems such as polymer mud, xanthan gum, guar gum and their derivatives, etc. In this study conducted to stabilize tactic, sepiolite-containing water based drilling fluids were used [6]. Parameters that should be considered in designing a fluid include the nature of the rock and the presence of hydrocarbons, the properties of the formation water from the well, the hydraulic stability of the fluid, the desired properties in the suspension, the physiological effects of the fluid on the components and the environment at the wellhead, and the security and ease of using the fluid at different times in the well work [9]. Due to the physical and chemical sensitivity of the drilling fluid to changes in the properties of the mud system, the objectives set for a fluid and the conditions in the borehole should be taken into consideration and intended results should be achieved.

1.2 Scope and objectives

This project is formulated to address different problems related to water based emulsion drilling fluids (WBM) formulated with ester as the external phase. The emphasis is on understanding the various chemical, physical, and rheological properties. The study has laid the foundation for formulating new generation drilling fluids based on dispersion technology for difficult drilling environments. The objectives achieved in this project include understanding the importance of variables and determining their constraints in relation to the final properties of drilling fluids [10]. New generation water based emulsion drilling fluids are versatile and have been successfully formulated and tested in the laboratory. Water based emulsions are designed to be tailored by the addition of polymers to reach the optimum density, shear rate, gel strength, thixotropic, and filtration loss properties. The filtration loss of water based emulsions is comparable with or exceeds that of oil-based or synthetic-based drilling fluids [11].

Oil-based drilling fluids have traditionally been preferred over water based drilling fluids because of their improved technical performance, flexibility, environmental benefits, and economic efficiency, especially in harsh drilling conditions. With the present emphasis on environmental responsibility and economic concerns, the acceptable level of permissible discharges and the need to take safety, health, and wellbore stability into account, a major effort has been made to implement research aimed at developing new generation water based drilling fluids with enhanced performance properties, which meet the requirements of deep water locations [12]. The use of water based emulsion drilling fluids for high-performance drilling applications has taken on renewed importance. Water based emulsion drilling fluids are designed to improve technical performance compared with conventional water based systems that were developed with surfactants and liquid-liquid emulsion technology [13].

A water based emulsion is a mixture of water with oil for three or more components and other raw material ingredients. There are essential oils and non-essential oils in a water based emulsion. Essential oils act as emulsifiers to allow the combination of water and other oil ingredients in the product formula to form the emulsion. Non-essential oils are included in the product to add moisture, lipids, and other nourishing and hydrating ingredients. However, too much of the oil phase may lead to a poor water quality emulsion that leads to some safety hazards related to the instability and incompatibility of WBM with oil well formation. Hence, Figure 3 formulated WBM as direct, invert, and multistage emulsion systems to meet field requirements.

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Figure 3. Mud balance

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Figure 4. De-sander

Saline water based emulsion drilling fluids (WBM) are systems wherein the proportion of water and emulsified external phase is much less than 60% water content by volume. Saline WBM, thanks to its rich properties, including high temperature and high-density tolerance, is commonly utilized in the current oilfield. The development of the drilling method has made it possible for the oil and gas fields to operate optimally. Because of that, WBM has recently become more popular and available as an environmentally conscious option as well due to environmental concerns being high. Although WBM possesses an increasing number of advantages over non-aqueous drilling fluids (NAEs) as showed Figure 4, it still has volatility problems that are severe in the upper shale while encountering the recycle conditions of dispersed solids [21]. To rein in the problem, some solid-control management methods and techniques, as well as circuits and processes, have been developed. Additionally, WBM is formulated with key substances as emulsifiers and inverse emulsifiers. The combination of the key substances in the formulation and the sequence of addition, high shear mixing, high temperature, and pressure conditions throughout the entire drilling operation will affect the drilling dynamics and drilling engineering input costs [22].

3.1 Definition and composition

Aqueous fluid systems are an essential category of drilling fluids in drilling operations, which supply the required hydrostatic pressure and cool the drill bit. These fluids can affect the stability of the wellbore and have other significant impacts on the evaluation of the formation. Aqueous drilling fluids can be divided into water based drilling fluids, oil-in-water emulsion drilling fluids, and water-in-oil emulsion drilling fluids. In recent years, water based fluids have become the predominant category owing to their lower environmental impact compared with oil-based fluids. The WBF systems typically require the optimization of the properties to meet different demands under various drilling conditions. As a critical component, the emulsion has an important impact on the properties and performance of WBF. In this survey, we detail the composition of WBM by summarizing the main features of the water phase, the dispersed phase, emulsifiers, viscosities, fluid loss reducers, and some additives. Emulsification, emulsion stability, rheology, and filter loss of WBM that contain the non-ionic and anionic emulsifiers are also presented.

Over the years, many methodologies and experimental studies have been performed by scholars to improve the drilling fluid performance for WBM by adding the right amount of emulsifier and compound based on emulsion stabilizer, fluid loss additive, rheology modifier, and corresponding adjustment of solid phase content. However, the questions of how to achieve several excellent characteristics such as the minimum emulsion phase volume, maximum emulsion intactness, maximum rheological and fluid loss property, and minimum consumption of chemicals, which are the focus of many research groups, are worth exploring and solving to develop excellent drilling fluids under current complex situations. Careful selection of these components and their amounts and forms may, to a certain extent, meet the design and demand of drilling projects.

Water based mud density must be adjusted to gelling formation pressures and must balance the borehole stability with the formation drilling rate as showed Figure 5. Density varies with the proportion of solids, such as baryte or bentonite. The first contributes to the volumetric increase of the mud and the second to the densification of the mud system, as a function of the mud purity. At the beginning of a drilling operation, the density of the mud is frequently below the density of the gravel containing formation "balancing the gravel," or it may be balanced with the overburden pressure. Gravel volume can be determined from well information anticipated from the drilling process. Even if the drilling idea or first pass is a dry run, drilling began for the field experience. Often, borehole security problems have involved high pressures occurring where the formation contains fluid and low pressures occurring where insufficient rock bonds exist to allow hole independence. These "bridging" and "balancing" techniques have sometimes entailed temporary clogging of the mud cake, bit balling, wedging, sticking, or reaming of the hole by the drilling assembly.

Figure 6 is investigated analysis is obtained by measuring the following parameters: loss of filtration and density (density, sodium chloride, calcium chloride, chromium lignosulphonate, walnut shell, and starch, bentonite, and PAC LV prices). The wet properties of mud are measured using a mud balance. Viscosities are measured using a six-speed viscometer, filtered return, and APARATUS LPLT HTHP. The methods are briefly discussed and reviewed for each of these measurements.

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Figure 5. Weighted salt saturated mud [14]

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Figure 6. The formulation for mixing drill-in mud, the strength alteration with the extended time of mud interaction

WBM quality control aims to prevent mud from deteriorating and losing its properties in circulation, particularly when it is a well-controlled drilling fluid in terms of viscosity, filtration, density, and the properties of the mud sludge at the borehole variance, particularly the rheological properties.

The WBM is generally formulated from bentonite, additives (calcium chloride, sodium chloride, chromium lignosulfonate, walnut shell, starch, PAC LV, etc.), sulfuric and hydrochloric acids. They are placed on the surface to be transported to the drill site in concentrate form. These additives ensure the density of the fluid, maintenance of filtration rate and loss of fluid, groove stability, the suspension of cuttings, cleaning of the well, protection of the wall of the well against hole problems and pressure loads, and transporting the cuttings from the bit to the surface without premature wear on the drill stem or pump elements. These are the properties of an efficient drilling fluid.

The chemical properties of drilling mud and the measurement procedures used to evaluate these properties (density, filter loss, rheology) were determined. The data provided by the tests and the specifications of these tests for the mud control are shown. The mud properties must fall within the standard range of specifications; otherwise, the base may be adjusted. The methods and specifications of standard tests are detailed in the three following sections.

Formation A:

Formation pressure of sand A = 0.48 x 5500 = 2,640 psi with over balance of 250 psi, the hydrostatic pressure required is 2,890 (2640 + 250) psi. Convert pressure into mud weight = 2890 ÷ (0.052 x 5500) = 10.2 ppg.

Formation sand B:

Formation pressure of sand B = 0.49 x 8800 = 4,312 psi with over balance of 250 psi, the hydrostatic pressure required is 4,562 (4312 + 250) psi. Convert pressure into mud weight = 4562 ÷ (0.052 x 8800) = 10.0 ppg The effect of the oil/water ratio can be observed in Figure 6 which shows an increase in emulsion viscosity as the oil content is increased. A slight increase existed in emulsion viscosity at 30% deionized water content to 40%. At the oil/water ratio 50%/50%, a significant increment in the water content causes a material falling down in the emulsion viscosity. Changes in emulsion viscosity at a lower oil/water ratio could be attributed to coalescing of water droplets through shearing forces while a lower viscosity at a larger water component to the abound surfactant preventing flocculation and subsequent eccentric steering effect. Therefore, 40% oil is a suitable oil-to-water ratio for fresh oil-based emulsified Nano drilling fluid with a suitable behavior in the storage stability of a prototype system at a negligible cost and the theoretic support validates the simulated results.

In the Gharraf oil field of Thi-Qar Oil Company, the first and second bore fields are made using water based clay as follows. Figure 7 shows the simulation of drilling proses:

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Figure 7. 3D modeling of drilling prosses

1- Betronite mud

Betronite mud is used in the first cavity instead of water to avoid loss of fluids and to reinforce the wall of the well from collapsing, as the mud has a high viscosity to clean the well and transfer the rock fragments from the bottom of the well to the surface. This is because the drilling speed is high in addition to the large size of the first cavity.

Table 1. Betronite mud mixed [14]

Preparation method: The mud is prepared by mixing water and bentronite with some additives to obtain the appropriate clay properties for drilling the first cavity, as shown in the Table 1.

2- Lime polymer

This type of mud is used in drilling the second cavity, where hydrophilic layers containing calcium such as anhydrite are drilled. The proportions of materials used in its preparation are as shown in the Table 2.

Table 2. Lime polymer mixed

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Figure 8. Mud type suitable for drilling each formation as well as the pore pressure for each formation

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Figure 9. Each type of mud suitable for drilling each formation as well as the density of clay suitable for each formation

Figure 8 shows each mud type suitable for drilling each formation as well as the pore pressure for each formation We notice that pore pressure increases with increasing depth. We also note that the first section represented by 18-5/8 casing is drilled by PHG Mud. The second section, which represents the rest of the formation, is dug using lime polymer mud.

Figure 9 displays each type of mud suitable for drilling each formation as well as the density of clay suitable for each formation. We notice that the first section represented by 18-5/8 casing is drilled with a small amount of mud, which is 8.7ppg. As for the second section, which represents the rest of the formation, it is drilled with higher mud densities, starting from 9.3ppg to 9.5ppg, depending on the pore pressure of each formation.

3.2 Advantages and disadvantages

These drilling fluids have higher weighted solids when compared with oil-based drilling fluids and hence are used in the drilling of high pressure, high temperature wells. The only cost-effective version of the water based drilling fluids, which are used in a certain set of environments, is the water based emulsion drilling fluids. The oil phase can be expensive, and the addition of emulsifier, wetting agent, pH control agents, etc. increases the costs. The development of water based drilling fluids enabled drilling of high pressure, high temperature wells in an environmentally friendly manner. Especially the technology related to drilling fluids has developed a lot in the last 20 years, which put drilling fluids as high-performance drilling fluids [2].

Advantages and Disadvantages Water based drilling fluids are very effective in preventing borehole instabilities and have very few environment-polluting properties. They are biodegradable, stable at down hole conditions, and provide excellent inhibition to clays, shale’s, and rock formations. These fluids are found to control filtrate loss effectively and can easily be maintained in the specific gravity. These drilling fluids are used in high pressure, high temperature wells, deep water wells, and UBD wells. The significant advancements in the additives and developments in the solid-free systems have improved the performance of the water based drilling fluids. The water based drilling fluids provide better lubricity, exceptional thermal stability, minimal reactive clays, etc. The lower prices of the raw materials and simpler system have substantially decreased the net expenditure on the drilling fluids.

Water based muds are the most commonly used muds. Besides, they have good lubrication and high performance. Today, many useful mud additives are marketed. The most important existing properties of the mud are obtained by these additional properties. To control and improve the mud properties, they should be used in the intended formulations and concentrations. These kinds of mud derivative products work in more than one way and have been produced by introducing more than one functional group. The following information is known in most of these materials: In more than one of these additives, some controlling activity might be expected as shown in the Table 3.

Table 3. Classification of drilling fluid systems [13]

The mud, prepared using these derivatives, will have several activity levels than others. This derivative system, parts or full of the chemical products, which are ordered in large numbers groups (salts, ester, acid, amine, alcohol, or one of the surfactants), has relationships with these forms, and they have ionic properties in these regions. This kind of situation is present in a couple of the same groups (alkyl or aryl, for example) pop out. There are many multifunctional chemical agents. Their structures are in an octal feel a circle. They have a quite high-level hydro carbonic region structure in their structures. These make contacts possible in more than one of amphiphilic groups that disperse mud rheological problems, problems of propagation and filtrate, stabilization of rocks, emulsification of oil, and so on. WBM chemical mud parts are usually water-soluble, and they disperse faster than synthetic oil-based mud materials. This usually means that the chemicals quickly form a useful, three-dimensional integrated polymeric network, bridges the surfaces, disrupt the plates, and make them the premud additive substances. Due to the presence of many functions in the octa branch structures, the amphiphilic organics must not be treated as a dietary polymer to produce these same effects. Since each amphiphilic material is often two monomeric, such behavior should be kept in mind. Use of LLENVD derivatives and other appropriate components, especially replacing water based muds, requires significant amounts of research and product development.

5.1 Density and pH

It is well known that water based mud systems (WBM) can be less expensive, stable, and more environmentally friendly than oil based mud systems (OBM). In addition to density, rheological behavior, and filtration, the ionic content and pH degree play a significant role in the WBM properties. In the case of muds with high ionic content, these properties are directly related to the presence of cationic and anionic polymers, which are used in their formulation. However, in the case of muds with low ionic content, the presence of salts and potassium or sodium hydroxide is required to obtain a suitable pH for drilling, and therefore, preserving the clay particle stability and rheological properties. In addition, the formation's interstitial brine's potential reactivity with the clays present in complex geological formations must also be considered. In this sense, a well defined mud compatibility study should always be carried out in order to provide the adequate mud system with the highest efficiency to drill the geological formation as shown in the Table 4.

Table 4. The standard formulation for mixing spud mud [14]

5.2 Salinity and alkalinity

One nonstandard one can encounter is formation water salinity. As discussed before, ion exchange properties may bring about phase separation. However, most clays have a salinity limit which is significantly higher than that typically encountered in formation water. Alkalinity, on the other hand, is an important specification as it is directly related to the pH of the mud. For the primary purpose of high temperature stability, the mud pH must be kept at an optimum level. This is 9 - 10.5 for primary mud and 9 - 10 for the second grade. If the pH is much less than that, alum will start to degrade and release OH groups. It is these groups that are responsible for the bridging of organophilic clays into sheets. The final jelly becomes a soup.

The next to take note of is filtration control. In a saturated salt solution of the right salinity, a WBM filtration is typically 2 - 4 cc. However, due to the viscosification, salt and other clay contaminants could be held on the filter medium, dropping the final cake volume to 1 cc. Finally, it means a saturated salt solution of 10% has formed, and the drilling operator has an immediate additive response in its mixing water. Restricted properties of the mud’s primary interest are always viscosity and gel strength. They are just as important as standard API muds. This is because they can hold cutting better than the thinnest API mud, and reduces erosion. It also helps in maintaining effective carrying capacity. After all, the mud exists to carry maximum tonnage. Anything that reduces its viscosifying ability is bad. However, other properties must be considered as well.

Water-based drilling fluids have environmental compatibility. Furthermore, they increase penetration rate, maintain wellbore stability, reduce fluid disturbance, and minimize problems of lost mud. Drilling fluids are made of a base substance, which is usually water, despite the term "oil" mud being often used. An addition of oil or synthetic material to the water should be significant enough to prevent the formation of emulsions under the severe conditions found in the deep hole of the well or to use as the external phase of the drilling fluid. Generally, when we use oil, prices tend to fluctuate widely because of problems worldwide. However, the problem with water is its high surface tension value. It is said that water has an apparent cohesion that allows the development of a strong and thick natural filter cake. Thus, many emulsions and foams are used in drilling fluids.

Drilling fluid formulation incorporates three generic systems: water based, oil- or synthetic-based, or gas, and so on. There are various types of drilling fluids used as base mud, such as unweighted mud, which is mud that has no solids added to it. It usually comes in three categories: Bentonite, Inhibitive or dispersion polymers, and combination. These additives frequently work together synergistically. This paper will provide a detailed study on the properties and optimization of water based emulsion drilling fluids and several related aspects.

7.1 Onshore and offshore applications

As for types (IOWEF), it can be applied for almost all fields such as drilling, completion, work over, coring, underground storage, reverse circulation, horizontal and deviated drilling, etc. And due to its better inhibitive property and its also balanced to High temperature High Pressure (HTHP) wells of having High Density. HPWBM will safeguard the Formation damage, enhance wellbore stability, raise the Rate of Penetration (ROP), and decrease the whole cost. Ensure good rate of penetration in sensitive formations. The clay platelets in whole mud will hold the drill cuttings but do not affect ROP while air and foam solutions will restrict the flow of drilled cuttings to the surface which will result in drop the ROP. The plastic muds present very high levels of fluid loss and having low level of wellbore stability related problems which can be solved by adding weighting agent to reach a higher level of filtrate control and also increased mud density at low range of shear rate and also to hold the drilled cuttings at high range of shear rate.

WBM is water and clay-based/modified muds which will produce few environmental impacts, low degree of borehole instability which can result in borehole collapse, loss of circulation, contamination of productive zones. Having low lubricity behavior during drilling, completion work, and cementing which the adverse effects can prevent by adding lubricants. LCM is an important part of the fluid system in which the problems occur. Power Law model is used for characterization of WBM properties while looking on the control of friction and minimize the well sliding during the advance and contraction of the drillstring. The purpose of mud additives is to eliminate the remaining cuttings and to enhance the well clean-up. Not only onshore, offshore also, WBM muds used. Accidental release drilling fluids and drill cuttings from offshore drilling operations may impact marine life and marine systems nearby the rig operation. Data of environmental elements after 5 years baseline study provides valuable data to assessing potential impacts, and was provided to the BHP Billiton via a report by BMT Oceanica. Summary of the assessment is as follows: About 100,000 t of drilling fluids will be discharged into the seafloor during drilling (tailed object).

7.2 Environmental considerations

The disposal of water based mud (WBM) is generally less expensive than oil-based mud (OBM) since WBM has lower chemical costs, causes fewer formation damage problems, and has lower environmental concerns. Furthermore, the cost associated with the disposal of WBM is less than that of oil-based muds since more treatment expenses are involved in treating oily cuttings from OBM. Furthermore, cuttings from WBM can be utilized as landfill, mixed with cement concrete, encapsulated, buried under the ocean seabed or on the land, and can be mixed with soil. The cuttings generated from drilling with WBM in the North Sea are generally discharged to the ocean since the environmental effects of cuttings disposal have been extensively evaluated in a number of studies. Land treatment is now more frequently applied to drill cuttings because of the increasing costs of water based mud and the reductions in allowable disposal of drill cuttings over land and water. The ability of the soil to retain the cuttings is also a factor to be considered.

The American Conference of Governmental Industrial Hygienists (ACGIH) has concluded that average daily exposures to free diesel fuel in the air of the workplace should be limited to 20 mg/m³ in a time-weighted average of 8 hr. /day during a 40 hr. work week required to be maintained by the Occupational Safety and Health Administration (OSHA). The transportation of diesel engines to the lease, to a dumpsite, and/or to the leasing company for rebuilding, repair, or replacement is sometimes used to reduce fuel exposure. The use of a high level of mud in mud systems leads to an increase in the proportion of oil to water and could increase fuel exposure to workers, resulting in irritant dermatitis, skin disorders, and respiratory symptoms commonly reported in the industry.