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Aiming at the problems of large load of rotation drive system, low efficiency of torque transmission and high cost for operation and maintenance of liner steering drilling system for the horizontal well, a new method of liner differential rotary drilling with double tubular strings in the horizontal well is proposed. The technical principle of this method is revealed, supporting tools such as the differential rotation transducer, composite rotary steering system and the hanger are designed, and technological process is optimized. A tool face control technique of steering drilling assembly is proposed and the calculation model of extension limit of liner differential rotary drilling with double tubular strings in horizontal well is established. These results show that the liner differential rotary drilling with double tubular strings is equipped with measurement while drilling (MWD) and positive displacement motor (PDM), and directional drilling of horizontal well is realized by adjusting rotary speed of drill pipe to control the tool face of PDM. Based on the engineering case of deep coalbed methane horizontal well in the eastern margin of Ordos Basin, the extension limit of horizontal drilling with double tubular strings is calculated. Compared with the conventional liner drilling method, the liner differential rotary drilling with double tubular strings increases the extension limit value of horizontal well significantly. The research findings provide useful reference for the integrated design and control of liner completion and drilling of horizontal wells. [ABSTRACT FROM AUTHOR]

In order to realize the efficient development of unconventional oil and gas, the measurement accuracy of wellbore spacing in the drilling of parallel horizontal wells is more and more required. Although the Rotating Magnet Ranging System or Magnetic Guidance Tool is used to achieve a good ranging effect in the drilling of dual horizontal wells, the position measurement of the magnetic sub leads to a large ranging error. A new ranging algorithm for the Two Sensor Packages-Rotating Magnet Ranging System is presented in this paper. The algorithm takes the magnetic signal generated by the rotation of the magnetic sub at a fixed position, the tilt measurement data of the two wells, the length of the magnetic sub, and the distance between the two fluxgate sensors as input parameters to avoid measuring the position of the magnetic sub and to reduce the influence of the degree of non-parallelism and the length of the magnetic sub. The simulation and experiment demonstrate that the inclination and azimuth angles of the two wells have a significant impact on the magnetic ranging results when the ranging well sections are not parallel and that the distance between the bottom of the drill bit and the center of the magnetic sub cannot be ignored. Moreover, the accuracy of the relative distance calculated by this new algorithm can reach 97%, and the error of direction calculation is less than 3°. Applying this algorithm in the field can successfully aid in controlling the spacing of cluster horizontal wells more accurately. [ABSTRACT FROM AUTHOR]

Under the uniform parallel well pattern widely used in shale gas cluster well, the directional drilling limits (DDL) can better reflect the productivity of shale gas cluster well than extended-reach limits (ERL). In this paper, the concept of directional drilling limits is proposed to predict the productivity of shale gas cluster well. Around this concept, the forecast model of mechanical directional drilling limits is established by introducing the objective function, geometric constraints, mechanical constraints and operation conditions. A shale gas cluster well developed by Sinopec in Fuling field is analyzed. The mechanical directional drilling limits for different constraints are calculated, and the laws of the directional drilling limits under different operation conditions are analyzed. The results indicate that the cluster well optimized by the established model can drill more horizontal wells than that without optimization. The mechanical directional drilling limits firstly increases and tends to stable with the increases in the holding angles. Besides, running-in is the limit operation in sliding and rotating mode, and high friction coefficient is the fundamental mechanical constraint for directional drilling limits. The constrained optimization model established in this paper can provide a theoretical guidance for shale gas cluster well engineering to improve outputs and avoid drilling hazards. [ABSTRACT FROM AUTHOR]

Abstract Dual-channel drillpipe drilling is an effective way to elongate the horizontal well's horizontal section length. In order to predict the horizontal well's maximum measured depth, a prediction model of extended-reach limit length with dual-channel drillpipe is established in this paper. Extended-reach limit length of horizontal well with dual-channel drillpipe is analyzed. Compared with the previously established extended-reach limit length model with conventional drillpipe, both the formation factor and the drilling pump's hydraulic factors are considered to investigate the horizontal well's extension ability with dual-channel drillpipe. Through this model, the well's extension limit length of horizontal section and extended-reach limit length can be calculated under different constraint conditions. In the paper, an application example is also analyzed for verification. Results show that the extended-reach limit length of horizontal drilling with dual-channel drillpipe is significantly greater than that with conventional drillpipe, which further proves that well's extension ability can be improved by dual-channel drillpipe. Besides, there is a decrease in the well's extended-reach limit length as the drilling fluid density and flow rate are increased. Meanwhile, when the rated pressure of drilling pump is increased, the constraint limitation of the well's extension ability changes from rated pressure to fracture pressure. Furthermore, the extended-reach limit length with dual-channel drillpipe in shales varies along with the anisotropic formation. This study provides guidance to both the shale gas production and the extension limit theory of horizontal well with dual-channel drillpipe in the shale formation. Highlights • A extended-reach limit length with dual-channel drillpipe model is established. • Several constraint conditions are presented to ensure safety and production. • Extended-reach limit results are compared with the results of conventional drillpipe. • The sensitivity analysis of some parameters on horizontal section length is made. • Longer horizontal section length can be achieved by dual-channel drillpipe. [ABSTRACT FROM AUTHOR]

In horizontal well drilling, the success of the drilling operation mainly depends on optimal selection of the drilling trajectory. In this paper-, we propose a method for optimizing horizontal well trajectory design based on the numerical optimization methods PSO (particle swarm optimization) and AHP (analytic hierarchy process). We selected four functions as the parameters which affect the selection of the optimal solution: the shortest length of the well trajectory, the highest target hitting accuracy, the lowest cost of drilling, and the least drilling string friction. The key parameters for a horizontal well (the KOP (kick-off point), BUR (buildup rate), and hold angle) were calculated by ththe PSO method in Matlab. Applying the AHP mathematical tool for a systematic approach to decision-making, we ranked the solutions according to the engineering and design requirements. The new method proposed in this paper lets us overcome the limitations of the optimization algorithm and to recast empirical judgments of experienced analyzers in mathematical language, thus avoiding subjectivity in selecting the best solution. The method was applied to and tested on conditions of the Yanchang field. As shown by the experimental study, the proposed method is a simple and reliable method for selecting the optimal trajectory. [ABSTRACT FROM AUTHOR]

Abstract Safety additional value is always added to the conventional mud weight window (MWW) to ensure the drilling safety in shales. However, the safety additional value is usually an empirical value. Since the horizontal well usually has a long horizontal section in shales, failing to accurately predict the well's MWW and corresponding safety additional value in shales may result in serious drilling hazards. In order to ensure that the horizontal well can reach the designed horizontal-section length in shales, the conventional MWW needs to be modified and the calculated value of safety additional value should also be given. In this paper, considering the effects of horizontal well's extended-reach limit and its horizontal-section limit (HSL) on the well's MWW in shales, the drilling process, tripping process and six constraint conditions are considered simultaneously. Results of the case study indicate that the corresponding safety additional value is calculated instead of using an empirical value. Moreover, the predicted MWW becomes narrower as the designed horizontal-section length is increased. In addition, in order to obtain a wider MWW, tripping velocity should be lower if the economic benefits can be satisfied. Additionally, the drilling pump with higher rated pressure is also necessary. Taking the maximum HSL as the objective function, there exists an optimal drilling fluid density, which is crucial for production in shales. The calculated value of safety additional value and the modified MWW can ensure the horizontal well reach the designed horizontal-section length, obtaining enough production and economic benefits as well as avoiding drilling hazards in shales. Highlights • The calculated value of safety additional value of MWW is given. • The MWW is predicted to reach well's designed horizontal-section length in shales. • Drilling process, tripping processes and six constraint conditions are considered. • There exists the optimal drilling fluid density within MWW. • The safety additional value and MWW can help to avoid drilling hazards in shales. [ABSTRACT FROM AUTHOR]

Mechanical analysis and optimal design of down-hole tubular strings with connectors are the key theoretical bases of design and operation in extended-reach and horizontal drilling and completion. However, the complex mechanical interaction between spring connectors and open wellbores are not fully considered in conventional tubular models and the conventional design methods are mostly based on experience and lack of rigorous mathematical derivations. To overcome these shortcomings, a new revised mechanical model and an optimal design method of connectors on down-hole tubular strings have been built. Firstly, the local loads on a unified connector which can depict common spring and rigid connectors constrained in open wellbores are studied. The local connector loads are further introduced into the local mechanical model of tubular strings. The integral mechanical model of tubular strings is amended by the local model. Next, the integral design model of connectors while considering friction reduction, tubular centricity and cost is built. The integral design model is divided into a series of local design models according to the properties of tubular mechanical behaviors on extended-reach and horizontal wellbores. At last, the mechanical model and design method are applied to drill strings with joints and casing strings with centralizers in horizontal drilling and completion. The results indicate that the revised tubular mechanical model and connector design model are stable and fast. The coupling effects of connector and buckling, local drags on connector and radial compression of spring connectors are all included in the mechanical model, so the new model gives a more sophisticated description of mechanical behaviors of tubular strings with connectors. The design results of anti-drag joints are closely related to the clean condition of wellbores. Proper optimal design of connectors and good clean condition of wellbores can inhibit helical buckling, decrease friction factor and reduce plough effect, leading to larger lateral extending limits. Compared with the initial design results of centralizers, friction force is decreased and casing centricity is increased through optimization design. The optimization results of centralizers are closely related to the weight values of friction reduction, casing centricity and cost. Therefore, the key problem is how to assign these three weight values under actual engineering conditions. [ABSTRACT FROM AUTHOR]

Helical buckling of tubular strings with connectors is divided into two sub-problems: inter-helical buckling and intra-helical buckling. The suspended section of the tubular string is depicted by beam-column model and the continuous contact section is depicted by helix. Further introducing the continuous conditions, boundary conditions and periodic conditions, the deflection curves of tubular strings can be determined. On the basis of energy stability condition, the critical helical buckling loads are deduced by introducing the potential energy factor. The contact forces on contact points and continuous contact sections and maximum bending moments on tubular strings are calculated. The above studied are further applied into a case study. At last, the supporting effect and boundary effect caused by connectors are introduced and the relationship between inter-helical buckling and intra-helical buckling modes is clarified. The results indicate that for connectors of smaller diameters, the supporting effect plays the most important role and inter-helical buckling is easier to initiate. However, for connectors of larger diameters, the constraint effect is dominant and intra-helical buckling is more likely to occur. Increasing connector diameter and decreasing the length between adjacent connectors can increase critical helical buckling loads. Both the contact forces and maximum bending moments in the intra-helical buckling mode are larger than that in the inter-helical buckling mode, so intra-helical buckling should be avoided in the optimal design of connectors on tubular strings. [ABSTRACT FROM AUTHOR]

This paper builds an analytical model to describe the comprehensive buckling behavior of coiled tubing (CT) with initial curvature in a horizontal well. The new buckling equation and contact force considering the effect of initial curvature is built on the basis of beam-column theory. With the new contact force expression, the work done by lateral friction can be obtained, thus the total potential energy of CT with initial curvature can be calculated. By use of the principle of virtual work and energy conservation, the critical sinusoidal and helical buckling load can be obtained. Moreover, the effect of initial curvature on axial load transfer is also calculated by a new axial load equation. The calculation results indicate that initial curvature has a strong influence on buckling loads and a CT with initial curvature is less efficient for axial load transfer compared to a straight CT. To verify the proposed model, the results of this paper are compared to experimental results, which support the proposed solutions. [ABSTRACT FROM AUTHOR]

To optimize sidetracking horizontal well trajectory in cluster wells, a new multi-objective optimization model has been established. The new model synthetically considers the total trajectory length, the well profile energy and the accuracy of target hitting as the objective functions and takes the anti-collision with adjacent well as constraint. A novel heuristic algorithm based on DS is presented to solve the established optimization model, and the constraint is handled by a penalty method using an S-type penalty function. The comparisons between multi-objective optimization and single-objective optimization indicate that multi-objective optimization is more superior in sidetracking well trajectory optimization which can obtain a relatively short total trajectory length, a low well profile energy and an extremely high accuracy of target hitting. Furthermore, the optimization model considering anti-collision can ensure the minimum distance with adjacent well no less than the safety distance which can avoid collision in cluster wells. At last, the convergence and stability of the proposed algorithm have been discussed, and the results indicate that d-DS has good convergence and numerical stability, thus the d-DS algorithm is excellent for solving trajectory optimization problem. [ABSTRACT FROM AUTHOR]

This paper builds an analytical model to describe the comprehensive buckling behavior of CT (coiled tubing) with residual bending in a horizontal well. The new model is built on the basis of beam-column theory and solved by the Galerkin method of weighted residuals. The initial configuration of CT with residual bending are assumed to be in two typical trigonometric shapes, sine mode or cosine mode. By using the new buckling equations, critical buckling force and radial contact force are calculated accounting for the residual bending. Axial compressive displacement and maximum bending moment are also calculated. The calculation results show that a CT with residual bending behaves more easily to buckle than a straight CT, and the maximum contact force of CT with residual bending is larger than that of straight CT. As for the two initial trigonometric shapes, the sinusoidal critical buckling force of these two initial modes is almost the same, but CT with initial cosine mode tends to buckle easier than CT with initial sine mode in helical buckling. To verify the proposed model, the results of this paper are compared to Saliés's experimental results, which support the proposed solutions. The comparison between buckling solutions of CT with residual bending and CT without residual bending show that the effect of residual bending on CT cannot be ignored in buckling analysis. [ABSTRACT FROM AUTHOR]

In drilling technology, adequate control over the distance between adjacent sections of twin parallel horizontal wells has a significant impact on the final recovery rate from unconventional oil and gas resources, such as heavy oil and natural gas hydrates. For this distance to meet design requirements and to reduce the duration of the drilling period, it is necessary to use a rotating magnet ranging system that helps drill an injection well starting from the build-up section. Usually, the build-up sections of the twin parallel horizontal wells are not parallel. Therefore, the spatial relationship between the build-up sections of the two wells can be divided into two types, namely, converging coplanar and non-coplanar. In this paper, we propose a method based on an algorithm for finding extreme values to calculate the radial distance between the build-up sections of the twin parallel horizontal wells. In addition, we propose and discuss a method for calculation of the direction between the magnetic sub and the probe tube in the build-up sections using coordinate transformations combined with the rotating magnet ranging calculation for the horizontal sections of twin parallel horizontal wells. The simulation results indicate that the magnet ranging algorithm for the build-up sections of twin parallel horizontal wells has a precision of a few percent and can meet the actual needs of the drilling site. [ABSTRACT FROM AUTHOR]

Accurate monitoring and determination of the trajectory and relative position are two very important concerns during drilling the connection of two wells to form a U-shaped horizontal well. The composite error circle based on trajectory uncertainty analysis is introduced. The timing of using the magnetic ranging tool is established by comparing the diameter of the composite error circle with that of the ranging scope of the magnetic ranging tool. The profile is designed, and the key extension formula is given according to the characteristics of the magnetic ranging tool. The measurement principle of a Rotating Magnetic Ranging System, which is widely used during the drilling of U-shaped wells, is introduced in order to analyze the relative position uncertainty. Through analysis of the error sources, a covariance matrix of the relative position uncertainty is constructed, and its error ellipsoid and error ellipse are determined. The error ellipse is found to be beneficial in using the magnetic ranging tool during the drilling of U-shaped horizontal wells by comparing the semi-axis of the error ellipse and the radius of the borehole. [ABSTRACT FROM AUTHOR]

The intersection between two horizontal wells is a form of U-shape well. Being efficient, economical, advanced and environmentally friendly, it holds broad application prospects in exploitation of resources and crossing of pipe lines and tunnels under rivers. However, it is very difficult to achieve intersection between two horizontal wells by conventional techniques due to borehole position uncertainty. In order to solve this problem, control technique on navigating path was put forward. It mainly consists of position locating technique, profile design method, trajectory control method and relative position error analysis. Firstly, the measurement of relative position between the bit and the intersection point was carried out by RMRS in closed-loop mode rather than traditional open-loop mode. Then the profile of the intersection between two horizontal wells was designed according to the ranging scope of RMRS, guide process and borehole position uncertainty. After that the trajectory control model in the intersecting process was established on the basis of an analogy between the intersection of the two horizontal wells and the plane landing process. Finally, the relative position error analysis was carried out according to the guide process of RMRS. The development of control technique on navigating path make it more feasible to achieve intersection between two horizontal wells, which will have a great reference value for in-depth study and field application in the future. [ABSTRACT FROM AUTHOR]

Drilling horizontal wells into natural gas hydrate (NGH) sediments may be one of the most promising methods to increase the cost effectiveness of the exploration of NGH. However, many challenges, such as wellbore collapse and wellbore fracturing, will be encountered. Therefore, an accurate prediction of the mud weight window (MWW) is very important. In this work, a model was built to calculate the MWW of horizontal wells drilled into offshore NGH sediments, considering the NGH saturation and the effects of inlet parameters of the drilling mud, and was combined with the transient heat transfer model to calculate the temperature distribution of the borehole. A case study was carried out, and the effects of several parameters were discussed: 1) When drilling horizontal wells in NGH sediments, the dissociation of NGH in the formation will not occur. 2) With increasing circulation time, the borehole will be cooled, and the cooling effect will lead to a decrease in both the fracture pressure and collapse pressure of the target zone. 3) The mud flow rate has a large influence on the mud temperature profile, especially in the horizontal section, and a higher mud flow rate leads to a lower fracture pressure and collapse pressure in the target zone. 4) The inlet temperature has limited influences on the mud temperature profile in the horizontal section and the MWW of the target zone. 5) The saturation of NGH in a formation has a significant influence on the collapse pressure but little influence on the fracture pressure, and higher saturation will lead to a wider MWW. This study will support the safe control of well stability and application of horizontal wells drilled into offshore NGH sediments. • Natural gas hydrate and drilling mud parameters are considered. • The model combines the transient heat transfer model. • The tensile failure of natural gas hydrate formation is considered. [ABSTRACT FROM AUTHOR]

Maximum extension length prediction model for horizontal wells can be used to evaluate the horizontal well's extension capability and predict its maximum measured depth, which is of great significance to the production and economic benefits of horizontal wells. However, the differential sticking is not considered in previous prediction model. To overcome this shortcoming, a modified model considering differential sticking is established based on constraints of wellbore stability, differential pressure, and filtration loss simultaneously during the drilling, tripping processes and static state. Then a horizontal well is analyzed and its maximum extension length is predicted. Results show that within the conventional mud weight window, three ranges of drilling fluid density can be determined, including the first range, the second range and the reasonable range of drilling fluid density. However, only the reasonable range of drilling fluid density can satisfy all constraints of the modified prediction model, including the wellbore stability, differential pressure, and filtration loss simultaneously. Compared with the original model, the predicted well's maximum extension length decreases when the differential sticking is considered. However, it is more accurate, avoiding drilling hazards in actual drilling operation due to the excessive designed measured depth and unreasonable drilling parameters. Moreover, the maximum speeds of casing running down/pulling out are also determined and added to the modified model. Therefore, the modified model with reasonable drilling fluid density and adjusted running down/pulling out speed is the optimal modified model to predict maximum extension length and avoid differential sticking, which can also ensure that the horizontal well's designed measured depth can be successfully achieved. This study is of great significance to improve the prediction accuracy of horizontal well's maximum extension length and avoid drilling hazards, especially the differential sticking. Moreover, it also plays a guiding role in the selection of reasonable drilling fluid density during horizontal drilling. • A modified maximum extension length prediction model of horizontal well is established. • The constraint of differential sticking is considered. • Three ranges of drilling fluid density within the mud weight window are determined. • Predicted maximum length in modified model is compared with that of original model. • The maximum speeds of casing running down/pulling out are also determined. [ABSTRACT FROM AUTHOR]

Drilling the horizontal extended-reach well (ERW) with the shortest time is of great significance for drilling safety, efficiency and economic benefits. Moreover, the reservoir damage can be reduced or eliminated only when the well's horizontal section is drilled fast enough. In this paper, considering the effects of horizontal well's extension ability on the rate of penetration (ROP) and tripping in/out velocity, a prediction model of the shortest drilling time for horizontal section in ERW is established. The horizontal ERW Z-42 is analyzed, predicting its shortest drilling time in horizontal section. Results show that the predicted shortest drilling time is mainly dependent on its maximum ROP and maximum tripping in/out velocity in horizontal section. Specifically, the maximum ROP must satisfy four constraints, and the predicted maximum tripping in/out velocity must meet three constraints. Moreover, the predicted shortest time of drilling process in horizontal section is very close to the actual time in Z-42 well. In addition, the actual ROP and tripping in/out velocity in horizontal section should be as close as possible but strictly less than the predicted maximum ROP and maximum tripping in/out velocity to avoid drilling hazards. The shortest drilling time is not fixed and can be predicted in real time. Furthermore, in order to reduce the drilling time, it is necessary to reduce the times of tripping as much as possible to shorten the total drilling time of horizontal section. The model provides a practical tool to predict the shortest drilling time for horizontal section in ERW. • Prediction model of the shortest drilling time in horizontal section is established. • Effects of well's extended-reach limit on ROP and tripping velocity are considered. • Maximum of ROP and tripping velocity are predicted. • Predicted shortest drilling time of horizontal section is compared with actual time. [ABSTRACT FROM AUTHOR]

Horizontal well is preferred for marine natural gas hydrate (NGH) production, while a robust completion method is required to control the associated sand production. In this paper, technical challenges, evaluation workflow, and deployment constraints of gravel packing in horizontal wells for marine NGH production are comprehensively analyzed. A virtual horizontal well located at the site SH2, northern South China Sea is involved to optimize packing operation parameters and analyze factors that affect the safety and effectiveness of packing operation. The results indicate that the extremely narrow safe operational window and high fluid-loss ratio are the main obstacles that affect packing effectiveness in marine NGH production horizontal wells. The safe operational window becomes narrower with the decrease of hydrate saturation within the reservoir; hence, the packing failure risk increases significantly. As for the virtual horizontal well located at the site SH2, the safe operational windows are 1.38–1.56 m3/min and 1.38–1.82 m3/min given the average hydrate saturation is 30% and 70%, respectively. However, the horizontal well is unpackable when hydrate saturation is less than 15%. Furthermore, the maximum packable lengths in horizontal wells for marine NGH production are found to be affected by hydrate saturation, fluid-loss ratio, gravel density, gavel concentration, and density/viscosity of sand-carrier. A joint application of lightweight gravel, low concentration slurry, viscosity reducer additives, and multiple β -wave packing technique could prolong the maximum packable length. • Gravel packing parameters in horizontal wells for marine NGH production are studied. • Safe operational window becomes narrower with the decrease of hydrate saturation. • Lightweight gravels are effective to prolong the maximum packable horizontal length. • Multiple β-wave packing widens safe operational window and improves packing safety. [ABSTRACT FROM AUTHOR]

In order to overcome the disadvantage that the previous model for predicting maximum allowable measured depth (MAMD) of a horizontal well only applies to overbalanced operation, a model to predict the horizontal well's MAMD by underbalanced operation is presented in this study. It is of great significance for obtaining higher horizontal section length as well as the oil and gas production. The prediction model is established based on the dynamic pressure balance of bottom hole. The pore pressure, instead of the leak off pressure or fracture pressure in overbalanced drilling, is taken as the critical point at which horizontal wells must stop extending to maintain the underbalanced state of bottom hole. Moreover, the water-based liquid coupled with the nitrogen is used in the simulation process. Furthermore, a horizontal well of C-A14H in China, drilled by underbalanced operation with aerated mud is analyzed to predict its MAMD, and some optimization control measures are also put forward to obtain higher well's MAMD. Results show that the MAMD can be achieved when the bottom hole pressure reaches the pore pressure of drilled formation. The predicted MAMDs are totally different with different water flow rates and gas flow rates. The well's MAMD first increases and then decreases with the increase in gas injection rate, and there exists the optimal gas flow rate. Its MAMD keep decreases with the increase in water flow rate. However, the underbalanced state will never be satisfied within the allowable range of gas flow rate if the water flow rate is too large. Moreover, there is a minimum gas flow rate under a certain water flow rate, and the underbalanced state cannot be maintained if the gas flow rate is too small. The study also shows that the underbalanced operation does not guarantee the improvement of horizontal well's extension ability, which mainly depends on the relationship between the bottom hole pressure and its corresponding critical point. Therefore, in order to obtain greater MAMD, optimum gas flow rate and lower water flow rate are all necessary. This work provides a practical tool for predicting the horizontal well's MAMD by underbalanced operation with aerated mud and achieving greater MAMD. The study is also significant to obtain good economic benefits of oil and gas development by underbalanced operation. The model established in this paper allows us to understand the well's extension capability before drilling, which is also crucial for avoiding drilling risk in underbalanced conditions. • A model to predict horizontal well's MAMD by underbalanced state is established. • The model is established based on the dynamic pressure balance of bottom hole. • Results of well's MAMD are compared with the results with overbalanced operation. • Underbalanced operation does not guarantee the improvement of well's MAMD. • Longer MMD can be achieved by optimum gas flow rate and lower water flow rate. [ABSTRACT FROM AUTHOR]