Equivalent Circulating Density Research Articles

Study Explores Challenges, Potential of Superlaterals in the Vaca Muerta

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3968851, “Breaking the 5-km Barrier: Superlaterals Delivery Challenges—Are They Feasible in Vaca Muerta?” by Julio Palacio, SPE, Walid Ben Ismail, and Richard Walker, K&M Technology Group, et al. The paper has not been peer reviewed. _ Driven by increased production rewards, multiple operators in the United States have been improving their unconventional wells by increasing lateral length. Several “superlaterals” with lengths greater than 23,000 ft have been drilled successfully in several US basins. The complete paper describes the technical challenges faced in drilling and running casing in superlaterals and the difficulties in implementing them in the Vaca Muerta unconventional play. Introduction In 2012–2015, many operators began to drill longer laterals. Because production did not appear to decline with increasing lateral length, one operator drilled 11 superlaterals in 2017 in the Utica shale, reporting critical cost reductions and a greater recovery per foot. This operator used the term “superlateral” to describe a lateral length of 15,000 ft or greater. At the time of writing, several wells have exceeded a lateral length of 23,000 ft and can be categorized as extreme-reach wells. Typically, any well in the extended-reach region requires a large focus on operational practices and may require important design changes and special technologies or techniques to achieve its goals. Geomechanics Challenges The Vaca Muerta/Quintuco system is a late Jurassic to early Cretaceous play with a depth of more than 8,200 ft true vertical depth (TVD). Pore pressure in Quintuco can vary between 14.2 and 18.8 lbm/gal. Fractures connecting different zones and depths lead to discontinuity and important uncertainties in both pore pressure and fracture gradient. Historically, Quintuco was isolated by running casing before entering the Vaca Muerta. However, several operators drill Quintuco and Vaca Muerta in the same section to reduce the well cost. Using this approach, Quintuco pressure uncertainties effectively limit the maximum lateral length. To reduce this uncertainty effect, managed pressure drilling (MPD) has been used successfully in current laterals. Bedding-plane instability limited early development of unconventional horizontal wells. Its effect is not commonly perceived while drilling but can affect bit trips and casing runs catastrophically. Higher mud weight (MW) has helped mitigate, but not eliminate, bedding-plane instability in unconventional plays around the world. However, higher MW can constrain more than the MW window requirements in the Quintuco/Vaca Muerta system. As the lateral progresses in length, the annular pressure increases proportionally. Given that the TVD remains almost constant in horizontal wells, the equivalent circulating density (ECD) change will increase proportionally to the lateral length. Because of this ECD behavior in horizontal wells, MPD cannot be used to manage the wellbore-stability (WBS) margin reduction in longer laterals or to eliminate pressure fluctuations during connections. In very long laterals, the only way to better manage the WBS margin, bedding-planes issue, and induced wellbore instability can be a well-design change to increase the annular clearance after performing extensive modeling. MPD and surface-parameter control can marginally help to control the problem.

MODELLING OF DEEP WELL CEMENTING PROCESS

The research aims to simulate Managed Pressure Cementing (MPC) for a deepwater field, focusing on optimizing the cementing process to ensure structural integrity and wellbore stability. The study addresses the challenges associated with conventional cementing methods, providing insights into the pressure dynamics, fluid properties, and pump performance crucial for deep well cementing operations. The methodology involves conducting a simulation to model the cementing process for a deep well with a total length of 9144 meters, where the previous casing's shoe is located at a depth of 6096 meters. Real data is utilized to obtain profiles of reservoir pressure, hydraulic fracturing pressure, and viscosities of essential fluids, including cement, drilling fluid, and buffer fluid. The simulation considers factors such as annular pressure loss, Equivalent Circulating Density (ECD) calculation, and pump performance under varying conditions. Additionally, the density of the cement slurry in the annulus during pumping is established. The study reveals that pump performance under the given conditions is 57 m³/h for drilling and buffer fluids, while for cement solutions, it can vary from 19 m³/h to 38 m³/h. These results offer actionable insights for operational planning and optimization of the cementing process in deep wells. The simulation successfully models the cementing process for a deep well, providing valuable data on equivalent circulation density and cement slurry density in the annulus. The determined pump performance under different conditions is critical for understanding the dynamics of fluid circulation during cementing operations. Practical implications of the research include the optimization of cementing processes, contributing to enhanced structural integrity, reduced wellbore instability, and improved efficiency in deepwater field operations. In conclusion, the study not only contributes to theoretical understanding but also provides practical data for optimizing the cementing process in deep wells, reflecting the industry's commitment to continuous improvement in drilling technologies and ensuring the reliability and efficiency of wellbore operations in challenging environments. Keywords: managed pressure drilling (MPD), wellbore stability, downhole conditions, real-time monitoring, managed pressure cementing (MPC), zonal isolation.

Study on Rock Mechanics Parameter Prediction Method Based on DTW Similarity and Machine-Learning Algorithms

Rock mechanics parameters are crucial factors for predicting rock behavior in oil and gas reservoirs, optimizing extraction strategies, and ensuring drilling safety. In this study, we propose a random forest (RF)-convolutional neural network (CNN)-long-term short-term memory network (LSTM) fusion model based on the dynamic time warping (DTW) algorithm to construct intelligent prediction models for elastic modulus, Poisson’s ratio, and compressive strength using real-time drilling engineering data. An autoencoder with a sliding window is employed to automatically identify abnormal points or segments in the calculated values of elastic modulus, Poisson’s ratio, and compressive strength obtained from drilled wells. These abnormal values are then corrected using a backpropagation (BP) neural network. Compared to single CNN-LSTM or single RF models, the RF-CNN-LSTM fusion model performs better. It achieves this by effectively combining the strengths of different algorithms in predicting outcomes. The accuracy of the RF-CNN-LSTM fusion model is over 94% when compared to the actual values. Furthermore, the analysis of the relative importance of input parameters reveals that weight on bit (WOB), temperature, displacement, equivalent circulation density (ECD), and mud density are the primary input features for predicting elastic modulus. For predicting Poisson’s ratio, the main input features include WOB, mud density, ECD, temperature, pumping pressure, displacement, and rate of penetration (ROP). Similarly, for predicting compressive strength, the main input features consist of WOB, temperature, displacement, ECD, and mud density. The research findings demonstrate that the rock mechanics parameter prediction models based on the RF-CNN-LSTM algorithm using DTW exhibit high computational accuracy in the B oil field of China. These results are significant for gaining a deeper understanding of the variations in rock mechanics parameters and optimizing drilling decisions.

Technology Focus: Drilling and Completion Fluids (November 2023)

Today, the industry faces tremendous challenges related to safety, efficiency, sustainability, and socioenvironmental responsibility. At every stage, well-construction projects must be concerned about those aspects to establish measurable barriers for preventing issues. Therefore, drilling and completion fluids are critical for achieving project goals and ensuring operations are executed as planned. Drilling and completion fluid selection is a complex process in which addressing future downhole conditions for predicting potential problems is vital to eliminating nonproductive time. Conventional deep high-pressure/high-temperature wells in South sub-Andean Bolivia or unconventional long horizontal wells in Argentina are pushing drilling-fluid design to its limits with regard to keeping equivalent circulating density (ECD) as low as possible while preventing formation damage. Paper SPE 211539 describes several successful applications of low ECD organophilic clay-free inverted emulsion fluid in reaching project goals in challenging environments. On the other hand, constant monitoring of drilling-fluid properties also is necessary. Fluid properties must be monitored so additives can be adjusted to prevent problems. Even though conventional monitoring relies on humans for performing periodic tests, recent technology developments offer a solution for complex drilling operations by allowing continuous real-time monitoring of drilling-fluid properties using sensors and artificial intelligence, as fully described in paper SPE 212443. Finally, discussion of drilling and completion fluids must mention solids-control equipment. Ensuring that fluid properties are within acceptable ranges without discarding valuable additives is the main objective of any solids-control-equipment arrangement. Things become more complicated when working with low-density drilling fluids, where a comprehensive understanding of solids-removal techniques and their customization for a particular application requires research and laboratory-scale trials, which are rare in the literature. Paper SPE 212470 provides relevant and novel information through a full-scale test program for solids-control-equipment efficiency optimization focused on treating low-density muds. Recommended additional reading at OnePetro: www.onepetro.org. SPE 211509 High-Fluid-Loss Squeeze and Reticulated Foam Lost-Circulation Material Plugs 40,000-Micron Laboratory Simulated Fracture/Vug Opening by Sharath Savari, Halliburton, et al. SPE 214171 Using Cerium Oxide (6.0 SG) as Weighting Material in HT/HP Drilling Fluids by Gholam Reza Soori, Cahya Mata Oiltools, et al.

Effects of Pipe Rotation on the Performance of Fibrous Water-Based Polymeric Fluids in Horizontal Well Cleanout

Summary The deposition of rock cuttings is a problem commonly faced during drilling, completion, and intervention operations. Using polymer-based fluids is a common technique to improve horizontal downhole cleaning. However, these fluids cannot always guarantee an efficient wellbore cleanout. One way to enhance cleanout efficiency is by rotating the drillpipe to mitigate the settling of solids and facilitate their removal. However, drillstring rotation often increases equivalent circulating density (ECD). Therefore, in this study, we explore how the impact of rotation on hole cleaning can be synergized by using fibrous water-based polymeric fluids to perform cleanout at reduced rotational speeds with limited effect on ECD. The flow loop used for this study consists of a 48-ft long eccentric annular (5×2.375 in.) test section. Each experiment began by forming a stationary bed of natural sand (an average diameter of 1.2 mm) in the test section. High-viscosity and low-viscosity polymer-based suspensions with and without fibers were used. The drillpipe rotation speed was varied from 0 to 150 rev/min. In each experiment, the flow rate was increased from 35 to 195 gal/min stepwise. The bed perimeter was measured at equilibrium condition for every test flow rate until a complete bed cleanout was achieved. In addition, the friction pressure loss was measured. Rotational viscometers were also used to measure fluid rheology before and after each test. Fiber particles improve the carrying capacity of the fluid by reducing solid settling and minimizing the redeposition of particles. The results demonstrate the effectiveness of fiber in synergizing pipe rotation effects on hole cleanout performance in horizontal wellbores. Fiber’s impact is more pronounced when used with low-viscosity fluid. The cleanout performance of the low-viscosity fluid is amplified significantly with rotation, almost entirely cleaning the bed at 75 gal/min and a rotational speed of 50 rev/min, compared with more than 195 gal/min without rotation. Even more improvement could be achieved by adding a small amount of fiber (0.04wt%). In addition, the fiber improved the cleanout performance of the high-viscosity fluid. The enhancement, however, was not as noticeable as with the low-viscosity fluid. In general, rotation combined with low-viscosity fibrous fluid exhibits the best cleaning performance. This is because rotating the pipe resuspends the settled solids, which are then easily carried by fibrous fluid that has high solids carrying capacity.

Modelling the Effects of Temperature and Pressure on Equivalent Circulating Density (ECD) During Drilling Operations Using Artificial Neural Networks

Incorrect evaluation of equivalent circulating density (ECD) while drilling oil and gas wells may result in drilling problems such as lost circulation, kicks, differential pipe sticking etc especially in narrow drilling margins. Due to the incompressible nature of liquids, increase in wellbore pressure will only have appreciable effect on the fluid rheology at higher pressures, whereas a small increase in temperature may cause a decrease in the rheology. One thousand and eleven (1,011) field data obtained from high pressure; high temperature (HPHT) wells were used to develop artificial neural networks (ANNs) for this study. Training data were used to train the network while validation data were used to guarantee that the network generalizes at the training stage. Test data were used to evaluate the prediction capability of the developed model. Four error metrics, namely R-square (R2), mean square error (MSE), root mean square error (RMSE) and average absolute percentage error (AAPE) were used to assess the performance of the developed networks. Forecasts from the testing data indicate the optimized ECD model produced a prediction accuracy; R2 of 0.9993, MSE of 0.000265, RMSE of 0.01628 and AAPE of 0.337. The optimized ECD model performed better than existing ECD models in terms of the prediction accuracy and the calculated errors. The developed ECD model will help in improving the ECD prediction during the pre-drill design phase, which is quite critical in narrow drilling margin wells.

The Impact of Drilling Operation Parameters on the Lost Circulation Problems for Oil and Gas Wells Based on Field Data

Lost circulation, the loss of drilling fluid into holes or fractures throughout the geological formations being drilled, is the most expensive problem encountered in drilling operations for oil and gas wells. It is known that when there is a loss of circulation during the drilling process, the operation activities are delayed or stopped for curing or treatment, resulting in extra time known as non-productive time (NPT). The NPT issues during the drilling operations are the most important priorities for planning any drilling program. Therefore, the lost circulation is one of the main problems which can control the NPT. To mitigate the lost circulation problems, an integrated investigation is necessarily needed for the main parameters which enhance/downgrade the rate of lost circulation.
 Drilling through the Dammam and Hartha formation is typically accompanied with substantial nonproductive time due to severe and often entire drilling fluid losses. The majority of the curing this problem require time for preparation, placement or setting. In this research, a field study was carried out to investigate the effect of 6 drilling parameters on the rate of the lost circulation. The investigated parameters are the rate of penetration, weight on bit, stand pipe pressure, mud weight, flow rate, and the equivalent circulation density. Furthermore, the effect of lithology type on the lost circulation rate was clearly determined and correlated. In addition, a graphical representation of bit depth vs the real drilling time/date was constructed to compare the lossy wells vs non-lossy wells named frithogram. This study was based on field data for 350 wells drilled in Rumaila Oilfield, southern Iraq. The results of this study showed that if these six operating parameters are standard and controlled, the significance of lost circulation problems could be reduced. However, the main factors which are responsible for the lost circulation problems are lithology types, facies and/or diagenesis process, which mainly distinguish the carbonate formations.

Geomechanics Analysis of Well Drilling Instability: A Review

Wellbore instability is a significant problem faced during drilling operations and causes loss of circulation, caving, stuck pipe, and well kick or blowout. These problems take extra time to treat and increase the Nonproductive Time (NPT). This paper aims to review the factors that influence the stability of wellbores and know the methods that have been reached to reduce them. Based on a current survey, the factors that affect the stability of the wellbore are far-field stress, rock mechanical properties, natural fractures, pore pressure, wellbore trajectory, drilling fluid chemicals, mobile formations, naturally over-pressured shale collapse, mud weight, temperature, and time. Also, the most suitable ways to reduce wellbore instability are selecting the appropriate drilling mud and maintenance, reducing the Equivalent Circulating Density (ECD) by using suitable hydraulics, selecting hole-trajectory, and compatibility of drilling fluid with the formation being drilled. Moreover, factors such as (minimizing time spent open hole, using offset-well data, and monitoring trend changes (torque, circulating pressure, drag) must be considered. As a result of this paper, wellbore instability problems can be controlled by careful study of reservoirs to find the solutions to some issues or reduce them.

A Developed Robust Model and Artificial Intelligence Techniques to Predict Drilling Fluid Density and Equivalent Circulation Density in Real Time.

When drilling deep wells, it is important to regulate the formation pressure and prevent kicks. This is achieved by controlling the equivalent circulation density (ECD), which becomes crucial in high-pressure and high-temperature wells. ECD is particularly important in formations where the pore pressure and fracture pressure are close to each other (narrow windows). However, the current methods for measuring ECD using downhole sensors can be expensive and limited by operational constraints such as high pressure and temperature. Therefore, to overcome this challenge, two novel models named ECDeffc.m and MWeffc.m were developed to predict ECD and mud weight (MW) from surface-drilling parameters, including standpipe pressure, rate of penetration, drill string rotation, and mud properties. In addition, by utilizing an artificial neural network (ANN) and a support vector machine (SVM), ECD was estimated with a correlation coefficient of 0.9947 and an average absolute percentage error of 0.23%. Meanwhile, a decision tree (DT) was employed to estimate MW with a correlation coefficient of 0.9353 and an average absolute percentage error of 1.66%. The two novel models were compared with artificial intelligence (AI) techniques to evaluate the developed models. The results proved that the two novel models were more accurate with the value obtained from pressure-while-drilling (PWD) tools. These models can be utilized during well design and while drilling operations are in progress to evaluate and monitor the appropriate mud weight and equivalent circulation density to save time and money, by eliminating the need for expensive downhole equipment and commercial software.

Numerical modeling of transient cuttings transport in deviated wellbores

Hole-cleaning optimization is one of the major challenges while drilling long-reach horizontal wells. Accumulation of cuttings can affect the equivalent circulating density (ECD) by decreasing the open flow area and increasing the average density of the drilling fluid. The transient development or removal of cuttings bed due to variation of operating parameters are often ignored in the majority of prior numerical studies. In this paper, it is aimed to develop a transient cutting transport model to predict ECD while drilling. A one-dimensional transient two-phase hydraulic model based on the drift-flux approach is developed to predict the cuttings transport considering cuttings deposition and entrainment. The numerical method employs an upwind scheme to discretize the governing equations. To account for the effect of operating parameters on the cuttings bed, two empirical correlations were employed from the literature. A new empirical correlation is also developed for the prediction of cuttings bed hold-up through regression analysis of the experimental results of a published study. A computer program is developed to solve the governing equations and predict the ECD taking into account the effect of suspended cuttings and cuttings bed along the wellbore trajectory. The numerical model is validated by comparing the predicted return weight of cuttings with measured data in the literature for the cases of no pipe rotation and pipe rotation. The effects of employed empirical correlations on predicted ECD profiles are also examined for a hypothetical well. It is realized that the predicted cuttings bed area of the proposed correlation falls between the predictions of the existing empirical correlations. It is concluded that the most conservative prediction in terms of cutting accumulation in the wellbore cannot necessarily yield a conservative prediction in terms of ECD for early times.

Door to diuretics time is longer among heart failure patients with atrial fibrillation

Hole-cleaning optimization is one of the major challenges while drilling long-reach horizontal wells. Accumulation of cuttings can affect the equivalent circulating density (ECD) by decreasing the open flow area and increasing the average density of the drilling fluid. The transient development or removal of cuttings bed due to variation of operating parameters are often ignored in the majority of prior numerical studies. In this paper, it is aimed to develop a transient cutting transport model to predict ECD while drilling. A one-dimensional transient two-phase hydraulic model based on the drift-flux approach is developed to predict the cuttings transport considering cuttings deposition and entrainment. The numerical method employs an upwind scheme to discretize the governing equations. To account for the effect of operating parameters on the cuttings bed, two empirical correlations were employed from the literature. A new empirical correlation is also developed for the prediction of cuttings bed hold-up through regression analysis of the experimental results of a published study. A computer program is developed to solve the governing equations and predict the ECD taking into account the effect of suspended cuttings and cuttings bed along the wellbore trajectory. The numerical model is validated by comparing the predicted return weight of cuttings with measured data in the literature for the cases of no pipe rotation and pipe rotation. The effects of employed empirical correlations on predicted ECD profiles are also examined for a hypothetical well. It is realized that the predicted cuttings bed area of the proposed correlation falls between the predictions of the existing empirical correlations. It is concluded that the most conservative prediction in terms of cutting accumulation in the wellbore cannot necessarily yield a conservative prediction in terms of ECD for early times.

Numerical Simulation on the Safety and Quality of Cementing by Using Pad Fluid in Horizontal Wells

The failure of wellbore sealing will cause leakage of greenhouse gases, such as carbon dioxide and methane, which will harm oil and gas recovery and environmental safety. Cementing is an important part of wellbore sealing. Only good cementing can keep the wellbore seal for a long time and improve the well life. In this study, we considered the construction of a horizontal shale oil well in eastern China as the background and analysed the rheological properties of the annulus fluid. We developed a displacement motion model and a calculation model for the annulus dynamic equivalent circulation density, and numerical simulations were used to study the impact of the dosage and injection sequence of the pad fluid on the displacement efficiency and annulus dynamic equivalent circulation density. The results show that when the pad fluid is composed completely of flushing fluid, the displacement performance is better than that of the spacer. By increasing the dosage of the flushing fluid from 0.3 times the annular volume to 1.0 times, the displacement efficiency can be increased by 3.3%, and the retention of the drilling fluid is also reduced by 3.6%. However, it can lead to a significant reduction in the annulus dynamic equivalent circulation density and increase in the risk of leakage. After adding the spacer, the structure of the flushing fluid–spacer provides the optimal injection sequence. Considering the application status in the field example well, it was shown that it can not only ensure the safety of cementing operations, but also improve the displacement efficiency. The results of this study have important theoretical significance and application value and can provide guidance for the optimisation design of the engineering scheme.

Extended-Reach Drilling (ERD)—The Main Problems and Current Achievements

With the development of different segments within the drilling technology in the last three decades, well drilling has become possible in harsh downhole conditions. The vertical well provides access to oil and gas reserves located at a certain depth directly below the wellsite, and a large number of vertical wells are required for the exploitation of hydrocarbons from spatially expanded deposits. However, the borehole can deviate from the vertical well, which means that the target zone can be reached by a horizontal directional well. With this type of well, especially in the case of drilling an extended-reach well (ERW), the length of the wellbore in contact with the reservoir and/or several separate reservoirs is significantly increased, therefore, it is a much better option for the later production phase. Unfortunately, the application of extended-reach drilling (ERD technology), with all of its advantages, can cause different drilling problems mostly related to the increased torque, drag, hole cleaning and equivalent circulation density (ECD), as well as to an increase in the well price. Overcoming these problems requires continuous operational change to enable operators to address downhole challenges. Today, the longest well reaches 15,240 m (50,000 ft), which raises the question of the technological and economic feasibility of this type of drilling project, especially with the lower oil price on the energy market. This paper provides a comprehensive overview of extended-reach drilling technology, discusses the main problems and analyzes current achievements.

Calculation of Cementing ECD for Well Annuli with Narrow or Varied Radial Sizes

In this present work, cement slurry flowing in well annuli with narrow or varied radial sizes is investigated, whose purpose is to precisely calculate the equivalent circulating density (ECD) during well cementing in the petroleum industry. The theoretical Metzner-Reed (MR) method and the direct numerical simulation (DNS) are applied to calculate the cementing ECD for different types of cement slurries by considering both the Bingham and Power-Law rheological models. The cementing ECD calculated by the theoretical MR method is verified to be in accordance with the DNS result. Moreover, for the narrow annulus, the cementing ECD is demonstrated to be sensitive to the rheological model. In addition, based on the obtained DNS results, the accuracies of the cementing ECD calculated by three commercial software, including DRILL BENCH (DB), LANDMARK (LM), and PVI, are compared, to determine their corresponding adaptability for different rheological models. According to the detailed comparisons, LM shows the highest accuracy in calculating the cementing ECD for the Power-Law fluid, while PVI is optimal for the Bingham fluid. However, sharp fluctuations of the calculation errors are observed when DB is applied.

Prophecy of Cutting Transport Ratio through a Relationship between Equivalent Circulating Density and Drilled Solid Concentration

This manuscript aimed to propose a new approach in estimating the cutting transport ratio through a relationship between equivalent circulating density (ECD) and drilled solid concentration from different formations in a nearly vertical well. A laboratory test utilising drilled cuttings from North Kuwait Field was conducted to simulate drilled solids-laden mud for accomplishing this purpose. The drilled solids were taken from four formations, namely Radhuma, Tayarat, Hartha and Sadi. The rheological behaviour of the drilled solids-laden mud was conducted according to API Recommended Practice 13B. In addition to laboratory tests, a database was established from drilled solids produced in the three wells of the North Kuwait field. As a result of the laboratory tests and actual field data, new empirical equation between drilled solid concentration and equivalent circulating density was proposed. ECD from laboratory works matched with the ECD field at an R2 value of 0.93, proving the data’s reliability. This empirical equation can be used to calculate the cutting transport ratio and later can be used to optimise drilling operations.

Prediction of the equivalent circulation density using machine learning algorithms based on real-time data

<abstract> <p>Equivalent circulation density (ECD) is one of the most important parameters that should be considered while designing drilling programs. With increasing the wells' deep, offshore hydrocarbon extraction, the costly daily rate of downhole measurements, operating restrictions, and the fluctuations in the global market prices, it is necessary to reduce the non-productive time and costs associated with hole problems resulting from ignoring and incorrect evaluation of ECD. Therefore, optimizing ECD and selecting the best drilling parameters are curial tasks in such operations. The main objective of this work is to predict ECD using three machine learning algorithms: an artificial neural network (ANN) with a Levenberg-Marquardt backpropagation algorithm, a K neighbors regressor (knn), and a passive aggressive regressor (par). These models are based on 14 critical operation parameters that have been provided by downhole sensors during drilling operations such as annular pressure, annular temperature, and rate of penetration, etc. In the study, 4663 data points were selected and included, where 80% to 85% of the data set has been used for training and validation according to the algorithm, and the remaining data points were reserved for testing. In addition, several statistical tests were used to evaluate the accuracy of the models, including root mean square error (RMSE), correlation coefficient (R<sup>2</sup>), and mean squared error (MSE). The results of the developed models show various consistencies and accuracy, while the ANN shows a high accuracy with an R<sup>2</sup> of nearly 0.999 for the training, validation, and testing, as well as the overall of them. The RMSE is 0.000211, 0.000253, 0.00293, and 0.00315 for overall, training, validation, and testing, respectively. This work expands the use of artificial intelligence in the gas and oil industry. The developed ANN model is more flexible in response to challenges, reduces dependence on humans, and thus, reduces the chance of human omission, as well as increasing the efficiency of operations.</p> </abstract>

Generalized Models for the Field Assessment of Drilling Fluid Viscoelasticity

SummaryRecent studies highlight the significant role of drilling fluid elasticity in particle suspension and hole cleaning during drilling operations. Traditional methods to quantify fluid elasticity require the use of advanced rheometers, which are not suitable for field applications. The main objectives of this study were to investigate the factors influencing drilling fluid viscoelasticity in the field and develop generalized models for determining the viscoelasticity of a drilling fluid using standard field testing equipment.Ninety-three fluid formulations used in this study included field samples of oil-based drilling fluids as well as laboratory samples of water-based, invert emulsion and other oil-based fluids. Basic rheological characterizations of these fluids were done by using a funnel viscometer and a rotational viscometer. Elastic properties of the drilling fluids (quantified in terms of the energy required to cause an irreversible deformation in the fluid’s structure) were obtained from oscillatory tests conducted by using a research-grade rheometer with double gap concentric cylinder geometry. Using an empirical approach, two noniterative models for quantifying drilling fluid elasticity were developed (one for unweighted and the other for weighted drilling fluids) by correlating test results from a funnel viscometer and a rotational viscometer to energy required to cause an irreversible deformation of the fluid’s elastic structure.The generalized models for the unweighted and weighted viscoelastic drilling fluids were able to predict the elasticity of drilling fluids with a mean absolute error of 4.67 and 5.28%, respectively. In addition, the models offer practical versatility by requiring only standard drilling fluid testing equipment to predict viscoelasticity. Experimental results showed that nonaqueous fluid viscoelasticity is inversely proportional to the oil-water ratio (OWR), and the presence of clay greatly debilitates the elasticity of the drilling fluids while enhancing their viscosity.In this paper, we present models for estimating unweighted and weighted drilling fluid elasticity using standard drilling fluid field testing equipment. Furthermore, we proposed a prudent approach for quantifying the viscoelastic property of a drilling fluid by measuring the amount of energy required to irreversibly deform a unit volume of viscoelastic fluid. The new models, combined with the recommended use of the energy dissipation (ED) concept, provide practical tools that can be used for developing optimum drilling fluid formulations and hydraulic programs for effective hole cleaning operations, improved equivalent circulating density (ECD) management, and mitigating barite sag problems.

Indicators of cutting removal efficiency when drilling directional wells

Borehole cleaning is still a major challenge for most directional wells despite a significant progress achieved in drilling fluids, tools and field practice, as well as in the development of academic and industry research. Insufficient cleaning of the borehole causes undesirable phenomena in the form of various complications. Therefore, the purpose of the conducted research was to present the main correlations that determine the nature and cleaning degree of the annular eccentric space of the well and to analyze these correlations presented in the form of indicators in order to improve them. The object of the research is the mechanics of cuttings removal from an inclined or horizontal well. In the frameworks of this research mechanics is mathematically displayed in the form of indicators reflecting one or another physical aspect of the cuttings removal process. The research methodology consists in the analysis of the composition of indicators, evaluation of the significance of the indicator constituents, identification of the quantitative contribution of the indicator to the cleaning degree of the annular space of the directional well from destruction products while sinking the borehole. The study resulted in the introduction of the following indicators: equivalent circulation density, slip velocity and cuttings removal index. The physical essence of indicators in their mathematical form is shown with the focus on the slip velocity. The definition of the latter, which is widely accepted among the specialists indicates the rate of washing of cutting particles by the drilling fluid during its transportation to the day-light surface. This indicator is one of the main ones that determine the hydrodynamics of the cuttings transport process. To simplify the calculation of the indicator, it is proposed to use the dimensionless Lyashchenko criterion.

Optimization of cementing displacement efficiency based on circulation pressure of a shale gas horizontal well in low pressure and leakage formations

The well trajectory of horizontal wells are constantly changing due to the variation of well inclination and azimuth with depth, leading to a large difference of displacement efficiency in the annulus compared to a vertical well. In low pressure and leakage formations, optimizing injection parameters to improve displacement efficiency is a hot and difficult research topic for researchers and field engineers, particularly the complex well. A fluid flow model inside the casing and annulus was established during primary cementing under an eccentric casing. Pressure distribution in the eccentric and concentric annuli were compared with the field data. Based on the principle of the maximum circulation pressure being lower than formation leakage pressure, the injection rate and fluid density were optimized to improve displacement efficiency, using Computational Fluid Dynamics (CFD) methods and investigating the mud retention volume on the wall. The results indicated that the pressure model in a casing eccentricity with an error of 1% to 3.5% is in good agreement with the actual pump pressure. Frictional pressure loss in the eccentric annulus was 13% to 25% lower than in the concentric annulus. Appropriately increasing the fluid density difference (spacer and lead slurry), the mud retention volume in the annulus of the horizontal section decreased significantly, while increasing the injection rate at the wellhead had little influence on displacement efficiency. The sequence of displacement efficiency from high to low was horizontal section > deflecting section > vertical section. The results of this study allow a better understanding of casing eccentricity effect on circulation pressure and equivalent circulation density (ECD) distributions in the annuls. The complex displacement mechanism analysis for the horizontal, deflecting, and vertical sections provides practical guidance in improving displacement efficiency by optimizing the most effective operation parameters.

Effect of Fluid Viscosity and Fiber Length on the Performance of Fibrous Fluid in Horizontal Well Cleanout

SummaryDuring drilling, completion, and intervention operations, solids can deposit in the wellbore. Innovative cleanout fluids reduce the problems associated with inadequate hole cleaning. Various methods have been developed to improve hole cleaning, but their effectiveness decreases as the wellbore inclination increases. One way to solve this issue is to add fibers to the drilling fluid and reduce the settling velocity of the solids to improve the fluid’s lifting capacity.The purpose of this study is to evaluate the cleanout performance of fibrous fluids in horizontal wells using a large-scale flow loop. Thus, flow loop experiments were conducted to assess the impact of fiber on equilibrium bed height. The experiment measures equilibrium bed height and pressure loss in an eccentric annular test section. During the investigation, the flow rate and apparent viscosity of the fluid and fiber length were varied.The results demonstrate the effectiveness of long fiber (length = 0.5 in.) in improving hole cleanout in horizontal wellbores. When a small amount (0.04% wt.) of long fiber was added, the cleanout performance of the high-viscosity fluid did not show a noticeable change. In contrast, the performance of the low-viscosity fluid improved. Even though adding fiber has minimal impact on the apparent viscosity of the fluids, the long fiber improved the cleaning performance of the low-viscosity fluid.Hole cleaning is challenging in operations such as coiled tubing (CT) in which rotating the drillstring is impossible. Hence, this study focuses on cleanout operations in horizontal wellbores without drillstring rotation. The novelty of this work lies in demonstrating how the adjustment of fluid viscosity can positively impact the hole cleaning performance of fibrous fluids in the absence of pipe rotation. The study also presents a new approach to modeling the effects of solids bed irregularity on wellbore pressure loss and equivalent circulating density (ECD).