Mud Weight Window Research Articles

Scaling-up dynamic elastic logs to pseudo-static elastic moduli of rocks using a wellbore stability analysis approach in the Marun oilfield, SW Iran

Wellbore stability analysis is a critical component of petroleum engineering, evaluating the risks of sanding, reservoir compaction, and casing failures. Laboratory rock mechanical measurements must be scaled up to reservoir scales to achieve accurate results. One challenge lies in upscaling dynamic measurements from petrophysical logs to pseudo-static elastic properties, which has significant implications for oil and gas operations. We present a novel approach that combines laboratory rock mechanical measurements with well-log data to develop a mechanical earth model (MEM) for an Iranian oilfield with over 350 wells. We conducted static elastic property measurements on 40 core samples from various layers and depths of carbonate and sandstone rocks, demonstrating the practical application of our approach. By integrating these measurements with dynamic log data and static-dynamic correlations, we established a framework for evaluating the mechanical properties of different layers. Our findings indicate that the safe mud weight window ranges from 41.5 to 118.59 pcf, while the stable mud weight window ranges from 41.5 to 156 pcf. We demonstrate the importance of conducting parallel rock mechanical studies on cores and logs to reduce uncertainties, costs, and risks during oil and gas operations. We also propose a novel methodology combining lithological characteristics, abnormally high pressure, and borehole instability mechanisms to evaluate the stability of borehole walls. This framework provides a fresh perspective on wellbore stability analysis and offers practical solutions for the industry. Essential novel techniques include developing a geomechanical model that integrates laboratory rock mechanical measurements with well-log data to evaluate mechanical properties and calculate safe and stable mud-weight windows. Our study advances wellbore stability analysis by providing a new method for addressing this long-standing challenge. It offers valuable insights for petroleum engineers working in the oil and gas industry.

Impact of long-term depletion on horizontal wellbore stability in tight reservoirs-including changes in petrophysical and geomechanical properties

The development of tight reservoirs using a horizontal well requires caution owing to the reservoir sensitivity to stress. Predicting the horizontal wellbore instability during reservoir depletion is critical for tight reservoirs. The present study investigated the wellbore failure criteria and stress orientation changes with reservoir depletion of a horizontal well in a tight reservoir, considering rock sensitivity to stress with pressure reduction. An integrated reservoir model coupled with geomechanics was used to predict pore pressure. A mechanical earth model (MEM) was constructed to examine the stability of horizontal wells. The unconfined compressive strength (UCS) was correlated with changes in porosity due to stress changes. The MEM shows that the failure criteria around the horizontal wellbore, including breakout, loss, and breakdown pressures, change considerably with reservoir depletion. A more significant response was observed in the stress-sensitive layer, which was characterised by a higher permeability. The safe mud weight window of the studied horizontal well narrowed significantly after production for five years, whereas the stability was completely absent after ten years. The deterioration of stability with depletion is governed mainly by permeability reduction, which may cause severe pressure reduction, whereas the stability improvement due to the increase in UCS caused by porosity reduction seems marginal. Relatively small changes in the direction of the stresses around the wellbore with depletion were observed, with the stress distribution concentrated in the predominant direction as the depletion continued. This study indicates that the sensitivity of petrophysical and geomechanical properties to stress amplifies the instability in tight reservoirs, particularly around wellbores.

Safe mud weight window in wellbore with mud-cake: A simple solution and verification

Under overbalanced drilling condition, a layer of particulates from drilling mud, called mud-cake or filter-cake, is often formed on the wellbore surface as the drilling fluid seeps through the surrounding geological formation. Mud-cake acts like a soft filter reducing the fluid pressure exerted on the wellbore surface by the fluid in the well. In this work, the safe mud weight window for wellbores with mud-cake is analytically derived by combining the long-term poroelastic wellbore stress solutions with steady-state flow solution for a two-layer cylindrical well. Parametric study on mud-cake permeability and thickness verifies that a wellbore with mud-cake transits smoothly from permeable wellbore to impermeable wellbore as the mud-cake accumulates. The new solution of breakdown pressure is also validated by a hydromechanical interaction numerical simulation.

Wellbore Instability Analysis to Determine the Safe Mud Weight Window for Deep Well, Halfaya Oilfield

Wellbore instability is one of the most common issues encountered during drilling operations. This problem becomes enormous when drilling deep wells that are passing through many different formations. The purpose of this study is to evaluate wellbore failure criteria by constructing a one-dimensional mechanical earth model (1D-MEM) that will help to predict a safe mud-weight window for deep wells. An integrated log measurement has been used to compute MEM components for nine formations along the studied well. Repeated formation pressure and laboratory core testing are used to validate the calculated results. The prediction of mud weight along the nine studied formations shows that for Ahmadi, Nahr Umr, Shuaiba, and Zubair formations ranges between 12.5 to 15 ppg. The predicted safe mud weight value seems to be narrow with a well deviation higher than 350. Therefore, for Ahmadi, Nahr Umr, Shuaiba, and Zubair formations, the wellbore appears unstable compared to other formations. The results of stability analyses indicate that the breakout mud weight wasn’t affected by wellbore azimuth because of low-stress contrast. Furthermore, shear failure can be prevented by drilling the well with an inclination of less than 350. As well as, to prevent breakdown the well should be drilled with an inclination between 25o to 65o in the direction of minimum horizontal stress. These outcomes could be used to prevent wellbore instability and determine a safe mud-weight window when planning to drill nearby wells in the future.

Quantitative risk analysis and parameter sensitivity evaluation of wellbore instability in poroelastic media considering uncertainty of geomechanical parameters

The randomness and fuzziness of geomechanical parameters make it difficult to directly determine the wellbore collapse and fracture pressures, and thus show significant influence on the risk assessment of drilling operations. Therefore, to effectively analyze the risk of wellbore instability in deep formation, this paper develops the evaluation models of wellbore stability for the vertical well drilled through the poroelastic rock formation subjected to borehole stresses under different time domains, including the instantaneous, modified instantaneous, short-time, long-time, and elastic ones. Meanwhile, based on the Monte Carlo method, one compares the difference between Taylor expansion and the Rosenbluth method in quantifying the uncertainty of the evaluation models. One analyzes the risk of wellbore instability under the condition that the geomechanical parameters satisfy the uniform, triangular, and normal distribution characteristics. In addition, different from the single factor sensitivity evaluation in previous uncertainty analysis, one introduces Morris and Sobol methods to conduct the comprehensive analysis of local and global sensitivity of geomechanical parameters. The main results show that the collapse pressure determined by the different cases of borehole stresses presents in descending order of short-time, long-time, and instantaneous. However, the fracture pressure shows in ascending order of long-time, instantaneous, and short-time cases. Besides, the different distribution characteristics of geomechanical parameters lead to the relationship of safe mud weight window in descending order of normal distribution, triangular, uniform distributions, and the uncertainty characteristics caused by the normal distribution of geomechanical parameters can be effectively quantified by Taylor expansion and Rosenbluth method. The strong sensitivity parameters affecting wellbore collapse and fracture are the maximum and the minimum horizontal in situ stresses, respectively. These two parameters present a strong difference in global sensitivity and local sensitivity analysis, which is manifested by the comprehensive effect of global parameters. The influence of the maximum horizontal in-situ stress on borehole collapse is weakened to a certain extent, while wellbore tensile fracturing is strengthened. On the contrary, the minimum horizontal in-situ stress is characterized by enhancing the borehole collapse whereas weakening the tensile fracturing. Besides, the influence degree increases with the increasing of parameter uncertainty.

Simultaneously improving ROP and maintaining wellbore stability in shale gas well: A case study of Luzhou shale gas reservoirs

The ROP (rate of penetration) within the horizontal section of shale gas wells in the Luzhou oil field is low, seriously delaying the exploration and development process. It is proved that reducing mud density mitigates the bottom-hole differential pressure (ΔP) and increases the ROP during overbalanced drilling. However, wellbore collapse may occur when wellbore pressure is excessively low. It is urgent to ascertain the optimal equilibrium point between improving ROP and maintaining wellbore stability. The safe mud weight window and the lower limit of mud density in the horizontal section of the Luzhou block are predicted using the piecewise fitting method based on conventional logging data. Then, the accuracy of the collapse pressure prediction was verified using the distinct element method (DEM), and the effect of wellbore pressure, in-situ stress, rock cohesion, and natural fracture density on borehole collapse was investigated. Finally, a fitting model of ΔP and ROP of the horizontal section in the Luzhou block is established to predict ROP promotion potential after mud density reduction. The field application of this approach, demonstrated in 8 horizontal wells in the Luzhou block, effectively validates the efficiency of reducing mud density for ROP improvement. This study provides a useful method for simultaneously improving ROP and maintaining wellbore stability and offers significant insights for petroleum engineers in the design of drilling parameters.

Compressive and Tensile Strength Anisotropy of Friable Sandstone and Thin-Bed Shale of the Pleistocene Erin Formation: Insights for Safe Operating Mud Weight Windows for Vertical and Horizontal Wells

Compressive and Tensile Strength Anisotropy of Friable Sandstone and Thin-Bed Shale of the Pleistocene Erin Formation: Insights for Safe Operating Mud Weight Windows for Vertical and Horizontal Wells

A thermo-mechanical simulation for the stability analysis of a horizontal wellbore in underground coal gasification

The stability analysis of horizontal wells is essential for a successful underground coal gasification (UCG) operation. In this paper, a new 3D coupled thermo-mechanical numerical modeling is proposed for analyzing the stability of UCG horizontal wells. In this model, the effect of front abutment stresses, syngas pressure, syngas temperature and thermal stresses is considered to predict the mud weight window and drilling mud pressure during UCG process. The results show that the roof caving in UCG panel has a greatest impact on the stability of horizontal well. Moreover, when the time of coal gasification is increased, the well convergence increases and for more stability it is necessary to increase the drilling mud pressure. This research was carried out on the M2 coal seam in Mazino coal deposit (Iran). The results showed that the mud weight window for horizontal well drilling is between 0 and 33 MPa. The appropriate stress for the maximum stability of the horizontal well, taking all the thermal and mechanical parameters into account, is 28 MPa. The suggested numerical method is a comprehensive and consistent way for analyzing the stability of horizontal wells in UCG sites.

An Investigation of Wellbore Instability in Problematic Formations from Eridu Oil Field, Southern Iraq

Wellbore instability is a main challenge and contribute to suspending the drilling operations that lead to over-well time, known as Non-productive time (NPT). The cost of drilling operation can be reduced by using a geomechanical model that contributed enormously to the design of an appropriate mud weight window and determined the optimum well trajectory for the plan well. Several wellbore instability encountered while drilling operations in the Eridu oil field, such as (hole collapse, losses, caving, and tight hole). In this study, a geomechanical model (MEM) was developed by using the related data (open hole log measurements, core analysis data, drilling observation data), then these data were utilized in software (Techlog, version 2021). Two failure criteria (Mogi –Coulomb and Stassi d’ Alia failure criteria) were used for the prediction the breakdown and breakout profile; moreover, address the optimum mud window to mitigate wellbore instability-related issue for different well trajectory. The geomechanics results demonstrated that the Mogi failure criterion produced reasonable results when combined with the caliper log. Also, the Eridu oil field fault regime is divided into two regions: strike-slip faults in carbonate rocks and normal faults in clastic rocks. To avoid a majority of wellbore instability problems in shale formations, the safe mud weight range is 11-12.5 ppg. The failure analysis, especially shear failure, showed that the mud weight used previously in this field is improper to support the rock on the wellbore wall. This study’s finding could be used as a cost-effective tool when the plan to drill a direction and horizontal well in Eridu oil field..

Prediction of mud weight window based on strain energy method

The article describes a new analytical method using strain energy to predict the mud weight window (MWW) to safely use in oil well drilling design and operations. Derivation of MWW equation using strain energy, in both pre- and post-drilling states, is crucial to wellbore stability analysis and design. Thus at first, the determination of internal stored strain energy for two; pre- and post-drilling states have been formulated. Then, these formulas, based on strain energy balance, have been employed to wellbore wall. Accordingly, a method to determine the MWW has been developed and proposed. To evaluate the credibility of the present developed method for MWW determination, the result has been compared with the actual drilling mud pressure that was used in the field. Then, the results of this method has been compared with the existing MWW determination methods, which are based on failure criteria. The results of comparative analyses, have shown very good accord with both cases. Finally, it has been shown that when the pore pressure and horizontal in situ stresses’ difference is insignificant, the width of mud window becomes narrow. On the contrary, when the difference between pore pressure and horizontal stresses is significant, the width of the mud window becomes wider. In the latter case, the well remains stable in a wider range of mud pressure.

Determination of the mud weight window and optimum drilling route, using the comparison of different failure criteria: a case study

Determination of the mud weight window and optimum drilling route, using the comparison of different failure criteria: a case study

1D Geomechanical Model For Wellbore Stability in Z Field, Y Well Sanga Sanga Working Area, Kutai Basin

This research is about 1D geomechanical model for wellbore stability in Z Field, Y Well Sanga Sanga Working Area, Kutai Basin where wells have been drilled. The Purpose of this Research is to analyze the stability of the well starting from knowing the stress regime that occurs, predicting the occurrence of wellbore failure, and determining safe mud weight window for next drilling. The method use in this Research is a numerical modelling method using log data and drilling data that has been obtained and then managed using Techlog Software. The result of this Research show the magnitude of mechanical properties of the rock that have been obtained, then in general the stress regime that occurs in the Z Field formation is the normal regime even though the strike slip and reverse regime are inserted at a certain depth, then based on the prediction results of failure in this well is wide breakout, which in general occurs in lithology with sandstone, finaly safe mud weight window can be estimated properly, so that it can be used for further well drilling. This research is about 1D geomechanical model for wellbore stability in Z Field, Y Well Sanga Sanga Working Area, Kutai Basin where wells have been drilled. The Purpose of this Research is to analyze the stability of the well starting from knowing the value of the mechanical properties of the formation, the stress regime that occurs, predicting the occurrence of wellbore failure, and determining safe mud weight window for next drilling. The method use in this Research is a numerical modelling method using log data and drilling data that has been obtained and then managed using Techlog Software. The result of this Research show the magnitude of mechanical properties of the rock that have been obtained, then in general the stress regime that occurs in the Z Field formation is the normal regime even though the strike slip and reverse regime are inserted at a certain depth, then based on the prediction results of failure in this well is wide breakout, which in general occurs in lithology with sandstone, finaly safe mud weight window can be estimated properly, so that it can be used for further well drilling.

Wellbore stability analysis and selecting safe mud weight window for Mishrif reservoir in Southern Iraq

Wellbore stability analysis and selecting safe mud weight window for Mishrif reservoir in Southern Iraq

Combined Mud-Cooling, MPD Techniques Enable HP/HT Drilling in Egypt

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210252, “Drilling the Deepest HP/HT Onshore Exploration Well Using a Combination of Mud-Cooling and MPD Techniques: A Field Case Study From the Nile Delta of Egypt Targeting a Mesozoic Carbonate Platform,” by Mahmoud El-Husseiny, Egyptian Natural Gas Holding Company, and Taher Elfakharany, Al-Azhar University. The paper has not been peer reviewed. _ The complete paper reviews the successful application of a mud-cooling and managed-pressure-drilling (MPD) system in a high-pressure/high-temperature (HP/HT) well to explore the potential of the Mesozoic carbonate platform with a pressure ramp and narrow mud-weight window (NMWW) in the Nile Delta. The constant bottomhole pressure (CBHP) variation of MPD in combination with mud cooling was used to drill from the middle of the pressure ramp to the target depth, maintaining the mud-inlet temperature at approximately 50°C. Geological Targets and Geohazards The primary objective of Well T-1 is the edge of a Mesozoic carbonate platform. These carbonates are expected to be high-energy shallow marine deposits with fair reservoir properties (20–50% net-to-gross, 5–10% porosity). The secondary objectives are turbiditic sandstone channels of the Oligocene. These sandstones are expected to have 9–20% porosity and 50–300 md permeability. Potential Middle and Late Miocene geohazards include pressure rampup associated with losses, kicks, and borehole degradation, including tight holes, overpull, and caves; and reported sticking and hangup events. The HP domain begins below approximately 4000 m. Potential Oligocene to Paleocene geohazards include NMWWs associated with losses, kicks, and simultaneous gains and losses (ballooning); borehole degradation, including tight holes, overpull, and caves; and sticking and hangup events. The HP and HT domains begin below approximately 4500 m. Potential Mesozoic carbonate geohazards include possible losses of fractured and pressure-regressed carbonates. Mud-Cooling Technique Concept and Equipment The mud cooler consists of two circuits. In the first, hot mud is circulated through a dual mud cooler using a centrifugal pump. Because of heat exchange through the plate heat exchanger, the mud is cooled and transferred back into the active mud system. The discharge of cold mud takes place upstream of the point where the suction of hot mud occurs. In the second circuit, a fluid mixed with water and glycol is circulated between a dual air cooler and the dual mud cooler using a dedicated pump. When passing through the plate heat exchanger, this mixture of water and glycol is evacuated. When this mixture returns to the dual air cooler, it is cooled using high-performance ventilators. The mud-cooling system features 16 ventilators. The efficiency of the mud-cooling system is adjusted with a number of operated ventilators. The mud-cooling units used in this well consist of two dry air coolers and two sets of air fans (Fig. 1), with each set containing 24 fans. A mixture of 10% glycol and water was used as a cooling fluid.

Study Investigates Casing Wear in the Culzean Field

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206221, “Casing Wear: Prediction, Monitoring, Analysis, and Management in the Culzean Field,” by Florian Aichinger, SPE, Loic Brillaud, SPE, and Ben Nobbs, SPE, H&P Technologies, et al. The paper has not been peer reviewed. _ This paper presents predicted vs. measured wear for six wells in the Culzean field, a high-pressure/high-temperature (HP/HT) gas condensate field in the central North Sea. The focus of the complete paper is on the monitoring and analyzing process, particularly how to use offset data to improve accuracy of casing-wear prediction. Field and Well Background Wells in the Culzean field are quite deep, with a measured depth (MD) of 15,000–16,500 ft, and are J-shaped with a slight sail angle (inclination 30–40°). These features result in significant tension loads at the buildup and, potentially, at unplanned curvatures in the vertical section. Combined with possibly high rotating hours, these factors create a considerable risk of high casing wear. Additionally, a challenging pressure regime is present. The steep pressure-transition zone (PTZ) overlying the target reservoir, and the expected predrilled narrow mud-weight window between the pore pressure and formation at the top of the Pentland reservoir of 0.060 ppg, called for a new well-design approach. To address this challenge, the production casing was designed as a 10-in. production liner and a 10¾×10-in. tieback production string. The well design and operations plan required drilling both 12¼- and 8½-in. sections without the 10¾×10-in. tieback production string installed. Consequently, the 14×13⅝-in. intermediate casing could be exposed to higher pressures than usual. Extensive work was performed to enhance casing-wear prediction and to determine the likelihood of failure if a well-control risk materialized. The 12¼-in. section and 10-in. production liner shoe were placed as deeply as possible into the PTZ in the Upper Valhall/Tuxen formation. An appreciable risk was the possibility of a kick while drilling the 12¼-in. section from the Pentland reservoir. The most extreme well-control event the 14×13⅝-in. intermediate casing could experience, however, would have been a well-full-of-gas event while drilling the 8½-in. section. The assessment of the risk associated with such an event was addressed by careful attention to an assessment of casing wear and remaining casing wall thickness and the probability of failure of the 14×13⅝-in. casing, assuming that the casing was worn. The failure-probability assessment of the 14×13⅝-in. intermediate casing was performed using a reliability-based design approach using survival design principles and probability-of-failure estimation. Methodology: Wear Computation and Measurement Analysis of casing wear between a drillstring and the inner surface of casing requires application of an appropriate casing-wear model. A stiff-string model, as used in this work, is advantageous because it can consider pipe clearance, pipe stiffness, and axial and radial casing contact-point location. The simulation uses an adaptable 3D mesh, allowing the calculation of wear in all radial orientations for every chosen MD. The multifinger-caliper-log (MFCL) interpretation methodology uses inner-diameter measurements to calculate an ellipse that best fits the casing shape. The methodology does not require a base log and increases accuracy compared with the traditional method of comparing the maximum inner diameter of MFCL logs taken before and after drilling. The methodology also can be applied to sonic logs as a second information source apart from the direct wall-thickness measurement if the latter is not available. A detailed overview of this process is included in the complete paper.

Integrated Analysis of the 3D Geostress and 1D Geomechanics of an Exploration Well in a New Gas Field

The aim of this study was to propose the workflow for integrated analysis of the 3D geostress and 1D geomechanics of an exploration in a new gas field. This integrated analysis will allow for problems associated with the inaccuracy of 1D geomechanical analysis to be overcome in a region with obvious anticline/syncline structures. The 1D geomechanical analysis of the well in the exploration of a new gas field mainly included the prediction of pore pressure and calculation of the mud weight window for safe drilling. In general, this integrated workflow included both a method for pore pressure prediction and a method for the calculation of the mud weight window, with the numerical solution of 3D geostress plus the interval velocity of formations. The procedure for the calculation of the 3D geostress of a target block was also introduced. Numerical solution of the 3D geostress of the target gas field, as well as solutions of 1D geomechanical analysis, have demonstrated the efficiency and practical use of the proposed theory in the successful drilling of the LT-1 well in the Junggar Basin, Xinjiang, China. For this LT-1 well in the target TS block, there was no logging data to refer to when predicting the pore pressure of undrilled formations. Only 3D geostress could be used to calculate the mud weight window. Influences of anticline structures were considered in the calculation of 3D geostress. Since the accuracy of the numerical solution of 3D geostress is higher than the accuracy of the 1D geostress solution for a single well analysis, the results of pore pressure and the mud weight window are more accurate than those obtained with conventional 1D geostress analysis. Details of the finite element modeling of the 3D geostress field of the TS block is presented along with the solution of the 3D geostress field. With the data of the interval velocity of formations and 3D geostress solution of the TS block, pore pressure prediction was carried out for the 7000 m-deep pilot LT-1 well. Finally, calculations were performed for the values of the mud weight window of the LT-1 well.

3D Geomechanical Model Construction for Wellbore Stability Analysis in Algerian Southeastern Petroleum Field

The main objective of this research work was the wellbore stability evaluation of oil and gas wells based on a 3D geomechanical model, which as constructed using seismic inversion in a southeastern Algerian petroleum field. The seismic inversion model was obtained by using an iterative method and Aki and Richards approximation. Since the correlation between the inversion model and the log data was high at the wells, the reservoir was efficiently characterized and its lithology carefully discriminated in order to build a reliable 3D geomechanical model. The latter was further used to suggest the drilling mud weight window for the ongoing wells (well 5) and to examine the stability of four previously drilled wells. The main contribution of this study is providing a 3D geomechanical model that allows the optimization of drilling mud weight parameters so that a wellbore’s stability is guaranteed, on the one hand, and, on the other hand, so that the reservoir damage brought about by excessive surfactant use can be prevented. Indeed, the mud parameters are not just important for the drilling process’s effectiveness but also for logging operations. Since the tools have limited investigation diameters, with excessive use of surfactant, the invaded zone can become larger than the tools’ investigation diameter, which makes their logs unreliable. Hence, the 3D geomechanical model presented here is highly recommendable for the proposition of new wells, entailing less exploration uncertainty and more controllable productivity.

Comprehensive Wellbore Instability Management by Determination of Safe Mud Weight Windows Using Mechanical Earth Model, Meleiha Field, Western Desert, Egypt

Comprehensive Wellbore Instability Management by Determination of Safe Mud Weight Windows Using Mechanical Earth Model, Meleiha Field, Western Desert, Egypt

Stress solutions for short- and long-term wellbore stability analysis

Numerous models have been proposed to address the time-delayed wellbore collapses or untimely mud losses that have been widely reported in the field. There is still reluctance in applying them in real-time field operations due to their complex mathematical appearance. In this technical note, we address the effective stress solutions for short- and long-term wellbore stability analysis. We present the poroelastic, porothermoelastic, and porochemoelastic wellbore effective stress solutions at t→0+ and t→∞. The concise expressions of these solutions are simple to implement into computational codes for the ease of engineering field data interpretation. We also improve a generic algorithm for calculating mud weight windows. Application of the asymptotic solutions and the algorithm in an example with a random set of data indicates that the long-term collapse and fracturing mud weights can be 32.5% higher and 25.6% lower than the short-term ones, respectively. Conventional time-independent elastic models cannot capture these behaviors.

INCORPORATING TOOL JOINT INFLUENCE ON MODEL FOR EQUIVALENT CIRCULATION DENSITY ESTIMATION IN HORIZONTAL WELL DRILLING

Modern drilling techniques involving horizontal well (HW) drilling for production of petroleum verify that the well is adequately planned prior to commencement of drilling or completion, especially in drilling of deep and ultra-deep water wells. Because of more rigorous and complex well geometries, planning ensures that drilling or/and completion engineers reach target depths in their respective operations. Equivalent circulation density (ECD) is one of the parameters that is monitored and controlled during well planning and drilling of wells. ECD, when properly managed, leads to successful drilling especially when working in areas of narrow mud-weight window. Poor management of ECD could result in severe problems during drilling such as loss of circulation and kicks. Mud column hydrostatic head and annular frictional pressure loss (AFPL) govern ECD. As such, several factors influence ECD viz: drill string (DS), well geometry, rheology of drilling fluid, and flow rates. Several literature studies have focused on fluid flow through annuli and pipes for AFPL computations. However, tool joint (TJ) effect in the estimation of pressure loss (PL) in annulus is either ignored or underestimated in several cases. The overall contribution of TJs effect on ECD is of great importance. In this paper, TJ effect on AFPL has been evaluated. Dimensional analysis and theoretical methods were utilized for model development that incorporates TJs effect for AFPL computation and, consequently, ECD prediction. AKUBU X12 well, a HW with measured depth (MD) of 11070ft from Niger delta was utilized as a case study. Mud of 8.6 ppg was utilized for the study with model simulation carried out using Matlab software (by Mathworks Inc.-version R2014B). Results show that as the rate of flow increases, TJs presence creates strong hydraulic resistance, which increases localized AFPL and ECD. Also, as the depth and rate of flow increases, the AFPL also increases, leading to an increase in ECD. Pipe rotation affects PL. Such increase in pipe rotation causes PL to either decrease or increase depending on shear thinning as well as inertial effect. Thus, for accurate prediction of ECD and wellbore pressure, TJ effects should be considered.