Equivalent Circulating Density Research Articles

Irregular Eccentric Wellbore Cementing: An Equivalent Circulation Density Calculation and Influencing Factors Analysis

In the field of cement, if the formation cannot be given sufficient pressure to maintain stability during construction, pressure control failure may occur, leading to the leakage of liquids and gasses from the formation to the wellbore. In addition, irregular wellbore diameter and casing eccentricity are important factors that are easily overlooked and affect the prediction of ECD (Equivalent Circulation Density) calculation. This results in major accidents and ecological disasters, further impacting the global environment. This study focuses on a well in the eastern oilfields of China, and based on a rheological experiment of high temperature and high pressure, an irregular eccentric wellbore model is established according to the measured wellbore diameter and eccentricity data to calculate the ECD of the whole cementing process. Then, a data set is constructed and analyzed using the random forest method to quantitatively evaluate influencing factors such as displacement, rheology, density, and eccentricity on the bottomhole and wellbore ECD. Results find that the density of cement slurry and drilling fluid has the most significant impact on the maximum ECD, with the impact reaching 0.3142 and 0.2902, respectively, and the main factors that affect the minimum ECD are the density and rheological changes in the drilling fluid, reaching 0.7014 and 0.2846. These research findings will contribute to the precise control of wellbore pressure during cementing operations, further ensuring the safety of cementing operations, and laying a technical foundation for the automation and intelligentization of subsequent cementing operations.

Transient temperature and pressure coupling model of cementing injection stage in ultra deep wells considering segmental rheological model, casing eccentricity and U-tube effect

The geological environments of ultra deep wells such as high temperature and high pressure (HTHP), narrow safety density window pose significant challenges to cementing operation. Considering segmental rheological model and density model, casing eccentricity, U-tube effect and viscous dissipation, this paper established a transient temperature and pressure coupling model during cementing injection stage of ultra deep wells. The segmental rheological model can describe the rheological properties of cementing fluids under HTHP much better. Considering casing eccentricity and viscous dissipation can accurately model the variation of temperature and pressure profiles. Taking U-tube effect into the model, the formation process of vacuum section at top of the casing can be simulated. The fully implicit finite-difference approach was used to solve the coupling model, and the calculation results were compared with field measurement data and simulation data to verify its accuracy. The calculation errors of the developed model are respectively 10% and 5% compared to field measurement data and Wellplan’s simulation data. Numerical simulations were conducted to reveal the cementing fluid distribution, transient temperature distribution and pressure distribution during the cementing injection stage. The simulation results show that the variety of cementing fluids with different density, rheological properties and thermophysical parameters complicates the change mechanism of temperature and pressure. The temperature and pressure distributions both present unsteady characteristics during cementing injection stage, which puts forward higher requirements of pressure control for narrow safety density window formation. The influence of temperature and pressure on rheology of cementing fluids cannot be ignored, and segmental rheological model should be considered for accurate pressure prediction. Also the casing eccentricity cannot be ignored for cementing pressure calculation in deviated or horizontal wells. Managed pressure cementing (MPC) has a greater advantage in dealing with narrow density window formation. The synergistic control of cementing fluid density and back pressure can keep the equivalent circulating density (ECD) within the safe density window. Through the application of the transient temperature and pressure coupling model, we can simulate the variations of key dynamic parameters during cementing injection stage and optimize the cementing parameters.

Study on the Equivalent Density Tool and Depressurisation Mechanism of Suction-Type Depressurisation Cycle

In order to further regulate equivalent circulating density (ECD), a novel downhole apparatus for reducing circulating pressure in high-temperature and high-pressure wells, the suction-type ECD reduction tool, was devised. The utilisation of this tool enables the bottomhole pressure of the equivalent circulating density to be attained in close proximity to its hydrostatic pressure, thereby facilitating the attainment of deeper drilling depths. The tool is composed primarily of a screw motor, scroll blades, annular seals, universal joints, and drilling columns. The tool operates by utilising the suction effect and hydraulic energy extracted from the circulating fluid by the screw motor, which is then converted into mechanical energy to create suction and enhance the flow energy of the drilling fluid within the annulus at the bottom of the well, thereby reducing the equivalent circulating density. Furthermore, based on ANSYS-FLUENT analysis simulations, the alteration of pressure drop characteristics in response to varying drilling fluid densities, displacements, and tool sizes was modelled. The simulation results demonstrate that the pressure drop effect is 1.0 MPa when the drilling fluid density is 1.2 g/cm3, 1.7 MPa when the drilling fluid density is 1.5 g/cm3, and 1.9 MPa when the drilling fluid density is 1.8 g/cm3. A pressure drop of approximately 2.3 MPa was observed when the drilling fluid density was 2.0 g/cm3. The maximum pressure drop is achievable with a flow rate ranging from 1500 to 2500 L/min. A maximum pressure drop of 2.3 MPa is observed when the flow rate is within the range of 1500 to 2500 L/min. Two distinct viscosity values (0.02 and 0.06 kg/(m·s)) were employed to assess the impact of viscosity on pressure drop characteristics in a suction-type ECD tool. The results demonstrated that the pressure drop remained largely unaltered, indicating that viscosity had minimal influence on this parameter. The flow rate emerged as the primary factor affecting pressure drop, with viscosity exerting a relatively minor effect.

Explainable machine-learning-based prediction of equivalent circulating density using surface-based drilling data

When drilling wells for energy explorations, it is important to regulate the formation pressures appropriately to prevent kicks, which can lead to unimaginable loss of lives and properties. This is usually done by controlling the equivalent circulating density (ECD), which responds to the dynamic conditions that occur during drilling. The conventional approach to determine ECD is via mathematical modeling or downhole measurements. However, the downhole measurement tools can be very expensive, and the mathematical models do not provide a high degree of accuracy. Some previous authors have proposed using machine learning (ML) techniques to improve the degree of accuracy of the ECD predictions. In this work, we employed an extreme gradient-boosting (XGBoost) methodology to predict ECD values. The model's accuracy was determined using correlation coefficients (R2) and root mean square errors (RMSE) as their performance metrics. The results showed a strong prediction capability with an R2 and RMSE of 1.00 and 0.0005 for the training data and an R2 and RMSE of 0.989 and 0.023 for the testing/blind data set, respectively. The developed model outperformed those obtained using other popular machine learning techniques. Lastly, an interpretation of the model results showed that mud weight, weight on hook, and standpipe pressure contributed the most to the ECD prediction values.

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.

Moore And Chien Correlation To Address The Issue Of Hole Cleaning In Guba Field – Libya

Hole cleaning and hydraulics are important part of drilling operations that need to be carefully reviewed and incorporated in drilling program. Poor hole cleaning could lead to various problems like slow rate of penetration (ROP), excessive torque and drag, excessive wear on bit, pipe sticking problems, and possibly fracturing of formation.In this work, Since hole cleaning is a major problem associated with drilling operations. There is an evaluation of the effect of the drilling fluid rheology parameters and flow rate on hole cleaning. Correlation methods such as Moore and Chien correlation have been made to provide the most suitable approach to address the issue of a hole cleaning. On the other hand, also explains the effect of the flow rate in the equivalent circulating density (ECD) in terms of frictional pressure loss in the annulus. The result of analysis demonstrates how the rheology parameters and flow do affect the hole cleaning and concludes that the ECD and frictional pressure loss in the annulus are affected by the flow rate.

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.

Research and application of low oil-water ratio organoclay-free oil-based drilling fluid technology

This paper introduces the formation and application of a low oil-water ratio organoclay-free oil-based drilling fluid. Shale oil and gas are important alternative energy sources. Due to the extremely complex geological conditions, oil-based drilling fluid technology is commonly used to reduce complexity. Although some achievements have been made, there are still problems such as unstable wellbore, difficult rheological control, and high cost. A stable and low-viscosity water-in-oil emulsion system was successfully prepared by using optimized fatty acid imidazolines emulsifier and alkyl alcohol ether wetting agent, which enabled the oil-based drilling fluid to have a larger solid and water phase capacity. On this basis, a special poly-fatty acid amide rheological modifier was used to assist in the regulation of rheological parameters, resulting in a low-viscosity and high-shear structure of the oil-based drilling fluid. This effectively ensured the efficiency of cuttings carrying while reducing the adverse effects of viscosity on Equivalent Circulating Density(ECD). The low oil-water ratio oil-based drilling fluid technology has been applied in a shale gas drilling platform in southern Sichuan, China, which greatly reduces the cost of oil-based drilling fluid while ensuring drilling efficiency.

Optimization of Wellbore Annulus Cleaning Tool Based on CFD-DEM and Box-Behnken Design

During the oil and gas drilling process, inefficient cuttings transport may elevate cuttings concentration, leading to higher Equivalent Circulating Density (ECD) and easily triggering a series of wellbore stability issues. In this paper, a new type of annulus cleaning tool is developed, incorporating the H- B non-Newtonian fluid model and a coupled CFD-DEM to construct a numerical model for analyzing the cuttings transport behavior within the multi-layer wellbore annulus using the cleaning tool. The model, validated against experiments, reveals factors affecting Cuttings Transport Ratio (CTR). Through Box- Behnken Design (BBD), Response Surface Methodology (RSM), and Analysis of Variance (ANOVA), a correlation function for CTR is derived to optimize the cleaning tool parameters. Findings show an initial increase then decrease in CTR with nozzle quantity, diameter, and angle. Decreasing hydraulic diameter enhances CTR, whereas nozzle diameter variation has minimal impact at smaller diameters. After optimization, CTR reaches 95.76% with 4 nozzles of 10mm diameter, 32° angle, and 57mm hydraulic diameter. These results guide cleaning tool optimization design , improving cuttings transport efficiency, and ensuring safe oil and gas production.

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.