Underbalanced Drilling Research Articles

Sealing performance and failure mechanism analysis of packing unit used in rotary blowout preventer for under-balanced drilling

The packing unit is the key part of a rotating blowout preventer (RBOP) and its sealing performance affects the operation of under-balanced drilling, but sealing failure often happens. This paper studies the influence of various parameters on its sealing performance and discusses the packing unit's failure mechanism. Firstly, the Yeoh constitutive model is chosen through a group of tensile tests of the packing unit material. Then, the finite element model of the packing unit is established, and the influence of well pressure, tripping and drilling speed, friction coefficient and five structural parameters on the contact stress between the packing unit and drill pipe are discussed. Finally, the failure mechanism of the packing unit is analyzed, and the structural parameters of the packing unit are optimized. The results show that during the tripping process, the contact stress is the largest when the drill pipe joint passes through the packing unit, and the contact stress of the packing unit increases with the increase of well pressure and friction coefficient. The tearing at the top of the packing unit is caused by shear stress. The failure mechanism of the packing unit at the inner angle is divided into two types, one is that excessive contact stress causes the tongue piece to fall off, the other is that alternating von Mises stress and shear stress cause lumpy to fall off. Alternating von Mises stress and CSHEAR 2 (Transverse friction shear stress) causes tearing at the inner lower angle. The drill pipe eccentricity causes the Y-shaped cracks at the side of the packing unit. The optimized parameters of the packing unit are as follows: The tripping and drilling speed is 0.15 m/s, the inner diameter of the primary sealing section is 107 mm, the outer angle is 154°, the inner angle is 150°, the inner lower angle is 135°, and the length of the primary sealing section is 107 mm. In this paper, the failure mechanism and various influencing factors of the packing unit were analyzed, and the reliability of the finite element model was verified, which has reference value for failure analysis and structural design of the packing unit.

Sensitivity Analysis of the Parameters Affecting Bottom-hole Pressure during Foam Underbalanced Drilling

With many advantages of protecting reservoir, increasing drilling speed and high capacity in carrying cuttings, foam drilling is suitable for drilling through the aquifer and natural fractured formation, and has been developed fast since 1990s. However, the change of the foam physical properties along wellbore, and the flowing state of the foam in the annulus is complex. Therefore, it is difficult to optimize the design of hydraulic parameters for foam drilling. In order to solve this problem, the mathematical model for foam-cutting flowing in annulus has been developed. In addition, the sensitivity analysis has been conducted about the factors affecting the parameters of foam drilling and the characteristics of foam flowing. The analyzing results can provide the foundation for designing the hydraulic parameters of foam drilling.

Effects of Annulus Geometry and Liquid Properties on the Well Conditions during UBD Operation

Well conditions during drilling operation can be predicted using numerical simulation. During under-balanced drilling (UBD) operation, controlling the bottom-hole pressure (BHP) in a suitable range and also appropriate hole-cleaning is essential. In this paper, numerical simulation of gas-liquid-solid three-phase flow in the annulus is used to study the effects of annulus geometry and also liquid properties on the BHP and hole-cleaning during UBD operation. To validate the numerical simulation, the results are compared with the experimental data from a laboratory study. Also, the gain results from developed code are compared with the actual field data from a real well, several mechanistic models from WellFlo software, and gas- liquid two- fluid numerical simulation. Due to the significance of controlling the BHP and hole-cleaning during UBD operation, the effects of annulus geometry and liquid phase properties on BHP and the solid volume fraction distribution are investigated. According to the results, changing the hydraulic diameter and cross-sectional area of the annulus can affect BHP and hole- cleaning in UBD operation. In other words, increasing the hydraulic diameter at a constant cross- sectional area improves hole-cleaning and decrease BHP. Also, decreasing the cross-sectional area at a constant hydraulic diameter improves hole-cleaning and increase BHP. The results show that the liquid viscosity affects hole-cleaning through two contrary mechanisms. In fact, by increasing the liquid viscosity, carrying capacity of the liquid phase is increased and cutting transfer velocity is decreased.

The performance optimization of the stripper rubber for the rotating blowout preventer based on experiments and simulation

The rotating blowout preventer (RBOP) is an essential safety-ensuring equipment in underbalanced drilling. RBOP is vulnerable to fatigue failure resulted from being subject to a cyclic alternating load during pressure drilling. To enhance the lifespan of RBOP, this paper used a finite element simulation combined with experiments to realize a structural optimization of RBOP. The results showed that the optimal thickness of the iron frame for the stripper rubber is 34 mm, the optimal radius of the fillet is 12 mm, and the optimal inner diameters for the stripper rubber that seals 2–3/8″, 2–7/8″, 3–1/2″, 4″, 4–1/2″, and 5″ drill pipes are respectively 48 mm, 58 mm, 75 mm, 87 mm, 95 mm, and 100 mm. The optimized RBOP was examined in a test center and demonstrated a lifespan that was 2.18 times the national standard. When it was deployed in the drilling site, its lifespan was 2.8 times that before optimization. The improvement in the performance and lifespan of RBOP is very meaningful for ensuring security in the drilling site and lowering drilling cost for oil production. • Constitutive model of the rubber matrix is described. • A dynamic finite element model for stripper rubber is established. • The dynamic sealing process of stripper rubber is simulated. • The structure of the stripper rubber for failed parts was optimized. • The optimized stripper rubber was verified in the indoor and oilfield test.

Application of artificial intelligence in predicting the dynamics of bottom hole pressure for under-balanced drilling: Extra tree compared with feed forward neural network model

This study used six fields data alongside correlation heat map to evaluate the field parameters that affect the accuracy of bottom hole pressure (BHP) estimation. The six oil field data were acquired using measurement while drilling device to collect surface measurements of the downhole pressure data while drilling. For the two case studies, measured field data of the wellbore filled with gasified mud system was utilized, and the wellbores were drilled using rotary jointed drill strings. Extremely Randomized Tree and feed forward neural network algorithms were used to develop models that can predict with high accuracy, BHP from measured field data. For modeling purpose, an extensive data from six fields was used, and the proposed model was further validated with two data from two new fields. The gathered data encompasses a variety of well data, general information/data, depths, hole size, and depths. The developed model was compared with data obtained from two new fields based on its capability, stability and accuracy. The result and model’s performance from the error analysis revealed that the two proposed Extra Tree and Feed Forward models replicate the bottom hole pressure data with R2 greater than 0.9. The high values of R2 for the two models suggest the relative reliability of the modelling techniques. The magnitudes of mean squared error and mean absolute percentage error for the predicted BHPs from both models range from 0.33 to 0.34 and 2.02%–2.14%, for the Extra tree model and 0.40–0.41 and 3.90%–3.99% for Feed Forward model respectively; the least errors were recorded for the Extra Tree model. Also, the mean absolute error of the Extra Tree model for both fields (9.13–10.39 psi) are lower than that of the Feed Forward model (10.98–11 psi), thus showing the higher precision of the Extra Tree model relative to the Feed Forward model. Literature has shown that underbalanced operation does not guarantee the improvement of horizontal well’s extension ability, because it mainly depends on the relationship between the bottomhole pressure and its corresponding critical point. Thus, the application of this study proposed models for predicting bottomhole pressure trends.

Modeling research on the extreme hydraulic extension length of horizontal well: impact of formation properties, drilling bit and cutting parameters

Horizontal well can increase well productivity and improve the economic benefit, which significantly promotes the development of shale gas, tight oil and heavy oil. Moreover, it plays an important role in the development of natural gas hydrate. Horizontal extension ability is one of the key indexes of horizontal well, but it is always impacted by formation properties and well structure. Therefore, a model is established to analyze the impact of formation properties and well structure as comprehensive as possible, which considers not only traditional influencing factors, like formation pressure and drilling bit parameters, but also other key factors, including cutting particle size, wellbore diameter and cross section. Based on the analysis, some advises are proposed for field application. The analysis indicates that horizontal well has stronger extension ability in the formation with low formation pressure and high fracture pressure, but it is still limited by pump pressure. Under-balanced drilling can strength the extension ability in high formation pressure by reducing drilling mud density. The natural fractures in formation should be noted when drilling long horizontal well. The extension length increases and then decreases with the cutting particle size, so cutting particle has optimal size for the horizontal extension length, which can be adjusted by the rate of penetration and rotation speed. The extension length increases first and then decreases with the gap between drilling string and hole. Considering the demand of rock breaking and cutting sweeping around drilling bit, it is not recommended to adjust the drilling bit parameters. Both the cutting bed height and drilling string eccentricity have impact on horizontal extension length by changing minimum cutting-carry pump rate and annular pressure drop. Under different combinations of above two parameters, minimum cutting-carry pump rate and horizontal extension length are determined by different factors and can be divided into three parts, including acceptable cutting bed height, cutting lifting efficiency, pump pressure and total circulation pressure loss and well bottom pressure and formation fracture pressure. The findings of this study can help for better understanding of horizontal well hydraulic extension length and optimization method.

A novel artificial intelligence automatic detection framework to increase reliability of PLT gas bubble sensing

Production logging tools (PLTs) and formation testing, even in logging while drilling (LWD) conditions during underbalanced drilling, are key technologies for assessing the productivity potential of a gas well and therefore to maximize recovery. Gas bubble detection sensors are key components in determining the fluid phases in the reservoir and accurately quantify recoverable reserves, optimize well placement, geosteering and to qualify the production ability of the well. We present here a new nonlinear autoregressive - breakdown artificial intelligence (AI) detection framework for PLT gas bubble detection sensors that categorize in real-time whether and which sensors become unreliable or have broken down during the logging measurements. AI tools allow the automatization of this method that is critical during data quality control of post-drilling PLT, but it is essential when the measurements are performed in LWD as data assessment and processing need to occur in real-time. This AI framework was validated on both a training and testing dataset, and exhibited strong classification performance. This method enables accurate real-time breakdown detection for gas bubble detection sensors.

A numerical method for potential implementation of underbalanced drilling in high pore pressure reservoirs

A numerical method for potential implementation of underbalanced drilling in high pore pressure reservoirs

Flow Characteristics of UBD Applied to Gas Reservoirs

Underbalanced drilling technology implemented in high pressure and low permeability gas reservoirs can better protect gas formation from drilling fluid damage, and can improve the drilling speed, but gas invade into the wellhole from the formation by the underbalanced pressure will make the borehole flow presented two-phase flow state. The gas phase compactness and slippage effect will increase the drilling of well control difficulty. In order to ensure the invaded gas is not appear violent slippage and rapid inflation, study the two-phase flow law is necessary to determine the size of the applied well backpressure, applying process of gas distribution law in borehole, and the bottom hole pressure, for the reasonable design of drilling fluid density, well backpressure design and the equipment selection. This paper applies the numerical difference method to two-phase flow one-dimensional equations were solved. Combined with an example of drilling, the gas void fraction distribution, migration and bottom-hole pressure change law is given, which provides theoretical basis for low permeability gas reservoirs in underbalanced pressure drilling borehole designing.

Designing Liquid-Gas Rate Window of Aerated Drilling Using Guo-Ghalambor Method

Loss circulation is a common problem in geothermal drilling due to naturally fractured formation and depleted reservoir pressure. This problem might lead to another problem such as a stuck pipe. In some cases, LCM is not effective in curing loss in a naturally fractured formation and cannot be used to cure loss circulation in the production zone. One of the methods that can be used to prevent loss circulation and also preventing reservoir damage in geothermal drilling is underbalanced drilling or aerated drilling. In an underbalanced or aerated drilling operation, the ratio of air injection rate ad liquid rate is critical to ensure the cutting carrying capacity while preventing hole problems. Usually, computer simulations are used to determine the safe gas-liquid rate limit due to the complexity of the multiphase flow in an underbalanced drilling system. Since the simulation software is not always available, a simpler and reliable method is needed to determine the gas-liquid rate limit in aerated drilling. the purpose of this paper is to design the operating window of the gas-liquid rate ratio in aerated drilling. the purpose of this paper is to design the operating window of gas-liquid rate ratio in aerated drilling using a simple yet reliable method such as the Guo-Ghalambor Liquid-Gas Rate Window method. The result of this research is a gas-liquid rate envelope that can be used to promote good cutting transport, preventing formation and borehole damaged while preventing loss circulation in geothermal well.

Geomechanical modeling using the depth-of-damage approach to achieve successful underbalanced drilling in the Gulf of Suez rift basin

Typical oil and gas reservoirs producing in the Gulf of Suez are now extensively depleted in terms of recovery of conventional resources and display declining production levels and heterogeneous pore pressure regimes. To continue production on a commercially viable basis and enhance the recovery of remaining oil and gas from the mature reservoirs currently in production, drilling decision-makers can no longer rely on traditional balanced or overbalanced drilling methods. Hence, underbalanced drilling is an essential requirement for such reservoirs. However, inducing underbalanced conditions increases the risk of the borehole instability. In the studied area, three previous wellbore stability studies were performed associated with the Hilal-X platform wells using the breakout-width-failure concept. Nevertheless, several wellbore instability issues were recorded there due to that method determining a mud-weight window that was too conservative. New wellbore stability analysis has been performed using a depth-of-damage approach. This analysis has helped to deliver excellent results during underbalanced drilling, after many attempts in previously drilled wells in overbalanced conditions that resulted in borehole instability and/or formation damage. This study documents how successful underbalanced drilling has been achieved in this basin for the first time by mud weights being guided by depth-of-damage analysis, highlight the requirements of that method using a case study for a specific well. In-situ stresses and an 1D-geomechanical earth model were generated using well log data from offset wells. The modified Lade method was used as a failure criterion, while the depth-of-damage approach was used for wellbore stability analysis in Hilal-X4 well. The study reveals that: 1) the Hilal field reservoirs have variable pore pressure regimes, 2) the breakout-width-failure concept provides misleading results in the studied reservoir formation, 3) the depth-of-damage approach reflects reservoir conditions more effectively and allows for successful underbalanced drilling without any instability events, 4) a new casing design for the Hilal Field wells has led to enhanced production performance, and 5) underbalanced drilling, when downhole pressures are carefully managed, is a safe and reliable technique for the mature fields of the Gulf of Suez rift basin.

The Effect of Well Completion Fluid Loss on Productivity Evaluation in Tight Sand Gas Reservoir: A Case Study from East China Sea Gas Well

Fluid loss is inevitable in the well drilling and completion, which may cause series of formation damage such as clay swelling, solid plugging and water blocking. In tight sand gas reservoir, water blocking has become the major damage factor for economical developing. In deliverability test, water blocking will bring an inaccurate productivity test result to affect the following development strategy. With the development of East China Sea gas field, well drilling is focusing on the deeper tight sand formation. The tiny pore throat and high capillary pressure can bring out serious water blocking damage during well drilling and completion. The damaged zone can mislead the resource assessment and productivity evaluation. In this paper, an exploration well X in East China Sea gas field is selected as the research target to investigate the water blocking mechanism and physical process during well drilling and completion process. This study compares the productivity performance of X well with fluid loss and no fluid loss models through numerical modeling approach based on the actual data. Sensitive studies are also performed in the simulation. Results show that the excessive fluid invasion pressure and lower matrix permeability will result in serious water blocking damage to mislead the resource assessment and productivity evaluation even in underbalanced well drilling. Interestingly, extending shut-in time can make the gas production rate quickly reach the peak value in the early production stage, while it can decrease the cumulative gas production in whole production process. This study can provide an avenue to initiate quantitative analysis on resource assessment, and gas productivity evaluation strategy after water invasion during the well drilling and completion in tight sand gas reservoir of East China Sea.

Evaluation of Aerated Drilling in K-01 Geothermal Well using Guo Ghalambor’s Gas-Liquid Rate Window

Common problem in geothermal drilling is loss circulation problem. One of the common methods to cure loss circulation problem is using Lost Circulation Materials (LCM), but in the production zone, using LCM can damage the production zone. Therefore, underbalanced drilling is method that can be used to prevent loss circulation problems in production zone in geothermal well. One of the most common underbalanced drilling methods is aerated drilling or foam drilling. Aerated drilling was used to overcome the loss of circulation problem in production zone in K-01 Geothermal Well. Even though, the aerated drilling was already used, but the loss circulation problem was still occurred. The purpose of this research is to evaluate aerated drilling operation in K-01 Well using Guo Ghalambor’s Gas-Liquid Rate Window and make recommended gas-liquid rate for the next drilling operation. Gas-Liquid Rate Window is constructed using characteristic of the formation, drilling parameters, daily drilling report and also fluid injection characteristics that was used for aerated drilling operation in K-01 geothermal well. Using the constructed Gas-Liquid Rate Window, an evaluation is carried out for the drilling operation in K-01 geothermal well. The gas-liquid rate parameters used in aerated drilling operations is evaluated while checking the loss circulation event from the mud logging data. After the evaluation of the aerated drilling is carried out in then a suggestion is made for the next drilling operation. Based on the evaluation, the combination of gas-liquid rates that was used on the 9.875"hole section in K-01 Well was in the outside of the constructed GLRW therefore loss circulation problem occurred. The recommended gas-liquid rate combination from this research can be used to determine the gas-liquid rate combination to prevent loss circulation problems, wellbore damage and cutting transport problems.

Fatigue life optimization towards rubber core sealing surface of under-balanced drilling rotating blowout preventer

In the process of under-balanced drilling, the rubber core of rotating blowout preventer (RBOP) subject to the alternating cycle load was prone to fatigue failure. Firstly, the sealing principle of RBOP was analyzed and the stress of rubber core in dynamic sealing process was obtained. Then, the Yeoh constitutive model in the deformation process was established by the tensile test of the rubber core material. Then we used ABAQUS software to establish the finite element model of the dynamic sealing of the rubber core, and the simulation of the sealing process of the rubber core during the drilling and tripping operations and the optimization analysis of the factors affecting the fatigue life of the sealing surface of the rubber core were carried out. In this paper, the structure of the rubber core was optimized, and the optimal outer angle of the rubber core was 155°, the inner angle was 153°, and the base angle was 125°. Then the inner diameter size of rubber core that was matched with different outer diameter drill pipes was optimized and the best combination of rubber core was obtained. The paper also optimized the lowering and lifting speed of drill pipe under different wellhead pressures. The higher the well pressure, the more likely the rubber core fatigue failure would be. The safe lowering and lifting speed of drill pipe under different pressures was obtained. At last, according to the Chinese standard, indoor seal test and field application test were carried out in the Well Control Equipment Quality Supervision and Inspection Center of China national petroleum industry to confirm the reliability of finite element optimization, which was of great practical significance to improve the service life of rubber core and oilfield operation safety.

Workflow for Sensitivity Analysis and Decision Making on the Lower Limit of the Mud-Weight Window in an Overpressured Formation

Summary When drilling a well, it is important to choose a reasonable mud density to ensure safe operations. This is not a trivial task because a balanced mud-weight has a complex relation to the uncertain formation conditions and properties. This paper presents a method for conducting sensitivity analysis (SA) over the uncertainties involved in the mud-weight window (MWW) assessment, to learn the most important input parameters for the mud density. The uncertainties in the parameters are taken into account using predrill realizations of the formation conditions (vertical stress, minimum horizontal stress, pore pressure, and temperature) and properties (unconfined compressive strength, tensile strength, friction angle, and porosity). The limit pressures of the MWW are computed to avoid shear and tensile failure. The software used to study well stability returns a mud window that could enable underbalanced drilling while still avoiding borehole collapse; this is emphasized by equating the lower stability limit with shear failure and not pore pressure. However, drilling below the pore-pressure limit entails risks with regard to kicks or blowouts. The Mohr-Coulomb failure criterion is used, but other possible shear failure criteria are discussed as well. The output from the SA is used to evaluate how the possibility of gathering more information about the most relevant parameters can improve our knowledge about the appropriate mud density. This is done in the form of value of information (VOI) analysis, coupling the uncertain variables with drilling decisions in a tradeoff between costs and risks. The interest is on deciding what information to acquire when, at a given depth, the drilling operator must decide on whether to keep drilling or set casing. Additional well data are valuable when they can materialize in improved decision making. The case study presented is from an overpressured shale layer in a field in the North Sea. The focus is on the lower allowed well pressure of the mud-weight window for a vertical well, exploring the possibility of underbalanced drilling. The SA shows that the most important uncertainties in this case are pore pressure, unconfined compressive strength, and minimum horizontal stress. The most valuable information-gathering strategy is to observe these main three parameters, which is worth USD 386,980 when acquisition costs are subtracted. The VOI analysis further indicates that data about the rock's unconfined compressive strength are the most valuable in this case, and if the decision maker can afford to acquire only one data type, this should be chosen. Although these results are case specific, we believe that a similar workflow could be useful in other drilling situations.

Managing Pressure To Mitigate Environmental Impact

Managed-pressure drilling (MPD) as the simple but effective principle that by managing downhole pressures, critical performance indicators such as risk, safety, efficiency, and cost are also controlled. As the energy world works to balance supply, demand, and the environment, efficient solutions such as MPD can help drive the promise of a compatible relationship. Globally, MPD is increasingly seen as an option to move drilling toward a “green” future. Beyond putting in place an adaptive drilling process to precisely control the annular-pressure profile throughout the well, MPD has consistently shown it can support green credentials for the wells where the application is utilized. This article discusses real-world examples of the less often considered but valuable environmental benefits delivered via MPD which include the following. Lowering the risk of spillage and blowouts Reducing mud chemicals; increasing use of simpler drilling fluids Optimizing drilling operations by reducing nonproductive time (NPT) from geopressure-related events and enabling a reduction of drilling carbon footprint through earlier achievement of well objectives Consuming fewer materials (casing, etc.) through streamlined well architecture These MPD benefits are well documented in the technical literature of the industry. In fact, a basic search for the exact phrase “managed pressure drilling” in OnePetro, the online library of technical literature for the oil and gas industry, shows 1,775 results. A majority of these papers was written in the past 10 years with each year averaging more than 100 technical papers and the average over the past 5 years increasing to 150 papers per year. The numbers tell the story of the growing technical interest in MPD technology which has been sustained even through the recent economic downturns. A further search of these MPD papers shows that 1,117 (63%) papers mention “safety,” 849 (48%) mention “efficiency,” and 47 (3%) specifically mention “environmental impact.” With the recent interest in green and environmentally friendly technologies, there is a need to highlight that the safety and efficiency benefits MPD applications already provide are also reducing environmental impact. Generally speaking, choosing MPD vs. conventional drilling methods is a step toward carbon neutrality. The following case studies showcase the improvements MPD has provided in land, shallow-water, and deepwater applications as seen from the perspective of environmental-impact mitigation. Mitigating Environmental Impact For land rigs, particularly in the US, where the majority have for decades now constantly deployed rotating control devices (RCD) that enable operations involving MPD and underbalanced drilling (UBD) methods, RCD technologies have consistently proven to reduce the risk of spillage and blowouts. Studies have shown that the use of a fit-for-purpose RCD has been statistically proven to “reduce the risk of a well-control event when drilling with an essentially incompressible fluid and not inviting the well to flow in the process,” underscoring the safety and environmental benefits of MPD in terms of minimizing unintentional hydrocarbon release.

Internet of underground things‐assisted performance evaluation for underbalanced drilling telemetry systems

AbstractThis paper presents recent developments with an emphasis on communication technologies, problems with networks, and localization techniques on the Internet of Underground Things (IoUT). Presently, Underground (sensors), communications and network protocols are enabled to allow IoUT validation in an effective way. A new IoUT model is designed to detect and incorporate communications between various industries, such as oil and gas, forestry, earthquake mapping, and the underground boundary protection. Such applications require data collection from the underground resources deployed. While, the challenging underground climate, including sand, rock and water drainages, does not allow a single system of communication. Hence, a new advanced distance‐based approach and Channel Modeling have been developed for performance analysis and the ideal selection of the drilling telemetry system has been potentially analyzed for the development of an extended reservoir region. The predictive value of research is to build a structured and user‐friendly framework for assessing telecommunications efficiency and supporting the decision optimization process. The proposed system has been validated and used for an adequate range of telemetry techniques in under‐balanced drilling operations on a developed reservoir. Expert evaluations show the results and needs of telemetry systems achieve better results.

An improved hydraulics model for aerated fluid underbalanced drilling in vertical wells

Abstract Inability to accurately model fundamental governing flow equation in a hole has resulted in erotic evaluation of flowing and shut-in bottom hole pressures (BHPs) for aerated fluid drilling in borehole. It is of practical important to derive an exact model for this case without ignoring any pressure resisting terms in the governing thermodynamic equation so as to enhance well control efficiently. An improved hydraulics model has been derived to demonstrate the impact of neglected pressure restriction due to kinetic energy and fluid accumulation in the fundamental energy equation used for predicting flowing and shut-in bottom-hole pressures for aerated mud drilling in petroleum well. These neglected terms have conceived to be a vital reason for the eroneous result between computed value from the existing models and actual value generated from field. The developed model has been tested using the same dataset obtained from the field of investigation by Guo et al and more desirable outcomes were got from the new model than the previous investigators with error margin of 2.7%. Realistic results that evident all pressure transverse behaviors after shut-in for aerated mud drilling in well which include the initial constant pressure regime, unsteady regime, semi-steady regime and stabilized state condition hence pressure transverse at any period of drilling operation has been established. The improved model has demonstrated that inaccuracy in the results of existing models were not only caused by the effect of pressure restriction due to friction as opined by Guo et al but may have due to oversight of all pressure restriction terms in the fundamental equation that govern flow of aerated drilling fluid in petroleum well. The new concept is useful for drilling engineers to estimate flowing and shut in bottom-hole pressure for better control of well stability at all flow conditions during aerated mud underbalanced drilling.

Development of a green multifunctional additive for applications in water-based drilling fluids

Dynamism associated with drilling conditions such as during well completion may necessitate switching between overbalanced drilling and underbalanced drilling in the same drilling operation. One possible way to easily facilitate this is to use appropriate drilling fluid suitable for any drilling condition. A multifunctional drilling fluid additive gives the opportunity to develop drilling fluids that have the same base composition but different functionality. In this study, a novel additive was developed via alkaline extraction and hydrolysis of date pits components in a freezing-defreezing technique. This additive was tested in a water-based bentonite drilling fluid which was characterized in terms of density and filtration properties. The results showed that the drilling fluids containing this novel additive have low filtration properties attributed to products of complete alkaline hydrolysis of fatty acids and amino acids, and the unreacted alkali. The drilling fluid containing the novel additive when neutralized resulted in another drilling fluid of higher filtration properties and lower density. The potential of the un-neutralized drilling fluid to form a thin filter cake of low permeability makes it a suitable candidate for overbalanced drilling while the synergistic effect of both the low density and high filtration property of the neutralized drilling fluid favours its efficacy for underbalanced drilling. The multifunctionality of this novel additive derives from its potential to be used to develop both the overbalanced drilling fluid and underbalanced drilling fluid.

Real-Time Interpretation Model of Reservoir Characteristics While Underbalanced Drilling Based on UKF

This study presents a novel interpretation model for reservoir characteristics while underbalanced drilling (UBD), by incorporating an unscented Kalman filter (UKF) algorithm in a three-phase variable mass flow model of oil, gas, and liquid. In the model, the measurement parameters are simplified to bottomhole pressure and liquid outlet flow, for decreasing the amount of the computation and time. By taking into account real-time measurements, the permeability and reservoir pressure along the well can be continuously updated. Three cases including single-parameter and double-parameter estimations have been simulated, and the performance is tested against the extended Kalman filter (EKF). The results show that single-parameter estimation of reservoir permeability or pressure achieves superior performance. The filtered values of bottomhole pressure and outlet flow trace the measured values in real time. When a new section of a reservoir is opened, the estimated reservoir permeability or pressure can always be quickly and accurately returned to its true value. However, it is not possible for the double-parameter estimation to obtain good results; its interpretation accuracy is low. UKF is superior to EKF in both estimation accuracy and convergence speed, which further illustrates the superiority and accuracy of the novel interpretation model based on UKF. Benefits from this model are seen in accurate bottomhole pressure and reservoir characteristic predictions, which are of major importance for safety and economic reasons during UBD and follow-up completion operations.