Jin, Fu (Petrochina Research Institute of Petroleum Exploration & Development) | Xi, Wang (CNPC Drilling Research Institute) | Shunyuan, Zhang (Petrochina Research Institute of Petroleum Exploration & Development) | Bingshan, Liu (CNPC Drilling Research Institute) | Chen, Chen (CNPC Drilling Research Institute)
Liaohe Oilfield is well-known for wide distribution of heavy oil resoures whose viscosity is around 6.2×104mPa·s (degassed crude oil at 45°C). Heavy oil resources are usually found at the depth of 500-1700m. An integrated research has been completed to study the most efficient utilization of steam huff and puff methodology.
In order to compare the new steam injection method with the conventional EOR method, we selected 7 wells in which steam injection was simulated by software. The high temperature gel particle plugging agents, high temperature frothers and resins were tested. The overall sweep efficiency and oil production rate of these wells were compared with that of adjacent wells that depended on conventional steam injection methodologies.
The multi-well steam injection requires injecting steam into a specific group of wells, so that an overall thermal field may be created. In this way, steam channeling caused by longitudinal heterogeneity of heavy oil reservoirs may be overcome. CO2 has the best role in reducing the oil viscosity, while natural gas and nitrogen follow it. So CO2 is the most appropriate EOR gas. CO2's dissolubility declines as temperature goes up and improves as pressure increases. Temperature of liquefied CO2 varies a lot with different injection speeds, in that the heat diffusion time is different. The faster CO2 is injected, the shorter the heat diffusion time is, which makes downhole temperature change less. As CO2 is injected into formation, it dissolves rapidly with heavy oil and makes it expand. Steam is injected then to heat the borehole, while CO2 diffuses rapidly and its dissolubility declines as temperature goes up, which makes CO2 separated from oil and diffused by scale. Thus, clean-up additives and steam are widely distributed. After shut-in CO2 spreads until it keeps balanced dynamically with viscosity reducers.
The daily production rate used to start to decrease after 5 rounds of steam injection. By injecting steam and CO2 into a group of wells we succeeded in improving the sweep efficiency and production rate.
Liqiu, Ping (CNPC Drilling Research Institute) | Xi, Wang (CNPC Drilling Research Institute) | Xiuling, Zhang (CNPC Drilling Research Institute) | Chenchao, Liu (Research Institute of Petroleum Exploration and Development) | Rui, Yang (China University of Petroleum)
The well construction operation in the pre-salt reservoirs of Santos basin faced great challenges such as the drill string stuck in big-thickness salt formation (more than 2000m) and low penetration rate in the reservoir formation from the beginning of X. Project. The average actual well construction duration of four wells completed in 2015 was 7 days behind the planed period caused by the above-mentioned problems. The well construction cost was more than the approved budget due to the delayed well construction duration. So efforts was concentrated to integrate drilling technology in ultra-deep water to solve drilling challenges in the pre-salt reservoirs to decrease well construction duration and increase exploration and development benefit.
This paper presents an integrated drilling technology to solve drilling challenges in pre-salt reservoirs of ultra-deep water. The combination of near bit reamer stabilizer and synthetic-based mud can prevent the salt formation creeping and decrease the drill string stuck frequency. The optimization of drilling parameters based on mechanical specific energy concept can clearly identify the transfer from the anhydrite formation to the salt formation and drilling penetration rates can be improved in salt formation by optimizing WOB, rotate speed and pump rate, etc. The combination of MPD, turbine drill and impregnated bit can control the mud losses and increase the penetration rates in the carbonate reservoirs which possess poor drillability. All the above-mentioned drilling technology has been applied in two wells and successfully solves the drilling challenges in the pre-salt reservoirs of X. Project.
The combination of near bit reamer stabilizer and synthetic-based mud has decreased the drill string stuck NPT from 11.7d to zero in two wells of X. Project. The average ROP record of the two wells by use of the integrated drilling technology is 24.6 m/h that has been improved 3.4 times comparing the completed four wells in 2015. The drilling duration for 2062m salt section has decreased to from 14 days to 7 days which saved about 14 millions dollars for the two wells. The average ROP in the reservoir formation of the two wells has been increased to 3.45m/h which was about 1.5 times of the four wells' average ROP completed in 2015. The reservoir section has been completed 4.6 days ahead of the planed duration and the comprehensive drilling cost has been saved 5 millions. The integrated drilling technology in pre-salt reservoirs in ultra-deep water made the average well construction duration of the two wells finished in 2016 have decreased to 111 days, however, the average well construction duration of the four wells completed in 2015 was 162 days.
The fastest record of the one well's construction duration was 76 days establishing a new benchmark in pre-salt reservoirs in ultra-deep water. The method to solve well construction challenges in the pre-salt reservoirs of Santos Basin of this paper presented will make a reference for deep water salt formation drilling and offshore oilfields high efficiency development.
Liqiu, Ping (CNPC Drilling Research Institute) | Xi, Wang (CNPC Drilling Research Institute) | Rong, Li (CNPC Drilling Research Institute) | Rui, Yang (China University of Petroleum) | Chenchao, Liu (Research Institute of Petroleum Exploration and Development)
The drilling operation in the more than 2000m thickness pre-salt formation with more than 2000m water depth faced great challenges from the beginning in X. Project of Atlantic due to drill string stuck caused by salt creeping and low ROP, so efforts were concentrated to obtain a better drilling performance as a consequence of the high daily rates of drilling ships.
In this paper, we look for a combination of high performance PDC bits, near bit reamer stabilizer, synthetic based-based mud, MPD, RSS and LWD systems to increase the drilling performance, both in ROP and salt creeping control in salt formations. ROP has been increased by more than three hundred percentages by high performance PDC bits. Near bit reamer stabilizer and synthetic based-based mud made drill string stuck frequency decrease drastically. The combination of MPD, RSS and LWD systems has improved drilling performance. The above-mentioned integrated drilling technology has been successfully applied in two pre-salt wells in one run whose halite formation thickness is 1870m and 2062m respectively in 2016.
The drilling duration for 2062m salt section has decreased to from 14 days to 7 days which saved about 14 millions dollars for the two wells. The average ROP record of the two wells by use of the integrated drilling technology is 24.6 m/h that has been improved 3.4 times comparing the completed four wells in 2015 in X. Project. The NPT caused by drill string stuck has been decreased from the average 11.7 days to zero that can save about 12 millions drilling cost. So the integrated halite drilling technology can not only solve the drilling problems in halite formation in ultra-deep water such as bore hole collapse and drill string stuck but also increase the ROP. The drilling performance in halite formation has been improved and the integrated halite drilling technology has been widely applied in big-thickness pre-salt formation Santos basin and will decrease the drilling duration of ultra-deep water pre-salt reservoirs wells and lower the oil cost per barrel in ultra-deep water development.
The method to increase drilling efficiency in halite formation of this paper presented will make a reference for deep water salt formation drilling and offshore oilfields high efficiency development. Also the method to control salt creeping and drill string stuck might give a light to the drilling operation in gypsum formation in onshore oilfields.
Huifeng, Liu (Tarim Oilfield Company of PetroChina) | Xiangtong, Yang (Tarim Oilfield Company of PetroChina) | Wei, Zhang (Tarim Oilfield Company of PetroChina) | Yan, Zhang (Drilling Research Institute of China National Petroleum Corporation) | Pengyao, Zhou (Tarim Oilfield Company of PetroChina) | Xi, Wang (Tarim Oilfield Company of PetroChina)
Wells in kuqa foreland area of Tarim Basin are mostly ultra-deep and HTHP wells. The well depths vary from 6000 m to 8000 m. The reservoir temperature and pressure are between 135-180℃, 100-135MPa respectively. Coiled tubing was introduced to conduct the down-hole operations in this field. Through improvements of many technologies, six operations were successfully conducted and operating time was saved by more than 50%.
CT operations in HTHP wells were made available by carefully evaluating and selecting the proper CT assembly and operating parameters. A standardized modeling workflow was established, including force analysis, hydraulic analysis and fatigue analysis, to systematically evaluate the operation, and then optimize the CT assembly, the wellhead equipment, the operating parameters, etc. A real-time CT detector was also developed to monitor the properties of CT while operating. Besides, a series of on-site operation criteria were established to control the process of CT operations.
With these modeling, optimizing and monitoring technologies, CT operations were firstly tried in ultra-deep wells in the basin area of Tarim Basin, whose well depths are more than 6000m but with normal pressure and temperature systems. Drilling and milling, acidizing, jet perforating, and staged proppant fracturing were all realized in these wells. Well YM704, with down-hole pressure of 82MPa and down-hole temperature of 148℃, was acid pickled with CT at vertical depth of 7287m. Afterwards these technologies were introduced to kuqa foreland area, where the wells are mostly HTHP gas wells. Six down-hole operations have been tried and only minor troubles occurred. Well KS2-2-12, whose down-hole pressure is 102MPa and down-hole temperature is 160℃, was sand flushed by CT at the depth of 6182m, and a 46m sand plug in the wellbore was cleaned out. Well DB101-1, with down-hole pressure of 92MPa and down-hole temperature of 130℃, was conducted workover by CT. CT was run to 5373m and successfully drilled and milled the bridge plug. By using CT operations in these wells, more than 50% of the operation time was saved.
CT has been proved to be an efficient tool for down-hole operations. It can reduce the cost of operations significantly. However, the use of it was restricted to conventional wells. This paper introduces trials of CT operations in ultra-deep and HTHP wells, providing a reference for CT operation design in tough conditions. Resistance of running in hole was also encountered occasionally, but it is hopefully to be avoided by optimizing run-in modeling.
Jin, Fu (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Xi, Wang (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute)
Located in south of Eastern Venezuela Basin, Orinoco Oilfield is the unique huge ultra-tight oilfield that has not been developed by scale in the world. The high-density tight oil is known for its high content of acids, heavy metals and asphaltenes with a viscosity of 1000-10000mPa·s. ML Block whose OOIP is 178*108bbl is situated in east of the oilfield, while cluster horizontal well drilling and cold production technologies are still under research there.
Based on precise geological researches numerical simulation was carried out to optimize cold production of ultra-tight oil with foamy oil flow patterns in horizontal wells, including optimization of well placement, well spacing and horizontal section length. The near-bit geo-steering drilling technology was applied on adjacent wells to test its performance, while an experiment was conducted with PVT apparatuses to examine the effect of pressure decline rates on foamy oil flow. A long core pressure depletion test was accomplished to reveal the effect of foamy oil flow on recovery factors.
Three-dimension cluster horizontal well drilling and completion technologies shall be applied to develop ultra-tight oil reservoirs in huge loose sandstones, with the near-bit geo-steering drilling technology that controls landing points and horizontal sections in real time, keeping the bit move ahead along the lower boundary of the reservoir. Therefore, recovery rates may be dramatically improved due to the gravity drainage of ultra-tight oil. The most appropriate spacing of horizontal wells (500-600m) and horizontal section length (800-1200m) were determined to achieve the maximum recovery rate. The experiment proves that the recovery rate improves as the formation permeability increases, which means the "worm hole" contributes to heavy oil extraction. Boreholes with relatively large diameters, extensive perforated holes and slotted liners may be used to complete wells. In order to take the most advantages of the foamy oil flow mechanism high displacement ESPs shall be used with the selected thinner squeezed at the bottom, otherwise PC pumps with the thinner added at the wellhead are recommended.
Cold production technologies applied in ML Block save the overall production cost by 15.2%, improving the ultimate recovery rate by 8.6%. The foamy oil flow theory is improved, while it is the first time to integrate foamy oil flow production technologies with cluster horizontal well drilling technologies and near-bit geo-steering drilling technologies. As a result, the overall production rate of tight oil was greatly improved and the average production life of wells was extended.
AbstractCNPC has undertaken several giant oilfields between Iran and Iraq border including N. Azadegan, S. Azadegan, Halfaya and Rumaila for oil development. As a result of an extended investigation and evaluation of existing risks, personnel safety should be given prority and countermeasures are discussed on the basis of dozens of years’ operation experiences.The HSSE challenges of those fields are many: a lot of unexploded ordnance were littered along the border as a result of Iran-Iraq war, so huge costs and longer construction duration for cleaning them prior to develop the oilfield; potential risks of war and terrorist attack always exist in Iraq as one of project managers was attacked by roadside bomb and one employee was kindnapped according to Media reported; sensitive wetland might be polluted by waste water/oil, drilling cutting, residual acid while local authorities have the strictest environment protection.This paper will focus on some causes of HSSE accidents such as lack of balance between fast operation and process safety, unsafe behavior. Furthermore, more HSSE management measures are provided: (1) Three Specialized Grand HSSE principles of CNPC have been established from the beginning of oilfield development. Grand Security is the foundation of HSSE; Grand Logistics is the safeguard of HSSE and Grand Harmony is the necessity of HSSE. Among of which impregnable fortress and safe camp are built, centralized management of logistics and accommodations for both Companies and all Contractors on basis of each project; the tri-sector partnership between the consortium, civil society and the government is established as one consortium for a harmony local community. (2) Emergency Plan for evacuation is submitted, meanwhile, some cases are introduced. (3) "Zero discharge and Zero pollution" scheme is addressed hereby. In sum, "Safety first" culture is established on the critical plan to meet development target of each oilfield.According to successful HSSE management, accident frequencies have been decreased sharply and nobody hurt in terms of terrorist attack. The intent of this paper is to share HSSE experiences and learning that may enable future safe operations in the oilfield between Iran and Iraq border, to avoid some of the operation and safe pitfalls.
Wang, Yuanqing (Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua University Beijing, China) | Hu, Zongwen (Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua University Beijing, China) | Shi, Yongjiu (Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua University Beijing, China) | Xi, Wang (Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Tsinghua University Beijing, China)
At a low temperature, the mechanical properties of thermit welding joints of rail steels get worse and brittle failures happen more easily. This threatens the railway transportation seriously. It is necessary to find out the mechanical properties of thermit welding joints of rail steels at low temperature because there are more and more railway constructions at low temperature such as Qinghai-Tibet railway. This paper studied the mechanical properties of tow common types of thermit welding joints in China, whose mother metal are U71Mn and U75V of 60kg/m, and got the Tensile strength, Proof strength (non-proportional extension), Percentage elongation after fracture and Percentage reduction of area of the two types of thermit welding joints at a series of low temperatures. Temperature sensitivity coefficients of the two types of thermit welding joints were calculated and then the tensile strengths and proof strengths at low temperature could be forecasted. At last, which type of rail steel should be chosen at low temperature was proposed through the comparison of U71Mn and U75V thermit welding joints.
Thermit welding is one of the most commonly used rail welding methods in seamless railway construction in China, while long rail locking and damaged rail repair both use it. From 1998 to 2000, the number of thermit welding joints came to 27,736.(Yang, 2005) According to China medium and long-term railway network plan, by 2020, the national railway operating mileage will reach 100,000 kilometers, which shows that the thermit welding has a large application market in future. At present, flux and welding equipment are more commonly from France RAILTECH Company, while China thermit welding materials are also gradually extended, for example, pearlite and bainite type flux can be produced in China, as well as one-time crucible and other auxiliary equipment supplies.