A Conceptual Framework for Machine Learning-integrated Drilling Fluid Systems: Toward Predictive Rheology in Complex Downhole Environments

The conventional drilling approach of employing a drillstring and bottomhole assembly with bit for drilling purposes and eventually running a casing string includes several tripping operations that leave the wellbore open for extended periods of time as an alternative to drilling-with-casing operations where the bottomhole assembly is attached to the casing. This eliminates additional drillstring tripping as drilling and running casing are performed simultaneously. This type of application reduces the number of string trips needed to complete a section, thus saving operational time and associated costs. As the diameter of a casing is larger than a drillstring, this method generally increases the Equivalent Circulating Density (ECD) as pressure losses increase owing to the reduction of the open hole and casing string annulus area. Casing directional drilling operations provide a much narrower drilling window with regards to restrictions in the annulus thus increasing the chances of reaching fracture pressure compared with conventional drillstring operations. To negate the resultant increase in ECD, the rheological profile of the drilling fluid must be designed appropriately. This paper discusses a unique oil-based drilling fluid system weighted with treated micronized barite slurry (TMBS) that has more recently been developed and used successfully in the Eldfisk field of the Greater Ekofisk area, Norway. The drilling fluid system provides low viscosity and a relatively low flat rheology, reduced torque values, and superior sag stability, thus delivering a fluid of low ECD contribution, low-pressure peaks, very effective hydraulics performance and static stability. These exceptional fluid characteristics make the system an excellent solution for drilling sections where the difference between pore pressure and fracture pressure is narrow. This was particularly so in this case where the stability of the fluid from sag potential was crucial for the improved success of the drilling-with-casing operation. Any solids sag onto the latching tools or bottomhole assembly (BHA) with the casing could have caused interference. The system had been used before for differing hole conditions including managed-pressure drilling and extended-reach wells, in high-temperature, high-pressure (HTHP) wells, and now with competence in a casing directional drilling operation.

Four wells were successfully drilled and completed, but high drilling fluid densities (1.95 to 1.98 SG) were necessary to maintain wellbore stability in the overburden section immediately above the depleted reservoir. The estimated hydrostatic overbalance from the drilling fluid was approximately 800 bar (11,603 psi) higher than reservoir pressure. A wellbore strengthening technique was selected to seal the calculated 1500 μm fractures induced by these high pressures. This paper highlights the engineering, logistical, and operational challenges encountered while successfully drilling and completing such wells. Geomechanical data was initially acquired, including Young's modulus, Poisson's ratio, and minimum in-situ horizontal stress; and, together with the operational parameters [hole diameter and equivalent circulating density (ECD)], these data were used to estimate fracture width (1500 μm). Subsequently, a drilling fluid system was engineered and customized to seal such fractures, thereby strengthening the wellbore to help minimize losses in the reservoir. The solution was validated at two separate laboratories. Large particulate materials with a D50 of 600 to 2300 μm were used. Improvement opportunities during execution were captured for the next cycle. A total drilling fluid loss of 512 m3 during a 16-hour period was experienced in one well after a drilling liner packoff occurred, and fractures greater than 1500 μm were initiated; however, the liner was successfully cemented in place. The coarse particulate materials (600 to 2300 μm) were mobilized in 500 and 1000 kg bags to minimize deck space requirements on the rig and help facilitate ease of mixing. Rig mixing and pit agitation capacity were important for effective mixing of the fluid system. The application also provided the opportunity to align testing procedures and equipment between the field and laboratory. With increasing reservoir depletion, the potential exists for fracture width increases that can impact the particle size of materials necessary to effectively design a solution. Engineered particulate solutions provided a pathway for sourcing and procuring the necessary wellbore strengthening materials.

The carbonate reservoir in the northern Yishan slope of the Ordos Basin presents significant challenges to gas field exploration and development. With its low pressure, limited porosity, low permeability, and abundance of micro-fractures, the reservoir is resistant to acid dissolution. Once solid particles block these fractures during drilling and completion, serious reservoir damage ensues. To address these obstacles, we engineered an acid-soluble, solid-free drilling fluid system in the lab. This involved incorporating sodium carboxymethyl cellulose, heat-resistant starch, fungicides, and lubricants. Contrasted with the commonly used potassium ammonium based drilling fluid system, our innovative solution showed notable improvements. Specifically, the density decreased by 0.04 to 0.06 g/cm3, and the solid content decreased by 4.0% to 6.50%, while the acid-soluble rate surged from 8.50% to 95.45%. In addition, the reservoir permeability recovery value saw an increase from 51.50% to 95.88%. In practical field application, we employed this novel drilling fluid system in ten horizontal wells. Following acid fracturing and reconstruction, these wells registered a 75.94% increase in gas production compared to nearby wells. Our findings demonstrate that the proposed system effectively mitigates the incursion of solid-phase particles into the reservoir while enhancing acidification during acid fracturing. This results in the swift removal of plugging, restoration of formation permeability, and improved well production. Our research thus introduces a drilling and completion fluid system of high efficiency with superior reservoir protection performance, potentially offering substantial benefits to the development of carbonate rock salt gas reservoirs.

Nanoparticles (NPs) have been recently used for different application in the oil and gas industry. Nanoparticles have proven their effectiveness for different applications including; drilling fluids, wellbore strengthening, and enhanced oil recovery (EOR). In this paper, different types of nanoparticles including Aluminum Oxide, Copper Oxide, and Magnesium Oxide were evaluated at two different concentrations. The main objective of this research is to investigate the effect of adding nanoparticles on the rheological properties of water-based drilling fluid. A simple 7% bentonite water-based mud was used in this study as a reference point. The rheological properties including plastic viscosity, yield point, and gel strength were evaluated at both; standard test temperature of 120°F and room temperature to understand the effect of nanoparticles on the rheological properties. In addition, the filtration characteristics were investigated using both; the standard API filter press at low-pressure low-temperature (LPLT) as well as the high-pressure-high- temperature (HPHT) filter press at 500 psi and 250°F. The results showed that plastic viscosity was reduced by 50% when NPs were added compared to the reference point. The yield point was improved by 84%, 121%, and 231% for 0.5%Vol Copper Oxide, Aluminum Oxide, and Magnesium Oxide, respectively. In addition, the 10 seconds gel strength was increased up to 95%. A reduction in the fluid loss up to 30% was observed at LPLT conditions. However, the filtration characteristics were negatively affected at HPHT. Based on the results, there is a good potential for using the above-mentioned nanoparticles to improve the rheological properties, especially the low-end rheology while maintaining low plastic viscosities, which in turns results in a better hole cleaning and more control over the equivalent circulation density.

Composition and Properties of Drilling and Completion Fluids

A conventional oil-based drilling fluid was determined not to be applicable for drilling narrow hole annuli in a mature field offshore Norway. Drilling these wells with a very narrow hydraulic window required an oil-based drilling fluid with reduced viscosity and improved sag stability. A totally reformulated drilling fluid system was developed. The combination of base oil and selected products produced a fluid with a flatter rheological profile, resulting in reduced plastic viscosity (PV) and increased low shear rate viscosity (LSRV). This rheological profile reduced equivalent circulating density (ECD) and improved sag stability. This rheological profile also directly impacted pump pressure and hole cleaning capabilities, delivering lower pump pressure and allowing for higher pump rates and improved hole cleaning. This paper presents the experimental work performed when developing the system for this specific application. The authors also will present field data and compare the performance of the new drilling fluid system with that of conventional systems.

Formate drilling and completion fluid system is a new type of clean organic salt brine system which has been developed from inorganic salt brine drilling fluid system. It is beneficial to protecte and find hydrocarbon reservoir. Due to the solid free system, the damage of solid phase particles on reservoir, especially low permeability oil and gas layer, can be greatly eliminated, at the same time, drilling fluid and completion fluid have greater compatibility. It will avoid that precipitation which is not compatible with drilling and completion fluid and generates damages on reservoir. And because mud cake of the solid free system is thin and resilient, it is conductive to improve cementing quality greatly. Experiments show that the formate drilling and completion system has good rheological property, strong inhibition ability, good lubricating performance, good compatibility with reservoir rocks and formation water at high temperature.

Increased global energy demand has forced the oil and gas industry to search for hydrocarbons in increasingly challenging locations such as high temperature, high pressure (HTHP) reservoirs. This paper presents the field performance of a new fit-for-purpose synthetic-based mud (SBM) used to drill an ultra-HTHP deep gas exploration well offshore Malaysia. The well was drilled to a total depth (TD) of 14, 380 ft (4, 383 m) and reached the highest recorded bottomhole temperature (BHT) of 488°F (253°C) in Southeast Asia. To overcome the anticipated drilling challenges in the extreme environments, the operator and service company collaborated to identify a thermally stable, high-density drilling fluid that met the operator's needs. The drilling fluid was formulated for a maximum density of 18 lb per gallon (ppg), but reached the Southeast Asia record of 19.1 ppg mud weight at TD. The use of dual weighting materials (barite and manganese tetraoxide) yielded lower plastic viscosity (PV) for the high-density mud, leading to improved hydraulics and lower equivalent circulating density (ECD). The drilling fluid encompassed excellent temperature stability with no weighting agent sag and no high-temperature gelation observed after remaining static for five days at BHT during wireline logging. In this respect, it eliminated the rig time spent for additional circulating or conditioning of drilling muds and fluid treatment cost. Moreover, the fluid also provided good wellbore stability with no non-productive time (NPT) from drilling fluid performance. Comparison of field data and laboratory results highlighted the benefits of competent drilling fluid design and testing. As a result of thorough planning and comprehensive laboratory testing, desirable drilling fluid properties were maintained despite extreme HTHP conditions, minimizing trips and operational costs.

This article investigates the disadvantages of polymer sulfonate and oil-based drilling fluids after use, such as pollutants seriously exceeding current standards and poor degradation. After the later stage treatments, like landfill and solidification, waste drilling fluids also have secondary pollution. Based on laboratory experiments, we established the green performance evaluation standards and specifications of drilling additives and drilling fluid systems, including chemical toxicity, biological toxicity, and biodegradability. We developed a green drilling fluid additive and drilling fluid system that are nontoxic, biodegradable, and reservoir protective. The green drilling fluid additive and drilling fluid system can effectively control the production of environmental pollutants from the source. The green drilling fluid system was successfully applied in Tarim oilfield and Karamay oilfield for the first time, fulfilling the pollution-free disposal of throwing waste drilling fluid onto the soil. This technique could be used in improving and enriching soil. The laboratory experiments and field applications indicated that the drilling fluid system had low chemical toxicity. The contents of heavy metals Cd, Hg, Pb, Cr, and As are respectively below 0.3, 0.02, 3.7, 4.9, and 3.1 mg/kg; the acute biotoxicity EC50 was greater than 30,000 mg/l; and the biodegradation index BC (Biological oxygen demand [BOD5]/Chemical oxygen demand [COD]) was greater than 0.35. Soil organic matter and the major fertility indexes, such as nitrogen, phosphorus, potassium, were increased by 40% after throwing waste drilling fluid onto the soil. The core permeability recovery value was greater than 80%. This drilling fluid system realizes the organic unity of low toxicity, biodegradability, improving soil conditions after throwing, and reservoir protection. This is an important advancement for the coordinated development of Chinese oil industry and environmental protection.

World's energy demand is on upsurge and Oil & Gas industry has been directed towards the exploitation of deepwater oil and gas resources. To make this operation successful petroleum industry is continuously demanding new innovative drilling technology that can be easily implemented. One of the constraints that hinders the deepwater exploration is its continuously shrinking narrow window between pore pressure and fracture pressure that further limits the reliability of old conventional riser drilling technique.Dual gradient drilling (DGD) is a managed pressure drilling that involves use of two different annular fluids for drilling a prospect providing a favorable annular pressure profile and simpler, safer & economical well design.In any of the rotary drilling operation, drilling hydraulics is the most complicated and least understood drilling variable as it involves complex relationship between drilling fluid, drill bit and formation. Riserless drilling, one of the type of DGD, eliminates the use of marine riser (u-tube is imbalance) and involves use of an additional subsea mud pump at seabed which, supplements to the complication for hydraulics computation as compared to conventional drilling.In drilling HPHT deepwater wells, drilling fluid is constantly exposed to its own column pressure and formations geothermal gradient which subsequently affects the mud rheology and density. These altered rheological parameters leads to inadequate hole cleaning and lowers the drilling efficiency. High temperature in the wellbore cause's fluid expansion and high pressure causes fluid compression and these changes get extremely severe as water depth and drilling depth increases. Hence it becomes necessary to consider the HPHT effects on Equivalent Circulating Density (ECD) and to correct & optimize the hydraulic program to ensure the best utilization of the hydraulic energy for effective hole cleaning.This paper presents a detailed study of Well hydraulics for riserless drilling considering the HPHT effect on Equivalent Circulating Density and its optimization so as to ensure riserless drilling operation is conducted in safe and effective manner. Also the paper is concluded with some recommendations on operational and design strategies.

For the period different drilling campaigns took place at the Tapi and Auca Fields, Ecuador. A downhole monitoring pressure tool helped identify some important pressure behaviors and scenarios. The ECD monitoring led to better wellbore cleaning, drop of mud weight detection not detected on surface and improvement of drilling operation times by deciding whether it was necessary to make short trips or not, based on the acquired data. All the gathered data allowed the creation of a database that will become the baseline to improve future drilling projects in those fields. The tool uses a quartz crystal type transducer that grants high resolution and accurate readings in real time and memory of annular pressures and bore pressures. Additionally, ECD (Equivalent Circulating Density) and ESD (Equivalent Static Density) measurements are calculated and this last one also defines an inherent value of the EMW (Equivalent Mud Weight). The tracing of these values show the performance of the drilling fluid and an ECD working frame could be defined to ensure effective cleaning of the well. In order to understand ECD, external factors affecting its behavior need to be denoted such as flow patterns, ROP or drilling fluid properties. Additionally, the applications of pressure records when performing FIT, CIT or LOT are explained. Different scenarios of how the data was analyzed, interpreted and the decisions taken during the operations are shown in this paper.

With oil fields shifting to deeper depths and higher temperatures, modern drilling operations face significant challenges in High Pressure High Temperature (HPHT) zones (Mitchell, 2007).Drilling fluid systems need to be capable of providing better thermal stability in such environments, which is currently a difficult task for water-based drilling fluids due to their tendency to degrade at high temperatures (Amanullah, 2009).As a result, oil-based drilling fluids are often preferred despite being more expensive, environmentally harmful, and difficult to manage.Various research has suggested diverse additives to enhance the heat resistance of water-based mud (WBM) systems.These additives encompass chemicals, polymers, nanoparticles, and zeolites.As a result, a wide array of chemicals and polymers are currently employed in formulating different mud systems.The objective is to fulfill specific functional criteria, including achieving suitable mud rheology, density, mud activity, and efficient fluid loss control (Anon, 2000).Zeolites are known for their unique thermal conductivity, electrical conductivity, and optical features, and they have not yet been expensively studied in the context of drilling fluid formations (Chai et al., 2014).This research aims to investigate the effectiveness of using fresh and equilibrium zeolites in enhancing the thermal stability of water-based drilling fluids in HTHP zones.The research also seeks to conduct a performance comparison between the fresh and equilibrium zeolites under high temperature conditions.

To overcome wellbore instability problems in deep coalbed gas reservoirs in the Ordos Basin, drilling fluid additives were evaluated and a drilling fluid system was designed. According to the SEM and CT analysis results, there were not only face and butt cleats in the coal rock but also bedding and layered fractures. Potassium chloride (KCl) and Potassium formate (HCOOK) drilling fluid systems were formulated. The recovery rate of shale and coal rock cuttings reached 99%, and the linear swelling rates for coal rock in both types of drilling fluid were less than 0.18%. Measured with a servo-controlled compression frame at a loading rate of 1 mm/min, the uniaxial compression strength of coal rock was 11.74 MPa, and it was 9.13 MPa and 10.35 MPa after immersion in KCl and HCOOK drilling fluid, respectively. This indicates that both systems have good inhibition properties. The invasion depth in packed sand was 15.5 mm for KCl drilling fluid and 8 mm for HCOOK drilling fluid, demonstrating good sealing performance by the systems. Compared to KCl drilling fluid, the HCOOK system exhibited better inhibition and sealing performance. After the removal of the 10 mm deep invasion section of drilling fluid, the permeability of the coal rock recovered by more than 90%, and the drilling fluid caused minimum damage to the reservoir. The optimized drilling fluid exhibits excellent sealing and inhibition capabilities, making it highly effective in addressing wellbore stability challenges in carbonaceous mudstone formations at 4000 m in depth in the deep coalbed methane reservoirs of the Ordos Basin.

Wellbore instability is caused by the radical change in the mechanical strength as well as chemical and physical alterations when exposed to drilling fluids. Unscheduled events that are related to wellbore instability account for more than 10% of the drilling cost, which is estimated to one billion dollars per annual cost. Understanding shale-drilling fluid interaction plays a key role in minimizing drilling problems in unconventional resources. The need for providing a more suitable drilling fluid system for drilling operations in unconventional resources is growing. The major consequences of improper fluid selection include bit-balling, hole sloughing, and most importantly low drilling rates. This study will evaluate the effect of different inhibitive drilling fluid systems on shale drilling performance. The mud systems use in this study include cesium formate, KCl based mud systems, and a conventional water-based mud. The conventional water-based mud is used as reference fluid. An innovative HPHT drilling simulator is used to perform real-time drilling operations on cylindrical shale core samples obtained from the Tuscaloosa Marine Shale (TMS). The process involved simulating real-time drilling operation at downhole conditions where different fluids served as drilling fluid. A comparative analysis of the impact of each drilling fluid systems on the drilling performance as then performed. The analysis focused on drilling parameters such as rate of penetration, torque, and friction factor during drilling. This paper evaluates the compatibility between different fluid systems and shale formations. The paper also provides an overview of the effect of the inhibitive mud systems on drilling performance. The inhibitive muds systems (KCl based fluids and cesium formate) provided improved drilling performance compared to conventional water-based mud.

The drilling fluid contamination is a major problem during oil and gas well cementation, especially when such contamination comes from cement. The treatment is usually done with sodium bicarbonate (NaHCO3) where pH control is not a problem but with sodium carbonate (Na2CO3) to increase the pH of the drilling fluids with low pH. Determining the effective concentrations of these treating agents have always been a challenge as either the drilling fluid is undertreated or over treated which could be detrimental to the entire fluid system and the drilling operations. Therefore, there is a need to determine the effective concentrations of the chemical agents for the treatment of cement contamination. During cementation, the calcium hydroxide[Ca(OH)2] released by the cement decomposes and disperses calcium ions in the drilling fluids which could lead to flocculation of the fluid system and consequently increases the rheological and the filtration properties. When this occurs, the contaminated fluid system may be treated with some chemical agents to precipitate the calcium ions formed depending on the severity. The challenge remained on the determination of the effective concentrations of the chemical agents that will optimally treat the fluid system without causing harm. This paper investigates the effects of cement contamination on the rheological and filtration properties of a typical KCL/Polymer Water Based Drilling Fluids and also determines the effective concentrations of the treating agents (Sodium Bicarbonate and Sodium Carbonate) in the treatment of the cement contamination. A fresh KCl/Polymer fluid was formulated to serve as a control standard and was then contaminated with certain amount of class-G cement at varying proportions. The contaminated fluids were treated with different amount of Sodium Bicarbonate and Sodium Carbonate respectively to determine the effective concentrations required for the treatment of the different levels of the contamination. The drilling fluids properties such as plastic viscosity, yield point, gel strength, pH and fluid loss were adversely affected when contaminated with the cement. Experimental data were generated and linear correlations were developed to determine the effective concentrations of the sodium bicarbonate and sodium carbonate required for optimal treatment of specific amount of the cement contamination during cementation. This will act as a proactive step during oil and gas well cementation to optimally treat cement contamination, thereby reducing drilling time and minimizing overall well cost.