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[a] Drilling Technology Research Institute， Shengli Petroleum Administration， Dongying， Shandong， China.
* Corresponding author.
Received 22 February 2013； accepted 18 March 2013
Abstract
The geologic condition in Yuanba Area is quite complex.The drilling problems of formation leakage， pressure differential sticking， narrow density windows and other issues are more and more prominent. Drilling efficiency is low with long drilling cycle because of abnormal complex engineering geological characteristics such as thick continental formation， interbeded sand shale， poor drillability， ultra-high pressure in J1z and T3x formation， narrow pressure window. 12 completed wells in Yuanba area are analyzed， the conclusion can be draw that improving drilling efficiency in Yuanba region is quite potential if complexity underlying can be decreased and ROP can be improved. In view of this， the matching drilling technologies and tools are introduced and applied， the result show that optimization technology of casing program， bit optimization， gas drilling technology， compound drilling technology and corresponding new tools has made great success in Yuanba area， the average ROP was increased by 20.25%， drilling period was shortened by 18.33%， and the average complex accident handling time was reduced by 25.40%， which provides a good reference for ultra-deep well drilling.
Key words： Ultra-deep well； Gas drilling； Bit optimization； Compound drilling； Drilling ROP
Sun， M. X. （2013）. Study and Application of New Technology to Increase Drilling Speed of Ultra-Deep Well in Yuanba Area. Advances in Petroleum Exploration and Development， 5（1），-0. Available from： URL： http：//www.cscanada.net/index.php/aped/article/view/j.aped.1925543820130501.1146
DOI： http：//dx.doi.org/10.3968/j.aped.1925543820130501.1146
INTRODUCTION
Yuanba area is full of large scale reef flat reservoir， locates in the south to Jiulong structural belt and west to Tongnanba anticline belt. It is another key exploration area of Sinopec after Pu Guang gas field， and it has been developed the dominant replacing position of transferring Sichuan gas to east project. However， the reservoir formations are buried deeply and have high hardness； all these disadvantages bring lots of difficulties for the highly-efficient drilling including flooding， well kick， well collapse， high hydrogen sulfide bearing and so on （Liu & Zhu， 2005； Yu， 2010）. In order to speed up the progress of exploration and development， the main influence factors of ROP are studied in Yuanba area and the matching drilling technologies and tools are introduced including casing program optimization， gas drilling technology， Managed Pressure Drilling technology， bit optimization， compound drilling technology， rock-breaking tools， down hole tools and ultra-deep well cementing in this paper. 1. Survey of ultra-deep well drilling in Yuanba area
From May 2006 to May 2010， 30 wells have been drilled with 16 completed wells （13 vertical wells and 3 sidetracking well） and 14 operating wells （13 vertical wells and 1 sidetracking well）.
Statistical data of 12 vertical wells are summarized （shown in Table 1） to draw the conclusion that the average drilled depth is 7044m， drilling circle is 469.06d， and completion circle is 528.74d. The drilling circles of different wells vary greatly， for example， the drilling circle of well Yuanba 1 is only 164.88d while that of well Yuanba 3 is 579.88d. Among the 12 vertical wells， the average middle completion interval is 164.88d， which is 31.2% of the average completion circle； net drilling prescription is only 36.71%. If complexity and accidents can be decreased， and then the non-productive prescription will be shortened， net drilling time and production efficiency will be improved， the drilling speed acceleration of ultra-deep wells in Yuanba area still has a great potential.
2. STUDY ON INFLUENCE OF ROP OF ULTRA-DEEP WELL IN YUANBA AREA
2.2 Accident and Trouble
From Table1 we can see that， the average non-production efficiency of ultra-deep wells in Yuanba area is 11.7% and some even more than 20%. The accident and trouble can be classified as followed：
（1） Drilling tools and bit problem： Sticking and breaking are likely to occur in gas drilling， sticking and bit problem are common in T3x complex layer. Statistical data study shows that these problems take up 33.97% of the accident time in this area.
（2） Flooding and lost circulation： The heterogeneity of pressure distribution causes frequent flooding and lost circulation， which takes not only lots of time but also a great quantity of drilling fluid， and causes serious economic loss.
（3） Accident in transfer to fluid drilling： Accident occurs frequently after gas drilling is transferred to conventional mud drilling， so it has no choice but to ream， sticking is likely to occur if worse.
（4） Cementing accident： Cementing engineering is difficult because of the high temperature and uncertainty of pressure bearing capacity. The accidents frequently occur， such as lost circulation， low return velocity and poor cementing quality.
3. NEW TECHNOLOGIES TO INCREASE ROP OF ULTRA-DEEP WELL IN YUANBA AREA
According to the engineering geological characteristics in Yuanba area， through study and introduce of foreign drilling technology， the drilling technical level in this area has greatly improved recently. 5 layers casing was adopted， which is suitable for ultra-deep well with complex pressure system； the main advantage lies in large scale section is decreased， the size of 4th spud is increased， intermediate casing is longer and the accident is decreased， the clearance between wellhole and the casing is more reasonable， cementing quality is improved， so the casing program is widely used in Yuanba area.
After isolating upper low pressure layer through casing program optimization， the 2nd spud is practiced with conventional drilling technology， which can not only avoid the coexistence circumstances of lost circulation and well kick as in Yuanba4， Yuanba21 and Yuanba22， but also increase the production effect.
3.2 Matching Technologies of Increasing ROP
The conventional drilling technology cannot meet requirement for rapid exploration and development of Yuanba area. In view of the difficulties of low speed， complex leakage， reservoir damage in Yuanba area， the corresponding technologies have been proposed to improve the ROP in this paper.
3.2.1 Gas Drilling Technology
In order to solve the difficulties of low speed， complex leakage， reservoir damage in Sichuan oil and gas fields， the gas drilling technology has been researched and tested since 2005.Four subject technologies have been formed including dry air drilling， atomization drilling， foam drilling and aeration drilling， at the same time， eight supporting technologies including geological adaptability evaluation， optimization design， underground fluid monitoring and control， air hammer drilling， medium conversion after gas drilling， gas coring， gas drilling horizontal well， dry casing cementing were proposed.The equipment and tools of gas drilling have realized localization of manufactures， the dry gas drilling technology has matured and been popularized （Hou et al.， 2008）. Since its 1st application in well Laojun 1 in 2005， gas drilling technologies have been important means to control well deviation and increase ROP in this section. Rich experience in solving malignant circulation loss and shale collapsing by hydration swelling in long open hole section is accumulated and matching equipment is further improved. In view of the characteristic of many water layers over this section， mist drilling is introduced on the base of gas drilling （including N2）. Until April 2010， accumulated footage of gas drilling in Yuanba area has reached 61044.18m and ROP has been greatly improved， average ROP reached 8.57m/h， which is 3～8 times of fluid drilling in northeastern Sichuan basin， the single well drilling cycle was decreased for 60～90 days， serious leakage， borehole deviation， and other complex issues were controlled. Gas drilling technology has been a core technique of in continental strata of Yuanba Area and northeastern Sichuan basin. Statistical data of examples of typical wells using gas drilling is： average ROP reached 20.6m/h in section of 206-1540m in well Yuanba 3 and 30.72m/h in section of 648.85-1573.68m in Well Yuanba 22.
3.2.2 Managed Pressure Drilling Technology
Managed Pressure Drilling is define as a drilling technology that uses a pressurizable fluid system and specialized equipment to more precisely control the well bore pressure profile （Kozicz， 2006）. The main advantages lie in it can optimize the drilling process by decreasing Non Productive Time（NPT） and mitigating drilling hazards associated with the pressure fluctuation that occur when conventional drilling techniques are used. Managed pressure drilling technology is potential in increasing drilling security and ROP of ultra-deep well drilling with narrow pressure window （Vieira， et al.， 2008）.
In 2008， pilot test was practiced in T3x formation section （4192.00 m-4611.73 m） of well Yuanba 12， with the footage of 419.73 m and average ROP of 1.39 m/h. Comparing with ROP of 0.75m/h in the same section of well Yuanba 1， the average ROP increases by 84%， lately it was practiced in T3x formation in well Yuanba 22 and well Yuanba 11. the statistical data as follows： the average ROP is 0.81 m/h with the footage of 91.67 m（3756.32 m-3847.99 m） in well Yuanba 22 and 1.34 m/h with the footage of 402.36 m （4494.01 m-4896.37 m） in Yuanba 11. Presently， Managed pressure drilling has been a feasible technology in J1z and T3x formation in Yuanba area.
3.2.3 Bit Optimization
Bit optimization technology is established based on stratigraphy and rock property， including processing of logging data， bit development and field application. The single logging parameter calculation models considering the factor of acoustic time or formation density and the multiple logging parameter calculation models are established in this block to determine the value of the rock drillability. The calculation errors that produce in the single logging parameter calculation models are corrected by the multiple logging parameter calculation models and the rock drillability profiles are found out （Figure 1）.
Generally， effective roller bit should be chose and PDC bit should be avoid in continental strata section of sandstone and sandy conglomerate layer， while PDC bit can be chose in large scale section of mudstone. In order to increase ROP， PDC bit is recommended in marine strata section of T2l formation to T1f formation， effective roller bit is recommended in P2ch formation， and impregnated bit is introduced in continental strata section in J1z to T3x formation. The results show that this method can meet the need of application in Yuanba area （Figure 2）. Figure 1
Drillability Grade with Depth
Figure 2
Increasing Proportion of ROP After Bit Optimization
3.2.4 Compound Drilling Technology
As an effective means of increasing ROP， compound drilling of PDC bit with screw is widely used in marine strata section， and pilot test in continental strata section has made much progress （Eddie & John， 1981； Feng， 2007）. By optimizing of screw size， bit type， drilling parameters， ROP can be increased by effectively in marine strata. As is showed in Figure 3， ROP is increased by 15.4%， 37.32% and 73.22% in T2l， T1j and T1f section using Compound drilling technology. At the same time， this technology is adaptive to fast drilling in middle and deep formation， high deviated structure， hole trajectory control in directional drilling and angle holding drilling.
Figure 3
ROP of Compound Drilling Technology with Conventional Drilling
3.3 Rock-Breaking Tools and Down Hole Tools
3.3.1 Hydraulic Thruster
Hydraulic thruster is a new drilling tool， which can convert the liquid pressure energy into drilling pressure by using of circulating pump pressure as a driving force （Lin et al.， 2003）. Changing rigid pressure of drill collar into hydraulic flexible pressure， it can overcome uneven bit feed， bit jumping， fake WOB and other defects. At the same time， the hydraulic pressure device can change the drill string stress state， improve the stability and direction of the drilling tool， so it is conducive to the vertical drilling and can achieve high speed， high quality and low cost drilling purposes. The structural diagram of hydraulic thruster is showed as Figure 4， and application results are showed in efficiency.
（3） The drill ability of J1z and T3x formation is rather poor and bit failure is common in this section. Super abrasive bit should be further developed to increase its life span and avoid frequent trip， so as to increase its ROP.
（4） Dry process cementing reduces the procedures such as drilling fluid transfer， formation pressure-bearing testing， casing accessories， so it reduces middle completion interval， avoids the replacement efficiency problems in the process of common cementing， It should be further studied and promoted.
（5） The integrated technology to increase drilling speed of ultra-deep well has achieved good field application results， which provides a good reference for ultra-deep well drilling.
REFERENCES [1] Liu， R. S.， & Zhu， D. W. （2005）. Main Technical Difficulties Encountered While Drilling Deep Wells and Countermeasures. Petroleum Drilling Techniques， 33（5）， 6-10.
[2] Yu， W. P. （2010）. Difficulty and Countermeasures for the Advance of the Deep Well Drilling Technology in China. Sino-Global Energy， 15（9）， 52-55.
[3] Hou， S. G.， Liu， X. Y.， & Yang， Y. K. （2008）. Application of Gas Drilling Technology in Northeast Sichuan Area. Petroleum Drilling Techniques， 36（3）， 24-28.
[4] Kozicz， J. （2006）. Managed Pressure Drilling-Recent Experience， Potential Efficiency Gains， and Future Opportunities. IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition， 13-15 November 2006， Bangkok， Thailand.
[5] Vieira， P. et al. （2008）. Constant Bottomhole Pressure， Managed Pressure Drilling Technology Applied in an Exploratory Well in Saudi Arbia. SPE/IADC Managed Pressure Drilling and Underbalanced Operations Conference and Exhibition， 28-29 January 2008， Abu Dhabi， UAE.
[6] Eddie， R. H.， & John， N. M. （1981）. Laboratory Evaluation of PDC Drill Bits Under High-Speed and High-Wear Conditions. Journal of Petroleum Technology， 33（12）， 2316-2321.
[7] Feng， D. （2007）. Study on Compound Drilling Technology of Turbodrill. Oil Drilling & Production Technology， 29（3）， 19-21.
[8] Lin， Y. H.， Huang， W. Z.， & Shi， T. H. （2003）. Development and Application of the Thruster. Oil Drilling & Production Technology， 25（3）， 1-3.
[9] Li， G. S.， Shen， Z. H.， & Zhang， S. P. et al. （2003）. Development and Field Tests of Self-Resonating Cavitating Water Jet Nozzle for Oilwell Drilling. Petroleum Drilling Techniques， 31（5）， 11-12.
[10] Li， G. S.， Shen， Z. H.， & Zhou， C. S. et al. （2005）. Advances in Investigation and Application of Self-Resonating Cavitating Water Jet. Engineering Science， 7（1）， 27-32.
[11] Guo， Y. H.， He， S. M.， & Song， J. W. （2012）. Application of TorkBuster Torsion Impactor to Drilling-Speed Increase in Yuanba Area. Natural Gas Technology and Economy， 6（3）， 52-54.
[12] Wang， C. L.， Sun， Y. H.， & Liu， B. C. et al. （2011）. Experiment and Rock Fragmentation Mechanism of Bionic Coupling Impregnated Diamond Bit. Journal of Central South University （Science and Technology， 42（5）， 1321-1325.
* Corresponding author.
Received 22 February 2013； accepted 18 March 2013
Abstract
The geologic condition in Yuanba Area is quite complex.The drilling problems of formation leakage， pressure differential sticking， narrow density windows and other issues are more and more prominent. Drilling efficiency is low with long drilling cycle because of abnormal complex engineering geological characteristics such as thick continental formation， interbeded sand shale， poor drillability， ultra-high pressure in J1z and T3x formation， narrow pressure window. 12 completed wells in Yuanba area are analyzed， the conclusion can be draw that improving drilling efficiency in Yuanba region is quite potential if complexity underlying can be decreased and ROP can be improved. In view of this， the matching drilling technologies and tools are introduced and applied， the result show that optimization technology of casing program， bit optimization， gas drilling technology， compound drilling technology and corresponding new tools has made great success in Yuanba area， the average ROP was increased by 20.25%， drilling period was shortened by 18.33%， and the average complex accident handling time was reduced by 25.40%， which provides a good reference for ultra-deep well drilling.
Key words： Ultra-deep well； Gas drilling； Bit optimization； Compound drilling； Drilling ROP
Sun， M. X. （2013）. Study and Application of New Technology to Increase Drilling Speed of Ultra-Deep Well in Yuanba Area. Advances in Petroleum Exploration and Development， 5（1），
DOI： http：//dx.doi.org/10.3968/j.aped.1925543820130501.1146
INTRODUCTION
Yuanba area is full of large scale reef flat reservoir， locates in the south to Jiulong structural belt and west to Tongnanba anticline belt. It is another key exploration area of Sinopec after Pu Guang gas field， and it has been developed the dominant replacing position of transferring Sichuan gas to east project. However， the reservoir formations are buried deeply and have high hardness； all these disadvantages bring lots of difficulties for the highly-efficient drilling including flooding， well kick， well collapse， high hydrogen sulfide bearing and so on （Liu & Zhu， 2005； Yu， 2010）. In order to speed up the progress of exploration and development， the main influence factors of ROP are studied in Yuanba area and the matching drilling technologies and tools are introduced including casing program optimization， gas drilling technology， Managed Pressure Drilling technology， bit optimization， compound drilling technology， rock-breaking tools， down hole tools and ultra-deep well cementing in this paper. 1. Survey of ultra-deep well drilling in Yuanba area
From May 2006 to May 2010， 30 wells have been drilled with 16 completed wells （13 vertical wells and 3 sidetracking well） and 14 operating wells （13 vertical wells and 1 sidetracking well）.
Statistical data of 12 vertical wells are summarized （shown in Table 1） to draw the conclusion that the average drilled depth is 7044m， drilling circle is 469.06d， and completion circle is 528.74d. The drilling circles of different wells vary greatly， for example， the drilling circle of well Yuanba 1 is only 164.88d while that of well Yuanba 3 is 579.88d. Among the 12 vertical wells， the average middle completion interval is 164.88d， which is 31.2% of the average completion circle； net drilling prescription is only 36.71%. If complexity and accidents can be decreased， and then the non-productive prescription will be shortened， net drilling time and production efficiency will be improved， the drilling speed acceleration of ultra-deep wells in Yuanba area still has a great potential.
2. STUDY ON INFLUENCE OF ROP OF ULTRA-DEEP WELL IN YUANBA AREA
2.2 Accident and Trouble
From Table1 we can see that， the average non-production efficiency of ultra-deep wells in Yuanba area is 11.7% and some even more than 20%. The accident and trouble can be classified as followed：
（1） Drilling tools and bit problem： Sticking and breaking are likely to occur in gas drilling， sticking and bit problem are common in T3x complex layer. Statistical data study shows that these problems take up 33.97% of the accident time in this area.
（2） Flooding and lost circulation： The heterogeneity of pressure distribution causes frequent flooding and lost circulation， which takes not only lots of time but also a great quantity of drilling fluid， and causes serious economic loss.
（3） Accident in transfer to fluid drilling： Accident occurs frequently after gas drilling is transferred to conventional mud drilling， so it has no choice but to ream， sticking is likely to occur if worse.
（4） Cementing accident： Cementing engineering is difficult because of the high temperature and uncertainty of pressure bearing capacity. The accidents frequently occur， such as lost circulation， low return velocity and poor cementing quality.
3. NEW TECHNOLOGIES TO INCREASE ROP OF ULTRA-DEEP WELL IN YUANBA AREA
According to the engineering geological characteristics in Yuanba area， through study and introduce of foreign drilling technology， the drilling technical level in this area has greatly improved recently. 5 layers casing was adopted， which is suitable for ultra-deep well with complex pressure system； the main advantage lies in large scale section is decreased， the size of 4th spud is increased， intermediate casing is longer and the accident is decreased， the clearance between wellhole and the casing is more reasonable， cementing quality is improved， so the casing program is widely used in Yuanba area.
After isolating upper low pressure layer through casing program optimization， the 2nd spud is practiced with conventional drilling technology， which can not only avoid the coexistence circumstances of lost circulation and well kick as in Yuanba4， Yuanba21 and Yuanba22， but also increase the production effect.
3.2 Matching Technologies of Increasing ROP
The conventional drilling technology cannot meet requirement for rapid exploration and development of Yuanba area. In view of the difficulties of low speed， complex leakage， reservoir damage in Yuanba area， the corresponding technologies have been proposed to improve the ROP in this paper.
3.2.1 Gas Drilling Technology
In order to solve the difficulties of low speed， complex leakage， reservoir damage in Sichuan oil and gas fields， the gas drilling technology has been researched and tested since 2005.Four subject technologies have been formed including dry air drilling， atomization drilling， foam drilling and aeration drilling， at the same time， eight supporting technologies including geological adaptability evaluation， optimization design， underground fluid monitoring and control， air hammer drilling， medium conversion after gas drilling， gas coring， gas drilling horizontal well， dry casing cementing were proposed.The equipment and tools of gas drilling have realized localization of manufactures， the dry gas drilling technology has matured and been popularized （Hou et al.， 2008）. Since its 1st application in well Laojun 1 in 2005， gas drilling technologies have been important means to control well deviation and increase ROP in this section. Rich experience in solving malignant circulation loss and shale collapsing by hydration swelling in long open hole section is accumulated and matching equipment is further improved. In view of the characteristic of many water layers over this section， mist drilling is introduced on the base of gas drilling （including N2）. Until April 2010， accumulated footage of gas drilling in Yuanba area has reached 61044.18m and ROP has been greatly improved， average ROP reached 8.57m/h， which is 3～8 times of fluid drilling in northeastern Sichuan basin， the single well drilling cycle was decreased for 60～90 days， serious leakage， borehole deviation， and other complex issues were controlled. Gas drilling technology has been a core technique of in continental strata of Yuanba Area and northeastern Sichuan basin. Statistical data of examples of typical wells using gas drilling is： average ROP reached 20.6m/h in section of 206-1540m in well Yuanba 3 and 30.72m/h in section of 648.85-1573.68m in Well Yuanba 22.
3.2.2 Managed Pressure Drilling Technology
Managed Pressure Drilling is define as a drilling technology that uses a pressurizable fluid system and specialized equipment to more precisely control the well bore pressure profile （Kozicz， 2006）. The main advantages lie in it can optimize the drilling process by decreasing Non Productive Time（NPT） and mitigating drilling hazards associated with the pressure fluctuation that occur when conventional drilling techniques are used. Managed pressure drilling technology is potential in increasing drilling security and ROP of ultra-deep well drilling with narrow pressure window （Vieira， et al.， 2008）.
In 2008， pilot test was practiced in T3x formation section （4192.00 m-4611.73 m） of well Yuanba 12， with the footage of 419.73 m and average ROP of 1.39 m/h. Comparing with ROP of 0.75m/h in the same section of well Yuanba 1， the average ROP increases by 84%， lately it was practiced in T3x formation in well Yuanba 22 and well Yuanba 11. the statistical data as follows： the average ROP is 0.81 m/h with the footage of 91.67 m（3756.32 m-3847.99 m） in well Yuanba 22 and 1.34 m/h with the footage of 402.36 m （4494.01 m-4896.37 m） in Yuanba 11. Presently， Managed pressure drilling has been a feasible technology in J1z and T3x formation in Yuanba area.
3.2.3 Bit Optimization
Bit optimization technology is established based on stratigraphy and rock property， including processing of logging data， bit development and field application. The single logging parameter calculation models considering the factor of acoustic time or formation density and the multiple logging parameter calculation models are established in this block to determine the value of the rock drillability. The calculation errors that produce in the single logging parameter calculation models are corrected by the multiple logging parameter calculation models and the rock drillability profiles are found out （Figure 1）.
Generally， effective roller bit should be chose and PDC bit should be avoid in continental strata section of sandstone and sandy conglomerate layer， while PDC bit can be chose in large scale section of mudstone. In order to increase ROP， PDC bit is recommended in marine strata section of T2l formation to T1f formation， effective roller bit is recommended in P2ch formation， and impregnated bit is introduced in continental strata section in J1z to T3x formation. The results show that this method can meet the need of application in Yuanba area （Figure 2）. Figure 1
Drillability Grade with Depth
Figure 2
Increasing Proportion of ROP After Bit Optimization
3.2.4 Compound Drilling Technology
As an effective means of increasing ROP， compound drilling of PDC bit with screw is widely used in marine strata section， and pilot test in continental strata section has made much progress （Eddie & John， 1981； Feng， 2007）. By optimizing of screw size， bit type， drilling parameters， ROP can be increased by effectively in marine strata. As is showed in Figure 3， ROP is increased by 15.4%， 37.32% and 73.22% in T2l， T1j and T1f section using Compound drilling technology. At the same time， this technology is adaptive to fast drilling in middle and deep formation， high deviated structure， hole trajectory control in directional drilling and angle holding drilling.
Figure 3
ROP of Compound Drilling Technology with Conventional Drilling
3.3 Rock-Breaking Tools and Down Hole Tools
3.3.1 Hydraulic Thruster
Hydraulic thruster is a new drilling tool， which can convert the liquid pressure energy into drilling pressure by using of circulating pump pressure as a driving force （Lin et al.， 2003）. Changing rigid pressure of drill collar into hydraulic flexible pressure， it can overcome uneven bit feed， bit jumping， fake WOB and other defects. At the same time， the hydraulic pressure device can change the drill string stress state， improve the stability and direction of the drilling tool， so it is conducive to the vertical drilling and can achieve high speed， high quality and low cost drilling purposes. The structural diagram of hydraulic thruster is showed as Figure 4， and application results are showed in efficiency.
（3） The drill ability of J1z and T3x formation is rather poor and bit failure is common in this section. Super abrasive bit should be further developed to increase its life span and avoid frequent trip， so as to increase its ROP.
（4） Dry process cementing reduces the procedures such as drilling fluid transfer， formation pressure-bearing testing， casing accessories， so it reduces middle completion interval， avoids the replacement efficiency problems in the process of common cementing， It should be further studied and promoted.
（5） The integrated technology to increase drilling speed of ultra-deep well has achieved good field application results， which provides a good reference for ultra-deep well drilling.
REFERENCES [1] Liu， R. S.， & Zhu， D. W. （2005）. Main Technical Difficulties Encountered While Drilling Deep Wells and Countermeasures. Petroleum Drilling Techniques， 33（5）， 6-10.
[2] Yu， W. P. （2010）. Difficulty and Countermeasures for the Advance of the Deep Well Drilling Technology in China. Sino-Global Energy， 15（9）， 52-55.
[3] Hou， S. G.， Liu， X. Y.， & Yang， Y. K. （2008）. Application of Gas Drilling Technology in Northeast Sichuan Area. Petroleum Drilling Techniques， 36（3）， 24-28.
[4] Kozicz， J. （2006）. Managed Pressure Drilling-Recent Experience， Potential Efficiency Gains， and Future Opportunities. IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition， 13-15 November 2006， Bangkok， Thailand.
[5] Vieira， P. et al. （2008）. Constant Bottomhole Pressure， Managed Pressure Drilling Technology Applied in an Exploratory Well in Saudi Arbia. SPE/IADC Managed Pressure Drilling and Underbalanced Operations Conference and Exhibition， 28-29 January 2008， Abu Dhabi， UAE.
[6] Eddie， R. H.， & John， N. M. （1981）. Laboratory Evaluation of PDC Drill Bits Under High-Speed and High-Wear Conditions. Journal of Petroleum Technology， 33（12）， 2316-2321.
[7] Feng， D. （2007）. Study on Compound Drilling Technology of Turbodrill. Oil Drilling & Production Technology， 29（3）， 19-21.
[8] Lin， Y. H.， Huang， W. Z.， & Shi， T. H. （2003）. Development and Application of the Thruster. Oil Drilling & Production Technology， 25（3）， 1-3.
[9] Li， G. S.， Shen， Z. H.， & Zhang， S. P. et al. （2003）. Development and Field Tests of Self-Resonating Cavitating Water Jet Nozzle for Oilwell Drilling. Petroleum Drilling Techniques， 31（5）， 11-12.
[10] Li， G. S.， Shen， Z. H.， & Zhou， C. S. et al. （2005）. Advances in Investigation and Application of Self-Resonating Cavitating Water Jet. Engineering Science， 7（1）， 27-32.
[11] Guo， Y. H.， He， S. M.， & Song， J. W. （2012）. Application of TorkBuster Torsion Impactor to Drilling-Speed Increase in Yuanba Area. Natural Gas Technology and Economy， 6（3）， 52-54.
[12] Wang， C. L.， Sun， Y. H.， & Liu， B. C. et al. （2011）. Experiment and Rock Fragmentation Mechanism of Bionic Coupling Impregnated Diamond Bit. Journal of Central South University （Science and Technology， 42（5）， 1321-1325.