Invert Emulsion Muds Research Articles

Experimental Study on Dynamic Barite Sag and Effects of Inclination and Pipe Rotation

Summary Barite sag causes pressure fluctuations in the wellbore, which is undesirable. These problems usually occur with oil-based muds (OBMs; invert emulsion muds) and are associated with fluid properties and operation parameters. Drilling issues related to this undesirable phenomenon include wellbore instability, lost circulation, and stuck pipes. As barite sagging is a complex phenomenon, the mechanisms that cause and aggravate it still need to be fully understood to mitigate these problems. This study examines barite sagging in the wellbore with inner pipe rotation to understand the process and develop prevention strategies. Thus, a flow loop study with OBM is conducted in a concentric annular test section with varying inner pipe rotation and inclination angles. The tests were performed at an elevated temperature (49°C) to simulate borehole conditions. By measuring the pressure profile in a mud sample trapped in the test section, barite sagging was evaluated. Using the data, we calculated the density difference between the top and bottom sections of the column. The novelty of the work lies in continuous monitoring of the density profile of the mud column, which is sheared between two coaxial cylinders to simulate drillstring rotation in the wellbore, and utilizing the data for evaluating barite sag. The results show the evolution of the pressure profile with time, indicating the sagging of barite particles at the bottom of the test section. Due to barite sagging, the density of the top portion of the mud column decreased over time, while the density of the bottom part increased. The lateral sedimentation of barite particles toward the annulus outer wall enhances barite sag in inclined configurations. The sedimentation creates two suspension layers with different densities, leading to secondary flow, which enhances sagging. Hence, the primary factor driving barite sagging is inclination. An increase in inclination angle from 0° to 50° resulted in a significant (more than twofold) increase in mud density difference. Also, the rotation of the pipe delayed sagging during the early phases of the testing process (less than 20 minutes). However, it did not have much effect as the sagging progressed, resulting in approximately the same density difference in both cases (i.e., with and without rotation).

Ilmenite Inclusion: A Solution towards Solid Sagging for Hematite-Based Invert Emulsion Mud

The sagging tendency of hematite in drilling mud is a common challenge occurring at high-pressure and high-temperature (HP/HT) applications. This work studies the performance of hematite-based invert emulsion mud for HP/HT conditions and provides a solution to prevent the hematite settlement using a combination of ilmenite with hematite. Practical mud formulation was utilized over a range of ilmenite/hematite ratios (0/100, 20/80, 40/60, and 50/50%) to study sagging behaviour. From the sag tests, the optimum combination proportion was determined. Thereafter, the density, emulsion stability, rheological and viscoelastic properties, and filtration conduct for the formulated mud were evaluated. The experiments were conditioned as per the standards of the American Petroleum Institute. The obtained results of sagging experiments indicated that including 50% of ilmenite mitigated the hematite settling and reduced the sag tendency towards the safe range. A slight drop (4%) in mud weight was noticed upon adding the ilmenite, whereas the emulsion stability was enhanced from 551 to 574 volts with the 50% ilmenite content. The rheology and viscoelasticity measurements showed that 50/50% combination improved the yield point (YP) by 50% with a trivial 1 cP increment on plastic viscosity (PV), hence enhancing the YP/PV ratio by 46%. Also, the gelling strength was enhanced resulting in flat rheology and better gel structure. The filtration behaviour of 50% ilmenite mud was improved compared to blank hematite as it resulted in 21, 15, and 17% reduction on the filtrated volume, filter cake weight, and thickness, respectively. This study provides a solution for hematite sagging issue at HP/HT using combined weighting agents, which contributes to enhancing the mud stability and avoiding several well control issues and related operational and technical challenges that eventually will economize the drilling cost and time.

Prediction of the Rheological Properties of Invert Emulsion Mud Using an Artificial Neural Network.

Successful drilling operations require optimum well planning to overcome the challenges associated with geological and environmental constraints. One of the main well design programs is the mud program, which plays a crucial role in each drilling operation. Researchers focus on modeling the rheological properties of the drilling fluid seeking for accurate and real-time predictions that confirm its crucial potential as a research point. However, only substantial studies have real impact on the literature. Several AI-based models have been proposed for estimating mud rheological properties. However, most of them suffer from non-being field applicable attractive due to using non-readily field parameters as input variables. Some other studies have not provided a comprehensive description of the model to replicate or reproduce results using other datasets. In this study, two novel robust artificial neural network (ANN) models for estimating invert emulsion mud plastic viscosity and yield point have been developed using actual field data based on 407 datasets. These datasets include mud plastic viscosity (PV), yield point (YP), mud temperature (T), marsh funnel viscosity (MF), and solid content. The mathematical base of each model has been provided to provide a clear means for models’ replicability. Results of the evaluation criteria depicted the outstanding performance and consistency of the proposed models over extant ANN models and empirical correlations. Statistical evaluation revealed that the plastic viscosity ANN model has a coefficient of determination (R2) of 98.82%, a root-mean-square error (RMSE) of 1.37, an average relative error (ARE) of 0.12, and an absolute average relative error of 2.69, while for yield point, this model has a coefficient of determination (R2) of 94%, a root-mean-square error (RMSE) of 0.76, an average relative error (ARE) of −0.67, and an absolute average relative error of 3.18.

Sagging Prevention for Hematite-Based Invert Emulsion Mud

Abstract The solids sagging in high-pressure high-temperature (HP/HT) reservoirs is a common challenge associated with hematite drilling fluids. This study provides a solution to hematite sagging in invert emulsion mud for HP/HT wells, which involves the combination of Micromax (Mn3O4) with hematite. The particles of both weighting agents were characterized to address their mineralogical features. A field formulation of the mud was used over a range of Micromax/hematite ratios (0/100, 20/80, and 30/70%) in laboratory experiments to address the sag performance and determine the optimal combination ratio. Then, density, emulsion stability, rheology, viscoelasticity, and filtration performance for the formulated mud were addressed. The tests were conditioned to 500 psi and 350 °F. The acquired results of sag tests indicated that incorporation of 30% Micromax solved the hematite sagging issue and brought the sag tendency within the recommended safe range. An insignificant reduction in mud density was observed upon the inclusion of Micromax, while the emulsion stability was obviously improved from 551 to 614 volts with the 30% Micromax mixture. The recommended 30/70% combination had almost no effect on plastic viscosity and yield point since they were increased by one unit, but the gel strength was improved resulting in flat rheology and better solids suspension capacity. The filtration behavior of the formulation with 30% Micromax was enhanced compared to pure hematite as it resulted in 10% and 14% reduction of the filtrate volume and filter-cake thickness, respectively. This study contributes to improve and economize the drilling cost and time by formulating a stabilized and distinguished-performance drilling mud using combined weighting agents at HP/HT.

Investigation of magnetite-based invert emulsion mud at high pressure high temperature

Investigation of magnetite-based invert emulsion mud at high pressure high temperature

Optimization of invert emulsion oil-based drilling fluids performance through heterocyclic imidazoline-based emulsifiers

In this work six structurally related imidazoline oligomers based on the reaction of liner polyamine with saturated and unsaturated long alkyl chains (C18 oleic and stearic) fatty acids were prepared, followed by a quaternization reaction to produce new conventional and gemini imidazolinium quaternary salts. The chemical structures of prepared amphiphiles were confirmed via spectroscopic methods and elemental microanalysis, also, the prepared emulsifier’s characterization has been studied through static interfacial tension, visual and microscopic examination of prepared emulsification systems. The static interfacial tension measurements show a high ability to reduce interfacial tension values between diesel oil and water. The visual and microscopic examination gave evidence of a multilayer interface around emulsion particles and an increase of emulsion droplets size as a function of time with acceptable emulsion stability and phase separation. For both oil-based mud cost and diesel oil toxicity, this article brings to light many important aspects of designing new emulsifiers for low toxicity invert emulsion muds with lower diesel oil content. The prepared emulsifiers were mixed to be investigated and evaluated as primary emulsifiers package to formulate the invert emulsion oil-based muds (IEOBMs). The electrical stability, rheological properties, and filter loss were evaluated before and after hot roller aging and compared with the reference mud sample formulated from the commercial-grade emulsifiers. The experimental investigations conducted based on the Herschel-Bulkley rheological model showed good rheological behavior compared to the reference mud sample, high resistance to the deformation that occurred to prepared mud systems due to hot roller aging, good electrical stability, and high pressure-high temperature filtration loss values.

Enhancing Hematite-Based Invert Emulsion Mud Stability at High-Pressure High-Temperature Wells.

Drilling fluids have a crucial continued role in drilling a successful well; however, most of the drilling technical and operational challenges are incorporated with the drilling mud stability and properties. The solid particles settling in drilling mud that deteriorates its stability is a common issue encountered in high-pressure high-temperature (HPHT) conditions. This issue, known as solids sagging, may eventually result in stuck pipes, wellbore instability, and loss of circulation. The objective of this work is to introduce garamite to enhance the stability of hematite-based invert emulsion mud under HPHT situations. The used garamite and hematite weighting material were analyzed using X-ray fluorescence, scanning electron microscopy, and particle size distribution to identify their compositions, morphologies, and particle sizes. The effects of adding different concentrations of garamite (0.5, 1.0, 1.25, and 1.5 g) to the field formula of hematite-based invert emulsion mud were investigated. The mud density, stability, sagging tendency, rheology, viscoelasticity, and filtration properties were studied to formulate a stabilized and distinguished-performance drilling mud. The obtained results indicated that garamite did not change the mud density while enhancing the emulsion stability by increasing the electrical stability proportionally with the added garamite quantity. The sagging experiments showed that adding 1.25 g of garamite is sufficient to prevent the sagging problem in both static and dynamic conditions as it was enough to enforce the sag parameters into the safe range of sag performance indicators. This 1.25 g of garamite improved the yield point by 152% from 19 to 48 lb./100 ft2 with a slight increase in plastic viscosity from 14 cP for base mud to 18 cP and significant increase in the gelling strength and viscoelastic properties. Adding 1.25 g of garamite showed a slight enhancement in the filtration properties as the filtrate volume was reduced by 8% from 3.7 to 3.4 cm3 and the filter cake thickness has 16% reduction from 2.69 to 2.26 mm. As a result, a mud with distinguished performance, in terms of rheology, suspension, sag performance, and stability, was obtained. Hence, a basis for safely drilling the HPHT formations was delivered, which reduces the drilling cost by minimizing the nonproductive time.

Novel Jatropha Oil Based Emulsion Drilling Mud Out performs Conventional Drilling Mud : A comparative study

ABSTRACT Drilling muds capable of drilling shale sensitive formations with negligible environmental effects are in great demand. The present work studies a 40% water in Jatropha oil invert emulsion illustrating a comparative study of the Jatropha oil invert emulsion, and conventional diesel oil-based mud (OBM). Jatropha oil is environmentally, chemically, and economically a better substitute of Diesel. The GC-MS (Gas Chromatography-Mass Spectrometry) confirms the composition of Jatropha oil and diesel oil are almost similar having a similar carbon number range. The effect of temperature, concentration of oil, and various additives on the rheology of Jatropha oil invert emulsion mud was investigated. The reduction in viscosity of Jatropha oil inverts emulsion mud after hot rolling at 16 h and 105°C was around 25% as compared to 56% with Diesel oil invert emulsion mud. The Jatropha oil invert emulsion mud was thermally more stable than Diesel oil invert emulsion mud. A drastic reduction in the fluid loss from 13 to 3.4 mL was observed while LPLT (low temperature low pressure) filter press test for Jatropha oil invert emulsion mud along with the mud cake thickness of only 0.793 mm (1/32 inch). The shale recovery test confirms the usage of Jatropha oil mud in dispersive shales.

Real-Time Prediction of Rheological Properties of Invert Emulsion Mud Using Adaptive Neuro-Fuzzy Inference System.

Tracking the rheological properties of the drilling fluid is a key factor for the success of the drilling operation. The main objective of this paper is to relate the most frequent mud measurements (every 15 to 20 min) as mud weight (MWT) and Marsh funnel viscosity (MFV) to the less frequent mud rheological measurements (twice a day) as plastic viscosity (PV), yield point (YP), behavior index (n), and apparent viscosity (AV) for fully automating the process of retrieving rheological properties. The adaptive neuro-fuzzy inference system (ANFIS) was used to develop new models to determine the mud rheological properties using real field measurements of 741 data points. The data were collected from 99 different wells during drilling operations of 12 ¼ inches section. The ANFIS clustering technique was optimized by using training to a testing ratio of 80% to 20% as 591 data points for training and 150 points, cluster radius value of 0.1, and 200 epochs. The results of the prediction models showed a correlation coefficient (R) that exceeded 0.9 between the actual and predicted values with an average absolute percentage error (AAPE) below 5.7% for the training and testing data sets. ANFIS models will help to track in real-time the rheological properties for invert emulsion mud that allows better control for the drilling operation problems.

Environmentally benign invert emulsion mud with optimized performance for shale drilling

Drilling muds having less environmental footprint are highly desired, especially for drilling into sensitive formation. In this research, an environmentally benign invert emulsion mud having Indian mango methyl ester (IMME) continuous phase was developed for shale drilling. The properties of the mud were tuned using nanoclay and gum acacia in order to minimize shale instability associated with rock-fluid interactions. The effect of nanoclay and gum acacia content on the rheological behavior and fluid loss of the developed mud was assessed. Furthermore, the thermal and mechanical stability of the mud were estimated. Results obtained with nanoclay and gum acacia were compared with the conventional bentonite and carboxymethyl cellulose additives. Muds containing nanoclay and gum acacia outperformed conventional additive-containing muds in all measures. The rheological properties, such as apparent and plastic viscosities, yield point and gel strength, of the mud formulated with gum acacia and nanoclay were remarkably enhanced. Moreover, the mud containing nanoclay and gum acacia was mechanically and thermally stable up to 100 °C. Particle size analysis of this mud confirmed the suitability of the additives toward shale plugging. The invert emulsion with the nanoclay and gum acacia achieved 95% weight recovery comparing with the conventionally used bentonite and CMC, which only achieved 64% weight recovery. Overall, the 40:60 (W/O) invert emulsion with IMME continuous phase and nanoclay and gum acacia additives portrayed ideal viscosity, rheology, fluid loss, particle size distribution and stability suited for shale drilling.

Utilization of egg yolk as a non-toxic emulsifier in environmentally friendly invert emulsion drilling mud

Vegetable oil such as Jatropha has been shown to be a comparable alternative to diesel and mineral oils for environmentally friendly oil based drilling mud. However compatibility of the vegetable oils with the usual chemical additives is still a major challenge that calls for compatible and non-toxic substitutes. This study examined the suitability of hen egg yolk as a non-toxic emulsifier in invert emulsion drilling mud using vegetable oil continuous phase. 8ml of the Egg yolk which was separated from the albumen was added dropwise as a primary emulsifier to a 70/30 oil-water ratio invert emulsion drilling mud formulated with Jatropha vegetable oil. The electrical stability was tested using electrical stability tester at the recommended test temperature of 48.9oC and later at 120oC to check any variation at elevated temperature. The stability values in volts were 398V and 289V respectively. A similar formulation using a standard emulsifier (versacleanVB) an amidoamine gave stability values as 201V and 188V respectively indicating that higher stability was attained with the egg yolk. The viscosities of the mud samples were also tested giving plastic viscosities of 52 and 49 centipoise at 50oC for the egg yolk and verscleanVB emulsified muds respectively. This study indicates that egg yolk could serve as an emulsifier for vegetable oil based invert emulsion mud in line with non- toxic additives for environmental compatibility Keywords: Environmental compatibility, Invert emulsion mud, non-toxic additives, electrical stability, emulsion stability.

Cleanup characteristics and mechanisms of reversible invert emulsion drilling fluid

Abstract Reversible invert emulsion muds (RIEMs) offer unique advantages over other oil-based muds for the completion of a well due to the pH-responsiveness of reversible emulsifiers. This paper presents new insights into the effects of pH-responsiveness on the completion performance of RIEMs and the mechanisms involved. At pH 4 and 6, RIEMs are easy to remove, but the formation damage is relatively severe. At pH 10, the removal of RIEMs is relatively difficult but can be facilitated by intense and repeated flushes. Once the mud has been removed, there is little formation damage. At pH 8, the mud is very difficult to remove, and the greatest amount of formation damage is observed. The spontaneous curvature of the surfactant layer changes at pH 4 and 6, resulting in the emulsion inversion and thereby enabling the removal of RIEMs by the solvent effect. These changes do not occur at pH 8 and 10. More emulsifiers adsorb to the rock surface at pH 4, 6, and 8, resulting in a strongly oil-wet condition and high formation damage. The desorption of emulsifiers occurs at pH 10, causing a water-wet condition and low formation damage. The variety in chemical states accounts for the changes in the adsorption behavior of the emulsifiers.

High-Performance Water-Based Drilling Fluids Offshore Cameroon

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163502, ’High-Performance Water-Based Drilling Fluids: An Environmentally Friendly Fluid System Achieving Superior Shale Stabilization While Meeting Discharge Requirement Offshore Cameroon,’ by Anuradee Witthayapanyanon, SPE, Baker Hughes; Jerome Leleux, SPE, Julien Vuillemet, Ronan Morvan, and Andre Pomian, Perenco; and Alain Denax and Ronald Bland, SPE, Baker Hughes, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed. Historically, invert-emulsion drilling fluids are the preferred system for drilling offshore Cameroon. However, with a regulatory environment moving toward zero discharge, associated costs are rising. Therefore, an operator planning to drill in this environment investigated high-performance water-based-mud (HPWBM) -system alternatives. HPWBM systems offer the potential advantage of offshore discharge of drilled cuttings and effluents (owing to the absence of oil contamination) and lowered waste-management costs. Experience in the field demonstrated that the selected drilling fluid met expectations by achieving the required drilling performance and high shale stabilization with zero environmental impact. Introduction Drilling with an overbalanced pressure is a common operational technique used to prevent formation fluids or gas from entering the wellbore, thereby minimizing the risk of well kick and blowout. However, overbalanced drilling can cause drilling fluid to invade the formation, resulting in formation damage, differential sticking, and sloughing if the formation consists of highly reactive clay and shale. To avoid these consequences, invert-emulsion drilling fluids have always been preferable for drilling highly reactive clays and shale formations. The HPWBM system is formulated with a concept of total inhibition. Unlike a conventional water-based-mud system, designed chemical additives are used explicitly in the formulation to achieve desired drilling characteristics that are similar to those of invert-emulsion mud. The key features of HPWBM systems include high shale stability, clay and cuttings inhibition, rate-of-penetration (ROP) enhancement, minimized bit balling and accretion, torque and drag reduction, and environmental compliance. A complementary benefit of its aqueous base is that HPWBM captures the growing need for more-environmentally- friendly drilling fluids. During the past 10 years, more-stringent regulations on drilling-waste disposal have been implemented worldwide. The industry anticipates that the zero discharge of oil-contaminated drilling wastes will soon be the global standard. By switching from invert-emulsion drilling fluids (oil-/synthetic- based mud) to an HPWBM system, operators can achieve substantial cost savings on waste management and logistics. These savings result from the use of on-site, offshore discharge allowed by an absence of oil contamination.

Synthesis and Some Applications of Schiff Base Surfactants

Schiff bases derived from the condensation reaction of benzaldehyde or anizaldehyde and diethylenetriamine were prepared. The products were neutralized with palmatic acid to pH 7. The chemical structures of the prepared compounds were confirmed using elemental analysis, FTIR, and 1H NMR spectroscopy. Various surface properties of the synthesized surfactants were evaluated particularly, critical micelle concentration, effectiveness, efficiency, maximum surface excess, and minimum surface area. These surfactants were also evaluated as corrosion inhibitors and biocide agents Gram positive and Gram negative bacterial strains. The rheological properties and the filter loss for oil-based mud (invert-emulsion mud) were evaluated. The result showed that they were good emulsifiers and filter loss control agents for oil-base mud. It was determined that they have good corrosion inhabitation for low carbon steel alloy and good bactericidal effect.

Optimized Drilling Techniques Significantly Decrease Drilling Time - East Apache Field

This paper describes the optimized drilling techniques used to decrease significantly the drilling time for a 20,000 ft (6096 m) Springer sand well in the Anadarko basin of Oklahoma. Use of these drilling parameters greatly increased the penetration rate and maintained excellent hole stability. With these results, the well was drilled quicker and at less expense than anticipated. Introduction The Anadarko basin is one of the most complex and challenging deep drilling areas in the world. In the East Apache (Springer sand) field, much difficulty was encountered in the drilling of the discovery well and three development wells in the field. On the average, these wells required more than 300 days to reach the final casing point. In the drilling of the Fort Sill Unit 2 Well 1 (the subject of this paper), the previously drilled wells were researched thoroughly, previously drilled wells were researched thoroughly, and from these findings evolved the optimized drilling techniques used. It was found that the maximum recommended revolutions per minute and weight on bit (WOB) could not be applied without hole deviation becoming a problem. To alleviate this problem, a three-point stabilization system was used problem, a three-point stabilization system was used in conjunction with tandem square drill collars. Also encountered were sloughing shales in the Atoka and Morrow zones. This problem was solved by using an invert-emulsion mud which had no effect on the hydratable clays in the shales. The last problem was low penetration rates. The wells previously drilled averaged between 1 to 2 ft/hr (0.305 to 0.61 m/hr) below 17,000 ft (5182 m). By using the previously cited parameters and by optimizing the hydraulics program, mud cleaning, and jet selection, the program, mud cleaning, and jet selection, the penetration rate was increased to an average of 4.83 penetration rate was increased to an average of 4.83 ft/hr (1.47 m/hr) below 17,000 ft (5182 m). This provided a saving in drilling time of 112 days when provided a saving in drilling time of 112 days when compared with the average of the best three wells drilled. Research of Previously Drilled Wells in the East Apache Field The East Apache field was discovered with the drilling of the Richard Vail No. 1 in 1971. This well was drilled 20,889 ft (6400 m), took a gas kick, and stuck the drillpipe. Fishing operations commenced, but the well could not be cleaned out and had to be abandoned. Three offset wells to the Vail No. 1 have been drilled, with two being producers and one a dry hole. The producers are the A.O. Belcher No. 1 and the Fort Sill Unit 4 Well 1, while the dry hole was the Fort Sill Unit 8 Well 1. A plat of the field is shown in Fig. 1. Sloughing Shales The East Apache field wells were drilled with freshwater mud using mud weights and casing setting depths as seen in Fig. 2. Sloughing shale problems were not severe until the Atoka formation was penetrated at approximately 13,400 ft (4084 m). penetrated at approximately 13,400 ft (4084 m). Freshwater filtrate from the mud adsorbed onto the shales, causing the water molecules to become "captured" and hydration to take place. JPT P. 1877

Cement Spacer Fluid

Introduction Completion problems during the cementing of casings or liners in wellbores have confronted the oil and gas industry for many years. Generally, after the borehole has been drilled, the drilling mud employed is displaced by the cement used in cementing the casing or liner. Compositions and properties of drilling muds and cement slurries vary widely. Such variation may result in detrimental physical and chemical reactions at the interfacial contact. For physical and chemical reactions at the interfacial contact. For example, when a high-viscosity, high-density drilling fluid is used, the incompatibility may contribute to channeling in the annulus and may prevent a satisfactory cement-to-formation bond. As a result, communication may occur between zones and possibly even to the surface.In view of the persistence of those problems, a serious need was recognized for a single type of spacer fluid that could be employed effectively between the cement slurry and any type of mud. Criteria for Development The following criteria were established as goals for research efforts in developing a universal spacer fluid:1. It should be compatible with all oil-base muds, invert-emulsion muds, and water-base muds, including chemical gel muds and polymer muds.2. It should not affect cement slurry viscosity, especially high-weighted cements at elevated temperature.3. It should not appreciably change the pumping time of cement slurries.4. It should allow for being weighted to any density required in the field.5. It should be able to tolerate high solids, as mud cake may be picked up, adding to what often is already a high solids content.6. It should tolerate the addition of wetting agents, dispersants, friction reducers, and retarders when needed.7. It should keep the calcium from cement slurries out of water-base muds and, especially, out of polymer muds.8. It should have low-fluid-loss properties.9. Its flow properties should permit turbulence at low pumping rates for better mud removal.10. It should be usable between various types of incompatible drilling fluids during displacement.11. It should be easy to mix and handle in the field.12. It should allow for the use of a variety of fluids in formulating the liquid phase so that specialty fluids are not necessary. In most cases the fluids are already on location.A field survey was conducted on several wells in South Texas and Mississippi to determine what cementing problems were being encountered with various drilling fluids and cements. The survey indicated that oil-base fluids and invert emulsions cause most of the problems. This is especially true when the oil-base mud contains a high-salinity internal phase composed of saturated sodium chloride or calcium chloride. As compatibility with oil-base muds and invert-emulsion muds as well as compatibility with aqueous slurries is necessary for an ideal spacer fluid, an emulsion was considered for development. JPT P. 856

Shale Control with Balanced-Activity Oil-Continuous Muds

The main cause of shale instability is water adsorption and subsequent swelling of the wellbore. By adjusting the activity of the water in the mud to that of the water in the shale, this adsorption can be prevented and gauge boreholes can be drilled through both hard and soft shales. Introduction Unstable shales have plagued the petroleum industry for more than 30 years. All boreholes drilled into shale formations experience some degree of washout, which may be tolerable in some wells but completely uncontrollable in others. Many causes of shale problems have been postulated: mechanical factors such as mud pressure, thermal stresses, pipe movement (both pressure, thermal stresses, pipe movement (both banging and swabbing), "rubble" shale, and plastic flow; chemical factors such as hydration of montmorillonite clay. One paper describes the dehydration of plastic "gumbo" shales with invert emulsion muds. The technique reportedly works on soft, wet shales and requires only that the salinity of the mud be greater than the salinity of the water in the shale. (The salinity of such shales seldom exceeds 40,000 ppm.) Causes of Unstable Wellbores Unstable wellbores occur when formation pressures exceed the pressure exerted by the drilling fluid. Two situations can produce such a condition:the wellbore fluid pressure is lower than the in-situ formation pressure andthe in-situ formation pressure pressure andthe in-situ formation pressure increases because of water adsorption. Too low a fluid pressure occurs when mud density is too low or when pressure occurs when mud density is too low or when bottom-hole pressures are reduced by swabbing with the drill pipe. This type of instability normally can be eliminated by drilling with increased mud weight or by minimizing pressure surges with low viscosity muds and slow pipe 'movement. Another more frequent cause of degradation is the excessive formation pressure that develops when argillaceous formations pressure that develops when argillaceous formations adsorb water. Problems due to hydration usually occur some time after the formation is exposed and can be prevented by using balanced-activity oil-continuous prevented by using balanced-activity oil-continuous muds. Laboratory and field data have shown that many formations are capable of adsorbing water or ions from water-base muds and are capable of adsorbing water from oil-continuous muds. Adsorption* occurs because of differences in chemical potential between the mud and the formation, and continues until equilibrium is achieved. When considering adsorption potential for oil-continuous muds, only aqueous potential for oil-continuous muds, only aqueous chemical potentials need be considered because ion transfer does not occur. In the case of water-base muds, the problem is more complex because, of ion and clay movement as well as water movement between the mud and the formation. It has been found that the more deeply buried shales are highly compacted and contain low quantities of water. As geologic compaction occurs, water is expelled from the shale and produces a degree of dryness in the shale. The scarcity of water and the abundance of charged clay surfaces results in an increase in the adsorptive potential of the shale. Balanced Mud Concept JPT P. 1309

A New Technique to Determine the Equivalent Viscosity of Drilling Fluids Under High Temperatures and Pressures

Abstract Knowledge concerning the behavior of drilling fluids under wellbore conditions is very desirable, and experimental results have shown that the extent to which the flow properties of drilling fluids are affected by high temperatures and pressures cannot be predicted by standard API pressures cannot be predicted by standard API tests. A Fann consistometer (Model 5S-TDL) is modified to obtain the experimental data reported in this study. Data obtained from the Fann viscometer Model 50 at elevated temperatures have been included to supplement the information derived from the modified Fann consistometer. Newtonian fluids of known viscosities are used in calibrating the modified consistometer. The technique followed here keeps the sample temperature constant and allows the pressure to vary at each desired temperature level. The equivalent viscosities of both laboratory-prepared and field muds of different densities have been obtained at temperatures up to 500 deg F and pressures up to 20,000 psi. The objective of this study is to show that the modified consistometer can give much more information concerning the flow behavior of muds under wellbore conditions than that derived in the past. It can show the pressure and temperature conditions under which the tendency to thicken begins, the gradual thickening, and also the conditions at which the mud completely gels and loses its fluidity. The study shows that both temperature and pressure affect the equivalent viscosity of invert pressure affect the equivalent viscosity of invert emulsion muds. The effect of pressure is very pronounced at low temperatures. Compared to the pronounced at low temperatures. Compared to the invert emulsion muds, the equivalent viscosity of water base muds is not affected to the same extent by temperature and pressure. Temperature is the dominating variable tin case of water base muds. However, the effect of pressure on the equivalent viscosity of water base muds seems to depend on composition and temperature of the system. Introduction Kennedy and Crawford designed and patented the consistometer to test the setting time of cement slurries. This consistometer as manufactured and later improved by Fann. Chisholm et al. adapted the first Fann consistometer for evaluating drilling fluids under wellbore conditions in 1961; their study was later continued by Cox and Pfleger. Weintritt and Hughes used a similar consistometer with a different recording device. They measured the relative viscosity of drilling fluids in seconds and pointed out the usefulness of this data when used with viscometric and fluid loss data. They applied the term "relative viscosity" to the time required for the bob to complete movement in one direction: it is not a ratio of two viscosities. In spite of its wide usage, no standard testing procedure has been established by the industry to procedure has been established by the industry to obtain correlative data. A consistometer similar to the ones mentioned above, has been further modified and used in this study along the Fann viscometer Model 50.

Varied Applications of Invert Emulsion Muds

Invert emulsion muds, compounded so as to have specific properties, can solve such divergent problems as are encountered in producing from water-sensitive pay zones; in drilling formations that dissolve, disperse and disintegrate in water; and in alleviating pipe corrosion. Introduction Within the last 7 years there has been a significant increase in the use of drilling and completion fluids having oil as the continuous phase. This extension in applications for oil-base muds has been due in large measure to the development of products designed to provide specific properties. Users are no longer provide specific properties. Users are no longer restricted to certain proprietary mixtures but can devise a suitable composition to satisfy the immediate requirements in much the same way as is done with water muds. "Oil mud" has oil as the continuous phase. AH oil muds after use contain some water. The term "invert emulsion" often is applied to oil muds having water as a component that has been added to produce a desired property. In this discussion, the term "oil mud" is applied without regard to specific water content, with the limitation that the filtrate is all oil under the conditions of use. Our purpose is to review briefly some of the varied applications for oil muds and thereby to demonstrate the wide adaptability of these compositions. Oil muds are not to be regarded as cure-alls for every type of drilling and completion problem. On the contrary, before the decision is made to use an oil mud, attention should be given to specific local conditions. Factors such as potential loss of circulation and rapid accumulation of drilled solids or inclusion of excessive amounts of water in the oil mud affect the economic practicability. Nor should oil muds be used without due regard to the importance of the rig equipment - specifically, facilities for mud mixing, removal of drill cuttings, storage, and the like. Qualified supervision is a necessity, of course. Oil Mud Additives for Specific Functions With the objective of affording oil mud compositions as versatile as water muds, products have been developed to control various properties. These products are:Gelling and suspending agents organophilic clays.Emulsifiers: anionic mixed calcium and sodium soaps of fatty acids; cationic amine derivative stable to salts and high temperature.Oil-wetting agent: organic phosphate.Filtration control agent: nonasphaltic oil- dispersible organic colloid. The development and characteristic properties of these materials have been dealt with in detail in several publications and will not be reviewed here. The selection of an oil mud for drilling or completion usually involves the recognition of a problem with water muds and the conclusion that savings will result from using the product of higher unit cost. Frequently, the use of oil mud to solve the basic problem brings equal or greater associated benefits. JPT P. 261

An Improved Water-in-Oil Emulsion Mud

Abstract A water-in-oil emulsion mud free of inert solids has been developed to provide a solution to certain problems associated with drilling, completing and servicing wells. Such invert-emulsion muds are satisfactory for use in wells with temperatures up to 300F and with pressures requiring densities up to 18 lb/gal. The emulsifier used in the preparation of these muds is the mixed salts of fatty acids. It is used in weighted muds in conjunction with a unique organophilic-clay suspending agent. The muds are prepared with ordinary mixing equipment at the wellsite. These muds have been used for drilling through the productive zone, for covering the zone to be perforated or to protect existing perforations during workover operations. Fewer difficulties in servicing wells and in getting wells back on production were experienced when these invert-emulsion muds were used as protective fluids to prevent water or mud from contacting exposed formations. Qualifications of Invert-Emulsion Muds An increasing number of wells are being drilled, completed and serviced with oil-base emulsion muds. These water-in-oil emulsions are commonly called "invert emulsions". The amount of water in an oil-base mud may vary from a trace to 60 per cent of the liquid volume of the mud. For purposes of this paper, the primary distinction between an invert-emulsion mud and an oil-base mud is based on whether the water is added as a definite part of the mud composition. In an invert-emulsion mud, the water phase has the important function of imparting controllable properties and characteristics to the mud. The muds described here have been found to have the most satisfactory properties when the water phase constitutes between 20 and 50 per cent of the liquid volume. In the experimentation and development of a general purpose invert-emulsion mud, certain requirements have gradually evolved. In the preparation of the mud:the emulsifier should be an easily handled, ground product, free of inert solids;the materials should be readily mixed with conventional rig mixing equipment in no longer time than required for mixing a water-base mud; andthe emulsifier should be effective for fresh and saline waters in a variety of crude and refined oils.