Scholarly article on topic 'Technologies in deep and ultra-deep well drilling: Present status, challenges and future trend in the 13th Five-Year Plan period (2016–2020)'

Technologies in deep and ultra-deep well drilling: Present status, challenges and future trend in the 13th Five-Year Plan period (2016–2020) Academic research paper on "Materials engineering"

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{"Deep well" / "Ultra-deep well" / "Drilling techniques" / Progress / Challenge / Strategy / CNPC}

Abstract of research paper on Materials engineering, author of scientific article — Haige Wang, Yunhua Ge, Lin Shi

Abstract During the 12th Five-Year Plan period (2011–2015), CNPC independently developed a series of new drilling equipment, tools and chemical materials for deep and ultra-deep wells, including six packages of key drilling equipment: rigs for wells up to 8000 m deep, quadruple-joint-stand rigs, automatic pipe handling devices for rigs for wells being 5000/7000 m deep, managed pressure drilling systems & equipment, gas/fuel alternative combustion engine units, and air/gas/underbalanced drilling systems; seven sets of key drilling tools: automatic vertical well drilling tools, downhole turbine tools, high-performance PDC bits, hybrid bits, bit jet pulsation devices, no-drilling-surprise monitoring system, & casing running devices for top drive; and five kinds of drilling fluids and cementing slurries: high temperature and high density water-based drilling fluids, oil-based drilling fluids, high temperature and large temperature difference cementing slurry, and ductile cement slurry system. These new development technologies have played an important role in supporting China's oil and gas exploration and development business. During the following 13th Five-Year Plan period (2016–2020), there are still many challenges to the drilling of deep and ultra-deep wells, such as high temperatures, high pressures, narrow pressure window, wellbore integrity and so on, as well as the enormous pressure on cost reduction and efficiency improvement. Therefore, the future development trend will be focused on the development of efficient and mobile rigs, high-performance drill bits and auxiliary tools, techniques for wellbore integrity and downhole broadband telemetry, etc. In conclusion, this study will help improve the ability and level of drilling ultra-deep wells and provide support for oil and gas exploration and development services in China.

Academic research paper on topic "Technologies in deep and ultra-deep well drilling: Present status, challenges and future trend in the 13th Five-Year Plan period (2016–2020)"

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Available online at www.sciencedirect.com

ScienceDirect

Natural Gas Industry B xx (2017) 1-8

Research Article

www.elsevier.com/locate/ngib

Technologies in deep and ultra-deep well drilling: Present status, challenges

and future trend in the 13th Five-Year Plan period (2016-2020)

Wang Haige*, Ge Yunhua, Shi Lin

Drilling Research Institute of CNPC, Beijing 102206, China Received 10 April 2017; accepted 25 April 2017

Abstract

During the 12th Five-Year Plan period (2011—2015), CNPC independently developed a series of new drilling equipment, tools and chemical materials for deep and ultra-deep wells, including six packages of key drilling equipment: rigs for wells up to 8000 m deep, quadruple-joint-stand rigs, automatic pipe handling devices for rigs for wells being 5000/7000 m deep, managed pressure drilling systems & equipment, gas/fuel alternative combustion engine units, and air/gas/underbalanced drilling systems; seven sets of key drilling tools: automatic vertical well drilling tools, downhole turbine tools, high-performance PDC bits, hybrid bits, bit jet pulsation devices, no-drilling-surprise monitoring system, & casing running devices for top drive; and five kinds of drilling fluids and cementing slurries: high temperature and high density water-based drilling fluids, oil-based drilling fluids, high temperature and large temperature difference cementing slurry, and ductile cement slurry system. These new development technologies have played an important role in supporting China's oil and gas exploration and development business. During the following 13th Five-Year Plan period (2016—2020), there are still many challenges to the drilling of deep and ultra-deep wells, such as high temperatures, high pressures, narrow pressure window, wellbore integrity and so on, as well as the enormous pressure on cost reduction and efficiency improvement. Therefore, the future development trend will be focused on the development of efficient and mobile rigs, highperformance drill bits and auxiliary tools, techniques for wellbore integrity and downhole broadband telemetry, etc. In conclusion, this study will help improve the ability and level of drilling ultra-deep wells and provide support for oil and gas exploration and development services in China.

© 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Deep well; Ultra-deep well; Drilling techniques; Progress; Challenge; Strategy; CNPC

Since the 12th Five-Year Plan, China National Petroleum Corporation ("CNPC") has worked systematically on the challenges to drilling and completion of deep and ultra-deep wells, with the support of research projects from the state,

* Project supported by Key Petroleum & Petrochemical Projects NSFC "Basic research on the safe and efficient drilling and completion for deep HTHP wells" (No.: U1562212) and Subject 20 "key drilling technology and equipments for deep and ultra-deep wells" of National Science and Technology Major Project "Large-scale oil and gas fields and coalbed methane development" (No.: 2016ZX05020-003).

* Corresponding author.

E-mail address: wanghaigedri@cnpc.com.cn (Wang HG).

Peer review under responsibility of Sichuan Petroleum Administration.

CNPC and PetroChina. As a result, CNPC has independently developed a series of new equipment, tools, instruments, and chemical materials to support the operations in the Kuqa piedmont of the Tarim Basin and the Sichuan—Chongqing gas region in the Sichuan Basin. Meanwhile, the capacity of drilling deep wells has gradually improved with the continuous advancement of drilling equipment and technologies.

At present, global oil and gas exploration and development is facing severe challenges induced by poor quality of resources, complicated oil and gas targets, and strict requirements of safety and environmental protection. Working targets are turning from shallow layers to deep and ultra-deep

http://dx.doi.org/10.1016/j.ngib.2017.09.001

2352-8540/© 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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layers. Under this background, deep and ultra-deep well drilling technologies encounter new problems and challenges.

1. Technological progress in deep and ultra-deep well drilling during the 12th Five-Year Plan period

During the 12th Five-Year Plan period, with the support of national oil and gas special projects, CNPC special projects and other projects CNPC independently developed a series of core technologies and equipment, such as automatic vertical well drilling system, managed pressure drilling, and innovative drilling rig, which helped to improve CNPC's self-sufficiency and core competitiveness. The improving optimized and fast drilling/completion technologies for deep and ultra-deep wells drove the time efficiency of complex accidents to drop continuously and the drilling cycle to shorten significantly, thus effectively contributing to the increase of oil and gas reserves and quick production in some key areas like the Kuqa piedmont of the Tarim Basin and the Anyue gas field of Sichuan—Chongqing gas region [1 — 11]. Meanwhile, the quantity of deep and ultra-deep wells grew rapidly in recent years, as shown in Fig. 1.

The average drilling cycle of available wells in key areas of the Kuqa piedmont was 290 days in 2015, shorten by 44% and 237 days fewer than that in 2010, and the drilling cost per well was more than CNY10 million. In the Dabei—Keshen block, the time efficiency of complex accidents was 6.2% in 2010, 55.3% lower than that in 2010. From 2014 to 2015, 23 ultra-deep wells over 7000 m were drilled completely, recording an average drilling cycle of 315 days, 347 days fewer than that in the Well Keshen 1 completed in 2010. Key drilling indices for the Kuqa piedmont during the 12th Five-Year Plan period are shown in Table 1. In the Anyue gas field in Sichuan—Chongqing gas region, the drilling cycle of the 5000—5800 m exploratory wells targeting the Sinian was 189 days in the first round and decreased to 149 days in the third round. In the Cambrian Longwangmiao Fm gas reservoirs, the average drilling cycle of vertical wells was only 97 days, and that of horizontal wells was 146 days or only 114 days as the shortest, contributing greatly to the efficient development of the Longwangmiao Fm gas reservoirs.

Table 1

Main drilling indice for Tarim Kuqa piedmont area in the 12th Five-Year Plan period.

Year Drilled depth/m Drilling cycle/d Penetration rate/(m h 1)

2011 6774 478 1.49

2012 6318 330 2.26

2013 6480 270 2.45

2014 6897 320 2.38

2015 7341 330 2.71

1.1. Rigs for 8000-m deep wells and quadruple-joint-stand rigs for 9000-m deep wells were developed rapidly and successfully as the major drilling equipment in the piedmont [12—14]

With the innovative design concept, rigs for wells up to 8000 m were developed rapidly and successfully as a supplement to domestic rigs, since the 7000-m deep well rigs suffer inadequate load under large casing setting depth and the 9000-m deep well rigs are too costly, depending on the conditions in the Tarim piedmont and other areas. During the 12th Five-Year Plan period, 23 rigs for wells up to 8000 m deep were used widely as the major drilling equipment for the complex deep wells in the Tarim Kuqa piedmont. The salt layers at the large casing setting depth could be sealed in one operation, and the casing program changed from "five sections" to "four sections". With the 8000-m deep well rigs in use, the purchase cost reduced by about 20% and the drilling operation expenditure dropped by 37% compared with the 9000-m deep well rigs.

With the innovative concept of "quadruple-joint-stand", the first quadruple-joint-stand rig for 9000-m wells was developed in China and successfully applied in the drilling of Well Dabei 305 with 7515 m in depth in the Tarim Basin. Compared with the three-joint-stand rig used in the adjacent 9000-m well, the quadruple-joint-stand rig achieved a tripping speed of 15% higher, downhole complexities of 20% less, a drilling cycle of 6% shorter, and a drilling cost of CNY4 million less. Thus, it presented as a new efficient tool with higher ultra-deep well drilling speed and efficiency, and a supplement to supporting optimized and fast drilling and completion technologies for deep and ultra-deep wells.

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1.2. Domestically-made precise managed pressure drilling (MPD) systems became an effective and safe drilling technology for strata with narrow mud density window [8,9]

The PCDS-1, CQMPD-1 and XZMPD-1 precise MPD systems respectively developed by CNPC Drilling Research Institute, CNPC Chuanqing Drilling Engineering Company Limited and CNPC Xibu Drilling Engineering Company Limited kept in line with the overseas similar advanced technologies, with a bottomhole pressure control accuracy of ±0.35 MPa. These MPD systems are applicable in near-balanced and underbalanced managed pressure drilling operations under various conditions. They helped to realize "drilling according to the bottomhole pressure" and effectively addressed the complexities caused by narrow mud density window, such as lost circulation, well kick, borehole instability, and drill pipe sticking. In the Tarim Basin, Sichuan—Chongqing gas region, and overseas blocks, these MPD systems were applied in over 200 wells to successfully solve the drilling problem of "coexistence of blowout and mud loss". Especially, they efficiently supported the implementation of horizontal well development plan for the Ordovician reservoir in the Tazhong #I structure, the construction of Anyue gas field, and the shale gas development in Sichuan—Chongqing gas region. Moreover, these MPD systems were expanded to Indonesia and other overseas markets, allowing the CNPC enterprises to be competitive with the world-known technology service companies. These MPD systems became preferred options in the exploration and development of marine carbonate reservoirs and HTHP reservoirs with narrow mud density window.

1.3. Automatic vertical well drilling tools were gradually domesticalized and became a core technology for deflection control in fast penetration in the piedmont area [15,16]

The BH-VDT and XZ-AVDS automatic vertical well drilling systems were successfully developed by the CNPC Bohai Drilling Engineering Company Limited and the CNPC Xibu Drilling Engineering Company Limited. They can make deflection control in fast penetration realized for boreholes of 0215.9 mm to 0558.8 mm, with the deviation angle controlled below 1°. These systems reach the level of foreign similar products in terms of overall performance. In the Tarim piedmont area, the automatic vertical well drilling systems had displaced gradually the foreign products, thereby lowering significantly technical cost, and provided an independent technology for deflection control in fast penetration under the complicated geological conditions such as high steep structure and overthrust nappe structure. By virtue of these systems, Well Keshen 2-1-14 recorded the highest daily footage of 742 m, Well Dabei 101-2 created the drilling footage of 2047 m in one trip, and Well Etan 1 in the Qaidam Basin set a record with drilling time of 395.5 h in a single trip. To sum up, the successful development and application of automatic

vertical well drilling tools had effectively ensured the deflection control in fast penetration in the high steep structure and overthrust nappe structure, with satisfactory wellbore quality, thus laying a good foundation for wellbore integrity control.

1.4. Improvement of gas/underbalanced drilling technology and equipment and promotion of capabilities in lost circulation prevention & control and water control contributed to ROP enhancement in the complex formations in the Sichuan—Chongqing gas region and other areas [4,7,17]

Based on the packages of gas/underbalanced drilling equipment developed during the 11th Five-Year Plan period, and considering the problems in practical operations, the devices, such as gas-tight casing valve, high-pressure rotary BOP, continuous circulation valve for gas drilling, were developed with their performance indicators meeting the international advanced level, which supported the gas/under-balanced drilling technologies, and made China's gas/ underbalanced drilling capacity equivalent to the world leading level. These technologies/equipment were applied in 331 deep and ultra-deep wells in Sichuan, Tarim, Songliao and other basins, with a total footage of 43.69 x 104 m. Specifically, they were used in 231 wells for ROP enhancement, with an average ROP 3.78—11.24 times that in mud drilling. After they were used in 40 wells for lost circulation prevention & control, the cumulative reduction of mud loss amounted to over 20 x 104 m3, and the time for lost circulation treatment was reduced by 12.5 days for each well.

1.5. Complete drilling fluid systems helped to reduce the time efficiency of complex accidents in deep and ultra-deep wells [2,3,7,17,18]

During the 12th Five-Year Plan period, the main progress of drilling fluid systems for deep and ultra-deep wells was embodied in the conversion from water-based drilling fluids to oil-based drilling fluids and the successful development of high-performance water-based drilling fluids (similar to oil-based drilling fluid) in response to the environmental requirements. Several core treatment agents (e.g. main/assistant emulsifiers, filtrate reducers, and flow pattern adjusting agents) for high-density oil-based drilling fluid systems were developed independently and industrialized, helping to reduce the cost by 30% for replacing the imported products. Three types of oil-based drilling fluids, i.e. pure oil-based drilling fluid, invert oil emulsion drilling fluid, and synthetic-based drilling fluid, were developed successfully to adapt to different temperatures and densities. Besides, the complete technical industrial chain and service system, including oil-based drilling fluid preparation, maintenance, and recycling, and harmless treatment of wastes, were formed to become the key options for safe and rapid drilling of complex deep wells. Compared with the imported drilling fluids, the BH—WEI drilling fluid system with strong inhibition and high lubricity developed by the CNPC Bohai Drilling Engineering Company Limited

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could cost 50% less, meeting the low cost and localization goals. The high-temperature and high-density saturated brine drilling fluid and potassium calcium-based organic salt drilling fluid, with their performance indicators improved greatly, made the average complex accident rate in pilot applications decrease by more than 50%, and thus became the major drilling fluid systems for enhancing ROP and efficiency in the Tarim Basin, Sichuan—Chongqing gas region, and overseas complex deep wells.

1.6. Improved cementing technologies met the requirement of wells with high-temperature and large temperature difference [3,7,19—21]

The high-temperature and large-temperature-difference cementing slurry system effectively contributed to the cementing in high-temperature long cementing intervals and the super-retarding cementing in wells with large temperature difference. It had been used widely in more than 1000 deep wells in the Tarim, Sichuan, Bohai Bay and other basins and Jilin area, with the maximum application temperature of 162 °C, the longest cementing interval of 3000 m, and the maximum temperature difference of 80 °C. The longest cementing interval in a single operation was recorded in Huabei Oilfield, Well Shutan 1H, and the maximum setting depth (5989 m) of 0177.8 mm liners was realized in Well Niudong 102. In Jilin Oilfield, the best cementing quality (98%) under the most complex downhole conditions was created in Well Longshen 2-P 1. In the Gaoshiti—Moxi block of the Sichuan Basin, the 0177.8 mm liner (gas channeling prevention) cementing technologies were developed, represented by high-density and large-temperature-difference slurry system, normal and reverse cementing, contamination-resistant spacer fluid, cement slurry's column structure optimization, and packer liner-hanger, helping to basically avoid gas breakthrough from the bell mouth. Ductile cement slurry system, with good adaptability to the cement mechanical strength under the alternating stress, was the principal cementing technology for deep and ultra-deep wells and gas storage.

1.7. Some ROP-enhancing drilling tools with independent intellectual property rights gradually became the mainstream technologies for deep and ultra-deep wells [1,3,7,11,17]

A number of ROP-enhancing drilling tools t were gradually popular for deep and ultra-deep wells, such as highperformance PDC bit, hybrid bit, impregnated bit, HT-resistant screw drill, iso-wall thickness screw rod, metal screw rod, downhole turbine tool, bit jet pulsation device, and smart driller indicator. The smart driller indicator represented a breakthrough in the optimization of rock-breaking energy efficiency. Through real-time acquisition of drilling parameters and automatic intelligent recognition of downhole conditions by a built-in software, the smart driller indicator could make realized the real-time tracking and quantitative

evaluation of the rock-breaking energy efficiency of downhole bits and the vibration status of downhole drill string, so that drilling parameters can be optimized and downhole vibration can be avoided. According to the real-time signal of the smart driller indicator, the driller could apply the optimal WOB, rotary speed, pump stroke and other parameters, so that the matching between drilling rate and rock-breaking energy consumption was optimized. It had been applied in 50 wells/ operations in Yumen, Tarim, and Sichuan—Chongqing gas region, with the actual ROP being 20%—50% higher than that of adjacent wells. As a result, in May 2015, CNPC won, for the first time, the 45th E & P Meritorious Award for Engineering Innovation (Fig. 2). In March 2017, CNPC won the CIPPE Innovation Award — Gold.

2. Challenges to deep and ultra-deep well drilling/ completion technologies during the 13th Five-Year Plan period

Deep formations, contributing 30% to total oil resources and 60% to total gas resources, containing the maximum quantities of onshore residual resources, have the largest development potential and face the most drilling challenges. Wells in the Kuqa piedmont of Tarim Basin, the Anyue block of Sichuan and deep formations of Bohai Bay Basin have an average depth of more than 6000 m. In the Keshen block, a key target in Tarim Oilfield for increasing natural gas reserves and quick production during the 13th Five-Year Plan period, the average well depth approaches 7000 m. In the pre-salt reservoirs in East Sichuan Basin and existing exploration areas in West Sichuan Basin, the average well depth is more than 7000 m. Fig. 3 shows the well depth statistics of CNPC's key exploration areas in Kuqa piedmont area and Sichuan— Chongqing gas region.

With oil and gas exploration and development targets becoming more complicated, well depth increasing, and high temperature and high-pressure being more common, new technical challenges (i.e. large temperature difference and large pressure difference) occur frequently, leading to a higher time efficiency of complex accidents during drilling and a higher drilling cost. Thus, the drilling of deep and ultra-deep

Fig. 2. CNPC won the 45th E & P Meritorious Award for Engineering Innovation.

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8000 r 7 100 7 237

7000 - 6357 _ H 6049

Dabei Keshen a. b. c.

Tarim Basin Sichuan Basin

a. Shuangyushi-Shejianhe in NE Sichuan Basin

b. Lower Permian in West Sichuan Basin

c. Lower Palaeozoic in East Sichuan Basin

Fig. 3. Average TVDs in Kuqa piedmont area and Sichuane—Chongqing gas region.

wells becomes more challenging. The progress of reservoir stimulation technique will affect the mainstream well type for drilling, and "ultra-deep wells + horizontal wells + reservoir stimulation" will become the biggest technical challenge in the future. Fig. 4 shows the statistics of time efficiency of complex accidents in ultra-deep wells above 6000 m in Kuqa piedmont area and Sichuan—Chongqing gas region in the past three years.

2.1. Benchmarking with overseas deep and ultra-deep well drilling/completion technologies [7,17,22—29]

In developed countries, deep and ultra-deep well drilling technologies are well established, with the drilling depth up to 15000 m. The auxiliary equipment is automatic and intelligent, and the automatic drilling rigs capable of continuous trip and continuous circulation are being developed. There are a full series of deep rock breaking bits and auxiliary tools, including durable PDC bits, HT-resistant cone bits, impregnated bits and hybrid bits which are mature and applied in a large scale. High-temperature water-based and oil-based drilling fluids are successfully used. The measurement while drilling (MWD) and control while drilling (CWD)

technologies are relatively mature, and the tools are characterized by high HT tolerance, multiple measurable parameters, high transmission rate, and high system reliability. Some highend products, including automatic vertical well drilling tools and rotary steering systems, are maturely applied, and the technologies in intelligent drill pipes and seismic while drilling (SWD) have been applied in field operations. Deep well cementing technology is adapted to the working conditions of large temperature difference and large pressure difference in HTHP and long cementing intervals. The available cementing equipment, cementing tools and cement slurry systems are mature, and a new generation of cementing materials is being developed. Moreover, deep reservoir stimulation and other technologies are relatively mature, and the HT-resistant fracturing fluids, staging tools and surface fracturing equipment are kept in place. Coiled tubing operation technology and equipment performance are improved continuously, and extended to more applications, including deep operations and reservoir stimulations.

In view of CNPC's technologies, the drilling and completion technologies for wells above 6000 m are becoming mature, and those for wells between 7000 m and 8000 m have demonstrated great breakthroughs. Especially, rigs for 10000 m deep wells and top drives, gas drilling, under-balanced drilling and managed pressure drilling, high-temperature and high-pressure cementing, and high-temperature and high-density water-based drilling fluid reach the advanced international level. Research on automatic and intelligent drilling technologies has just started, and high efficient rock breaking technology for highly abrasive formations needs to be further improved. Rock-breaking tools have poor stability and reliability. MWD and CWD tools have low resistance to high temperature and pressure and poor adaptability. There is only one single reservoir stimulation technology. Moreover, the bits and downhole motors for deep and ultra-deep wells, HT-resistant MWD tools, and cementing/ completion tools for ultra-deep wells rely on import or overseas services.

2.2. Challenges of CNPC's deep and ultra-deep well drilling/completion technologies [7,17,29—31]

Fig. 4. Statistics of time efficiency of complex accidents in ultra-deep wells above 6000 m in the Kuqa piedmont area and Sichuan—Chongqing gas region.

In a long run, there are still many challenges in deep and ultra-deep well drilling. The deep and ultra-deep rocks are too tight to be drilled. Many rock strata reflect complexities and complicated pressure systems, which are difficult to be accurately predicted. Rigs show low efficiency in deeper formations. The drilling tools at Level-II high-temperature (204 °C) and high pressure (137.9 MPa) are less adaptable, and the drilling/completion technologies for Level-III hightemperature (260 °C) and high pressure (206.8 MPa) are not available yet. Drilling in deep formations with high abrasiveness is inefficient and slow. Deep reservoirs are less stimulated. Multi-pressure system is in conflict with the level of casing program.

To meet the above challenges, it is necessary to develop more advanced technologies. Typically, the technical R&D efforts should and will focus on automatic and intelligent

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drilling/completion technologies and equipment, high-efficient HT-resistant downhole rock breaking tools and MWD/CWD tools, HTHP well bore working fluids and cementing/ completion technologies, HTHP well test and formation test equipment, and efficient deep reservoir stimulation technology and equipment.

3. Future development of CNPC's deep and ultra-deep well drilling/completion technologies during the 13th Five-Year Plan period

3.1. Development ideas [32,33]

With the concept of "main business strategy driven, production target oriented and top-level design" as a guidance, great efforts should be made to acquire and develop cutting-edge technologies. Independent technological innovation and the introduction and absorption of new technologies should be reinforced to keep their technical capabilities at a leading level in the dominant sectors. The core technologies should be upgraded to further improve their competitiveness. The unique technologies should be integrated, and more researches should be conducted on specific technologies against the "bottlenecks" in production. The technologies facilitating business chain extension should be developed to ensure the business sustainability.

Wellbore life-cycle integrity management concept should be reinforced and the most effective technical means should be taken to prolong the borehole life, so as to maximize oil and gas exploration and development benefits.

With the concept of engineering-geology integration and collaborative innovation as a guidance, a group of cross-discipline and cross-domain core technologies should be developed to tackle the bottlenecks in deep and ultra-deep wells.

With automatic and intelligent drilling equipment for deep wells as leading technology, more efforts should be made to accelerate the development of domesticalized drilling equipment for deep and ultra-deep wells, so as to improve the guarantee for main business and the international competitiveness. With the support of informatization, large data and engineering software, drilling information and service businesses should be upgraded. With speed, quality and reliability as the key indexes, MWD leapfrog development should be promoted by collaborative innovation. With reservoir stimulation as a focus, geology-engineering integration should be carried out to promote reserves and production increase. Revolutionary measures should be taken to achieve more R&D innovations.

3.2. Development objectives [32,33]

During the 13th Five-Year Plan period, CNPC is committed to improve its deep and ultra-deep well drilling technologies to the advanced international level. CNPC will research and develop many core equipment, tools and softwares, including automatic drilling rigs for deep wells, and intelligent drilling

optimization and remote decision support systems. CNPC will develop innovatively and reserve proactively such key technologies as rigless drilling, seismic and geosteering while drilling, deep reservoir stimulation, and rotary preliminary exploration geosteering. Furthermore, drilling and completion cycle for deep and ultra-deep wells will be shortened by 15% and the time efficiency of complex accidents will be reduced by 50%.

During the 13th Five-Year Plan period, some new R&D results are expected, including core equipment (e.g. automatic drilling rigs for deep wells, and well/production testing packages for 140 MPa/175 °C), working fluids (e.g. large pressure difference cementing working fluids, and novel dual-protective drilling fluids), high-end tools (e.g. high-efficient bits, small-size downhole safety monitoring systems, and high-speed high-capacity information transmission drill pipes), and key softwares (e.g. drilling intelligent optimization and remote decision support system).

3.3. Development orientation and planning [32,33]

According to CNPC's drilling science and technology development thought and goal for the 13th Five-Year Plan, and the planning principles of focusing on the integrated design of national and corporate projects, main business demands, long-term scientific and technological development capabilities, and transformation and application of scientific and technological achievements, both national and corporate major science and technology projects will be arranged as a whole with the consideration to basic and common issues, equipment/ technology, and integrated/associated facilities.

3.3.1. New drilling/completion technologies and methods for deep complex wells

In view of deep and complex formations where the wellbore conditions are poor and challenging, researches will be made on rigless drilling, efficient rock breaking, new materials of working fluid, deep reservoir stimulation, and while-drilling preliminary formation exploration. Such technologies as rig-less drilling and efficient rock breaking are expected to reach an advanced international level, and new theories of non-contact rock breaking and wellbore integrity will come into being. Specific efforts will be made on while-drilling preliminary formation exploration and well test of reservoir stimulation for ultra-deep wells, and key drilling/completion technologies for deep wells will be developed for industrialized application, so as to provide a basic support for sustainable development of drilling technologies.

Main researches will focus on:

(1) new technologies in improving cementing quality and wellbore integrity under the condition of large-scale volumetric fracturing, including micro expansive ductile and large temperature difference cement slurry, high strength-toughness and large pressure difference cement slurry, anti-leakage cement slurry, and pre-flush fluids for high-performance oil-based drilling fluids;

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(2) rigless drilling technologies, including general design of novel drilling devices, laboratory construction, and unit experimental prototype;

(3) new technologies, methods and materials for efficient rock breaking in high abrasive formations, including new type bits, high frequency vibration for rock breaking, while-drilling downhole vibration management, and non-contact rock breaking;

(4) new materials and a new system of wellbore working fluids, including new generation of wellbore working fluid, environment-friendly drilling fluids and treating agent, widely acceptable admixture, and new cementing materials;

(5) mechanical mechanism and control technologies of wellbore integrity for complex deep wells and horizontal wells, including cement sealing completeness mechanism, life-cycle drilling and completion string design, micro fracturing in-situ stress detection for shale reservoirs, casing failure prevention, and wellbore integrity detection technology;

(6) OCTG engineering application in the harsh service conditions, including high-performance tubular goods;

(7) key technologies of reservoir stimulation and well test for ultra-deep wells, including integrated completion string and technological process, related technology/ equipment, and jet perforation technology; and

(8) downhole control engineering and while-drilling preliminary formation exploration, including while-drilling preliminary formation exploration methods.

3.3.2. New equipment and tools for automatic and high-efficient drilling and completion of deep and ultra-deep wells

In terms of deep and ultra-deep wells, their engineering and geological conditions are complicated, and core technologies are inadequate. Therefore, efforts will be made on automatic and intelligent drilling technology and equipment, as well as MWD/CWD technology and equipment, to form safe and high-efficient drilling and completion technologies. These technologies will provide a technical support for the efficient exploration and development of oil and gas in deep reservoirs.

Main researches will focus on:

(1) automatic drilling technologies and equipment for deep and ultra-deep wells, including efficient and fast drilling technology and equipment for deep and ultra-deep wells, while-drilling seismic wave measurement technology, and while-drilling high-temperature measurement equipment;

(2) key technologies and equipment for continuous tripping;

(3) key tools for high-performance assisted rock breaking and completion & well testing, including supporting tools for ROP enhancement, high-performance rock breaking bits for deep reservoirs, HT-resistant rotary automatic unlocking liner hangers, down hole safety valves for high-pressure gas wells, HP-resistant

packers, and completion and well testing integrated tools;

(4) high-strength and low-density OCTGs, including pipes with high strength, low density and high performance/ price ratio;

(5) drilling engineering design & control integrated software, including the upgraded version of drilling engineering design & control integrated software, and realtime drilling optimization and remote expert consultation decision support system.

3.3.3. Integration tests and popularization of drilling/ completion technologies

A batch of core drilling/completion technologies and equipment will be improved, upgraded and finalized by tests. Specific efforts will be made on such core technologies and equipment as high-speed large-capacity information transmission system, automatic processing devices of rig/strings for wells between 5000 m and 7000 m in depth, and expandable tubular drilling, and the core matching technologies such as deep well and ultra-deep well drilling, completion and well testing will be formed and put into large-scale application.

Such tests will include:

(1) field tests of major new drilling technologies, equipment and tools, including automatic processing system of rigs/ strings for wells between 5000 m and 7000 m in depth, electric rig 175 diesel generator set, particle impact drilling technology, high-speed large-capacity information transmission and intelligent drill pipes, while-drilling down hole safety monitoring, and expandable tubular drilling technology and equipment;

(2) integration and application of safe drilling/completion technologies for complicated sulfur-containing formations;

(3) integration and application of completion technologies for HTHP wells with high acidic medium; and

(4) integration and application of optimized and fast drilling/completion technologies in complex exploration areas.

4. Conclusions and suggestions

During the 12th Five-Year Plan period, CNPC achieved fast development of deep and ultra-deep well drilling/completion technologies and made breakthroughs in terms of new type rigs, managed pressure drilling, vertical drilling, oil-based drilling fluid, large temperature difference cementing, ductile cement slurry and others. As a result, complex accidents were effectively controlled, ROP was increased significantly, and drilling cycle was shortened. These technologies played an important role in supporting CNPC's exploration and development operations and improving the competitiveness of drilling at home and abroad.

As oil and gas exploration and development extends further to deep reservoirs, the Sichuan—Chongqing gas region, the Kuqa piedmont area of the Tarim Basin and other key regions

+ MODEL

8 Wang HG et al. / Natural Gas Industry B xx (2017) 1—8

of CNPC for oil and gas reserves and production increase during the 13th Five-Year Plan period are still facing many technical challenges and cost pressure brought by low oil price. Therefore, it is suggested that during the 13th Five-Year Plan period, researches and tests will be focused on new drilling/completion technologies and methods for deep and complex wells, new equipment and tools of automatic and high efficient drilling/completion for deep and ultra-deep wells, and integration and application of drilling/completion technologies. CNPC's deep and ultra-deep well drilling technologies are expected to reach advanced international level by the end of the 13th Five-Year Plan period.

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