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Xu, Dongsheng (China University of Petroleum-Beijing) | Yang, Jin (China University of Petroleum-Beijing) | Zhao, Ying (China University of Petroleum-Beijing) | Huang, Yi (CNOOC China Ltd. Zhanjiang) | Luo, Ming (CNOOC China Ltd. Zhanjiang) | Chen, Yuan (China University of Petroleum-Beijing) | Li, Lei (China University of Petroleum-Beijing) | Yang, Yupeng (China University of Petroleum-Beijing) | Wang, Jie (China University of Petroleum-Beijing) | Zhang, Minghe (China University of Petroleum-Beijing)
Ultra-HTHP reservoirs are Contained in the deep strata of Yingqiong Basin in the South China Sea. The formation pressure coefficient is about 2.30, and the reservoir temperature is about 230℃. So the reservoir has the characteristics of low pressure bearing capacity and high collapse pressure, it poses great challenges to drilling operations.
Aiming at the difficulties of Ultra-HTHP wells, we carried out a series of studies. Firstly, We have done 2170 sets of experiments on rock properties to study drillability and viscoplasticity of rocks, the test conditions is 200℃ with confining pressures of 20 Mpa, 35 Mpa and 50 Mpa. Secondly, focusing on the problems of large surface casing and high risk of anti-collision in HTHP cluster wells, We improved drilling efficiency by pre-inclination drilling and anti-collision drilling. Finally, to protect reservoirs and reduce pollution, we invented a dual-effect drilling and completion fluid system with megatherm resistance.
After decades of research and public relations, we had completed a series of successful exploration and practice. Based on the law of viscoplastic change of rock under HTHP and rock breaking mechanism, we innovatively expounded a composite impactor acceleration tool with rotating and axial high frequency impact force characteristics. According to the principle of jet pump, a new type of speed-increasing jet-suction bit with bottom jet and reverse jet-suction dual-fluid channel had been creatively invented, it can increase the ROP of Ultra-HTHP wellbore by 162%. Ultra-HTHP cluster well surface drilling, pre-inclination, anti-collision one-trip high-efficiency drilling technology realizes the cluster well large-scale borehole drilling, pre-inclination, anti-collision three-in-one operation mode, it reduced the risk of anti-collision while improving the operation time, the single well construction period saved 2.5 days, and the average drilling cost saved 600 thousand RMB per day.Compared with conventional solid-phase drilling and completion fluids, the dual-effect drilling and completion fluids have high temperature, high density and low solid content decrease by 20%, mud cake thickness decreases by 60%, and permeability recovery value increases from 70% to more than 90%. Compared with the single well cost of cesium formate system in the world, single well saves 48 million RMB.
Ultra-HTHP wells had been successfully drilled 16 wells in the South China Sea, and the success rate is 100%. The average drilling cycle reduced from 175 days to 52 days, it is of great reference value for Ultra-HTHP drilling. It can be recommended to make Ultra-HTHP offshore areas such as the North Sea of Britain and the Gulf of Mexico of the United States.
Gao, Yongde (CNOOC Zhanjiang) | Chen, Ming (CNOOC Zhanjiang) | Du, Chao (CNOOC Zhanjiang) | Wang, Shiyue (CNOOC Zhanjiang) | Sun, Dianqiang (CNOOC Zhanjiang) | Liu, Peng (Schlumberger) | Chen, Yanyan (Schlumberger)
Drilling in Ledong field at Yinggehai basin of South China Sea faces challenges of high-temperature and high-pressure (HTHP). The high pore pressure and low fracture gradient results in a narrow mud weight window, especially when drilling close to overpressured reservoir. Well LD10-C was the first exploration well targeting at reservoirs in Meishan formation. Well LD10-A and LD10-B were offset wells in a distance of 15-20km drilled for reservoirs in Huangliu formation, which is above Meishan formation. During drilling, both wells encountered severe gas kick, mud loss and did not reach target.
In order to drill and complete well LD10-C safely, a real-time pressure monitoring solution was introduced with integration technique of logging while drilling (LWD) and look-ahead vertical seismic profile (VSP). It helped to monitor pore pressure and fracture gradient while drilling and predicted top of the overpressured reservoir. This enabled to keep the mud weight and equivalent circulation density (ECD) within a safe margin to avoid kick and mud loss, helped to set casing as close as possible to the top of reservoir. The reservoir section was drilled with a manageable mud weight window.
The main achievements of this task were: 1) accurately monitor and predicted pore pressure coefficient at reservoir. The predicted pore pressure coefficient was 2.25 SG versus 2.24 SG from actual measurement. 2) accurate prediction of reservoirs top. The predicted top depth of Sand C was 2m error with accuracy of 0.05%. The top depth of Sand D was 10m error with accuracy of 0.2%. 3) 12.25in section and 8.375in section was successfully drilled deeper with pressure monitoring. The 9 5/8in casing was set 491m deeper and 7in line was set 80m deeper than plan. As a result, well LD10-C was drilled and competed without any drilling complexities.
This was first application of LWD and VSP together for pressure monitoring while drilling in Yinggehai basin. The successful completion of well LD10-C confirmed that this integrated solution was an efficient technique to predict and reduce drilling risks, optimize mud weight and casing diagram, improve operational safety and save cost in HTHP offshore drilling.
Copyright 2014, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference Asia held in Kuala Lumpur, Malaysia, 25-28 March 2014. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright. Abstract Burial of submarine pipelines and cables is common practice in the North Sea where potentially damaging threats such as fishing gear interaction and dragged anchors are high, or where burial is required for flow assurance. Whilst the requirement to bury pipelines in Asia-Pacific has not had the same imperative as in the North Sea, there is now a growing requirement for pipelines to be trenched, particularly to increase mechanical protection and improve on-bottom stability. Trenching is considered to be one of the offshore activities that carry most commercial risk. It is therefore important to ensure that the correct tool is selected for the anticipated field conditions and to establish realistic performance criteria based on regional experience in the prevailing seabed soils. This paper compares the primary differences between seabed sediments of the North Sea to those that prevail in Asia-Pacific and discusses where differences in these conditions can affect the choice of burial equipment and tool performance when planning trenching in this region. Performance benchmarks for most trenching systems are based on experience and empirical relationships developed for seabed soils typically found in more northern latitudes. Consequently, the main body of burial performance data does not account for the carbonate rich seabed sediments for example that are prevalent in the Asia-Pacific region. Carbonate cemented soils and weak rocks pose a significant challenge to burial and trenching experience in these materials remains very limited.
CNOOC is operating in YingGehai Basin and QiongSouthEast Basin of South China Sea. Formation testing has been routinely used by this operator in field exploration to confirm hydrocarbon presence, define the hydrocarbon type as well as getting PVT samples. Due to the high cost of DST operation in the offshore environment, formation testing is considered as the main testing method to test the small to medium size sand bodies. And the result is accepted to claim reserve of hydrocarbon.
As the recent offshore exploration has focused more on deeper formation where the sand permeability is between low to ultra-low, the pressure pretest mobility is easily lower than 1md/cp. In some particular formation, the formation mobility is even lower than 0.1md/cp. For this type of permeability of sand, testing becomes very difficult and getting fluid sample to claim reserve becomes a huge challenge. If the formation tester fails to obtain the samples, very often the later DST operation would not achieve a success.
A new probe module of formation tester has been introduced to the industry early 2013 and it has been designed to perform formation testing in low permeability environment. Especially it could apply a much higher drawdown than previous technology to move the tight hydrocarbon.
In this paper, a few cases will be presented to demonstrate how this new probe work in Yinggehai and QiongSouthEast basins fluid sampling operation where we sampled successfully at formation with the mobility is less than 0.1md/cp. With this result, great amount of reserve can be claimed and this new probe has been considered as the unique solution of testing these formation as well as predicting the possible production capability. .
Deng, Huifeng (COOEC Shenzhen Subsea Technology CO., LTD.) | Song, Chunna (COOEC Shenzhen Subsea Technology CO., LTD.) | Miao, Chunsheng (COOEC Shenzhen Subsea Technology CO., LTD.) | Dai, Wanbao (COOEC Maintenance Company)