Synthetic-based Muds Research Articles

Exploring technological and operational challenges in high-pressure: High-temperature drilling techniques

This comprehensive review explores the complex landscape of HPHT drilling, examining the underlying principles, innovative technologies, and operational strategies used to overcome challenges such as wellbore stability, fluid management, equipment reliability, and downhole conditions. By understanding and addressing these challenges, the oil and gas industry can advance HPHT drilling capabilities and unlock new sources of energy to meet growing global demand. High-pressure, high-temperature (HPHT) drilling techniques have become indispensable for the oil and gas industry to tap into deep hydrocarbon reservoirs located in challenging environments. Despite their significance, HPHT drilling operations pose a myriad of technological and operational challenges that demand meticulous attention to safety, efficiency, and success. This comprehensive review embarks on an exploration of the intricate landscape of HPHT drilling, delving into the fundamental principles, innovative technologies, and operational strategies pivotal in surmounting obstacles such as wellbore stability, fluid management, equipment reliability, and downhole conditions. The review begins by delineating the distinctive characteristics of HPHT environments, highlighting the formidable challenges inherent in drilling operations conducted under extreme pressures and temperatures. Subsequently, it elucidates the critical importance of maintaining wellbore stability amidst such conditions, elucidating the risks of collapse and blowouts and offering insights into mitigation strategies ranging from meticulous drilling fluid selection to advanced wellbore monitoring techniques. Fluid management emerges as a focal point, as the review navigates through the complexities of selecting, formulating, and managing drilling fluids tailored for HPHT environments. Innovative technologies such as nanotechnology applications and synthetic-based mud systems are explored for their efficacy in addressing fluid-related challenges and enhancing drilling performance. The reliability and integrity of equipment constitute another critical aspect examined in the review, with emphasis on mechanical challenges, material selection, and proactive maintenance strategies essential for safeguarding equipment performance and longevity in HPHT operations. Furthermore, the review presents case studies and best practices gleaned from successful HPHT drilling projects, offering valuable insights and lessons learned to inform future endeavors.

Comparison of Gas Signature and Void Fraction in Water- and Oil-Based Muds Using Fiber-Optic Distributed Acoustic Sensor, Distributed Temperature Sensor, and Distributed Strain Sensor

Summary Accurate estimation and prediction of gas rise velocity, length of the gas influx region, and void fraction are important for optimal gas kick removal, riser gas management, and well control planning. These parameters are also essential in monitoring and characterization of multiphase flow. However, gas dynamics in non-Newtonian fluids, such as drilling mud, which is essential for gas influx control, are poorly understood due to the inability to create full-scale annular flow conditions that approximate the conditions observed in the field. This results in a lack of understanding and poor prediction of gas kick behavior in the field. To bridge this gap, we use distributed fiber-optic sensors (DFOS) for real-time estimation of gas rise velocity, void fraction, and influx length in water and oil-based mud (OBM) at the well scale. DFOS can overcome a major limitation of downhole gauges and logging tools by enabling the in-situ monitoring of dynamic events simultaneously across the entire wellbore. This study is the first well-scale deployment of distributed acoustic sensor (DAS), distributed temperature sensor (DTS), and distributed strain sensor (DSS) for investigation of gas behavior in water and OBM. Gas void fraction, migration velocities, and gas influx lengths were analyzed across a 5,163-ft-deep wellbore for multiphase experiments conducted with nitrogen in water and nitrogen in synthetic-based mud, at similar operating conditions. An improved transient drift flux–based numerical model was developed to simulate the experimental processes and understand the gas dynamics in different wellbore fluid environments. The gas velocities, void fractions, and gas influx lengths estimated independently using DAS, DTS, and DSS showed good agreement with the simulation results, as well as the downhole gauge analysis.

Fixed Choke Constant Outflow Circulation Method for Riser Gas Handling: Full-Scale Tests in Water- and Synthetic-Based Mud with Gauges and Distributed Fiber-Optic Sensors

Summary Conventional methods of managing gas-in-riser events are not optimal when the drilling riser is isolated from the formation by a closed subsea blowout preventer (BOP) on rigs equipped with mud gas separator (MGS), managed pressure drilling (MPD), or riser gas-handling equipment. The industry is concerned about exceeding the pressure limit of the riser and the flow capacity of the MGS and hence has not been able to reach a consensus on a circulation method for riser gas. This work is an analysis of the first-ever demonstration of the fixed-choke constant-outflow (FCCO) circulation method in synthetic-based mud (SBM) carried out in June 2022. The first-ever demonstration of the FCCO circulation method in water was performed in March 2021. The results from the water tests were discussed in IADC Gas-in-Riser/Riser Gas-Handling Subcommittee meetings, and the new fixed-choke method was named FCCO in November of 2021. The reason for using the acronym FCCO for the new method is that it allows the use of a fixed-choke opening percentage throughout the circulation period by managing the outflow and backpressure by varying only the pump rate. This work includes the comparison of the actual test results from the March 2021 FCCO tests in water with results estimated using a new model. This is followed by a discussion of the results from the June 2022 FCCO test in SBM. Nitrogen gas was injected into the bottom of an annulus 5,200-ft deep, vertical test well (9 5/8×2 7/8 in. casing/tubing) initially filled with water and instrumented with four downhole pressue and temperature gauges, and distributed fiber-optic sensors [distributed temperature sensing (DTS) and distributed acoustic sensing (DAS)] for water tests, and later filled with SBM. We started direct circulation to produce flow out of the annulus through a choke kept at a fixed open position (%) required for a preplanned applied surface backpressure (ASBP). We reduced pump rate if/as necessary to maintain this ASBP to ensure outflow rate within MGS flow capacity. We performed tests at different fixed-choke positions, different average ASBPs, and initial pump rates. We tested constant bottomhole pressure (CBHP) circulation and fixed pump rate methods also for comparison with the FCCO circulation method. The results from the FCCO tests demonstrated better control of outflow compared with the other methods. There is no need to use high ASBP. The use of a high ASBP suppressed the value of peak pressure. Installation of more than one gauge inside the riser enhances safety by allowing real-time influx detection capability, estimation of gas position, gas velocity, and gas void fraction. The FCCO method can be preplanned and easily substituted as the preferred circulation method for staying within the handling capacity of the existing MGS on the rig during gas-in-riser situations.

Modelling and Simulating Eulerian Venturi Effect of SBM to Increase the Rate of Penetration with Roller Cone Drilling Bit

Drilling bits are essential downhole hardware that facilitates drilling operations in high-pressure, high-temperature regions and in most carbonate reservoirs in the world. While the drilling process can be optimized, drilling operators and engineers become curious about how drill bits react during rock breaking and penetration. Since it is experimentally expensive to determine, the goal of the study is to maximize the rate of penetration by modeling fluid interactions around the roller cone drilling bit (RCDB), specifying a suitable number of jet nozzles and venturi effects for non-Newtonian fluids (synthetic-based muds), and examining the effects of mud particles and drill cuttings. Ansys Fluent k-epsilon turbulence viscous model, a second order upwind for momentum, turbulent kinetic energy, and dissipation rate, were used to model the specified 1000 kg/m3 non-Newtonian fluid around the roller cone drill bit. The original geometry of the nozzles was adapted from a Chinese manufacturer whose tricone had three jet nozzles. The results of our six redesigned jet nozzles (3 outer, 39.12 mm, and 3 proximal, 20 mm) sought to offer maximum potential for drilling optimization. However, at a pressure of 9.39 × 104 Pa, the wellbore with particle sizes between 0.10 mm and 4.2 mm drill cuttings observed an improved rate of penetration with a rotation speed of 150 r/min.

Investigating the Effectiveness of Tiger-Nut Oil (Cyperus esculentus L.) as Base Fluid in Synthetic-Based Mud

Due to the environmental effects and following the stringent regulations on drilling operations and the associated drilled cutting disposal, drilling fluid with less environmental impact are highly desirable over the conventional diesel based mud. This study seeks to determine the effect of ester derived from the oil of tiger nut using alkali catalyzed transesterification as base fluid for the formulation of a synthetic base mud. A total of four mud samples were formulated, three samples of 10ppg synthetic based muds were formulated using the ester at 70:30, 75:25, and 80:20 Oil-water ratio. The last mud sample was formulated using diesel as base fluid but at 75:25 Oil-water ratio. The fresh oil and its ester were characterized. The tiger nut ester was purified and the compositional analysis of the ester was carried out using the Fourier transform infrared spectrometry. The API recommended procedure was used to determine the mud samples density, rheological, filtration and emulsion properties. The result of the FTIR shows an absorption band at 1743.56 cm-1 indicates the presence of C=O of an ester. The result of the density of the fresh Tiger Nut Oil (TNO) and the ester are 0.98 and 0.87respectively, the viscosities are 25.7cp and 3.25cp respectively, the flash point and pour point are 173oC and -25oC, and 160oC and -15oC respectively. The plastic viscosity and yield point of the synthetic based mud ranges between 7.0cp to 16.0cp and 9.0lb/100sqft to 46.0lb/100sqft, while 9.0cp to 14.0cp and 20lb/100sqft to 27lb/l00sqft was measured for diesel oil-based mud. The filtrate volume and mud cake thickness for the synthetic based mud at 70:30, 75:25, and 80:20 oil-water ratio are 2.6ml and 1.2mm, 3.8ml and 1.1mm, 4.1ml and 1,0mm respectively, while 15.6 and 5mm were recorded for diesel oil based mud. The gel strength at 10sec and 10min of the synthetic based mud ranges between 6.0 and 11.0, while 7.0 and 8.0 were recorded for the oil based mud. These result shows that the ester based synthetic oil compared favorably with diesel in the formulation of drilling mud. From the result, it is observed that esterified TNO can as a base fluid for a synthetic base mud, but further research on the most cost effective way of producing the oil from tiger nut.

Rheological properties of Class F fly-ash based alkali-activated materials (AAMs) for oil and gas well cementing applications

Class F fly ash-based alkali activated materials (AAMs) have shown promising strength and durability properties for oil- and gas-well cementing applications. Furthermore, they provide a sustainable and cost-effective means to dispose of non-aqueous drilling fluids and replace ordinary Portland cements for cementing purposes. This paper investigates the rheological properties and thickening time behavior of AAMs prepared using four different Class F fly ashes (FA), with varying calcium oxide (CaO) contents, and sodium/potassium silicate activators. The effect of the addition of synthetic based mud (SBM) and polycarboxylate ether-based (PCE) dispersing agent on the rheology of AAMs was also quantified. Potassium silicate-based AAMs demonstrated appropriate viscosity and thickening times (4–9 h) for cementing deeper zones of oil and gas wells. Sodium silicate-based AAMs, although more viscous than potassium silicate-based AAMs, showed suitable thickening times (2–8 h) for shallow cementing jobs. Overall, it was demonstrated that AAMs could be tailored to obtain desirable rheological properties and thickening times by altering the Class F FA, varying the activating solution, and adding PCE and/or SBM.

A CFD Validation Effect of YP/PV from Laboratory-Formulated SBMDIF for Productive Transport Load to the Surface

Several technical factors contribute to the flow of cuttings from the wellbore to the surface of the well, some of which are fundamentally due to the speed and inclination of the drill pipe at different positions (concentric and eccentric), the efficacy of the drilling mud considers plastic viscosity (PV) and yield point (YP), the weight of the cuttings, and the deviation of the well. Moreover, these overlaying cutting beds breed destruction in the drilling operation, some of which cause stuck pipes, reducing the rate of rotation and penetration. This current study, while it addresses the apropos of artificial intelligence (AI) with symmetry, employs a three-dimensional computational fluid dynamic (CFD) simulation model to validate an effective synthetic-based mud-drilling and to investigate the potency of the muds’ flow behaviours for transporting cuttings. Furthermore, the study examines the ratio effects of YP/PV to attain the safe transport of cuttings based on the turbulence of solid-particle suspension from the drilling fluid and the cuttings, and its velocity–pressure influence in a vertical well under a concentric and eccentric position of the drilling pipe. The resulting CFD analysis explains that the YP/PV of SBM and OBM, which generated the required capacity to suspend the cuttings to the surface, are symmetric to the experimental results and hence, the position of the drill pipe at the concentric position in vertical wells required a lower rotational speed. A computational study of the synthetic-based mud and its potency of not damaging the wellbore under an eccentric drill pipe position can be further examined.

Assessment of frictional torque and lubricity of waste-tire bio-oil as lubricant additive for stuck pipe

The optimal approach to reducing surface torque when drilling uses oil-based or synthetic-based mud systems instead of aqueous mud systems. However, lower surface torque and drag can be achieved by lowering the water-based mud friction factors using lubricant additives. Torque can be reduced up to 25% with the suitable mud lubricant additives. Lubricant additives are viable methods for decreasing frictional resistance in drill strings during oil and gas drilling operations. In this study, bio-oil was produced from waste tire distilled pyrolytic oil and added to formulated standard aqueous drilling fluid to investigate its ability to reduce frictional torque during drilling. The lubricating properties of the proposed lubricant additive was compared with commercially used lubricant additive as reference samples (control). The simulation results were compared with measurements from the OFITE Lubricity Tester. The result shows that adding the distilled waste tire pyrolytic oil and produced bio-oil to the drilling mud decreased the coefficient of friction and torque to generate oily films on the contact-surface. The distilled pyrolytic oil and produced bio-oil torque values were in the range of 23.50–32.98 and 21.30–30.82 respectively. The commercial lubricant additive (control) gave 42.85% maximum torque reduction, while the produced bio-oil gave a similar maximum torque reduction of 41.88%. The result shows that, for a water-based drilling fluid, the friction coefficient between the drill string and rock formation, can be reduced with the application of the produced bio-oil. Thus, the produced bio-oil can be used to prevent differential sticking or free the stuck pipe during drilling.

CFD Validation for Assessing the Repercussions of Filter Cake Breakers; EDTA and SiO2 on Filter Cake Return Permeability

ABSTRACT Drill-in-fluids create what are known as filter cakes. Filter cakes, in some cases, lead to well abandonment because they prevent hydrocarbons from flowing freely from the formation into the wellbore. Cake removal is essential to avoid formation damage. A previous study on filter cake breakers was considered for computational fluid dynamic (CFD) validation. Matlab-CFD and Navier-Stokes equations aimed at predicting and validating visual, multiphase flow under finite element analysis (FEA). The interactions of separate chemical breakers and drill-in-fluid such as ethylenediaminetetraacetic acid (EDTA), silica-nanoparticle (SiO2), and biodegradable synthetic-based mud drill-in-fluid (BSBMDIF) were monitored under a particle size distribution, viscosity, density, and pressure. Predicting return permeability of filter cake was considered under a simple filtration process. The particles’ deposition created pore spaces between them; barite 74 μm, nano-silica 150 nm, and EDTA 10 μm generally closed up the pores of the filtration medium. Under extreme drilling conditions, barite formed thicker regions, and EDTA chemical properties easily disjointed these particles, while SiO2 entirely did not. The experimented results of (EDTA) and SiO2 for return permeability were in full force agreeable with the 2D simulation. A hybrid computational analysis considering CFD under discrete element analysis and neural network can be employed for further research validations.

Maximizing well productivity by using filter cake breaker for synthetic-based mud drill-in fluid (SBMDIF) system

• Formation damage has a significant impact on the overall performance. • An effective filter cake breaker selection is critical to minimize formation damage. • The straightforward reaction of meso‑surfactant and nano-surfactant filter cake breakers with barite. • Surfactant-based filter cake breaker was more efficient in removing synthetic-based drilling mud. Formation damage has a significant impact on the overall performance of the well productivity. Removal of filter cake which is deemed to be the main strategy of formation damage remediation is crucial in open hole completion with pre-slotted liner or stand-alone screen (SAS) as a mean of sand control. Without proper planning, inefficient filter cake removal can lead to tremendous consequences since filter cake can plug the sand control component. Making the condition worse, sand control component is susceptible to plugging. This highlights the importance of selecting an effective filter cake breaker that can successfully remove the filter cake through dissolution of the main solids that constitute the major portions of the filter cake which could be the weighting material, barite, or calcium carbonate. Besides that, a proper understanding of the mechanism of the filter cake breaker chemical would be very beneficial to comprehend the filter cake breaker efficiency. The laboratory study attempted to emulate the reservoir condition. Regained permeability testing using High Pressure High Temperature (HPHT) Filter Press aimed to test the ability of several commercial filter cake breakers in removing synthetic-based-mud drill-in-fluids (SBMDIF). Chelating-based filter cake breaker, meso‑surfactant-based filter cake breaker and nano-surfactant-based filter cake breaker were the samples to be tested in the laboratory work. The condition of the filter cake after being soaked statically was visually interpreted and the regain permeability was recorded. The mechanism of each filter cake breaker to remove the SBMDIF filter cake was also examined. Based on the experimental study, meso‑surfactant-based filter cake breaker was found to be more effective to remove SBMDIF filter cake compared to chelating-based filter cake breaker and nano-surfactant-based filter cake breaker.

Determining the difference of kick tolerance with single bubble and dynamic multiphase models: Evaluation of well-control with water/synthetic based muds

Determining the magnitude of an influx into the wellbore when a kick event occurs is very important during well design as well as the well execution phases. This research is conducted to determine the kick tolerance where the single bubble phase model is applied and also to compare it with the dynamic multiphase model. The information on the well and the parameters used are taken from the high pressure and high temperature well drilled in Malaysia. Dynamic multiphase modelling is capable of supporting more kick volume compared to single bubble gas phase modelling where it considers multiple fluid phase in an influx and applies the gas characteristic to have a multiphase pressure loss. Dynamic multiphase gives more kick tolerance to fracture the weakest point at the casing shoe where single bubble gas phase is more conservative when it allows influx. The effect of pore pressure, mud weight, mud type, oil composition in mud, as well as the circulation kill rate are explored in dynamic multiphase. Increasing the mud weight in either case reduces the maximum allowable kick volume of an influx due to the reduction in MAASP between fracture pressure and hydrostatic pressure at the casing shoe. Higher kick volume can be achieved using WBM compared to SBM. In addition, a sensitivity analysis is performed from the dynamic multiphase simulations to analyze the impact on the kick tolerance during the increase in mud weight as well as the pore pressure uncertainties. Moreover, the impact of kick tolerance has been investigated when different types of mud are used, such as water-based mud and synthetic-based mud. Based on the accuracy of the presented procedure, the prediction of kick tolerance from dynamic multiphase modelling can be used as a guideline to identify the behavior of an influx when a kick event occurs.

Quantification of synthetic-based drilling mud olefins in crude oil and oiled sediment by liquid column silver nitrate and gas chromatography

Synthetic-based drilling muds (SBMs) are complex mixtures of man-made fluids used during the drilling of oil and gas wells. SBM-derived chemicals can enter the environment through failed wells and routine or poor disposal practices, where they can persist and thereby warrant measurement. SBMs are commonly formulated with linear and methyl branched α- and internal-olefins mostly in the C14 to C20 carbon range, which are not native to crude oils. Thus, SBM-derived olefins can provide a basis to recognize the impact of these drilling wastes in the environment. However, the presence of abundant native hydrocarbons in oils and sediments can hinder the detection of trace level SBM-derived olefins by conventional organic sample preparation and analytical methods. Silver ion chromatography using silver nitrate (AgNO3) impregnated silica gel can serve to physically separate olefins from saturated aliphatic hydrocarbons native in crude oils, which can subsequently be analyzed and measured by conventional one-dimensional gas chromatography-flame ionization detection (GC-FID). In this study, SBM-derived olefins are measured in crude oils from the Deepwater Horizon oil spill and in their laboratory mixtures to a detection limit of approximately 5000 µg/g (0.5 wt%). In oiled sediment, SBM-derived olefins were reliably detected at concentrations as low as 1 µg/g-dry. An application of this method is demonstrated through analysis of crude oils and oil-contaminated seafloor sediment from the Taylor Energy oil spill site in the northern Gulf of Mexico where SBM was historically used and discharged.

Lubricity performance of non-ionic surfactants in high-solid drilling fluids: A perspective from quantum chemical calculations and filtration properties

Quantum chemical calculations and mud filtration analysis were used to assess the performance of three types of non-ionic surfactants as lubricating additives in synthetic-based drilling mud (SBM) contaminated with drilled solids. High solid contaminants can have an impact on mud lubricity and can contribute to thicker a mud cake. Experimental results showed that all non-ionic surfactants reduced the coefficient of friction (COF) of mud by approximately 27%. Quantum chemical parameters and molecular electrostatic potential (MEP) provided further insights into the interaction between non-ionic surfactants and metal surfaces. MEP indicated the most lubricious non-ionic surfactant based on polar sites and the electron density distribution. Dipole moment represented the dipole interaction between the polar head of non-ionic surfactant with the metal surface of the drilling tools. Filtration tests showed that despite solid contamination, non-ionic surfactants decreased the fluid loss by 20% due to better solid dispersion in the mud. The mud cake formed was thinner, which may reduce the differential pressure sticking tendency. XRD and SEM observations of the mud cake confirmed the presence of non-ionic surfactants layer adsorbed to the solid particles of SBM. The adsorbed non-ionic surfactants could contribute to a higher lubricity of mud cake, thus minimizing friction during drilling.

Evaluation of rheological and filtration properties of a polymeric water-based drilling mud in presence of nano additives at various temperatures

Over the past decades, utilizing water-based muds (WBM) in drilling operations has been significantly increased due to their environmental-friendly characteristics. However, the performance of WBM in drilling operations compared to oil-based muds and synthetic-based muds is lower. Hence, some additives (i.e., polymers, nanoparticles (NPs)) have been added to improve WBM’s rheological properties. The objective of this research is to evaluate the impacts of silica (SiO2) and titanium dioxide (TiO2) NPs on rheological and filtration properties of a polymeric-WBM at 25, 50, and 75 °C. The NPs at concentrations from 0.01 to 0.5 wt% were dispersed in the polymeric WBM. The results revealed that by increasing the concentration of SiO2 NPs, the yield point (YP) and gel strength (GS) values of the base mud were increased by approximately 20% at all temperatures, while TiO2 NPs could only increase YP and GS values at 50 and 75 °C, and to a lesser extent than SiO2 NPs. Both NPs also resulted in decreasing of PV values by more than 20% at all temperatures. The lowest amount of PV was achieved at 0.1 wt% for both NPs. Besides that, both SiO2 and TiO2 NPs reduced fluid loss from the polymeric WBM at all applied temperatures. The lowest amount of fluid loss was obtained at 0.1 wt% SiO2 NPs, by roughly 35% reduction. Furthermore, both NPs also resulted in a higher quality mud cake as compared to the base mud. Overall, it can be concluded that SiO2 NPs followed by TiO2 NPs have great potential to improve the rheological and filtration properties of polymeric WBMs at operational conditions.

Rheological investigation of synthetic-based drilling fluid containing non-ionic surfactant pentaerythritol ester using full factorial design

Non-ionic surfactant pentaerythritol ester (PE ester) can be used as a lubricant and chemical thinner in flocculated synthetic-based mud (SBM). However, its adsorption on surfaces and at oil-water interfaces may interfere with anionic secondary emulsifier and organoclay additives in the mud. The interactions between these additives may significantly affect the viscosity of SBM emulsions. Therefore, in this study, we systematically developed SBM formulations containing a non-ionic surfactant PE ester and evaluated the interactions between the surfactant, secondary emulsifier, and organoclay that influence the rheology of SBM using a full factorial design. Three rheological properties were chosen as responses: plastic viscosity (PV) and yield point (YP), and YP/PV ratio. Factorial analysis of the interaction between the secondary emulsifier and PE ester showed that the interactions caused significant effects on PV, YP, and YP/PV ratio. These multiple responses were optimized using the desirability function, and the optimum formulation was at concentrations of 1.0 lb/bbl, 6.2 lb/bbl, and 1.0% for secondary emulsifier, organoclay, and PE ester, respectively. A quantitative relationship between the various factors and responses was established, allowing a prediction of desirable rheological properties for drilling operations.

Evaluation of <i>Pleurotus</i> as Fluid Loss Control Agent in Synthetic Base Mud for Oil and Gas Drilling Operations

Pleurotus as a fluid loss control additive in synthetic based mud for oil and gas operations was conducted in the laboratory in accordance with API standards using high temperature-high pressure filter press. The effectiveness and compatibility of Pleurotus to synthetic based mud was also evaluated. Its rheological properties were also carried out. Sodium Asphalt Sulfonate was used as a control sample. Synthetic base mud was formulated and the concentrations of 2ppb, 4ppb, 6ppb and 8ppb of Pleurotus were used in four mud formulations with the same materials and in equal concentrations. 4.6ml, 4.0ml, 3.5ml and 3.1ml of fluid loss volumes were obtained respectively. 1mm thick filter cake, with increase in electrical stability was observed. From the laboratory measurement, the optimum effective concentration of Pleurotus to be applied as a fluid loss control agent for fresh non-aqueous mud for field operation is 2ppb which gave the fluid loss volume less than 5ml. The result was compared with the field standard of less than or equal to 5ml fluid loss volume. These results were comparable with control sample and field standard. Also, the thin impermeable filter cake obtained reflects one of the qualities of a good fluid loss control agent. It also showed that Pleurotus contribute very minimal effect on the rheological properties of the synthetic base mud. Improved electrical stability which is the function of emulsion stability confirmed the compatibility property of Pleurotus as fluid loss control additive in the synthetic based mud. The volume of the filtrate improved in geometric progression with the concentrations of the additive applied which summarizes the characteristics of a good fluid loss control agent.

Use of Low-ECD Synthetic-Based Mud During Topdrive Failure

While drilling in deepwater Gulf of Mexico, a topdrive failure forced the shutdown of all drilling operations for the rig operator and lasted for 114 hours (almost 5 days). At the time of the failure, the equivalent static density (ESD) was 11.36 ppg and the equivalent circulating density (ECD) was 11.5 ppg. The rate of penetration (ROP) was 100 ft/hr. Troubleshooting It was recommended that there be no utilization of the pumps while drilling was stopped, to reduce the chance of packing off the annulus with cuttings until the rotating and reciprocating could continue. During this time, a 100-psi backpressure was maintained using the managed-pressure drilling system. Kronos low-ECD synthetic-based mud (SBM) at a weight of 10.9 ppg was utilized during this event. During troubleshooting and repair work, a 1,500-bbl 11.4-ppg riser cap was spotted. Following the repair of the topdrive, a malfunctioning packer had to be replaced, causing additional delays. After the packer was set and the blowout preventers tested, the 11.4 ppg riser cap was displaced and subsequently replaced with 10.9-ppg low-ECD mud. The Kronos system was designed and maintained to have adequate suspension properties to maintain wellbore integrity without sag during unexpected downtime, even with cuttings left in the hole. The rig continued to trip into the hole to 9,800 ft. At that time, a bottom-up was circulated and a maximum of 575 units of gas was circulated out. Drilling then continued using a base oil and premix for dilution. The lost circulation material in the background continued to be blended into the dilution products being used at the time. During the drilling from 11,636 to 12,845 ft, the decision was made to increase the mud weight to 11.15 ppg. When the drilling continued from 12,845 to 13,234 ft, formation water was detected from the mud check entering the mud system. The system was treated to minimize the damage caused by formation water and maintain the properties sought by the operator. To assist in maintaining the desired weight and to prevent low-gravity solids from impacting the mud weight, two shakers were screened up to API Standard 120. At roughly the same time, the mud weight was increased to 11.2 ppg and then to 11.4 ppg. While continuing to drill, one of the engines that provided power to the mud pumps broke down, reducing the flow rate required to clean the hole. A cement unit was added to the pump to replace much of the volume lost with the broken mud pump. At 13,155 ft, the decision was made to call this current interval at total depth. The back-reaming process also started at that time. To assist with the hole cleaning, a high-viscosity sweep was blended and circulated. An additional high-viscosity sweep was blended and circulated, the second time at 9,058 ft. With continued back reaming through some tight spots to 7,272 ft, operators decided to wash back down 7,938 ft and pump one more high-viscosity sweep. Once the hole was clean, a flow check was performed and operators began to pull out of the hole.

Improving the rheological properties of alkali-activated geopolymers using non-aqueous fluids for well cementing and lost circulation control purposes

Typical alkali-activated low-calcium fly ash (AAF) geopolymer formulations are yet to deliver acceptable rheologies for applications such as oil and gas well cementing, where the cement slurry needs to be pumped, and few effective superplasticizers have been identified. The work reported here centers on the discovery that the rheological properties (mixability and pumpability) of AAFs can be significantly improved by incorporating an organic-based non-aqueous fluid (NAF). NAFs such as oil-based muds and synthetic-based muds are water/brine-in-oil invert emulsions that are widely used in the oil and gas industry for drilling and completion operations. Adding NAF can significantly improve the rheological properties of AAF geopolymers, to the point where the rheology of the mixture approaches that of a Portland cement slurry. Overcoming the poor pumpability issue of AAF opens up a large variety of well cementing applications for AAF slurries including primary cementation and plug cementing in severe lost circulation zones.To modify the gelation and setting characteristics multiple fly ash sources and activators were considered in this study. The alkali activators tested in this study were sodium hydroxide and sodium hydroxide with addition of liquid or solid form sodium silicates. Sodium hydroxide activated AAFs showed improved rheological properties with the addition of NAFs. The liquid sodium silicate activated AAFs resulted in unfavorable rheology readings, gel strength measurements and accelerated the pumping time in comparison to use of pure sodium hydroxide activator. The addition of NAF further accelerated the pumping time, increased the viscosity of the AAF, leading to an unpumpable slurry with a rapid setting behavior. In contrast, activation with solid sodium silicate did not negatively affect the rheological behavior of AAF in the presence or absence of NAF. The use of a solid activator showed an initial high consistency peak that broke down with continued shearing. This early high consistency behavior may be exploited to combat lost circulation problems on troublesome oil and gas wells.

Appraising the impacts of SiO2, ZnO and TiO2 nanoparticles on rheological properties and shale inhibition of water-based drilling muds

In recent decades, utilizing of water-based muds (WBMs) in drilling oil and gas wells is ever increasing comparing to oil-based muds and synthetic-based muds due to the lower environmental issues. However, the main drawbacks with WBMs are rheological properties inefficiency and shale swelling which have caused attentions turn to improvement of WBMs’ rheological properties. In this study, the effects of various nanoparticles (NPs) namely titanium dioxide (TiO2), silicon dioxide (SiO2), and zinc oxide (ZnO) on improving rheological properties and shale recovery rate of a WBM sample at two temperatures (25 and 50 °C) were investigated. The concentrations of NPs in the base mud were set at 0.01, 0.05, 0.1 and 0.5 wt%. The results revealed that by adding NPs, the plastic viscosity (PV) of base mud was noticeably increased at the both temperatures. The optimum concentration of all NPs for increasing PV was found to be 0.01 wt%. Furthermore, by increasing concentration of ZnO and SiO2 NPs up to 0.5 wt%, the base mud yield point value was considerably risen to around 13.3%, while by increasing concentration of TiO2 NPs, the mud yield point values were reduced to 23.5 and 20.2 (lb/100 ft2) at 25 and 50 °C, respectively. The optimum ZnO, TiO2, and SiO2 NPs concentrations for this purpose were found to be 0.05, 0.01, and 0.1 wt%, respectively. Moreover, ZnO and SiO2 NPs at concentrations below 0.05 wt% had the best performances for filtration loss control. The related reason is higher stability of these NPs in the aqueous phase and consequently, better mud cake pores filling act by them which caused the mud cakes permeabilities were noticeably reduced. Besides that, SiO2 NPs caused the highest 10 s and 10 min gel strength values and ZnO and TiO2 NPs in order had the lowest 10 s and 10 min gel strength values at all applied concentrations and temperatures. Finally, by increasing concentrations of all NPs, shale recovery rates have noticeably risen comparing to the base mud. SiO2, ZnO and TiO2 NPs in order were successful additives for shale recycling.

Evaluation of blended lime-stabilised spent synthetic-based drilling mud and cement for oil well cementing operations

Most current oil and gas wells are drilled with synthetic-based muds. During drilling, two types of wastes: spent muds and drilled cuttings, are generally generated. Several methods are used in the treatment of these wastes. However, after treatment of these wastes, they are disposed into the environment. Although they seem to be environmentally friendly, greater accumulation may degrade the environment. Nonetheless, some additives used in cement slurry formulation are also present in most of the spent drilling muds, therefore they could be stabilised for reuse in oil and gas wells cementing operations. In recent times, lime is used to stabilise spent synthetic-based drilling mud before disposal or for further treatment. These lime-stabilised muds find use as feedstock of cement kiln, raw material for the production of construction material and wetland restoration materials. This research studies the performance of blended lime-stabilised drilling mud and cement at varied concentrations for oil and gas wells cementing operations. The cement was blended with lime-stabilised mud with concentrations from 0% to 100% at a step of 10% and their properties evaluated. Slurry properties like density, free fluid, rheology and compressive strength results obtained showed that these properties decreased with the increase in percentage blend of the lime-stabilised spent synthetic-based mud. However, it was observed that concentrations of 10% and 20% blends of lime-stabilised mud with cement performed better with good potential to be considered in minor cementing works by the industry to help reduce the cost of waste management. Cited as : Amorin, R., Opoku Appau, P., Osei, E. Evaluation of blended lime-stabilised spent synthetic-based drilling mud and cement for oil well cementing operations. Advances in Geo-Energy Research, 2019, 3(2): 141-148, doi: 10.26804/ager.2019.02.03