Africa (Sub-Sahara) A drillstem test was performed on the Zafarani-2 well--located about 80 km offshore southern Tanzania. Two separate intervals were tested, and the well flowed at a maximum of 66 MMscf/D of gas. Statoil (65%) is the operator, on behalf of Tanzania Petroleum Development Corporation, with partner ExxonMobil Exploration and Production Tanzania (35%). The FA-1 well--located in 600 m of water in the Foum Assaka license area offshore Morocco--was spudded. The well targets Eagle prospect Lower Cretaceous resources. Target depth is 4000 m. Kosmos Energy (29.9%) is the operator, with partners BP (26.4%),
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.
Chen, Zhaoming (CNOOC China Limited, Shenzhen Branch) | Yang, Dengfeng (CNOOC China Limited, Shenzhen Branch) | Luo, Wei (CNOOC China Limited, Shenzhen Branch) | Xu, Yingjing (CNOOC China Limited, Shenzhen Branch)
The Huizhou sag of the Pearl River Mouth Basin is one of the first areas to try to operate the broadband seismic acquisition with variable-depth streamer in the offshore seismic exploration of China. Different from the conventional acquisition, the streamer of the broadband seismic acquisition is depth variable. Through broadband seismic acquisition and processing, the ghost waves can be effectively identified and removed to broaden the seismic frequency band. In order to make good use of the broadband seismic data, we firstly test the reliability of broadband seismic data through a forward model and post-stack seismic inversion. Then the targets in Huizhou sag is taken as an example to do the inversion experiments. The results show: the broadband seismic acquisition can effectively suppress the interference of the wavelet side-lobe and the multiples and can obviously improve the signal-to-noise ratio; meanwhile, it can enhance the accuracy to identify the thickness of the reservoir and can improve the fidelity of seismic data.
A bulk of near-term output will come domestically, but the subsidiary of state-owned China National Offshore Oil Corporation is leaning on its international projects to boost production longer-term. The company said it expects to produce 1.33 million BOE/D in 2019, an increase of 2% from its 2018 average, with domestic output accounting for 67% of this year’s production. The ExxonMobil-operated Guyana consortium has tallied 10 discoveries to date. CNOOC expects six new projects to come on stream this year. The four other projects are the Shell-operated Appomattox project in the US gulf and CNOOC’s Bozhong 34-9 oil field, Caofeidian 11-1/11-6 comprehensive adjustment project, and Wenchang 13-2 comprehensive adjustment project off China.
Bian, Li’en (China National Offshore Oil Corporation (CNOOC) Ltd. Tianjin Branch) | Zhang, Jingsi (China National Offshore Oil Corporation (CNOOC) Ltd. Tianjin Branch) | Xu, Jialiang (China National Offshore Oil Corporation (CNOOC) Ltd. Tianjin Branch) | Yang, Wei (China National Offshore Oil Corporation (CNOOC) Ltd. Tianjin Branch) | Yu, Qian (China National Offshore Oil Corporation (CNOOC) Ltd. Tianjin Branch)
A good time-depth projection method plays an important role in improving the accuracy of depth prediction. When designing a new well, we need a time-depth relationship to predict the depth of the target layer and then design the well trajectory. The traditional approach is to directly use the time-depth relationship of adjacent well. However, as the target reservoir becomes more and more complex, the lateral change of the formation velocity is more and more large. In this case, the traditional approach is difficult to meet the research needs. This study proposed a new high precision time-depth projection method, which firstly establishes a high precision space-varying velocity model under the constraint of geological structure, then extracts the average velocity at each point of the well trajectory, and finally creates a high precision time-depth relationship based on MD (Measured Depth) of well trajectory which is different from the traditional time-depth relationship based on TVD (True Vertical Depth). The application result of real seismic data demonstrates the effectiveness of our method.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: 210A (Anaheim Convention Center)
Presentation Type: Oral
Yi, Cong (CNOOC Research Institute) | Li, Da (CNOOC Research Institute) | Liang, Wenzhou (CNOOC Research Institute) | Zhao, Jingrui (CNOOC Research Institute) | Bian, Xiaoqiang (SBM Offshore) | Feng, Jiaguo (CNOOC Research Institute) | Cao, Peimin (SBM Offshore)
Deep draft SEMI production platforms have been proposed and used for more and more deepwater oil or gas field development. The concept is also proposed for the Lingshui17-2(LS17-2) gas field in South China Sea. The proposed SEMI concept is also the first Semi-submersible floater with condensate storage in the world.
For most of deep draft SEMI production platforms, the facility payload is nearly constant and operated under constant draft. Their stability, or GM, and motion performance does not change on a day to day basis. However, for LS17-2 SEMI design, there is significant condensate storage on board. The cargo storage will vary during production and offloading, thus affecting the weight, stability and performance of the Semi.
For the stability requirement, the GM value should be large enough to provide sufficient restoring moment. For the deep draft SEMI, improved motion performance is also required to satisfy SCR strength and fatigue performance requirements. Vessel GM affects pitch and roll responses, and thus influences the overall global performance as well. Therefore design of vessel GM range should not only satisfy the minimum stability rules, but also the global performance requirements. In this paper, a deep draft SEMI platform in LS17-2 gas field is discussed. Operational envelope with various load conditions, platform draft and hull global performance are presented. Model test covering critical loading combinations are conducted and numerically calibrated. GM is an important sizing parameter during Semi configuration. For semi with storage, a range of GM needs to be incorporated to consider various loading conditions and drafts, while meeting the global performance and SCR design requirements. The paper presented the impact of Draft, GM values and complex loading conditions on the optimal and robust performance of the floater. The paper also discusses the critical design conditions for the subsystems.
Lingshui17-2 (LS17-2) gas field is located in the northern part of the Qiongdongnan Basin in the western continental shelf of the northern South China Sea, with water depth of 1220m to 1560m. The development of LS17-2 gas field consists of subsea production system, subsea pipelines and host SEMI platform. The subsea production system comprises one west manifold and three east manifolds. LS17-2 SEMI is located near Manifold EAST1. Well fluid from west production loop will be transported to LS17-2 SEMI for process through pipelines and SCR risers. Well fluid from all east manifolds will converge at Manifold EAST1 and then be transported to LS17-2 SEMI for process through SCR risers. After processing, qualified natural gas shall be pressurized and transported to subsea pipelines through an 18” subsea export pipeline. Condensate oil will be sent to the storage tank on LS17-2 SEMI and be exported by DP Shuttle oil tanker (Jia Xu and Li Da, 2018).
Lingshui17-2/18-1/25-1 subsea production systems have a vast chained layout with complex future tieback demand, which brings a significant challenge to subsea power distribution design.
Although subsea control system power requirements are highly vendor specific, this paper gives an impartial design philosophy of subsea power distribution to meet the power demand of Lingshui 17-2 and future Lingshui18-1/25-1 gas fields. Feasibility of AC single phase with/without subsea transformer and DC power supply are studied. Umbilical conductor numbers and sizes, as well as topside supply voltages for each gas field are recommended based on study result. A workflow for complex chained subsea control system power distribution has been summarized with special attention highlighted.
The subsea control system of Lingshui17-2 gas field (hereinafter referred to as LS17-2) is an electro-hydraulic multiplexed control system and capable of operating and monitoring the LS17-2 field, which initially comprises 11 subsea production trees and 5 future subsea production trees. Functionality shall be incorporated to allow for further expansion of the system, which includes future Lingshui18-1 (hereinafter referred to as LS18-1) and Lingshui25-1 (hereinafter referred to as LS25-1) gas fields.
When a SPS has a cluster layout and short power distance, it is easy to come up with a power distribution plan to meet a subsea control system power demand. Shi W et al. (2011), MAO JY et al (2014), HU YR et al (2016) presented relevant methodology. However, LS17-2 wells spread broadly on the seabed, with approximately 50km distance between the easternmost A12H well and the westernmost A15H well. The nearest Manifold EAST1 has only 3.9km power supply distance, while the farthest A12H well in east region has approximately 33km power supply distance. The chained layout of subsea production system brings a significant challenge to subsea power distribution design.
All the SCMs in LS17-2 SPS share one EPU output voltage, which need to, on the one hand, ensure input voltage of the nearest SCM not exceeding its upper limit, while on the other hand, guarantee input voltage of the farthest SCM not violating its lower limit.
Applications of electric variable speed centrifugal compressors in the offshore oil and gas production are very important for the limited power rating generators. This paper investigates the challenges presented by electrical driven centrifugal compressors from VFD and hydraulic variable speed respectively. The large capacity motor starting will influence the voltage drop and power balance of isolated power grid. The ETAP simulation model will be used to analyze the dynamic motor-start and transient stability to guarantee the power system safety.
Lingshui17-2 gas field is developed using a semi-submersible floating platform, subsea production system and subsea pipelines with water depth 1220m to 1560m in South China Sea. The Lingshui 17-2 platform will be the world’s first SEMI platform with condensate oil storage. Four 20MW gas turbine generator sets, including 1 set reserved for future, supply power for the SEMI platform and subsea production system. Seven large capacity electric-driven compressors, including three 5.5MW dry gas compressors and four 8.5MW future wet gas compressors, will be the major power load. The largest power load will be up to 45MW during production and offloading scenario. Whereas the seven compressors will be up to 70% of total power load of Lingshui SEMI, which will bring a greater challenge to the isolated power system of SEMI.
Gas turbine and electric driven compressors have applied in offshore oil and gas production. It was proposed (Kurz et al., 2005) that the driven method should be decided according to the comparison including first costs, maintenance costs, fuel consumption, availability, weight, and space requirements between the different solutions, which have to be made on the overall system level. Component comparisons will lead to incomplete results and incorrect conclusions. For Lingshui 17-2 project, electric driven compressors decision is made from the compassion including the main generators, compressors and waste heat recovery unit, related electrical equipment, general layout and installation plan. The result of study points out that the electric-driven compressor requires less area, reduced local emission of greenhouse gases, less weight, lower cost and higher energy efficiency. As a result, electric motor driven compressor will be applied in Lingshui 17-2 project. While electric-driven system has many advantages, it was noted (Ganesan, 2016; Cortinovis, 2017) that it also brings some challenges to the power system. The variable speed shall be considered to meet the process requirement. Selection of variable-frequency drive versus hydraulic variable speed drive is very critical, since it leads to two different designs for the power system.
Wang, Chong (Institute of Geophysics and Geomatics, China University of Geosciences) | Gu, Hanming (Institute of Geophysics and Geomatics, China University of Geosciences) | Liu, Chuncheng (CNOOC Research Center, China) | Liu, Zhibin (CNOOC Research Center, China) | Xu, Ziqiang (CNOOC Energy Technology & Services - Development & Prospecting Geophysical Co., Zhanjiang, China) | Fang, Zhongyu (CNOOC Energy Technology & Services - Development & Prospecting Geophysical Co., Zhanjiang, China)
Deghosting is widely used to obtain broadband data. The error of streamer depth will give birth to a biased ghost-delay time with respect to primary reflection. The amplitude difference coefficient between ghost and primary reflection varies with offset due to rugged seabed and target depth variation. The ghost filtering operator and optimal inversion algorithm was proposed to solve up-going wavefield in frequency-slowness domain. The ghost filtering operator is related to the ghost-delay time and the amplitude difference coefficient between ghost and primary reflection at each horizontal slowness. They are optimally inverted by the optimal inversion algorithm through a least-squares fitting between the theoretical and actual down-going wave. The results of synthetic and marine VDS seismic data show that the method can availably deghost for marine VDS data and achieve the purpose of broadband seismic data.
Presentation Date: Wednesday, September 27, 2017
Start Time: 8:30 AM
Presentation Type: ORAL