Extended-reach Well Research Articles

Open-hole extension limit of offshore extended-reach well considering formation collapse

The current extension limit prediction model for offshore extended-reach well (ERW) in mudstone does not consider the formation collapse, which poses a huge risk to offshore drilling construction. To address this problem, this paper presents new open-hole extension limit prediction model for ERW. By considering formation collapse, rate of penetration (ROP), and annular pressure loss, the extension limit models during normal drilling and tripping were derived. The sensitivity of geological and engineering factors was evaluated by analyzing limits for wells 1H and 2H. The research results showed that: (1) The extension limit increases with the ROP and formation collapse duration, but decreases with the increase in mud weight, plastic viscosity, and flow rate. (2) In ERWs, the mud flow rate has a significant impact on the extension limit than the plastic viscosity of mud fluid. However, mud weight has the least impact compared to the two. (3) Considering various parameters, the predicted extension limit of well 1H, when the mud weight is 1.16 g/cm3 [9.67 ppg], is 1593.28 m [5225.96 ft] less than the limit when the collapse period is not considered.

Interaction between Pipe Rotation and Cuttings Transport in Extended-Reach Drilling: Mechanism, Model, and Applications

Summary High drag and torque on drillstring and difficulty in hole cleaning are two major challenges in extended-reach drilling, and these two challenges are usually coupled with each other. However, previous studies considered the drillstring mechanics and hole cleaning as two relatively independent issues and studied them separately, which cannot fully reveal the complex mechanisms of pipe sticking and obtain proper drilling parameters to ensure hole cleaning and reduce drag and torque. To solve this problem, in this paper we present the concept of pipe-cuttings interaction and elaborate on the two interaction mechanisms, which are the effect of pipe rotation on cuttings transport and the effect of cuttings distribution on pipe load. Second, we introduce the stirring diffusion factor and pipe-cuttings contact stress to quantify the pipe-cuttings interaction, and we obtain their mathematical expressions through nonlinear regression of numerical simulation results. Third, we establish the mechanical pipe-cuttings interaction model by modifying and combining the tubular mechanical model and the cuttings transport model. Finally, we validate the interaction model and apply it to a case study of extended-reach drilling in the South China Sea. The results show that the interaction model is of high prediction accuracy and is superior to the conventional tubular mechanical and cuttings transport models because the interaction between pipe rotation and cuttings transport is sufficiently considered. The problem of poor hole cleaning for a 12¼-in. section is serious, and pipe sticking occurs frequently for the extended-reach well in the case study because the stationary bed height is more than 10% in actual drilling. It is usually difficult to ensure hole cleaning of a 12¼-in. section by only optimizing a single parameter of rate of penetration (ROP), flow rate, or rotational speed, but optimizing two of the parameters at the same time can achieve better results. Lastly, we establish a recommended chart of drilling parameters, which can aid engineers in making comprehensive recommendations on drilling parameters.

A study on the flow behavior inside fluidic oscillation tools for friction-reduction in extended reach well

The drilling distance of extended-reach wells is limited by mechanical friction between the drill string and the borehole wall. The fluidic oscillator axial vibratory tools (AVTs) can effectively reduce friction and increase the weight on bit, thereby extending the reach of horizontal wells. However, few studies have delved into the evolutionary mechanism of the internal flow field of fluidic oscillator AVTs. In this paper, two types of fluidic oscillators with different flow path are presented. One is the reverse-feedback oscillator, and the other is sweeping-chamber oscillator. Through computational fluid dynamics method, the internal flow field of these two fluidic oscillator AVTs were analyzed, and the frequency and pressure drop were verified by experiments. The results show that the LES turbulence model provides more accurate simulations, showing an error range of less than 9%. The pressure drop and vibration frequency of the two tools are linearly related to the flow rate. The pressure drop of the reverse feedback oscillation tool is in the range of 0.1–1 MPa, and the vibration frequency is between 13 and 50 Hz. The sweeping-chamber oscillator can reduce vibration frequency to below 15 Hz. The results also show that it is crucial to consider the lag in pressure signals when designing and analyzing fluid oscillator systems, as it can affect the timing and behavior of the system. This research provides profound insights for understanding and optimizing fluidic oscillator systems.

Numerical simulation of fracture temperature field distribution during oil and gas reservoir hydraulic fracturing based on unsteady wellbore temperature field model

In the hydraulic fracturing oil and gas reservoir, the temperature variation of the fracturing fluid has a great impact on its flow and rheology, affecting the sand-carrying capacity and friction resistance of the fracturing fluid, and also affecting the settling speed of proppant in the fracture, thus changing the sand setting profile and sand laying concentration, and finally affecting the geometry of the fracture. Based on the energy balance and continuity equations, a numerical model for the distribution of wellbore temperature field in an extended-reach well is developed, and a variation law for the wellbore and reservoir temperature fields during fracturing also is formulated. A 3D mathematical model of the temperature distribution in hydraulic fracture and near-fracture formations has been developed based on heat transfer theory and finite-difference methods, taking into account the temperature gradients of fracture length and height according to the energy balance principle and fracture fluid continuity equations. The sensitivity factors of the temperature field are clarified, the wellbore temperature field and the fracture matrix temperature field model are coupled, and the influence rule of the temperature field change of the construction layer on the fracture shape while fracturing is revealed, which provides a theoretical basis for the hydraulic fracturing design optimization.

Combining Magnetic and Gyroscopic Surveys Provides the Best Possible Accuracy

Summary A survey program is designed for every well drilled to meet the well objective of penetrating the target reservoir and avoiding a collision with nearby offset wells. The selection of the wellbore survey tools within the survey program is limited in number and accuracy by the current surveying technologies available in the industry. This article demonstrates how a higher level of accuracy can be achieved to meet challenging well objectives when the accuracy of the most accurate wellbore surveying tools and technologies taken individually is insufficient. This high level of wellbore positioning accuracy is achieved by combining two independent wellbore positions of the same wellbore trajectory. The first wellbore position is calculated using the latest technology of magnetic measurement-while-drilling (MWD) definitive dynamic surveys (DDS). The accuracy of the MWD DDS can be further improved by minimizing error sources such as misalignment of the survey package from the borehole, drillstring magnetic interference, the use of localized geomagnetic reference, using high-accuracy accelerometer sensors, and a high-accuracy gravity reference. Furthermore, the MWD DDS inclination accuracy is improved using an independent inclination measurement from the rotary steerable system. A first wellbore position is calculated from the magnetic MWD DDS after applying in-field referencing (IFR), multistation analysis (MSA), bottomhole assembly (BHA), sag correction (SAG), and dual-inclination (DI) corrections to improve both azimuth and inclination accuracy. A second wellbore position is calculated using gyro-MWD (GWD) technology. The results and comparisons of multiple combined survey runs are presented. The highest accuracy of wellbore positioning had been proved in this successful case study by penetrating a very small reservoir target on an extended-reach well that was unfeasible using either the most accurate enhanced MWD DDS or GWD technology individually. The presented case study shows how the wellbore objectives of penetrating a very small reservoir target had been confirmed by logging-while-drilling images and the reservoir mapping interpretation of the client subsurface team. This gave a high-accuracy wellbore position during drilling and provided higher confidence in wellbore placement to maximize reservoir production without colliding with nearby offset wells. Wellbore survey accuracy limits a borehole’s lateral and true vertical depth (TVD) spacing, constraining reservoir production in those sections. In the top and intermediate sections, wellbore survey accuracy limits how close the wellbore can be drilled to other offset wells due to collision concerns. This directly impacts the complexity of the directional work and the cost per section. Combining independent wellbore surveys unlocks the potential to improve the wellbore positioning accuracy significantly. It demonstrates the highest wellbore positioning accuracy that can be achieved to date compared with the latest magnetic MWD surveys after correcting all known errors or compared with GWD.

Numerical analysis of the connector effect on cuttings bed transportation while Tripping

This study investigates the cuttings transport while tripping with a connector. First, a transient two-layer model is enhanced to simulate the cutting transport while tripping with a connector. Two mechanisms are thus analyzed regarding the cutting's pile up around the connectors: on the one hand, the difference in the cross-sectional area around the connectors and the corresponding change in the fluid velocity may cause cuttings to accumulate behind the connectors; on the other hand, the connector will push or pull the bed layer and suspension layer, like a “bulldozer”, which make the cuttings bed pile up behind the connector. Second, the backreaming operation can be further analyzed by combing the circulation and pipe rotation. The results demonstrate that the cuttings pile up behind the connectors while tripping, and the stacking height increases with initial bed height, the tripping velocity, the diameter, and the length of the connector, and decreases with the flow rate. Moreover, the stacking height behind the connector decreases with the drill pipe rotation speed significantly while backreaming, especially when the rotation speed is more than 120 rpm. Furthermore, the safety of the tripping procedure is highly related to the remaining cuttings bed. Thus the total circulation time to remove the residual wavy cuttings bed is optimized, which increases with the flow rate, ROP, the well depth, and initial bed height significantly; however, the total number of bottom-up operations changes very little, basically around 2 to 3. This can serve as a guide to reduce the high-risk tight spots, especially for an extended-reach well.

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

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

Extended-Reach Drilling Hits Mainstream To Squeeze Difficult Reservoirs

Though expensive and complex, extended-reach drilling (ERD) is moving more into the mainstream as the industry is driven to develop frontier reserves in fragile environments like the Arctic where drilling from shore to off-shore targets reduces a project’s infrastructure costs and environmental footprint. A form of directional drilling, ERD is also being used increasingly to tap into hard-to-produce reservoirs, making viable projects that might otherwise be written off as noncommercial. This article highlights how the Russian Far East became the ERD epicenter in the past decade, given ExxonMobil and Rosneft’s extensive use of ERD in developing Arctic resources offshore Sakhalin Island, and how ERD is becoming more widely used in regions as diverse as the Gulf of Thailand, off-shore Brazil, and the Arab Gulf. By definition, an extended-reach well (ERW) is one in which the ratio of the measured depth (MD) vs. the true vertical depth (TVD) is at least 2:1 (PetroWiki). An ERW differs from a horizontal well in that the ERW is a high-angle directional well drilled to intersect a target point, a feat requiring specialized planning to execute well construction. ExxonMobil subsidiary Exxon Neftegas Limited (ENL), which operates the Sakhalin-1 license area offshore Russia’s Sakhalin Island (Fig. 1), has been pushing the limits of ERD for nearly 2 decades with innovative technologies and sophisticated well planning, making the Sea of Okhotsk a place where any ERD drilling record set today may easily be broken tomorrow. Russia’s state-owned Rosneft (which has a 20% stake in Sakhalin-1) owns bragging rights for having drilled the longest ERW well on record to date. Rosneft announced in November 2017 it had drilled a 15000-m horizontal ERW from the offshore Orlan gravity-base platform at Chayvo field situated in 14 m water depth in the Sea of Okhotsk, topping four previous records set between 2013 and 2015 that had reached between 12450 m and 13500 m (Fig. 2). In a news release at the time, Rosneft called the well “super complex with a DDI [directional drilling index] of 8.0 and a 14129-m stepout.” The release went on to say that the Sakhalin-1 Consortium could (as of the 2017 announcement) claim to have drilled nine out of the world’s 10 longest ERD wells. According to Rosneft, the project had set five world records for measured depth of wells between 2013 and 2017. In April 2015, development well O-14 was drilled with a length of 13500 m. That broke a 2014 record when the 13000-m Z-40 well was completed. In 2013, records were announced for wells Z-43 and Z-42 which were drilled, respectively, in April and in June 2013 with lengths of 12450 m and 12700 m. Rosneft credited ExxonMobil’s patented “Fast Drill” drilling optimization process that can increase rates of penetration (ROP) by up to 400% as a significant innovation contributing to the ERD success story at Sakhalin-1. One of the largest foreign direct investments in Russia, Sakhalin-1 operates under a production sharing agreement (PSA) with its license area off the northeastern coast of Sakhalin Island, comprising the Chayvo, Odoptu, and Arkutun Dagi fields.

Study of Radial Vibration Impact on Friction and Torque of Rotary Drill String

During extended-reach well drilling, the torque of a rotary drill string is too large in the horizontal section, which results in the failure of the drill string. The effect of radial vibration on the friction and torque of the rotary drill string is unclear. In this work, first, the principle of the impact of radial vibration on the friction and torque of the rotary drill string in the horizontal section is analysed. Then, joints with an elliptical outer edge of the section are designed, which can generate low-amplitude vibration as the drill string rotates owing to the interaction with the wellbore wall. The radial vibration characteristics can be tuned by changing the major to minor radius ratio of the ellipse. A self-developed experimental device was designed to test the performance of tools with reduced friction and torque. The drill string torque with different penetration rates, rotation speeds, and ratios of the major radius to minor radius of the ellipse were systematically studied. The experimental results show that the average and the maximum amplitudes of the torque fluctuation first decrease to the lowest value and then increase with the increase of the ratio. When the ratio reaches 1.065, the average and the maximum amplitudes of the torque fluctuation evidently reduce; therefore, a joint with a ratio of 1.065 can effectively reduce frictional torque. The average torque reduces when the penetration rate and rotation speed decrease. At rotation speeds of 45 and 60 r/min, the maximum amplitude of torque fluctuation increases first and then decreases with an increase in penetration rate, and it reaches a maximum value at a penetration rate of 22.5 m/h. The fundamental frequency of torque fluctuation is almost linearly related to rotation speed, which is irrelevant to the penetration rate and the ratio of major to minor radius of the ellipse.

Failure analysis and improvement measures of step transition zone of drill pipe joint

With the wide application of ultra-deep well, horizontal well, directional well, extended-reach well and highly-deviated well logging technologies in petroleum drilling engineering, the failure problem of drill pipe joints caused by complex alternating loads has become one of the main factors to restrict drilling efficiency. In recent years, scholars from around the world have performed large numbers of research studies on drill pipe joints, but these studies have mainly focused on the analysis of drill pipe joint threads, and have rarely involved the failure analysis of step transition zone of drill pipe joints. In order to solve the above problems, the author has carried out several aspects of research. Firstly, the chemical composition, mechanical properties and microstructures of the failed model materials were analyzed by experiments. Secondly, a three-dimensional numerical simulation model of the drill pipe joint was established based on the finite element analysis method, and the static stress characteristics and fatigue life of the drill pipe joint under multi-axial alternating loads were analyzed. Finally, the effects of structure, surface quality and residual stress of step transition zone on fatigue life were analyzed. The research results show that: (1) the chemical composition and mechanical properties of the materials for the failure model meet the requirements of the standard, and the failure reason of the transition zone of the drill pipe joint is a fatigue failure caused by composite alternating loads; (2) the structure, surface quality and residual stress of the step transition zone of the drill pipe joint have great influence on fatigue life; (3) the fatigue life of the model can be greatly improved by improving the structure, improving the surface processing quality and introducing controllable residual compressive stress.

A prediction model of the shortest drilling time for horizontal section in extended-reach well

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.

Technology Focus: Multilateral and Complex-Trajectory Wells (May 2019)

Technology Focus When students ask me about the most important way to maximize recovery, my answer is long directional wells. These wells have revolutionized the oil industry and are drilled under conditions never imaginable years ago. One outstanding example is the Troll field in Norway. The field consists of large, very thin reservoirs, down to 30 ft thick, which are drained by multibranch horizontal wells with horizontal departures approaching 18,000 ft. Not only have many drilling challenges been overcome, but also, from a production perspective, the wells are equipped with intelligent technology such as autonomous gas stop to maintain the pressure drive for the oil. Initially of no commercial interest because of a lack of technology, this field has been a very important driver for the current state of the art for long horizontal wells. Troll has been Norway’s largest oil producer in recent years. This has been made possible by the development of long-horizontal-well technology. The oil industry is currently undergoing a technological transformation that will add value, improve processes, and reduce cost. Future drilling engineers will have knowledge of robotics, automation, and organizational efficiency, which is highly appealing for recruitment. A prerequisite for this step change is the industry’s high level of technology. The selected papers address various aspects of horizontal wells. A field case of how to plan and drill through highly depleted reservoirs is given in paper OTC 28517. Three depleted zones must be penetrated before drilling into the untapped reservoir with a low drilling margin. This is a good example of drilling an extended-reach well using an integrated approach between various disciplines. Another example is given in paper SPE 191436, which shows how a complex U-shaped well path from old wells can be used to obtain good reservoir exposure to drain depleted wells further. Equipment is continuously improved, and paper SPE 189947 presents new ultrasonic technology to evaluate the state of multilateral junctions. SPE 191271 Extended-Reach Wells in Unconsolidated Sands in Bolivia by Gabriel Dordoni, Pluspetrol Bolivia OTC 28971 Correlation of Numerical Simulation and Digital-Image-Correlation Strain Measurements for a Multilateral Junction While Subjected to High Internal Pressure by Aihua Liang, Halliburton, et al. SPE 192672 Wireline Tractor Conveyance—A Technology Game Changer for the Gulf of Thailand by Sarunya Jongnarungsin, Mubadala Petroleum, et al.

A high-efficiency development mode of shale gas reservoirs in mountainous areas based on large cluster horizontal well engineering

With the basic characteristics of conventional horizontal wells, the so-called complex wells including horizontal extended-reach wells, multi-lateral horizontal wells, U-shaped wells, cluster horizontal wells, etc., are advanced well types for the efficient development of low-permeability, unconventional, deep-water, and deep oil and gas reservoirs, which have been highly concerned all over the world. Significant progress at home and abroad has been made in relevant researches and practices and is expected to play an important role in the efficient development of shale oil and gas. To meet the basic needs of environment & safety, land conservation, cost reducing and efficiency improving, it is urgent to create a unique and efficient mode for developing shale gas. Therefore, an efficient shale gas development mode for mountainous areas and an engineering and technical support system are presented based on large cluster horizontal-well engineering. An equation is thus obtained for calculating the maximum number of horizontal wells arranged allowably in “Well Factory” on a single platform. The general research and development of large extended-reach well technology are analyzed by expounding the basic concept of an extended-reach well and its drilling extension limit. And a calculation method is thus established to predict the maximum measured depth of open hole in extended-reach drilling. Moreover, some relevant research results and their significance for downhole tubular mechanics & mechanical extension limits in extended-reach drilling are also briefly introduced in this paper. The conclusions are drawn that, by following the idea of “integration of geology and engineering” in oil and gas development, these research results have a foreseeable application prospect in shale gas development in the mountainous areas in the future, and will contribute to new progress in China's “Shale Revolution”.

Study on aggressively working casing string in extended-reach well

Running casing in extended-reach well (ERW) can be extremely difficult because of high drags. Once running casing is hindered by high drags, a special operation, aggressively working casing string, sometimes is employed to help casing overcome the high drags. During this operation, drillers first pick casing string up to a certain height and then slack it off rapidly (or drop it), so that casing string seems to “fall” from that height with relatively high speed. Because of the kinetic energy, casing string is more likely to overcome high drags and reach the target depth (TD). However, the operation also has many uncertainties. For example, whether casing string can really overcome high drags is hard to predict. Moreover, the operation sometimes is violent and may cause safety problems.To study this operation, a new drag model is built to describe the behavior of casing string during aggressively working string. The model is an improved soft string model which considers dynamic motion of casing. The model is able to calculate forces and motion of casing string in falling process during aggressively working string. Two case studies are presented where casing string was aggressively worked to overcome high drags. Mechanical behavior of casing string in each case is studied and the safety issues are discussed. Finally, suggestions on this operation are also proposed.

Simulation Study on Influences of Wellbore Tortuosity on Hole Cleaning in Extended-Reach Drilling

Summary Wellbore tortuosity or spiraling can lead to the trapping of a cuttings bed in a trough of a tortuous hole, thereby leading to poor hole cleaning in extended-reach drilling. The objectives of this study included quantitatively evaluating the influences of wellbore tortuosity on hole cleaning and cuttings-transport behavior in extended-reach drilling. In addition, the study provided a recommendation of effective drilling practices. The study involved performing hole-cleaning-optimization studies for an extended-reach well with a long horizontal section aiming for maximum reservoir contact, by use of a transient cuttings-transport simulator. The planned trajectory of the well was assumed to have a certain degree of wellbore tortuosity in the horizontal section. The pump rate and bottoms-up circulation operation were optimized on the basis of parameter studies and additional transient simulations by considering the effects of penetration rate and variation in cuttings size. Simulation results indicated the formation of a considerably high cuttings bed, particularly in the downdip intervals (updip in mud-flow direction) at an insufficient pump rate; one-third to one-half of the drillpipe diameter could be potentially buried in a cuttings-deposit bed, and this can result in a packed-off hole or stuck pipe. A higher rate of penetration (ROP) can also cause insufficient hole cleaning. In this case, controlled drilling that maintains a reasonably low penetration rate may be effective. Furthermore, borehole breakout may enlarge hole diameter and generate large-sized cuttings. Both of these can have negative impacts on hole cleaning, and, thus, borehole stability and smooth wellbore-trajectory controls should be carefully considered. To clean these holes, frequent bottoms-up circulations were effective at each stand of drilling even if the optimization of other drilling parameters was limited. The findings also revealed that accumulated cuttings in a tortuous wellbore were trapped in the trough of the hole, and that the bed height of locally trapped cuttings in the downdip intervals could be much higher than that indicated by previous studies.

A Comprehensive Prediction Model of Hydraulic Extended-Reach Limit Considering the Allowable Range of Drilling Fluid Flow Rate in Horizontal Drilling

Hydraulic extended-reach limit (HERL) model of horizontal extended-reach well (ERW) can predict the maximum measured depth (MMD) of the horizontal ERW. The HERL refers to the well’s MMD when drilling fluid cannot be normally circulated by drilling pump. Previous model analyzed the following two constraint conditions, drilling pump rated pressure and rated power. However, effects of the allowable range of drilling fluid flow rate (Qmin ≤ Q ≤ Qmax) were not considered. In this study, three cases of HERL model are proposed according to the relationship between allowable range of drilling fluid flow rate and rated flow rate of drilling pump (Qr). A horizontal ERW is analyzed to predict its HERL, especially its horizontal-section limit (Lh). Results show that when Qmin ≤ Qr ≤ Qmax (Case I), Lh depends both on horizontal-section limit based on rated pump pressure (Lh1) and horizontal-section limit based on rated pump power (Lh2); when Qmin < Qmax < Qr (Case II), Lh is exclusively controlled by Lh1; while Lh is only determined by Lh2 when Qr < Qmin < Qmax (Case III). Furthermore, Lh1 first increases and then decreases with the increase in drilling fluid flow rate, while Lh2 keeps decreasing as the drilling fluid flow rate increases. The comprehensive model provides a more accurate prediction on HERL.

Cuttings-Transport Simulation Combined With Large-Scale-Flow-Loop Experimental Results and Logging-While-Drilling Data for Hole-Cleaning Evaluation in Directional Drilling

SummaryThe authors have developed a 1D two-layer-model transient-cuttings-transport simulator that predicts the transient behaviors of cuttings transport, including the concentration and slip velocity of suspended cuttings, bed height of cuttings, annular pressure, and equivalent circulating density (ECD) along the entire trajectory of a complex extended-reach well. Model parameters, such as annulus-friction factor, cuttings-deposition rate, and re-entrainment rate, were determined from numerous experiments previously performed by use of a large-scale cuttings-transport flow-loop apparatus. This apparatus simulates the complex flows in borehole annuli at various inclination angles, ranging from vertical to horizontal. In this study, the authors validate the model and analyze the cuttings transport by use of field data in a directional well, in which the annular ECD was measured by logging while drilling (LWD), and the rate of the returned cuttings was measured at the surface. On the basis of the simulation study, the potential of the developed transient-cuttings-transport simulator for the predrilling- and post-drilling-phase analyses is discussed. Moreover, the authors evaluate the transient-hole-cleaning conditions and the ECD behavior from the LWD data.

Study on the prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings

An open-hole extended-reach limit model was established and published by the authors to determine how far a horizontal extended-reach well (ERW) can extend. The published model shows that the open-hole extended-reach limit (the maximum measured depth of the horizontal ERW) is mainly dependent on the annular pressure drop and the fracture pressure of drilled formation. Moreover, some optimal control methods, such as lowering drilling fluid density, reducing drilling fluid flow rate and optimizing drill pipe eccentricity, were also presented to obtain greater open-hole extended-reach limit. However, the published model was established based on the assumption that the annular fluid is ideal single-phase flow. Failing to consider the effects of cuttings may lead to an inaccurate prediction of the open-hole extended-reach limit and even drilling safety hazards. In this paper, in order to overcome the shortcomings of the published model, a prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings is established and analyzed. The study shows that due to an increase of annular pressure drop, the horizontal-section limit (the maximum measured depth of horizontal-section for the horizontal ERW) is relatively smaller when considering the effects of cuttings. Meanwhile, a case study is carried out, and the results show that the horizontal-section limit is 1610 m when the cuttings are considered. In contrast, when the cuttings are ignored, the limit is 1941 m based on the published model. Furthermore, since several main parameters of the established model may greatly affect the annular pressure drop and the horizontal-section limit, parameters sensitivity analysis are also performed and some conclusions are drawn. First, the horizontal-section limit first increases and subsequently decreases with the increase in drilling fluid density. Second, there is an increase in horizontal-section limit when the drilling fluid flow rate increases. Third, the horizontal-section limit gradually increases with the increase in the drill string rotation speed. Finally, there is also a decrease in the horizontal-section limit when the rate of penetration (ROP) and the consistency coefficient increase. In sum, the simulated condition in this paper is more consistent with the situation of field drilling practice than that of the published model. This study will also provide a more accurate result of the open-hole extended-reach limit, which is of great significance to the drilling design and drilling safety.

Проектирование и строительство разведочной скважины с большим отходом от вертикали на Ростовицком нефтяном месторождении

Проектирование и строительство разведочной скважины с большим отходом от вертикали на Ростовицком нефтяном месторождении

General approach for the calculation and optimal control of the extended-reach limit in horizontal drilling based on the mud weight window

There are two shortcomings in the previous open-hole extended-reach limit model: 1) only the drilling process is analysed, while the whole processes should also include the tripping process; 2) the optimal control methods have not been fully considered.To overcome these shortcomings, a set of calculation and optimal control methods of the open-hole extended-reach limit in horizontal drilling are presented in this paper. First, the horizontal section limit expressions of a horizontal extended-reach well (ERW) for different drilling processes are obtained. A modified mud weight window (MWW) for a horizontal ERW is determined according to those expressions, and the modified MWW can be used to solve the problem that the conventional MWW may fail to satisfy the operation window of horizontal extended-reach drilling (ERD). Second, the horizontal section limit values of the drilling process (sliding drilling mode and rotating drilling mode) and the tripping in and tripping out processes are calculated, and the minimum of these values is taken as the maximum horizontal section limit. Finally, several optimal control methods of obtaining the greater horizontal section limit are also provided from three aspects: drilling modes, drilling parameters and mud performance parameters.The results of the case study show that the modified MWW can change with the different operating parameters, rather than remain constant range. Moreover, the modified MWW is narrower than the conventional one. The maximum horizontal section limit should be simultaneously determined by the processes of drilling, tripping in and tripping out. The tripping velocity has little effect on the optimal mud density, whereas the maximum horizontal section limit decreases with the increase in tripping velocity. In addition, both the optimal mud density and the maximum horizontal section limit decrease with the increase in drill string rotation speed. Moreover, the sliding drilling mode can provide greater extension ability than rotating drilling mode. Furthermore, methods of optimizing the drilling parameters and mud performance parameters are also given in detail.