Oil-based Mud Research Articles

Epsom Salt-Based Natural Deep Eutectic Solvent as a Drilling Fluid Additive: A Game-Changer for Shale Swelling Inhibition.

Shale rock swelling poses a significant challenge during drilling a well, leading to issues related to wellbore instability. Water-based mud with specific shale inhibitors is preferred over oil-based drilling mud due to its lower environmental impact. Recently, ionic liquids (ILs) have emerged as potential shale inhibitors due to their adjustable properties and strong electrostatic attraction. However, research has shown that the most commonly used class of ILs (imidazolium) in drilling mud are toxic, non-biodegradable, and expensive. Deep Eutectic Solvents (DESs), the fourth generation of ionic liquids, have been proposed as a cheaper and non-toxic alternative to ILs. However, ammonium salt-based DESs are not truly environmentally friendly. This research explores the utilization of Natural Deep Eutectic Solvent (NADES) based on Epsom salt (a naturally occurring salt) and glycerine as a drilling fluid additive. The drilling mud is prepared according to API 13B-1 standards. Various concentrations of NADES-based mud are tested for yield point, plastic viscosity, and filtration properties for both aged and non-aged samples. The linear swell meter is used to determine the percentage swelling of the NADES-based mud, and the results are compared with the swelling caused by KCl- and EMIM-Cl-based mud. FTIR analysis is conducted to understand the interaction between NADES and clay, while surface tension, d-spacing (XRD), and zeta potential are measured to comprehend the mechanism of swelling inhibition by NADES. The findings reveal that NADES improves the yield point and plastic viscosity of the mud, resulting in a 26% reduction in mudcake thickness and a 30.1% decrease in filtrate volume at a concentration of 1%. NADES achieves a significant 49.14% inhibition of swelling at the optimal concentration of 1%, attributed to its ability to modify surface activity, zeta potential of clay surfaces, and d-spacing of clay layers. Consequently, NADES emerges as a non-toxic, cost-effective, and efficient shale inhibitor that can replace ILs and DESs.

Monitoring and Characterization of Gas Migration in Oil-Based Mud Using Fiber-Optic DAS and DTS

Summary Understanding gas dynamics in mud is essential for planning well control operations, improving the reliability of riser gas handling procedures, and optimizing drilling techniques, such as the pressurized mud cap drilling (PMCD) method. However, gas rise behavior in mud is not fully understood due to the inability to create an experimental setup that approximates gas migration at full-scale annular conditions. As a result, there is a discrepancy between the gas migration velocities observed in the field as compared to analytical estimates. This study bridges this gap by using distributed fiber-optic sensors (DFOS) for in-situ monitoring and analysis of gas dynamics in mud at the well scale. DFOS offers a paradigm shift for monitoring applications by providing real-time measurements along the entire length of the installed fiber at high spatial and temporal resolution. Thus, it can enable in-situ monitoring of the dynamic events in the entire wellbore, which may not be fully captured using discrete gauges. This study is the first well-scale investigation of gas migration dynamics in oil-based mud with solids, using optical fiber-based distributed acoustic sensing (DAS) and distributed temperature sensing (DTS). Four multiphase flow experiments conducted in a 5,163-ft-deep wellbore with oil-based mud and nitrogen at different gas injection rates and bottomhole pressure conditions are analyzed. The presence of solids in the mud increased the background noise in the acquired DFOS measurements, thereby necessitating the development and deployment of novel time- and frequency-domain signal processing techniques to clearly visualize the gas signature and minimize the background noise. Gas rise velocities estimated independently using DAS and DTS showed good agreement with the gas velocity estimated using downhole pressure gauges.

Green drilling fluid additives for a sustainable hole-cleaning performance: a comprehensive review

AbstractDrilling fluids are the core of drilling operations, and they are responsible for many roles, such as lubricating drill string, cooling down drilling equipment, maintaining wellbore integrity, and transporting cuttings to the surface. High-energy demands have caused the oil and gas production rates to increase by orders of magnitude, which is accompanied by increased usage of different drilling fluids, including oil-based muds (OBM) and water-based muds (WBM). Large amounts of fluids used without caution can cause severe consequences to the environment if not well monitored. Therefore, the field has been exploring the utilization of biodegradable and environmentally friendly additives (green). These green formulations can promote a safer alternative to the currently available commercial additives, meet sophisticated drilling requirements, and ensure resource sustainability. A comprehensive overview of the literature has been conducted in this review, starting with a background on oil and gas reservoir types and cuttings transportation mechanisms, followed by a discussion on various recent green fluids or additives emerging in the field. In addition, an economic comparison has been conducted to assess the feasibility of the reviewed green formulations. Finally, the review ends with a summary and future prospective on the topic. In conclusion, this review suggests the development of multifunctional drilling fluids with good hole-cleaning properties, utilizing additives studied for different functions (e.g., filtration). Enhancement of rheological properties achieved through the addition of these additives indicates their suitability for hole-cleaning applications, which must be confirmed through additional studies. Consequently, filling the existing gap in the literature is by triggering research topics in this area.

Waste to a commodity: the utilization of waste cooking oil for the formulation of oil-based drilling mud with H2S scavenging capability bestowed by the incorporation of ZIF-67

Waste to a commodity: the utilization of waste cooking oil for the formulation of oil-based drilling mud with H2S scavenging capability bestowed by the incorporation of ZIF-67

Comparative study of bentonite and Ikwo clay for oil-based drilling mud formulation

As the demand for energy rises, drilling activities and the use of drilling mud by oil and gas industries keep increasing, leading to large consumption and high importation cost of drilling mud materials. The study is conducted to replace high cost of drilling mud materials (bentonite) which is a burden on the companies and our economy at large, with respect to foreign exchange challenge. Locally sourced drilling mud material, clay precisely, from Ebonyi State, particularly Ikwo clay, is yet to be explored as alternative to commercial bentonite. The specific objective of this study is to analyse and compare Ikwo clay in replacement to commercial bentonite as viscosifiers for formulating oil-based drilling mud. The driving motivation is to utilize local content (Ikwo clay) which is in abundance and has remained unprocessed substitute for bentonite. The clay undergoes activation using sulfuric acid (H2SO4) following conventional procedures. XRF spectrophotometers determine chemical compositions and functional groups of bentonite and clay samples. Oil-based muds are separately formulated using bentonite and Ikwo clay additives. The mud weight, pH, apparent viscosity, plastic viscosity, yield point, and gel strength of the respective muds are evaluated. The interactive effects of the process variable on viscosities of each mud sample are determined, and the viscosity of the respective muds was optimized using the Central Composite Design (CCD) tool of Design Expert software (version 12) based on RSM. Activation of the local clay improved its properties, as results of the chemical composition revealed that Ikwo clay contains exchangeable cation like potassium ion (K+)) and an essential metal (iron (iii) ion (Fe3+)), with the presence of alumina signifying its suitability in terms of plasticity and swelling ability. The Ikwo clay mud had a higher sample mud weight than the bentonite mud, which indicates that Ikwo clay can manage formation pressure and improve wellbore stability. The optimum viscosities of the oil-based muds with bentonite and Ikwo clay additives are obtained at 15.49 cP and 18.82 cP, respectively. The optimum values are realized at a bentonite/Ikwo clay dosage of 8 wt%, a temperature of 313 K and a mixing time of 35 min. The novelty of Ikwo clay compared to imported bentonite is its ability to offer structural stability to drilling mud (Rana et al., 2020). This feature is used to control wellbore instability during drilling operations. Ikwo clay is a good fit for bentonite replacement as a viscosifier in formulating drilling mud.

Construction of pavers from drilling cuttings as an alternative for environmental management of waste

The management of drilling waste represents a problem of high economic and environmental impact for operating companies. This is due to its polluting components that, besides being dangerous for the environment, must be treated with special care. The cuttings generated during drilling which are normally impregnated with water-based and oil-based muds, represent most of this solid waste. In this work, it is proposed to treat the drilling cuts to be used as raw material for construction of paving stones that can be used as construction material in platforms and facades of buildings or houses, being an alternative of innovative and high impact disposition. For the foregoing, a determined volume of drilling cuttings from a well of a Magdalena Medio field was used as a test, performing all the usual solids control treatment, passing through shakers, desander, desilter and mud cleaner. After treating the perforation cuts, they were dried in an oven between 110 and 150 °C for 24 hours. Then the sample was allowed to cool to grind it and bring it below 45 microns; where it was finally used as material for the construction of the paving stone, to which the resistance tests established in the NTC 2017 standard were carried out. Results show that the use of some drilling cuttings in the construction industry is viable. Conversely, the comparison was made with a conventional way of managing the gravel when it was reused in the production of cobblestones, obtaining a reduction of up to 34% of the associated costs and when there are greater than 12,000 barrels of waste. Additionally, it is used to generate valuable items and avoids the disposal of waste material

Empirical Correlations for Predicting Flow Rates Using Distributed Acoustic Sensor Measurements, Validated with Wellbore and Flow Loop Data Sets

Summary Distributed acoustic sensing (DAS) is an emerging surveillance technology that is becoming increasingly popular in the oil and gas industry for real-time flow monitoring. However, there are limited studies that rigorously quantify flow rates using DAS. This work expands the existing literature by presenting a detailed workflow for accurately estimating fluid flow rates from DAS data using time- and frequency-domain signal processing. Three simple empirical correlation functions (linear, exponential, and cubic) are developed and tested to predict flow rates from DAS. The proposed correlations are demonstrated for flow rates ranging from 50 to 300 gallons per minute (GPM) in a vertical 5,163-ft-deep wellbore and from 12 to 36 GPM in a horizontal surface flow loop. Tests were performed using a single-phase flow of water as well as using synthetic oil-based drilling mud. Time-domain DAS processing using root-mean-square (RMS) value and frequency-domain processing using frequency band energy (FBE) is evaluated, followed by a statistical approach to minimize the influence of outliers. The RMS and FBE approaches are individually compared for flow prediction, and the performance of the correlations is rigorously evaluated on a blind data set that was not originally used for developing the correlations. For both the wellbore and flow loop data sets, a coefficient of determination (or R2) greater than 0.95 with an average flow rate prediction error of less than 10% was achieved for the best-performing correlation for the blind test data. The analysis procedure and workflow presented in this study can be adopted and extended to different operating conditions for quantitative flow rate prediction using DAS.

Temperature distribution of shale oil wellbore considering oil-based mud and formation fluid displacement

Oil-based mud is widely used in shale oil well drilling because of its good stability and high temperature resistance at high temperature. However, during the drilling process of shale oil wells, fluid displacement between the annulus and the formation occurs. The existing temperature field model cannot predict the temperature distribution of the wellbore annulus under this condition. Based on the equations of heat conduction and conservation of energy, a new model of wellbore heat transfer in shale oil wells considering the displacement between downhole fluids is established in this paper. By comparing the temperature distribution of annular fluid under normal circulation, lost circulation and overflow, the accuracy of this model is confirmed. Taking the parameters of a shale oil well in a certain area as an example, the factors that affect the temperature of the annular fluid are analyzed and solved. Numerical analysis and simulation results show that the flow rate remains unchanged, and the annular temperature decreases by about 1.42 °C/L when the flow rate of the annulus increases. As the specific heat capacity of shale oil increases, the annular temperature increases by about 0.0012 °C/J/(kg·°C). In addition, when displacement between fluids occurs in the upper open-hole segment, there is an inflection point on the temperature distribution curve of the annular fluid, and the location of the inflection point is consistent with the location of the fluid displacement point. The results can provide a theoretical reference for drilling in complex formations with frequent formation-annulus fluid displacement, leakage and overflow.

Waste cooking oil invert emulsion drilling mud formulation with an effective H2S scavenging performance

Encountering hydrogen sulfide while drilling/stimulating subterranean formations is very common in upstream oil and gas industry. If not effectively scavenged in-situ, this lethal gas will escape to the surface causing serious health and safety problems and potential losses in human lives, in addition to significant economic penalties. Additionally, the release of waste cooking oils to the drainage/sewage systems will lead to some serious operational problems during the treatment of the collected sewage wastewaters. Thus, the key objective of this study is to convert the waste cooking oils from a burden into a valuable commodity via utilizing them for the formulation of invert emulsion drilling fluids. The waste cooking oil invert emulsion drilling mud was stabilized partially by rhamnolipid biosurfactant as a secondary emulsifier. The mud also contained hydrophobic zinc nanoparticles (NPs) as a weighting agent. To provide these waste cooking oil-based drilling muds with an effective H2S scavenging performance, a small quantity (1 wt%) of potassium permanganate was added. Despite the small quantity of the added scavenger, the mud formulation was able to scavenge 99.4 and 237.7 mg H2S/g scavenger at the breakthrough and saturation time, respectively. These H2S scavenged capacities demonstrate the feasibility of incorporating potassium permanganate, which is cheap and abundant material, into waste cooking oil invert emulsion drilling mud formulations. The flow behavior and the viscosity of the waste cooking oil-based mud comprising the H2S scavenger were found to be comparable to those reported in the literature for oil-based muds (OBMs) containing NPs.

Wear factors and mechanisms of L-80 steel casings

Casing wear in directional drilling is inevitable and may result in catastrophic failure of the casing column. It is thus essential to understand its mechanisms and quantify its extent by estimating the casing wear factor. In this research, actual field casing samples, drilling pipe joints and muds were considered. An in-house built testing facility was used to test several L-80 casing samples by considering three rotational speeds of the drill pipe tool joint (DP-TJ) (115, 154, and 207 rpm) and three side loads (1000 N, 1200 N and 1400 N). The influence of the water- and oil-based muds on the coefficient of friction, wear volume, wear factor and wear mechanisms were investigated. The results revealed that under water-based mud (WBM) lubrication casing wear volume and wear factors were more than twice that of oil-based mud (OBM) lubrication. Moreover, it was observed that as the side load increased under both OBM and WBM lubrication at a constant rpm, both wear volume and wear factor increased. However, increasing the rotational speed while maintaining the side load constant decreased the wear factor, owing to the localized softening effect caused by the high heat generation at the contact area and the possible hydrodynamic lubrication regime change at higher speeds. The analysis of the digital microscopic images taken at the wear region shows that abrasive mechanism was dominant in the case of OBM lubrication. On the other hand, both abrasive and adhesive wear mechanisms were present under WBM lubrication.

Influence of simple oil-based muds on fluidic down-the-hole hammer performance

A feasibility study is important when determining the viability of a drilling tool. This paper considers several aspects of this drilling tool, including the relationship between the oil-water ratio, bentonite content, and drilling fluid temperature with the performance of the drilling tool, so that field engineers can make actionable plans. Based on the full stroke data measured by the laser sensor, time-displacement, and time-velocity curves compared across different OBM were graphed to characterize the impact body motion. Fluidic hammer driven by WBM is commonly higher than OBM in the tested supply flow rate range. Compared with WBM, adding bentonite is indispensable for a fluidic hammer powered by OBM to achieve good performance. The oil does not have a significant lubricating effect on the movement of fluidic down-the-hole hammer. The performance of the fluidic hammer driven by OBM exhibited higher elevation with temperature than that of WBM, which explains the susceptibility of oil to temperature. The fluidic down-the-hole hammer can work efficiently and reliably with OBM.

Applications of sodium silicate in oil and gas well operations

Silica and silicates are the most abundant minerals in the Earth's crust and mantle. They are critically important as both raw materials and finished products. Nanosodium silicate (SS) has been shown to increase the effectiveness and efficiency of several standard well operations now in use. The precipitation and polymerization of silicate colloid particles makes this whole thing possible. Nanosilicate is advantageous since it is inorganic, safe, inexpensive, water-soluble, nonflammable, and nonexplosive. Nanosodium silicate (SS) has been used since the 16th century and finds major applications in the building and paper industries as well as in water purification and cleaning products. Nanosodium silicate is studied in this article for its manufacture, chemistry, health and safety (HSE) benefits, existing applications, and potential future applications in oil and gas well operations. Drilling fluids using nanosodium silicate have been shown to be more effective at working tough shales and restoring circulation after it has been lost than traditional oil-based muds (OBM). Borehole zonal isolation and improved primary cementing results can be attained with the use of nanosidum silicate as a spacer in the preflush. When used as an accelerator to shorten thickening time and a lightweight extender when cementing, nanosodium silicate is a common cement addition. Nanosodium silicate techniques are commonly used in restoring casing integrity, enhancing EOR compliance, and shutting off water. Reservoir stimulation techniques like acidizing and hydraulic fracturing benefit greatly from the addition of nanosodium silicate to the stimulation fluids. Nanosodium silicate improves the efficiency of well abandonment. Learning the chemistry behind the processes improves our comprehension of their many practical uses. In addition, this technology paves the way for a wide variety of upcoming improvements in well operations.

Comprehensive analysis of membrane efficiency of shale: descriptive statistics & laboratory data analysis

This study presents a broad set of prior experimental data for shale membrane efficiency when interacting with water-based and oil-based drilling fluids. The assessment of the experimentally measured membrane efficiencies of shale reveals that shales are leaky semi-permeable membranes. Results suggest that shale permeability and cation exchange capacity play a determining role in its membrane efficiency, as higher cation exchange capacity and lower permeability are strongly consistent with higher membrane efficiency of shale. Furthermore, it has been found that the ratio of hydrated ionic size relative to shale pore throats’ size regulates the movement of ions into the shale, thus directly controlling its membrane efficiency. Ions with large hydrated diameters exhibit higher membrane efficiencies than those with small hydrated diameters. Results also show that the measured membrane efficiencies of oil-based muds were higher than those reported for shales. While shale gets its membrane quality from its tiny pores and inherent surface charge, oil-based mud gets its membrane quality from the stability of its emulsion. We believe that when using oil-based muds to drill shale formations, the emulsifier assumes responsibility for screening out ions, however, if the emulsion stability is breached, shale will become the regulator for ions flow.

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.

Data-Driven Framework for Real-time Rheological Properties Prediction of Flat Rheology Synthetic Oil-Based Drilling Fluids.

Appropriate mud properties enhance drilling efficiency and decision quality to avoid incidents. The detailed mud properties are mainly measured in laboratories and are usually measured twice a day in the field and take a long time. This prevents real-time mud performance optimization and adversely affects proactive actions. As a result, it is critical to evaluate mud properties while drilling to capture mud flow dynamics. Unlike other mud properties, mud density (MD) and Marsh funnel viscosity (MFV) are frequently evaluated every 15-20 min in the field. The goal of this study is to predict the rheological properties of flat rheology synthetic oil-based mud (SOBM) in real time using machine learning (ML) techniques such as random forest (RF) and decision tree (DT). A proposed approach is followed to first predict the viscometer readings at 300 and 600 RPM (R 600 and R 300) and then estimate the other mud properties using the existing equations in the literature. A set of data contained MD, MFV, and viscometer readings (R 300 and R 600) for different samples from the same mud type. The mud samples were collected after going through a shale shaker. MD and MFV are measured by a mud balance and a Marsh funnel, respectively, while rheology is evaluated using a viscometer. The data were randomly split into training, testing, and validation data sets. The ML models' performance was evaluated through average absolute percentage error (AAPE) and correlation coefficient (R). The proposed models predicted the viscometer readings as a middle stage with a low AAPE that did not exceed 4.5% for both models. The suggested models forecasted the rheological properties with a good degree of accuracy, with an AAPE being less than 7% for most of the parameters. The proposed models can save costs and time since there is no need to include additional tools in the rig location. Furthermore, these models will significantly aid in avoiding serious problems and achieving better rig hydraulics and hole cleaning, which in turn will technically and economically enhance drilling operations.

Experimental and modeling studies on dynamic barite sag and effects of particle size, shear rate, and fluid rheology

Barite is often utilized to control the weight of drilling muds. However, in inclined wellbores, barite particles settle out of the mud in a lateral direction and quickly reach the wellbore wall. Over time, deposited particles form unstable barite beds that slide intermittently downward, causing downhole pressure fluctuations. The observation is often referred to as barite sag, which occurs prominently when the system is in a dynamic state. Barite sag leads to density variation in the mud system, resulting in drilling issues such as stuck pipe, fluid loss and lost circulation, loss of well control, and wellbore instability. Various experimental studies have been conducted on barite sag, but limited mathematical modeling has been undertaken.This article presents the results of experimental and mathematical modeling studies on barite sag. First, particle size distribution tests were performed with API barite. Then, different oil-based muds (OBMs) were prepared using barite samples with various particle size distributions. Next, the apparent viscosities of the muds were measured with a rheometer. Then, the Viscometer Sag Shoe Test (VSST) method was used to study barite sag at 49 °C varying rotational speed and barite particle size distribution. Furthermore, the settling behavior of barite particles under dynamic conditions was simulated using a sedimentation-consolidation model. The model is solved numerically by applying a fully implicit finite difference method. The accuracy of the numerical solution is validated using simulation results presented in a previous study. The model has been improved to handle non-Newtonian fluids and simulate dynamic conditions.According to the apparent viscosity measurements, barite particle size has a minor effect on OBM rheology. The VSST results also show that barite sag increases with particle size and rotational speed. The improved model predicts VSST results fairly well. Additionally, a model-based parametric study indicates that barite sag decreases with increasing OBM rheological parameters (consistency index, yield stress, and fluid behavior index).

Study on Pyrolysis of Shale Gas Oil-Based Drilling Cuttings: Kinetics, Process Parameters, and Product Yield.

The main reaction range (350-550 °C) of oil-based drilling cutting (OBDC) pyrolysis was studied by a thermogravimetric analyzer and a vacuum tube furnace. The average activation energies calculated by four model-free methods were 185.5 kJ/mol (FM), 184.16 kJ/mol (FWO), 166.17 kJ/mol (KAS), and 176.03 kJ/mol (Starink). The reaction mechanism was predicted by the Criado (Z-master plot) method. It is found that a high heating rate is helpful to predict the reaction mechanism, but it cannot be described by a single reaction model. Under the conditions of target temperature higher than 350 °C, residence time higher than 50 min, laying thickness less than 20 mm, and heating rate lower than 15 °C, the residual oil content is lower than 0.3% and the recovery rate of mineral oil is higher than 98.43%. Solid phase products accounted for more than 70%, reached the maximum 17.04% at 450 °C, and then decreased to 15.87% at 500 °C. Aromatic hydrocarbons, as coking precursors, are transformed from a low ring to a high ring. Recycled mineral oil can reconfigure oil-based mud (OBM). The research results can provide a theoretical basis for process optimization.

Artificial Neural Networks to Predict Lost Circulation Zones at Southern Iraq Oilfield

Drilling soft and fragile areas such as (high permeable, cavernous, fractured, and sandy formations) have several problems. One of the most critical problems is the loss of drilling fluid into these formations in whole or part of the well. The loss of drilling fluid can lead to more significant and complex problems, such as pipe sticking, well kick, and closing the well. The drilling muds are relatively expensive, especially oil-based mud or those that contain special additives, so it is not economically beneficial to waste and lose these muds. Artificial neural networks (ANN) can predict drilling fluid losses before they occur based on drilling parameters data and drilling fluid properties of wells effected by lost circulation problems located in the same area. This paper developed two artificial neural network models to predict drilling fluid losses in the Dammam formation- Rumaila oil field in southern Iraq. The two models have the same topology and structure. The first model used the early stopping technique to stop the training when we get the global minimum and the second model used specific epochs to complete the training. The models could predict various types of losses with high accuracy. The accuracy of implementing R2 for the first and second models was 0.9302 and 0.9493, respectively. The early stopping technique lead to obtain a model with acceptable accuracy in a short time without relying on a specific number of epochs.

Evaluations of Polyacrylamide Water-Based Drilling Fluids for Horizontal Drilling in the Shaly Wolfcamp Formation

Summary The Permian Basin, located in southeastern New Mexico and west Texas, is treated as the largest province of oil and gas production in the United States (US). The majority of hydrocarbon production from the Permian Basin is from the Wolfcamp shaly formation. Drilling horizontal and extended reached wells is continuously increasing day after day in the Permian Basin. Oil-based mud (OBM) is used to drill these horizontal wells for enhancing shale inhibition, reducing torque and drag, and supporting thermal stability of mud rheology. Due to environmental regulation for limiting use of OBM, the petroleum industry has tried to develop water-based fluid (WBF) that approaches the performance advantages of OBM. The main objective of this research is to formulate and develop WBF by using polyacrylamide anionic friction reducer (AFR) for drilling the lateral sections of horizontal wells in the shaly Wolfcamp formation. Shale inhibition, barite sagging, lubricity, and thermal stability of the formulated WBF with AFR will be studied to evaluate the developed WBF. Laboratory experiments were conducted to develop and evaluate the performance of the formulated WBF with AFR. The shale inhibition capabilities of the developed WBF with AFR were evaluated by using zeta potential, shale dispersion test, and immersion test. The results prove the capability of the formulated WBF with AFR to prevent both shale swelling and shale dispersion. AFR limits water penetrations to shale through encapsulation. The mixing procedures of AFR with WBF affect both the thermal stability of mud rheology and shale inhibition. Adding AFR to WBF helps to suspend weighting materials and mitigate barite sag. Besides, AFR decreases torque and drag by decreasing the coefficient of friction (COF). Furthermore, AFR supports enhanced stability of mud rheology with time up to 14 days at temperatures up to 180°F. The formulated WBF with AFR can be used for enhancing shale inhibition, supporting thermal and time stability of fluid rheology, improving lubricity, and minimizing barite sagging for drilling shaly Wolfcamp formations. This study presents a promising WBF to replace OBM to drill lateral sections in the Permian Basin.

Fatty Alcohol Polyoxyethylene Ether Sodium Sulfate–Modified Cement to Improve the Bonding and Sealing of Cement to Oil-Wet Casing or Formation Surface in Shale Gas Wells

Summary In shale gas wells, oil-based mud (OBM) changes the casing and rock surface wettability during drilling. It negatively affects the bonding and sealing of cement sheaths with casing or formation rock. Although the spacer is widely used in primary cementing, the casing and formation rock surface are wetted by OBM or oil phase due to poor displacement. For this work, a novel oleophilic cement slurry modified by fatty alcohol polyoxyethylene ether sodium sulfate (AES) was investigated to decrease the negative effect of OBM- or oil-wetted surface. The contact angle of nonpolar solvent 1-bromonaphthalene on the cement surface decreased from 35° to 8°, showing an ideal oleophilic property. The hydraulic isolation capacity; microstructure of the cement-casing or cement-rock interface; and the pore structure, hydration, and mechanical property of AES-modified cement were investigated by interfacial hydraulic isolation test device, computed tomography (CT), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), thermogravimetric analyses (TGAs), and mechanical test. The results showed that the oleophilic cement could directly bond with an oil- or OBM-wetted surface and significantly eliminate the microchannel and connected pores caused by the oil phase or OBM on the interface. The fluid channeling on the OBM-wetted cement-rock and casing interface was prevented, and the sealing pressure of the interface was increased from approximately 3 to 7 MPa/m (fluid channeling occurred) to higher than 275 MPa/s (fluid channeling did not occur), respectively. Besides, the hydration degree, porosity, and mechanical property of the oleophilic cement remained at the same level as the conventional cement, indicating that the AES has no adverse effect on cement hydration and properties. The findings of this study can contribute to the cement slurry design in shale gas well cementing to improve the interface bonding and sealing when poor displacement happens.