Experimental Study on Towing Characteristics of Composite Bucket Wellhead Platform

With the rapid development of large-scale development of marginal oilfields in China,simple wellhead platforms that are simple in structure and easy to install have become an inevitable choice in the process of oilfield development.However,traditional simple wellhead platforms are often discarded after a single use.In pursuit of a more costeffective approach to developing marginal oilfields,this paper proposes a new offshore oil field development facility—an integrated bucket foundation for wellhead platform.To verify the safety of its towing behavior and obtain the dynamic response characteristics of the structure,this paper takes a bucket integrated bucket foundation for wellhead platform with a diameter of 40 m as the research object.By combining physical model tests and numerical simulations,it analyzes the static stability and dynamic response characteristics of the structure during towing,complete with the effects of the draft,wave height,wave period,and towing point height,which produce the dynamic responses of the structure under different influence factors,such as roll angle,pitch angle,heave acceleration and towing force as well as the sensibility to transport variables.The results show that the integrated bucket foundation for wellhead platform is capable of self-floating towing,and its movement is affected by the local environment,which will provide a reference for actual projects.

Lateral bearing characteristics of subsea wellhead assembly in the hydrate trial production engineering

Conductor and suction anchor are the key equipment providing bearing capacity in the field of deep-water drilling or offshore engineering,which have the advantages of high operation efficiency and short construction period.In order to drill a horizontal well in the shallow hydrate reservoir in the deep water,the suction anchor wellhead assembly is employed to undertake the main vertical bearing capacity in the second round of hydrate trial production project,so as to reduce the conductor running depth and heighten the kick-off point position.However,the deformation law of the deep-water suction anchor wellhead assembly under the moving load of the riser is not clear,and it is necessary to understand the lateral bearing characteristics to guide the design of its structural scheme.Based on 3D solid finite element method,the solid finite element model of the suction anchor wellhead assembly is established.In the model,the seabed soil is divided into seven layers,the contact between the wellhead assembly and the soil is simulated,and the vertical load and bending moment are applied to the wellhead node to simulate the riser movement when working in the deep water.The lateral bearing stability of conventional wellhead assembly and suction anchor wellhead assembly under the influence of wellhead load is discussed.The analysis results show that the bending moment is the main factor affecting the lateral deformation of the wellhead string;the anti-bending performance from increasing the outer conductor diameter is better than that from increasing the conductor wall thickness;for the subsea wellhead,the suction anchor obviously improves the lateral bearing capacity and reduces the lateral deformation.The conduct of the suction anchor wellhead assembly still needs to be lowered to a certain depth that below the maximum disturbed depth to ensure the lateral bearing stability,Thus,a method for the minimum conductor running depth for the suction anchor wellhead assembly is developed.The field implementations show that compared with the first round of hydrate trial production project,the conductor running depth is increased by 9.42 m,and there is no risk of wellhead overturning during the trial production.The method for determining the minimum conductor running depth in this paper is feasible and will still play an important role in the subsequent hydrate exploration and development.

深水隔水管-水下井口耦合系统双向涡激振动特性

深水隔水管-水下井口系统极易受外部海流影响产生涡激振动(VIV),其VIV分析通常将底端水下井口简化为固支约束.考虑水下井口下部非线性管-土耦合建立深水隔水管-水下井口耦合系统顺流(IL)及横流(CF)向VIV三维分析模型.基于胡克定律将管-土相互作用产生的时变非线性土壤抗力转化为时变土壤等效刚度并与系统结构刚度叠加.采用有限单元法进行分析模型离散,采用Newmark-β法与4阶龙格库塔法进行VIV数值求解.随后分别研究了管-土耦合作用及环境因素如海流流速、土壤硬度等对深水隔水管-水下井口系统CF及IL方向VIV特性的影响.结果表明,考虑管-土耦合的深水隔水管-水下井口系统约束弱化,系统整体刚度减小,固有频率降低,深水隔水管-水下井口系统CF及IL方向的均方根(RMS)位移及振幅增大,振动频率减小.深水隔水管-水下井口系统VIV对土壤硬度的敏感度较低,原因是系统结构刚度与土壤初始附加的等效刚度较大,而土壤硬度变化额外附加的土壤等效刚度在系统总刚度中的占比较低.

水下卧式采油树在役工况安全风险分析

深水油气生产对水下采油树系统的可靠性有着极高的要求。为保障我国首套国产化深水水下采油树在役生产工况下的安全运行,建立了改进型危险与可操作性分析法(HAZOP),将改进后的发生可能性和严重度等级划分及风险矩阵作为风险评判的依据,通过对油气生产过程、化学药剂注入过程以及水下控制系统电力/通信过程等3个生产节点进行风险评价,得到水下采油树在役过程中的36个中度风险点,并提出了相应措施;采用数值模拟方法,建立了水下采油树-井口系统力学模型,对系统在役过程中所受到的海流载荷、地震与腐蚀等风险进行分析。研究结果表明,水下采油树在各类工况下的最大应力在20 MPa以下,最大弯矩在0.3 MN·m以下,安全性满足生产要求;但在腐蚀后百年一遇海流及大于6.5级地震载荷下,系统最大弯矩超出极端环境许用值,安全性不能保障。所得结论可为我国水下采油树的应用提供指导,能够有效保障采油树服役期间的安全性。

Simulating the Effect of Hydrate Dissociation on Wellhead Stability During Oil and Gas Development in Deepwater

It is well known that methane hydrate has been identified as an alternative resource due to its massive reserves and clean property. However, hydrate dissociation during oil and gas development(OGD) process in deep water can affect the stability of subsea equipment and formation. Currently, there is a serious lack of studies over quantitative assessment on the effects of hydrate dissociation on wellhead stability. In order to solve this problem, ABAQUS finite element software was used to develop a model and to evaluate the behavior of wellhead caused by hydrate dissociation. The factors that affect the wellhead stability include dissociation range, depth of hydrate formation and mechanical properties of dissociated hydrate region. Based on these, series of simulations were carried out to determine the wellhead displacement. The results revealed that, continuous dissociation of hydrate in homogeneous and isotropic formations can causes the non-linear increment in vertical displacement of wellhead. The displacement of wellhead showed good agreement with the settlement of overlying formations under the same conditions. In addition, the shallower and thicker hydrate formation can aggravate the influence of hydrate dissociation on the wellhead stability. Further, it was observed that with the declining elastic modulus and Poisson's ratio, the wellhead displacement increases. Hence, these findings not only confirm the effect of hydrate dissociation on the wellhead stability, but also lend support to the actions, such as cooling the drilling fluid, which can reduce the hydrate dissociation range and further make deepwater operations safer and more efficient.

Evaluation of the Customer Satisfaction Index for Wellhead Blowout Preventers of China’s Petroleum Industry——A new method based on PLS

This paper establishes an evaluation model of the customer satisfaction index for the wellhead blowout preventers of China＇s petroleum industry based on evaluation models of the customer satisfaction index at home and aboard, and by considering the consuming situation in China and the features of the China＇s petroleum industry. For the existence of： （1） multiple correlations among the factors in the model; （2） the variables need to be explained, but that are hard to observe; （3） the customer satisfaction degree of observation variables appears the shape of skewness or two or three peaks, the correlations between the satisfaction index and its factors cannot be described by common multiple regression. This paper uses a partial least squares （PLS） method based on principal components and typical correlative analysis to solve the problem. When PLS is used in the model of the customer satisfaction index of the wellhead blowout preventers, the latent variables and the explanation degree coefficient of the manifest variable to the corresponding latent variables are estimated by PLS path analysis, and the influencing coefficient among the latent variables in the model is estimated by PLS regression analysis. PLS is also be used to calculate and analyze the model and disclose the correlations among the structural variables as well as the correlation between structural variables and its corresponding observation variables, evaluating results of which provide useful information for petroleum industry to improve the product quality and to the enhancement of the customer satisfaction to the product.

Multistring analysis of wellhead movement and uncemented casing strength in offshore oil and gas wells

This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.

Metal Sealing Performance of Subsea X-tree Wellhead Connector Sealer

The metal sealing performance of subsea X-tree wellhead connectors is crucial for the safety and reliability of subsea X-trees. In order to establish the theoretical relation between metal sealing ring＇s contact stress and its structural parameters and working pressure, a mechanical analysis method for double-cone sealing of high pressure vessels is applied in analyzing the metal sealing ring under the condition of preload and operation. As a result, the formula of the unit sealing load for the metal sealing ring under operation with residual preload is shown in this paper, which ensures that the metal sealing ring has an excellent sealing effect and can prevent the metal sealing ring from yielding. Besides, while analyzing the sealing process of the metal sealing ring, the change rule of contact stress and working pressure is concluded here, putting forward that the structural parameters of the metal sealing ring are the major factors affecting the change rule. Finally, the analytical solution through theoretical analysis is compared with the simulation result through finite element analysis in a force feedback experiment, and both are consistent with each other, which fully verifies for the design and calculation theory on metal sealing ring＇s contact stress and its structural parameters and working pressure deduced in this paper. The proposed research will be treated as an applicable theory guiding the design of metal seal for subsea X-tree wellhead connectors.

Application of wellhead suction anchor technology in the second production test of natural gas hydrates in the South China Sea

Traditional suction anchor technology is mainly used in the fields of subsea structure bearing foundations,single-point mooring systems and offshore wind power.It is characterized by providing sufficient lateral and vertical bearing capacities and lateral bending moment.The anchor structure of a traditional suction anchor structure is improved with wellhead suction anchor technology,where a central pipe is added as a channel for drilling and completion operations.To solve the technical problems of a low wellhead bearing capacity,shallow built-up depth,and limited application of conductor jetting in the second production test of natural gas hydrates(NGHs)in the South China Sea(SCS),the China Geological Survey(CGS)took the lead in independently designing and manufacturing a wellhead suction anchor,which fulfilled the requirements of the production test.This novel anchor was successfully implemented in the second production test for the first time,providing a stable wellhead foundation for the success of the second production test of NGHs in the SCS.

南海某深水高温高压气井SS-15型井口头系统薄弱点安全评价

为应对深水高温高压气井生产过程中井口系统复杂性、井口抬升等对整个井口系统完整性的破坏情况,研究环空压力、上顶力、温度、产量对井口头系统薄弱点的影响。基于数值模拟方法建立井口系统有限元力学模型,分析在不同环空压力与上顶力条件下,井口系统各部件的应力大小变化情况,为井口系统薄弱点位置的确定提供理论依据,进而提出深水高温高压井井口系统完整性的管控图版及方法。研究结果表明:环空密封本体与套管挂、锁环与限位槽的接触部位是薄弱点;同一环空压力下,上顶力越大,套管挂等效应力与锁环变形量越大;当上顶力超过700 t时,不论环空压力是否存在,均达到井口系统薄弱点屈服强度。因此,深水高温高压油气井应制定合理生产制度或管理措施,研究结果对保障井口系统完整性,降低深水高温高压井生产阶段风险具有一定参考意义。

基于动态贝叶斯网络的水下井口系统RUL预测

为了及时发现水下井口服役期间的失效隐患,保证海洋油气资源的安全高效开采,提出了一种将马尔科夫过程与动态贝叶斯网络模型相结合的水下井口剩余使用寿命(Remaining Useful Life,RUL)预测方法。将水下井口系统全寿命周期的服役过程多级状态转移与时间相关联,考虑环境、装备及设计等疲劳损伤因素对井口系统性能的影响,预测水下井口系统全寿命周期不同工况、系统降级状态、不同维修状态下的RUL。以南海东方气田某水下井口系统为例开展分析,结果表明:不完美/完美维修可延长系统的剩余使用寿命;水下井口系统各部件中,临时导向基座对系统剩余使用寿命影响最大;防喷器(Blow-Out Preventer,BOP)质量和尺寸、大浪、隔水管设计缺陷、涡激振动事件是影响水下井口系统疲劳损伤程度的主要因素。

边远气井井口智能生产控制技术的应用实践与探索

为解决边远井管理难、管理成本高等问题,提高边远井的生产和管理效率,详细阐述了井口智能控制系统中数据采集、数据传输、远程控制、以及智能辅助技术等原理;在深层页岩气田边远井进行应用,实现了对边远井的实时监测、报警推送、远程控制等功能,为边远井无人值守提供了有力的支撑,彻底打破传统的人员驻井值守管理模式,新型的智控管理模式具有广阔的推广应用前景。

Study on Load Bearing Characteristics of Novel Expandable Deepwater Drilling Conductor Based on Laboratory Experiment and Field Test

A novel expandable conductor was designed and applied in deep-water drilling to improve the vertical and lateral bearing capacity with a significant reduction of conductor jetting depth and soaking time. The vertical and lateral bearing capability of expandable conductors was depicted based on the ultimate subgrade reaction method and pile foundation bearing theory. The load-bearing characteristics of a laboratory-scale expandable conductor were analyzed through laboratory experiments. The serial simulation experiments are accomplished to study the bearing characteristics(vertical ultimate bearing capacity, lateral soil pressure, and lateral displacement) during the conductor soaking process. The laboratory experimental results show that the larger the length and thickness of expandable materials are,the higher the bearing capacity of the wellhead will be. During the conductor soaking process, the soil pressure around the three expandable conductors increases faster, strings representing a stronger squeezing effect and resulting in higher vertical bearing capacity. Furthermore, the lateral displacement of novel expandable conductor is smaller than that of the conventional conductor. All the advantages mentioned above contributed to the reduction of conductor’s jetting depth and soaking time. Lastly, the application workflow of a novel expandable deep-water drilling conductor was established and the autonomous expandable conductor was successfully applied in the South China Sea with a significant reduction of conductor’s jetting depth and soaking time. According to the soil properties and designed installation depth of the surface conductor, the arrangement of expandable materials should be designed reasonably to meet the safety condition and reduce the construction cost of the subsea wellhead.

深水石油装备疲劳寿命预测及定制软件研制

利用Visual Studio软件平台以及C++语言开发水下井口疲劳寿命预测软件,实现了通过海况以及材料参数对水下井口疲劳寿命进行预测,并将随机载荷谱、雨流计数法结果以及模型寿命结果进行了可视化等功能。不仅基于线性波浪叠加法、PM谱以及波流联合作用力公式对随机载荷谱进行计算,还通过线性累积损伤模型对模型寿命进行了预测。结果表明,对水下井口的疲劳寿命预测非常必要,因此,该软件的开发对水下装备寿命自动预测具有指导价值。

车载井口加药系统的设计与应用

天然气井加注药品的种类繁多,性质不一,对加注工况和存储环境有着不同的要求,不适合集中建站加注,为此,设计研发了一套车载井口加药系统。考虑到采气现场禁止使用电驱动设备,加药系统采用液压驱动、控制加药泵加药作业,利用已知工况参数对液压元件进行选型计算,确定液压元件的型号,将其合理布局进行撬装,整体安装固定在车体上,完成了加药系统的整体设计。利用车载加药系统对生产井进行加药作业,对采集的数据整理分析表明:车载井口加药系统能够将不同比例的泡剂溶液加入到不同油套压的气井中,并且注入的起泡剂达到了使气井增产的目的,说明系统以保证药品质量为前提能够在不同工况下完成加药作业;车载井口加药系统依靠液压驱动、控制,安全性高,操作简单,使用方便;车载井口加药系统整体结构简单,具有较高的机动性,可以满足气井的加药周期。

海上无人井口平台的工业数据中心(IDC)研究

工业数据中心(IDC)汇聚多元数据资源,是具备安全可靠能力、提供高效算力服务的新型基础设施,而IDC在海上平台的应用较少。随着虚拟化技术日渐成熟,以及产业的数字化转型需求,将IDC应用到海上平台成为一种趋势,尤其是无人井口平台,以实现统一操作平台、统一信息入口和统一数据标准,提高软硬件资源的高可用性,为大数据分析与迭代服务升级夯实基础,从而助力海上智能油田的建设。

直排式真空预压在地基处理中的应用

直排式真空预压技术针对传统真空预压技术中砂垫层及滤管传递载荷效率较低的问题进行了创新改进,利用更高效的支管和软管构建主管与排水板有效连接,显著降低了真空载荷的损耗效率。文章介绍了直排式真空预压技术的研究现状,从地基处理效果、施工效率、施工成本等方面将其与传统真空预压技术进行了对比,并结合广州某工程实例进行了分析,验证了直排式真空预压技术在地基处理施工中的优良效果。

环形金属密封总成密封机制及性能分析

环形金属密封总成是水下井口头系统重要组成部分,其性能直接影响到水下井口头系统的安全性,甚至整个水下油气系统的可靠性。分析环形金属密封总成的密封机制和工作原理,结合有限元分析结果,从密封环在密封过程中的变形情况来分析其密封性能。结果表明:密封环在弹性变形阶段可以实现密封,但对密封环的表面粗糙度和表面质量有很高的要求,在环形密封总成工况条件下无法保证,应避免在此阶段实现密封;密封环在塑性变形阶段能够填补环表面存在的缺陷,实现良好的密封;在塑性变形阶段,密封环接触面的变形情况成为影响密封性能的唯一因素。

一种适用于水下井口力学分析的新型砂土p-y模型

深水海底浅层土壤是影响水下井口系统动态响应的重要因素,对井口系统的疲劳评估至关重要。目前水下井口动态分析时常采用API推荐的p-y模型模拟导管—土壤相互作用,但该模型没有考虑水下防喷器组(Blowout Preventors,简称BOPs)竖向重载对管土交互的影响,导致水下井口动态分析存在较大计算误差。为此,首先根据常规和新型p-y曲线的理论模型进行数值计算,然后采用ABAQUS软件建立实尺寸水下井口管土相互作用模型,加载计算得到BOPs重载下导管变形—土壤抗力仿真结果并与理论模型进行对比,最后采用缩尺土箱实验验证新型p-y模型在水下井口动态响应分析的正确性。研究结果表明:①采用新型p-y模型得到的导管弯矩、土抗力等数值计算结果与ABAQUS仿真和缩尺实验均吻合良好;②相对于常规管土模型,采用新p-y模型得到的水下井口弯矩、位移响应幅值等降低15%左右,得到的导管弯矩、位移响应幅值等降低幅度介于25%~30%;③新型砂土p-y模型充分考虑了BOPs竖向重载对管土相互作用的影响,在隔水管—水下井口系统力学分析中具有更好的适用性。结论认为,考虑到BOPs竖向重载对管土交互的影响,通过数值模拟及缩尺试验研究了新型p-y模型,并验证了其适应性,新模型有效提高了水下井口疲劳载荷计算的准确性,为水下井口系统疲劳评估提供了理论计算依据,为深海油气的开发提供了保障。

井口头系统密封总成关键部件设计与分析

制约我国海洋油气开采发展的主要瓶颈就是深水井口头设备,而密封总成又是水下井口头系统的关键组件。为此,设计了井口头系统多级金属密封结构的密封总成,主要包括上下2个密封圈、锁紧套筒和驱动套筒。利用有限元分析软件对密封关键部件进行了强度分析,同时提出判断密封总成密封效果的理论依据,并对锁紧套筒进行了结构强度分析,对驱动套筒和密封环做了接触应力分析。分析结果表明,密封总成的结构和材料符合作业要求。该密封总成的结构设计和分析为水下金属密封技术的进一步研究奠定了基础。