New Achievements in Multilateral Drilling and Completions in Western Siberia, Part 1

CJSC “Investgeoservice” Damir Tuktarov, General Director;

CJSC “Investgeoservice” Artur Gulov, Project Manager;

JSC “NOVATEK” Evgeny Glebov, Deputy Director, Technology Department of Boreholes Technologies and Supervising;

JSC “NOVATEK” Ivan Shokarev, Deputy Head, Technology Department of Downhole Borehole Technologies and Supervising;

LLC “NOVATEK-Yurkharovneftegas” Alexander Kurasov, Deputy General Director – Drilling, Head of Drilling.

Engineering and Construction of ERD Wells at the Yurkhar OGCF

Introduction

NOVATEK-YURKHAROVNEFTEGAZ LLC, a subsidiary of NOVATEK JSC, in co-operation with Investgeoservice CJSC, have successfully completed construction of the longest extended reach drilling (ERD) wells in the Russian Federation.

The final TD (Total Depth) of wellbores No 1-A and 2-A of the Yurkhar field totaled 8,497 and 7,274 meters respectively. The final TD (Total Depth) of wellbore No 3-A (a multilateral well) totaled 7,418 and 7,438m respectively.

Investgeoservice CJSC, the general drilling contractor for the project, has accomplished these record-breaking wells by applying the most advanced technologies from leading Russian and international oilfield service companies.

By coordinating the efforts of experts from the operator, general contractor and subcontractors, the well construction program not only produced outstanding success in the application of new technologies, but it also resulted in an excellent occupational health and safety performance record as well.

In addition, it is worth noting that NOVATEK JSC and Investgeoservice CJSC have paid special attention to environmental protection issues. This is an important factor because of the geographical location of the project, near the Taz Estuary wetlands and in the close vicinity of the Kara Sea shoreline which has abundant creeks, rivers, marshes and lakes.

Regional operations contain strict requirements regarding safety and environmental protection, challenging ice and geocryologic conditions, protection of the indigenous people’s traditional farming areas, as well as habitats of threatened and endangered species of flora and fauna.

The technologies used in the construction of these wells can be successfully applied in the development of Northern and Arctic fields, including the deposits within the Yamal, Taz, and Gydan Peninsulas (parts of the Yamal-Nenets Autonomous District), which are strategic objectives for Russia’s gas industry.

About NOVATEK

NOVATEK JSC is the largest [1] independent producer and the second largest producer of natural gas in Russia.

Established in 1994, the Company is engaged in the exploration, production and processing of gas and liquid hydrocarbons.

The various fields and licensed blocks belonging to the Company are located in the Yamal-Nenets Autonomous District, the world’s largest region of natural gas extraction, which accounts for about 90% of the natural gas extracted in Russia, and for about 17% of the global gas production.

NOVATEK aims to continuously strengthen its resource base by carrying out exploration activities. By using modern methods of exploration and development, the Company provides cost-effective development of their resources, while achieving maximum hydrocarbon production rates.

According to the results of an independent evaluation carried out by DeGolyer & MacNaughton, as of December 31st, 2014, the proven hydrocarbon reserves of the Company (including its shares in the reserves of joint ventures), in accordance with the SEC standards, totaled 12,578 mln BOE, including 1,747 bln m3 of gas and 135 mln tons of liquid hydrocarbons.

About Investgeoservice

The Investgeoservice group of companies [2] brings together  entities specialized in the construction of exploration wells, directionally-controlled wells, horizontal wells and ERD wells, as well as interpretation of geological and geophysical data, calculation of hydrocarbon reserves, development of geological and hydrodynamic field models, field development plans, well testing, and site management.

The Investgeoservice group of companies carries out the functions of an oil service provider and coordinator on the basis of a general contract, or integrated project management.

The key competencies of Investgeoservice group of companies are as follows:

✓ specialization in drilling technologically complicated exploration and production ERD wells;

✓ individual approach toward the selection of technologies from the leading providers in order to provide the most effectively solutions to meet the needs of the Customer;

✓ long-term experience in drilling operations in the Arctic areas, even under stand-alone projects.

The considerable experience of Investgeoservice group in the fields of drilling and geological exploration studies enables them to successfully resolve the complicated challenges of the Customer.

About the Field

The Yurkhar oil and gas condensate field (YOGCF) is the main producing asset of NOVATEK.

The field was discovered in 1970 and is located above the Arctic Circle in the south-eastern part of the Taz Peninsula’s Nadym-Pur-Taz district. The western part of the field is located in the Taz Peninsula, the central and eastern parts are located in the basin of the Taz Estuary, where the average depth of the estuary is four meters. The development of the offshore part of the field shall be carried out from land through the use of horizontal wells.

According the SEC standards, as of the end of 2014, the field reserves totaled 363.4 bln m3 of gas and 17.2 mln tons of liquid hydrocarbons. The bulk of the gas reserves fall on the Valanginian horizon. The productive deposits are compactly located in a relatively small area (approximately 260km2), which increases the efficiency of their development and deployment in terms of capital and operating costs (see Figure 1). The field is located approximately 300km north of the town of Novy Urengoy and about 50km east of the Yamburg field.

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The field development model includes the drilling of large-diameter, multilateral horizontal wells, which enables the reduction of the total number of wells required to develop all the reserves of the field and the minimization of capital investments.

There is one natural gas deposit, 24 gas condensate deposits and 3 oil condensate deposits in the field. The hydrocarbon depth ranges from 1,000 to 4,400m (incl. Jurassic sediments), while the Valanginian deposits are characterized by the presence of permeable sandstone, which is the main production zone. The Yurkhar oil-and-gas condensate field (OGCF) is the scond largest in production output is the second largest field after the Yamburg field and of all the fields operated above the Arctic Circle. YOGCF provides approximately 10% of the gas consumed in the Russian domestic market. The production output at full capacity is 37 bln m3 of natural gas per year. The Yurkhar field is characterized by the use of cutting edge technologies, which reduces the potential environmental impact on the vulnerable environment of the Far North. For instance, amongst others, a drilling waste thermal treatment unit was put into operation in 2008, which eliminates the release of drilling waste into the environment.

History of YOGCF Well Construction

The development drilling in the Yurkhar field started in May 2002. The commercial extraction of natural gas and gas condensate commenced in January, 2003.

The construction of the wells was complicated by the considerable difficulties posed by a complex geological cross-section, the presence of permafrost rocks, unstable clay, and various fluid saturated beds, hard-to-reach reservoirs due to drilling from onshore under the bed of the Taz Estuary water area, climatic conditions and logistic issues.

From 2007 to 2011, significant work was conducted, in order to optimize the field development plan, by drilling large-diameter, bilateral and ERD wells, which result in drilling fewer overall wells for field’s development. This program succeeded in reducing the overall costs and potential environmental risks. On average, in these new wells, the production string diameter is up to 245mm in diameter, the horizontal section is more than 1,000m long and the initial flow rate is up to 4.5 mln m3 per day.

In order to develop the reserves in the eastern part of field and to provide an even recovery from the field, the drilling of horizontal ERD wells continued in 2014. Three new gas-condensate wells were put on production and workover was conducted on two previously drilled wells.

Currently, more than 70 gas-condensate wells have already been drilled, but the success of the well construction for No’s. 1-A, 2-A and 3-A deserve special attention.

Why ERD Wells?

The geological structure of the field determines the development strategy. As the main reserves are located in the shelf area of the Taz Estuary, the well pads are placed along the coastline and wells reach out under the water (see Figure 2). After the relatively simple wells were drilled (their length however, reached up to 5000m), it was the turn for the ERD wells. The economic and technical analysis has shown that ERD well construction is the most economical and environmentally efficient solution that allows access to the remote reservoirs pay zones of the Yurkhar field.

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Economic efficiency results in the optimization of the investment into the infrastructure with the aim of increasing the fields profits, which is necessary for the development of the field.

The ERD wells (global classification – ERD wells: Extended Reach Drilling) are wells with an extended-reach and a deviated to vertical ratio of more than 2:1. The characteristic features of the construction of these types of wells are as follows:

• high mechanical loads – increased axial loads and often excessive torque occurs as a result of the high friction ratios given by the excessive length of the inclined section of the wellbore;

• high hydraulic loads – annulus pressure (ECD)  is far higher, even when compared to horizontal wells with lower kickoff, more so – to vertical wells (even deep ones);

• hindered wellbore cleaning for drill cuttings, especially in case of the high PHAR (pipe-hole area ratio) well design – the higher the PHAR, the harder it is to clean the well and remove cuttings;

• difficulties with reaching the casing strings and liners – high friction ratios and underweight top-hole assemblies that are insufficient for reducing the column’s «pushing» efforts;

• problems with the stability of the  wellbore and a narrow mud weight window;

• problems with the load delivery during the drilling and completions, such as creating the necessary load when hanging the liners;

• in addition, the large distance between targets resulted in additional geological uncertainties as regards to the structures, which are not homogeneous by stratification and bedding course.

ERD well is not just a more complicated directionally-controlled well. The following serves as a basis for the successful construction of such wells: the use of advanced technologies, professionalism of the staff, proper arrangement of processes and established communication between the various stakeholders. That’s why the preparations for these record wells started long before the spudding of wells. At the request of NOVATEK-YURKHAROVNEFTEGAZ LLC, the design of wells No 1-A and 2-A was carried out by the design contractor ‘BUROVAYA TEKHNIKA’ NPO JSC [3] with the obligatory involvement of Investgeoservice CJSC as a General Contractor for the well construction, and with involvement of the  K&M Technology Group [4], a Schlumberger Co. [5] unit specialized in the drilling of ERD wells. Various criteria and factors have been taken into account and analyzed during the designing stage – project design and the well path (including the first section of drift deviation and the path turn), proper selection of drilling tools and equipment, stability of the wellbore, solving the wellbore cleanout issues – lifting the cuttings to the surface, real-time monitoring of the drilling parameters and equivalent circulating density of the drilling mud, as well as casing running and cementing technology (particularly the production casing and the deep-set tie-back casing), and mounting the filter-liners. The designing of well No. 3-A commissioned by NOVATEK-YURKHAROVNEFTEGAZ LLC was carried out by the design contractor NOVATEK SEC LLC. Prior to the spudding of wells, the Investgeoservice CJSC took account of the geological data changes and made timely adjustments to the project. There, special attention was paid to the operational risk assessment and preparation of an emergency action plan.

It was obvious that along with all other well design criteria, the drilling rig should be able to perform all the operations associated with drilling, tripping, casing and completion of the wells. For the construction of these record wells, the Investgeoservice CJSC used modified drilling rigs for the Yurkhar field, which enabled them to perform the scheduled operations, with enough necessary reserve capacity remaining.

About the Record Wells

• Purpose

The drilling of the production wells No 1-A, 2-A and 3-A with the horizontal section in the BU8 pay zone was necessary for the extraction of hydrocarbons from the BU8-0 – BU8-2 beds of the Tangal formation.

• Well profile and design

The wellbore of well No 1-A is presented below (see Figure 3).

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The drift deviation is designed in a way to ensure minimal tortuosity and a «smooth» wellbore, the parameters that play an important role for the final well construction and the possibility of runing in with the drill pipe and setting casing strings and downhole production equipment to design depths.

The results achieved are record-breaking not only for the region but across the whole of mainland Russia, and they speak for themselves:

The 393.7 mm (15 ½») section was successfully drilled to a measured depth of 1,610 meters. The zenith angle in this section was 73.8° in a vertical depth of 1,403.8 meters. The wellbore casing, using 340mm (9 ⅜») intermediate production string with premium connectionswas successfully set at 5,626 meters.

The 311.15mm (12 ¼») section was successfully drilled to a measured depth of 5,632 meters along the wellbore, the zenith angle in this section was 74.2° and the horizontal displacement in this section totaled 4,359 meters at a vertical depth of 2,494 meters. The wellbore casing, was set using 245mm (9 ⅝») intermediate production string with premium threaded joints, which was successfully set at a depth of 5,626 meters.

The 215.9mm (8 ½») section was successfully drilled to a depth of 6,999 meters along the wellbore, the zenith angle in this section was 76.8° and the horizontal displacement in this section totaled 5,678 meters at a vertical depth of 2,818 meters. The wellbore casing, was set using 177.8mm (7») deep-set tie-back string with premium threaded joints, which was successfully set at a depth of 6,997 meters.

The 155.6mm (6 ⅛») section was successfully drilled to a measured depth of 8,497 meters and the horizontal displacement in this section totaled 7,059 meters at a vertical depth of 2,906 meters. 127mm (5») liner-filter was successfully set at a measured depth of 8,495 meters.

The path of well No 2-A is designed similar to well No 1-A, but with less horizontal reach, thus we are describing in this article only the well with the longest horizontal displacement.

The projected path of multilateral well No 3-A is presented below (see Figure 4). The upper sections were designed similar to wells No 1-A and 2-A, but at the same time it was planned to drill two lateral wells with 7,399 and 7,416m TD’s respectively, including the installation of a whipstock plug at a depth of 6,100m along the well with a zenith angle of 77.5 degrees.

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The 311.15mm (12 ¼»)section was successfully drilled to a depth of 5,049 meters along the wellbore, the zenith angle in this section was 71.1° and the horizontal displacement in this section totaled 3,825 meters at a vertical depth of 2,471 meters.

The 215.9mm (8 ½») section was successfully drilled to a measured depth of 6,119 meters, the zenith angle in this section was 77.6° and the horizontal displacement in this section totaled , meters at a vertical depth of 2,807 meters. There, the «head” of hanger of the tie-back string was set at a depth of 4,541m.

The 155.6mm (6 ⅛») section was successfully drilled to a measured depth of 7,418 meters and the horizontal displacement in this section totaled 6,065 meters at a vertical depth of 2,904 meters. The distinctive feature of No. 3-A well is a window cut in the 178mm tie-back string within the range of 6,054-6,059m measured depth (vertical depth of 2,794 m, with displacement at window totaling 4,777m). Thereby, the whipstock completed with a cutting mill layout was run through the tie-back string hanger and the window has been cut at a global record depth. Then, the 155.6mm (6 ⅛») section of the second hole was successfully drilled to a measured depth of 7,438 meters and the horizontal displacement in this section totaled 6,155 meters at a vertical depth of 2,880 meters.

More details on the preparation and performance of well construction operations are contained in the following sections of this article.

Preparation for Construction and Equipment Selection

The lack of drilling experience and information on remote offshore deposits posed high risks to the wells construction.

The project’s complexity consisted of a narrow mud weight window, drilling within the range of a depleted layer and the unstable clay.

At the same time, there were other specificities and complexities:

• Unusual design for an extended reach well, involving the use of small size bits in the horizontal section diameter, which raised additional difficulties for the annulus pressure control;

• Lack of ERD well drilling experience in the region increased the risk of failure, specifically on the projected path;

• Potentially high tortuosity level in the upper section, which could lead to increased loads on the drill pipe when drilling the horizontal section;

• Insufficient structural and geological information on the target formations, high probability of drilling out of the pay zones;

The specialists from NOVATEK JSC, Investgeoservice CJSC and Schlumberger have developed a close interaction between all stakeholders involved in drilling, likened to a silver bullet in solving problems; it was considered necessary to build a preliminary geo-technical model and apply real-time geo-mechanical tracking of drilling operations. Under the leadership of specialists from Investgeoservice CJSC, key technologies for directionally-controlled drilling, mud, drill bits and casing were applied in close collaboration with the rock mechanics engineers and geo-steering specialists, as well as the drilling contractor and operating company. The invested efforts resulted in the record-breaking performance for ERD drilling in mainland Russia.

In the first phase, a technical assessment was conducted regarding the capacities of the drilling rig (BU-6500), which was used in the development of the Yurkhar field in a period from 2008 to 2012. The analysis showed that a reinforced and updated drive system was required, this would increase the rigs torque. The replacement of the top drive system was performed in a short period. The modified BU-6500/450-ECRK-BM drilling rig (see Figure 5) has a lifting capacity of 450 tons and a reserve capacity for drilling wells up to 8,000m deep (depending on the design, drilling of even deeper wells is also possible).

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In addition, renovation to the drilling tools and pipe was also required for the successful construction of these record wells [6]. Since the rated torsion loads were close to and in some cases, exceeding the maximum make-up torque of standard threaded joints (API and GOST), as well as due to a  narrow window for drilling mud densities and formation frac gradients, these well construction projects initially contained the specification of second-generation bilateral joints (see Figure 6).

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Based on the previous application of SBT-139mm and SBT-127mm conventional drill pipe, traditionally used in this field, as well as pipes with first-generation double-shouldered joints, previously they were significant fluid losses during drilling the 5,000-6,500m deep wells and this required the operation of mud pumps and high pressure drilling equipment.

During the drilling preparation phase, it was thought necessary to minimize hydraulic pressure resistance in the drill string and annular space while simultaneously ensuring that there was sufficient reserve torsion strength in the joints. Several alternative layouts and previous field experiences [7] were analyzed and, as a result, the optimal combination of the drill string required for each of sections was successfully determined after a series of comparative calculations.

Based on these principles, it was decided [8] to change the size of the drill pipe at the top of column from 139.7mm to 149.23mm pipe stipulated by the project. Meanwhile, the selection of SBT-149.23*9.17mm with VX-57 joint (second-generation double-shouldered joints, see Figure 7), in comparison with the SBT-140 (5 ½ FH), ensured the increase of reserve torsion strength by 8.5%, with a simultaneous decrease of the external diameter of the joint by 13mm and increase of the internal drift diameter of the joint from 76.2 to 107.95 (more than 40%).

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The VX-50 joint was selected for SBT-127*9,19mm size pipe, as it ensures the increase of make-up torque by 96% compared to a standard NC-50 joint and increasing the internal drift diameter by 7%. For a pipe of 102*8.38mm size, it is necessary to ensure increased internal drift diameter of the box-and-pin joint in order to reduce the hydraulic pressure resistance as well as maintaining the necessary rate of make-up torque. Compared with the NC-40 joint, the VX-39 joint made it possible to increase the internal diameter of the joint by 34% with a simultaneous increase of make-up torque by 10% and reduction of the external diameter of the joint up to 127mm. More detailed comparison of characteristics are presented in Table 1.

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In order to reduce the wear on the external surface of the joint and the walls of the casing, which is caused by prolonged drill string rotation in the well, the drilling string was ordered and shipped with hard banding at the tool joint.

Lining the drill pipes with an internal plastic coating (IPC) ensured a slight decrease in hydraulic pressure resistance and most importantly, protected the internal surface of pipes from corrosion while they were out of the well.

All the drill pipes were manufactured in accordance with API 5DP, with additional requirements of PSL 3, including the impact tests at a temperature of -20 {1>°<1} c (for comparison, the usual pipe, without the additional requirements, is impact-tested at room temperature). Such hardy drill pipes are best suited for operations under the low temperature conditions of the fields above the Arctic Circle.

It is worth noting that for carefree operation of premium drill pipe with high-torque double-shouldered joints, refitting the setbacks of the drilling rig is required. One should be aware that the standard cover for the setbacks is made of sheet steel with notches, while the drill pipe in the stand, set by the nipple on such a cover that it may leave marks on the surface of the stop face of the drill-pipe nipple because of its high weight. After some time, such an operation may lead to the damage of the stop face, which will require re-facing or repair. To reduce the probability of damaging the drill-pipe nipple and to extend the drill-pipe overhaul intervals, the surface of setbacks on the mentioned drilling rigs were covered with boards made of solid wood with additional shock absorbers made of rubber. Operational experience has shown that this decision was justified, because from the start of handling the pipes and up to now, there was no rejection of pipe due to poor condition of the internal drill-pipe thread and nipple.

Another challenge, which was successfully resolved by specialists from Investgeoservice, is a necessity to install a drill pipe screen while using drilling tools, including high-tech drilling equipment (RSS, measurement-while-drilling (MWD) and logging while drilling (LWD)). As it is known, the drill pipe screen should be placed on coupling of the drill pipe tool joint and fixed by a landing ring, which sits in gap between the nipple spout and the groove coupling, in standard connectors (API/GOST). In double-shouldered joints this clearance is absent, as a second stop face is located there instead. Sets of protective top-drive adapters and removable landing filter rings were manufactured as a solution to this problem and the spout of the double-shouldered joint was shortened by the thickness of the rings (see Figure 8). As a result, a secure mounting of the screen, within the pipe, was provided and the high torque characteristics of upper joint of the drill string remained unchanged.

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The callipering of drill pipes with internal polymer coating was performed by the use of a special nylon drift gage (see Figure 9) in order to keep the internal lining from damaging (compared to the usage of universally applicable drift diameter gages made of steel).

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Using assemblies including the drill pipes with VX joints enabled a solution to the following issues:

• Reduction in the total hydraulic pressure losses in pipes and drill-pipe annulus by 20 – 40%, i.e. the opportunity to increase the hydraulic power on drill bit and the hydraulic shock force by 20 – 40%, in order to optimize the drilling performance indicators;

• Maintaining the annulus pressure values within a safe operating window, at the expense of a reduction of the diameters of the box-and-pin joints, which enabled the following:

•Minimization of risks of the well collapses;

•Minimization of risks of differential sticking;

•Minimization of risks of mud loss in the high-permeability formations.

• Improving the cleaning quality in the upper sections by increasing the drill pipe diameter from SBT-140 to SBT-149 (augment the rate of upstream speed in annulus);

• The strength of drill string throughout the pipe body remains the same despite the reduction of wall thickness (the project stipulates the use of 139.7mm
drilling tool with wall thickness of 10.6mm);

• In the second-generation double-shouldered joint thread, the loads are distributed more evenly along the length of threaded joint, so it reduces the probability of breaking the joint pin in emergency situations;

• Improving the cleaning quality in the middle and lower ranges at the expense of the annulus pressure and the increase of pumped solution because of the smaller diameter of joints;

• Higher make-up torque, which generates additional reserves for drilling the well with high values of torque on the upper drive;

• Minimization of torque at the expense of reducing lateral efforts;

• Lower cost of non-productive time and reduction of project costs due to decrease in the number of handlings, additional leaching and lack of sticking and therefore the costs of their replacement.

Thus the experience of Investgeoservice CJSC engineering group of companies, proper planning of the drilling processes and proper selection of drilling tools, pipe and equipment made it possible to successfully implement the project of drilling three ERD wells at the Yurkhar field.

Geo-mechanical Support

Prior to developing the project, special attention was paid to the project risk assessment and identification of the  varies ways and solutions for their prevention.

As it has already been noted, the sustainability of extended reach wellbore presented a serious problem during the drilling operations, especially while drilling with high zenith angles through the shale sections. At the Yurkhar field, there are specific problems related to the stability of the borehole:

• Depletion of the producing beds and a decrease the of reservoir pressure contribute to the fracture gradient reduction and lost drilling mud;

• Unstable shale sections, in particular the «chocolate clay» sections.

The presence of both those particular cases drastically narrowed the safe mud weight window and assigned significance (in terms of wall sustainability) to the changes in the drilling mud density, even for 0.01g/cm3.

The combined chart of pressure gradients based on the preliminary drilling geo-technical model of one of the project wells is shown in Figure 10.

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The above figure gives a good view of pressure gradient changes depending on the depth. It is visible, how the fracture and wall collapse gradients change in one of the points depending on the values of the azimuth and zenith angles. The zenith angle changes have the strongest impact, when, at zero degrees, the safe window between the gradients of borehole walls collapse and fracturing is maximum; but with increase of the zenith angle up to 90 degrees, a narrowing of its borders takes place, up to and almost a complete disappearance of the safe window. This is due to the significantly higher accident rate at drilling horizontal wells in comparison with the directionally-controlled wells. There is also the impact of azimuth angle on the path’s position in space, delineated by the value of the safe window between gradients of fracturing and wall collapse.

One of the key solutions consists in application of geo-mechanics prior to drilling and in real time mode. The use of a geo-mechanical model at planning stage enabled identification of «difficult» sections and safe limits of equivalent circulating density, which served as a basis for making and choosing solutions and technologies. To get the most accurate values on the safe limits of equivalent circulating density, the geo-mechanical model was updated in real-time mode, based on logging carried out in the BHA  during the drilling operations via the use of geophysical research tools (GIS). Based on the equivalent circulating density (ECD) data measured by a bottom hole pressure sensor, drilling modes were selected to ensure adherence to the established safe limits.

In order to ensure the safety of drilling within each section, a special formula of drilling mud was selected to provide acceptable values of ECD and low friction ratios. Based on the results of this modeling, the drilling and wash-out modes, rate of tripping and of direct/back reaming, as well as the speed of running the casing strings and liners were selected. For trouble-free drilling at the preliminary modeling stage, the mechanical properties models (MPM) were obtained and the calculation for the borehole wall stability (CBWS) was carried out for three projected wells. The synthetic well-logging curves transferred from the key wells, the reservoir pressure data and the test results of the core samples taken from previously drilled wells, all served as data for building the MPM and CBWS models.

The main purpose of the borehole stability calculation for the designed wellbore is to define the limits of the equivalent mud weight, the awareness of which will allow one to avoid problems with wellbore stability. In the course of this survey, the calculation of the fracture and collapse gradients, calculation and calibration of the elastic properties of the rocks in the borehole environment and the calculation of the wellbore wall stability to determine the safe windows of the specific gravity of the drilling mud, as well as identification of the risks associated with borehole instability were determined.

The available logging data was enough to carry out detailed calculations on the borehole wall stability. The logging tools used in the BHA allowed further validation of the constructed model. The validation was carried out on the basis of the comparison of the calculation results from the caliper measurement records (before and after tripping). Moreover, an extended leak-off test (ELOT) was carried out during drilling operations in the casing shoe area, which allowed the calibration of the stability model.

The following tasks were resolved to achieve the target goals:

• Initial data audit;

• Calculation and calibration of the mechanical properties and the hardness of rocks for the key wells;

• Calculation and calibration of the key well stresses on the bearing drilling string

• Calculation on borehole stability as regards to the key wells;

• Transfer of elasticity and strength properties for the designed wellbores;

• Conclusions and recommendations on drilling

Because of the narrow window regarding the equivalent circulating density and high risks associated with the wellbore sustainability, the necessity to renew the calculations under the geo-mechanical model in a real time mode and to monitor the operating parameters of the drilling operations within the calculated limits was made evident. Based on the preliminary calculations of the wellbore wall stability, the safe boundaries of the mud weight parameters were identified and a set of engineering technologies required for this calculation were selected, for which purpose the GIS bottom hole assembly in the BHA was furnished with additional broadband acoustic (BALD) density (GGK-p) and neutron (NL) logging tools. Based on the data transmitted to the surface from the BALD, GGK-p and NL tools in real time mode, the elasticity and strength properties of the formation were calculated. Based on which, a continuous calculation of the wellbore wall stability was conducted in real time (see Figure 11).

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During the drilling operations, a team of geo-mechanical engineers carried out the monitoring and control over the following basic parameters:

• Renewal of wellbore stability model in a real time;

• Optimization of specific weight and rheology of the drilling mud based on the geo-mechanic calculation results;

• Monitoring and analysis of mechanical drilling parameters;

• Monitoring and provision of the recommendations on the drilling optimization and trips;

• Monitoring of wellbore conditions.

As a result of the reliable information received, in real time, the maximum control over the wellbore conditions was successful and the most effective selection of the modes and other various drilling operations were ensured and optimized as well. As a result, the Operator managed to cut some of the previously planned tripping operations while retaining the high quality of borehole and managing to increase the rate of penetration (ROP) by 30% compared with the planned drilling program.

Unique Set of Well Construction Technologies

At the planning stage, special attention had already been paid to the proper selection of drilling technologies. The techniques used for development of the drilling system at the Yurkhar field were based on carefully detailed planning and modeling of the borehole and sub-soil conditions, as well as the evaluation of the results by combining all of the different technologies. The appropriateness of the drilling system (see Figure 12) for achieving effective results should not be underestimated, because many operational conditions, such as the wellbore stability, do not allow for a trial-and-error situation, as any negative outcome would have had an impact on achieving the desired results and in some cases – on the overall well construction [9].

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BHA

Currently, the proposed Rotary Steering Systems (RSS) are the best choice for ERD well drilling, as they provide directional drilling with continuous rotation of drilling string, i.e. they provide conditions for effective cuttings removal that minimize the risks of the BHA sticking.

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RSS (see Figure 13) allows for the control of the borehole deviation in all three planes during drill string rotation. To change the drilling direction, this unique tool has drill-powered arms pushing off from the formation being drilled whilst the drill string is rotated. Technologically, this tool may be used independently or in combination with telemetry and logging tools providing a real-time communication with surface during the drilling works (MWD/LWD). The system consists of two main components:

• Diverter Node   &   •  Control Node

The Diverter Node is located immediately above the bit and represents a solid mechanical structure including three drill-powered arms and a hydraulic control system. The arms can be actuated by turning a valve, which selectively directs the high-pressure mud into each of drives in the order of their rotation. The angular position of the turning valve, compared to the body of diverter node, determines which of the starters are under load against the rocks.

The Control Node is connected with the Diverter node and is intended to manage the system’s performance for the deviating the drill bit. It consists of a gyroscopically stabilized platform with on-board electronics and sensors, freely rotating impellers, installed at the bearing face and powered by the drilling mud. The platform is mounted on bearings inside a specially designed drill collar. These bearings provide only one degree of freedom in turning the platform during column rotation around the drill collar. At the same time, the drill collar is connected with a torque drive through the drive tool joint for turning the valve of the diverter node, and controls its angular position, which determines, in turn, the deviation angle of the drill bit.

The impact of drilling mud flow passing through impellers is used to rotate the control node around the drill collar. The torque transfer from impellers to platform is regulated by electrical resistance changes in the generator installed in the control node as a source of permanent magnetic force during the impeller’s rotation. The positive and negative effective torque is achieved by rotating the impellers in the opposite direction. During the rotation of the control node around the drill collar, an arm actuation takes place. Generator delivers power to the on-board system. The control node is equipped with accelerometers and magnetometers; it allows determining the angle and azimuth of the longitudinal axis of the control node platform, thereby defining the bit feeding direction. The control node fixed at a constant angle leads to the maximum deviation in the specific direction relative to the top position of the diverter or magnetic north. The reduction of the deviation rates should be done by order, resulting in a rotation of the control node in a special mode.

During the drilling operations, tool settings may be configured by changing the mud flow rates, usually within 20 % of the specified value. Such an opportunity ensures the continuation of drilling operations, if a communication channel with the tool is available. During this process, the control node perceives the telemetry orders by monitoring the changes of upper impeller torque and selects from a specified range of torque values one that is required to achieve the required deviation. Two-way communication is provided by the use of the MWD system through the impulse transmission system between the nodes. With commencement of each mud injection cycle, the device transmits the control signal, as well as the measured data (angle, azimuth, the total value of the earth’s gravitational field, magnetic field and status code). In the drilling mode, data received from the driver includes angle, azimuth and status code of device, confirming the current configuration of tool and the good quality of data reception.

When drilling the wells in question, rotary steering systems were used on drilling the following sections: 311.1mm under 244.5mm production string, 215.9mm under 177.8mm tie-back string, and 155.6mm under 127mm liner.

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To achieve the best performance indicators and drilling efficiency, to conduct real-time control over the drilling modes and to provide data for targeting the well, key directionally-controlled drilling and measurement technologies were applied (see Figure 14), including the broadband acoustic logging, high-speed telemetry, multifunctional logging tools with neutron porosity, density, resistance profiles in combination with the controlled rotary systems and PDC bits. Several new technologies were applied to conduct measurements and logging during drilling, amongst them a new generation of instrumentation and telemetry tools for logging the formation pressures that were used for the first time on Russia’s mainland.

These devices have successfully coped with the assigned tasks. Below is a list of the main advantages of RSS in comparison with DDM, as exemplified by drilled wells:

• Improved dynamics of drill string operations (no problems with the load transfer to bit);

• Increased rate of penetration;

• Improved cleaning of borehole (rotating frequency 140 min-1 minimum);

• Less risk of sticking the drill string;

• Improved quality of the borehole due to the reduction of micro-tortuosity (successful descent of production casing string);

• Time savings.

This article will continue in the March edition of ROGTEC Magazine.

Links and list of references

1. Official website of NOVATEK JSC

http://novatek.ru/

2. Official website of Investgeoservice CJSC
http://ingeos.ru/

3. Official website of PB VNIIBT JSC NGO
 http://www.vniibt.ru/

4. Official website of K&M Technology Group
http://www.kmtechnology.com/

5. Official website of “Schlumberger” company
http://slb.com/

6. Tuktarov D.H., Korchagin P.N., Okhotnikov A.B. Smith Production Technology LLC. Ways of optimization of long holes drilling hydraulics // Scientific e-Journal “Neftegazovoe Delo”-2011- #1.

7. Shokarev I.V., Gulov A.R., Vlasovets E.N., Suleymanov R.N. Integra-Drilling LLC; Vyalov V.V. NOVATEK- YURKHAROVNEFTEGAS LLC; Glebov E.V. NOVATEK JSC – Construction of record-breaking multilateral ERD well in the Taz Estuary water area. // Oil&Gas Innovations. -2011 -#12.

8. Vakhrushev A.V. Vallourec; Zhludov A.V., Gulov A.R., Chutskov S.P. Investgeoservice CJSC. Experience of implementation of high-torque threaded joints of VAM Express drill pipes by “Investgeoservice” group company // Report for international applied research conference “Construction and servicing of wells 2015”, “The Black Sea Oil & Gas Summit”, Anapa, September 21 to 26.

9. Glebov E.V. Shokarev I.V. and others NOVATEK JSC; Gulov A.R., Zhludov A.V. “Investgeoservice” CJSC; Chetverikov D.M., Dymov S.U., Yakovlev A.V., Dobrokhleb P.U., Petrakov U.A., Gainullin M.A. and others “Schlumberger”. Construction of
record-breaking multilateral ERD well in Yamal region // article SPE-171328 presented on 2014 SPE Russia Oil & Gas Conference & Exhibition, Russian Federation, Moscow, October 14-16, 2014.

10. Glebov E.V. “NOVATEK” JSC; Shokarev I.V. “Integra-Drilling” LLC; Zhludov A.V. “NES” LLC; Chimerebere O. Nkwocha “Geopro Technology Limited”; David Kay “Tercel Oilfield”. Technology of reduction of down drag for casing running in ERD wells in Arctic region of Russia // article SPE-149720 presented during SPE Russia Oil & Gas Conference and Exhibition-2011, Russian Federation, Moscow, October 17-18, 2011.

11. Glebov E.V., Shokarev I.V. “NOVATEK” JSC; Gulov A.R., Zhludov A.V. Investgeoservice CJSC; Dymov S.U., Dobrokhleb P.U., Kretsul V., Zadvornov D.A., Kondarev V., Fedotov A. “Schlumberger”. New records for drilling and multilateral completion as part of campaign on construction of ERD wells in Yurkhar field // article of SPE-176507, presented during SPE Russian Petroleum Technology Conference-2015, Russian Federation, Moscow, October 26-28, 2015.

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