CNPC has a well-established drilling engineering & technical service system comprising five specialized companies engaged in drilling services and capable of providing drilling services for customer from home and abroad under various geographic, climatic and geological conditions.
We have gained substantial experiences in the drilling of ultra-deep wells, horizontal wells, directional wells, underbalanced wells, non-conventional wells and special reservoirs. A series of underbalanced drilling techniques involving different medium such as air, nitrogen or natural gas are available.
In 2012, our 1,019 drilling rigs spudded 13,272 wells and completed 13,153 wells, with a total footage of 27.2 million meters, 0.79% more than in 2011. The drilling speed was further increased, with the average penetration rate increasing by 4.64% despite the average along-hole depth increasing by 85 meters year-on-year. In particular, the average drilling cycle of wells deeper than 4,000 meters was reduced by 10.4% year-on-year, and the average drilling cycle at Kuqa Mountain Front of the Tarim Basin decreased by more than 20%.
With the active expansion of the overseas drilling market, we won drilling contracts in Venezuela, Algeria, Kazakhstan, Uzbekistan, Iraq and Australia. Great Wall Drilling Company (GWDC) signed a comprehensive service contract for 80 geothermal wells in Kenya. An integrated upstream and downstream service mode for geothermal resource development took shape in the country. High-yield gas flows were obtained from the well WAEX-1 and well WA-2A drilled by Xibu Drilling Engineering Company as part of the Aral Sea project in Uzbekistan. This was an important exploration discovery in the Aral Sea Basin.
The sub-salt reservoir at Kenkiyak, Kazakhstan is known for its great depth, high pressure and complicated stratigraphic section. Lost circulation, blowout and sticking of drill tools were common during the drilling process, all contributing to a low drilling success ratio and presenting prominent technical difficulties.
Given the circumstances, CNPC used zwitterionic polysulfonate saturated salt-water as the drilling fluid to inhibit halite dissolution while preventing the destabilization and collapse of strata by adding anti-collapse and anti-sticking chemical agents. As a result, the 3,000-meter gas-bearing halite layer was penetrated smoothly.
Located in southern Iran, South Pars Gas Field is characterized by complex stratal configuration, formation fractures and well-developed pores, which had resulted in serious mud loss at most well intervals when drilling with conventional mud.
CNPC solved the problems of lost circulation, blowout, sticking of drill tools and borehole shrinkage by using air drilling and air-foam drilling while reducing the drilling cycle from 230 days to 80 days and less by optimizing drilling parameters and improving drilling fluid formulas.
Underbalanced drilling was used to prevent borehole deviation and lost circulation while facilitating drilling and eliminating formation damage. With the increasing scale of its application, underbalanced drilling is playing a more significant role in reservoir protection and boosting per-well production. In 2012, we completed 502 underbalanced wells, an increase of 43.4% year-on-year. By using underbalanced drilling technology, Chuanqing Drilling Engineering Company obtained favorable oil and gas shows in well Penglai-101 and other wells in central Sichuan Province. Daqing Drilling Engineering Company increased its average production per individual well by 27.5% through the widespread application of micro-foam underbalanced drilling, and has developed a low-cost technical package for reservoir protection.
Moxi Gas Field in Central Sichuan features low-permeability and leaky reservoirs requiring long drilling cycles. Taking advantage of the underbalanced drilling method, CNPC used high-efficiency drilling bits to boost the drilling speed by 3 to 6 times and reduce the drilling cycle from 5 or 6 months to 50 or 60 days, while avoiding formation damage and lost circulation.
A nitrogen UBD horizontal well in the Southwest Oil & Gas Field saw an 90% oil formation encountering rate, and has directly produced 56,300 cubic meters of natural gas, four to six times as much as each adjacent vertical well prior to reservoir reconstruction.
Horizontal drilling is used in large number of applications. In 2012, we drilled and completed 1,701 horizontal wells, 31.3% more than in 2011, including 1,351 wells at home and 350 wells abroad. We have put into production a total of 350 horizontal wells at Sulige Gas Field since the start of its development, accounting for just 6% of the total producing wells, but contributing 30% to the field’s total gas output.
Well Jing 52-H1Z, the first 20-lateral horizontal well in China, was completed in Damintun Sag of Liaohe Basin in May 2008, at a depth of 4,244 meters. Total footage of the well is 7,587 meters and the total horizontal reach of the main wellbore is 1,800 meters. It is a fishbone-type multilateral well drilled in the condensate reservoir of buried hill structure with the largest number of branches and largest horizontal footage in China.
Well Zhuanghai 8Nm-H3 and Well Zhuanghai 8Es-H5 drilled by CNPC in Dagang Oilfield, reached an H/V (Horizontal/Vertical) ratio of 3.92, and a horizontal reach of 4,842 meters respectively.
In Sudan's Block 3/7, we completed two horizontal wells in 2009 by using sophisticated IGD technology. Daily output from each of the wells was consistently 2.5 times greater than that from vertical wells.
Great Wall Drilling Company built up 1bcm/a gas production capacity in Sulige by drilling horizontal wells, equivalent to that by 300 vertical wells according to the original plan.
Bohai Drilling Engineering Company drilled the horizontal well Su-76-1-20H, whose 2,856m horizontal interval registered a record among of onshore horizontal wells in China.
Chuanqing Drilling Engineering Company finished the first horizontal shale gas well Wei-201-H1 in China, with a regional record footage of 1,688.48 meters per drilling bit.
Well Moshen-1, Fenshui-1 and Lundong-1 drilled by CNPC in onshore China all have a completion depth or depth of drilling over 7,000 meters.
Well Moshen-1: Located in the Junggar Basin with a designed well depth of 7,380 meters, the drilling began in August 2006. A CNPC-made 9,000-meter rig and matching top drive system were used together with high-density and high temperature resistant KDF water-based drilling fluid system and PDC drilling bits. The well was completed at a depth of 7,500 meters in July 2008.
Well Fenshui-1: Located in the Huangjinkou structural belt in Sichuan Basin with a designed well depth of 6,500 meters, the well was spudded in July 2006. Nitrogen drilling was used in combination with a top drive system. The well was completed at a depth of 7,353.84 meters in September 2007.
Well Lundong-1: Located in the east ramp region of Lunnan area in the Tarim Basin with a designed depth of 7,650 meters, drilling began in April 2007 and ended in December, with a drilling cycle of 253 days and a completed depth of 7,620 meters.
Geothermal Power Generation in Kenya
The government of Kenya developed a new power development plan to help hydroelectric plants meet domestic electricity demand in the dry season. It expects to convert the rich geothermal resource available in the country into electricity, thereby enabling the state grid to serve 90% of the country’s population by 2030 and increasing the percentage of electric consumption in rural and mountainous regions.
In 2006, CNPC Great Wall Drilling Company (GWDC) won a drilling contract for the geothermal power generation in Kenya, which would add 70MW generating capacity to the country. In 2007-2008, GWDC concluded a contract for the drilling of additional 25 geothermal wells in Kenya. The average daily output of steam per single well is 5 MW. Especially, well OW909 achieved a daily testing rate of 12MW, which is now the No.1 high-yield geothermal well in Africa. In 2010, GWDC worked with China Import and Export Bank to financially and technically help Kenya promote the exploitation and utilization of geothermal resources under a framework agreement in the field of energy cooperation between the governments of China and Kenya. The company will provide comprehensive drilling services for 26 geothermal wells in the OLKaria 4 Block, 140 kilometers west of the capital city Nairobi.
Firefighting in Turkmenistan
On October 28, 2006, an enormous blowout and fire occurred at well Osman-3 in the Amu-Darya basin, Turkmenistan. Upon Turkmenistan's request for help in early November, CNPC immediately sent an experienced firefighting crew.
Despite the fact that the hydrogen sulfide level was as dangerously high at 34.5 g/m3 and there was no adequate logistical support in the desert, CNPC's firefighting crew used unconventional methods and successfully controlled the blowout and put out the fire by removing the damaged wellhead and installing a new wellhead. In February 2007, the difficult rescue and firefighting operation at well Osman-3 was completed in close cooperation with Turkmenistan and US rescue teams.