Riser String Research Articles

Mechanical analysis for deepwater drilling riser system with structural parameters uncertainty

Uncertain structural parameters increase the mechanical failure risk of the drilling riser system. The effect of uncertain structural parameters on the mechanical characteristics of the drilling riser system is unclear. Therefore, the mechanical characteristics of the drilling riser system with structural parameter uncertainty are analyzed. A mechanical model with uncertain structural parameters is established based on the basic analysis model and the local average theory. The basic analysis model takes into account the combined effects of platform motion, tensioner, riser string, and marine environment. The local average theory is suitable for situations where there is a lack of uncertainty information. A solution approach is proposed using the second-order central perturbation method and the Newmark-β method. The solution method reduces the load by simplifying degrees of freedom and random variables. The correctness of the solution method is verified using the Monte Carlo method. The analysis results indicate that uncertain structural parameters significantly affect the static response, while the dynamic response is less affected. The failure risk due to static axial stress and static shear stress is heightened by uncertain structural parameters. The failure risk arising from static shear stress at the bottom of the riser system experiences a significant increase.

Numerical and experimental investigation for extreme storm-safe drilling riser

ABSTRACT Extreme storm-safe drilling riser, a solution to overcome high time cost of riser emergency retrieval under the situation of the imminent typhoon arrival, is to modify the existing drilling riser to make it disconnectable and leave the long riser string below in a freestanding mode to survive. The buoyancy can maintains neutral during the normal drilling operation. However, locally the buoyancy can will have some effect on the riser system nearby. Numerical analysis and a hybrid scaled truncated model test in the water tank are conducted for the two critical configuration modes: connected mode and freestanding mode. A series of load cases under various current and wave, buoyancy upthrust are conducted in the experimental test to evaluate the hydrodynamic and strength performance of the riser near buoyancy can. The numerical analysis, experimental model design, data post-process method and result discussion can be a valuable reference for deepwater drilling engineering.

Study on key performance parameters of hydro-pneumatic tensioner for top tensioned riser

In this paper an improved mathematical model of a hydro-pneumatic tensioner (HPT) system for top tensioned riser (TTR) is derived by consideration of friction, mass of piston and piston rod, tension loss in hydraulic oil piping, and compressibility of hydraulic oil. The vertical motion of the riser string is also considered. Subsequently, the proposed detailed model and the conventional simplified model are comparatively studied. Finally, the tension characteristic and performance parameters of the HPT are analyzed based on the proposed model. Results show that the conventional simplified model indeed overestimates the tension of tensioner as it neglects some performance parameters resulting in tension loss. The diameters of piston and piston rod and the initial pressure of high pressure (HP) gas have the most significant influence on the tension of the tensioner. The initial volume of HP gas and the initial pressure of low pressure (LP) gas also have some impact. The influence of the initial volume of LP gas and the inner diameter and length of the piping is relatively small. The research has some reference value for HPT and TTR design.

A comprehensive study on composite risers: Material solution, local end fitting design and global response

Two up-to-date composite riser solutions, specifically, the thermoset and thermoplastic based ones are studied in a global-local framework to examine their technical feasibility for offshore applications. At the local scale, the riser pipe body with multi-layered structure is homogenized through an analytical approach, obtaining equivalent material properties of the riser string model for the global analysis. The metal-composite interface (MCI) end fittings between the riser body and standard connector are examined using finite element (FE) simulations to understand their load-transfer mechanisms for both solutions. At the global scale, an in-house analysis code is performed to study the risers' static and dynamic response in a certain sea condition due to top-tension, current drag and vortex induced vibration (VIV). The analyzed parameters include the resulting riser deflection, axial stress, tension and bending moment distributions. Following that, an integrated analysis utilizing the global results and the local failure envelopes is performed to determine if the maximum stress states of the riser exceed the equivalent structural strength boundary. It is concluded that composite risers exhibit a larger safety margin than traditional steel riser under the same sea condition.

Modeling Approach of Hydropneumatic Tensioner for Top-Tensioned Riser

A three-dimensional (3D) finite element analysis (FEA) model of top-tensioned riser (TTR) with hydropneumatic tensioner is proposed in this work. First, the tension calculation equation of the hydropneumatic system is derived, and the kinematic relationship of the platform–tensioner–riser system is established. Second, a 3D FEA model is established based on the FEA code ABAQUS, considering the actual riser string configuration and the Christmas tree. At last, four kinds of tensioner models, i.e., a constant vertical tension model, a conventional simplified model, a linear spring–damper model, and a nonlinear spring–damper model, are compared and analyzed in this study. Results show that the constant vertical tension model is not recommended as it cannot reflect the actual tension in the tensioner and the response of the TTR. The conventional simplified model indeed overestimates the tension of tensioner and may lead to inaccurate estimation results of the TTR response. The linear model is applicable when the environmental condition is relatively mild, but it is strongly recommended to use the nonlinear model especially in harsher environmental conditions.

Deep water drilling riser mechanical behavior analysis considering actual riser string configuration

A dynamic analysis model considering the actual riser string configuration is established to analyze the mechanical behavior of a drilling riser. The riser in this model is regarded as a simply supported beam located in the vertical plane and is subjected to axial and lateral ocean environment loadings. The model is solved using the finite element method. The validity of the analysis model has been proved by a similar experiment conducted in a deep water basin and ANSYS. Riser lateral displacement, bending moment, and deflection of the deep water well considering actual riser string configuration in South China Sea are simulated. The effects of top tension, drilling platform drift distance, surface current speed, wave height, wave period, wave length, wind speed and damping coefficient on riser lateral displacement, bending moment, and deflection are also discussed. Results indicate that riser string configuration has a significant effect on riser mechanical behavior, particularly in the distribution of bending moment. Riser string configuration designing according to concrete ocean environment can significantly improve the riser’s mechanical behavior. The distribution of riser lateral displacement, bending moment, and deflection increases with the increase in surface current speed and drilling platform drift distance, whereas decreases with the increasing top tension and damping coefficient. The distribution of riser lateral displacement, bending moment, and deflection significantly increases with the increase in surface current speed and large current speed may lead to large lateral displacement, bending moment, and deflection. Increasing top tension can significantly decrease riser mechanical behavior parameters and avoid large lateral displacement, bending moment, and deflection when suffering extreme ocean environment conditions in deepwater drilling field. Drilling platform should avoid a large drift distance, which may result in the deflection over the flex joint working range and the enlargement of the riser bend moment.

Dynamic simulation of the wireline riser tensioner system for a mobile offshore drilling unit based on multibody system dynamics

In this study, a wireline riser tensioner (WRT) system was dynamically simulated to analyze the dynamic response of the riser string in a mobile offshore drilling unit (MODU) such as a drilling rig or a drillship. The main function of the WRT system is to sustain the tension to avoid buckling, regardless of the MODU motion. The WRT system consists of a tensioner ring, a wireline, pneumatic cylinders, and air pressure vessels (APVs). It reduces the vertical (heave) motion of the top of the riser string caused by the MODU motion. In this study, the equations of motion of the drilling rig and the WRT system were formulated based on multibody system dynamics. The discrete Euler–Lagrange equation was used to formulate the equations of motion. For the external forces, both the hydrostatic and hydrodynamic forces were considered. Several simulations were performed with various sea states to analyze the motion of the riser string and the efficiency of the WRT system. Furthermore, the gas volume inside the APVs was changed to investigate its impact on the efficiency and performance of the WRT system.

Simulation of Drill String Vibration inside Well Bore due to Riser's Oscillation

This study attempts to explain the motion behavior of the marine riser coupled to drill string when the vortex induced vibration is involved. Vibrations have been reported to have a major effect on drilling performance, affecting the Rate of Penetration (ROP), causing severe damage to drilling tools and also reduces the efficiency of the drilling process. There are two major components of drilling tools that are subjected to vibration, namely the marine riser and the drilling string. Analysis of vibration in the marine riser and drill string are two topical areas that have individually received considerable attention by researchers in the past. While these two subjects are interrelated, borne by the fact that the marine riser encapsulates and protects the drill pipe, they have been little attempt to investigate them together as an assembly. Due to the complexities of the models, simplifying assumptions were made in order to undertake the investigation. Using staggered approach, the results were compared with experimental and simulation data from the open literature. It was found that the maximum displacement with negative damping occurs at low frequency and rotation speed. The addition of vortex shedding forces caused the drill string to deform from its vertical axis and thus increased the risk of failure of drill string and riser.

Wear Properties of Oil Palm Cellulose Fibre Reinforced Polymer Composites

This paper attempts to explain the motion behaviour of the marine riser coupled to a drill string when the vortex induced vibration (VIV) is involved. Vibrations have been reported to have a major effect on the drilling performance, affecting the rate of penetration (ROP), causing severe damages to the drilling tools and also reduces the efficiency of the drilling process. There are two major components of drilling tools that are subjected to vibration, namely the marine riser and the drilling string. Analysis of vibration in the marine riser and drill string are two topical areas that have individually received considerable attention by researchers in the past. Though these two subjects are interrelated, borne by the fact that the marine riser encapsulates and protects the drill pipe, there have been few attempts to investigate them together as a unity. Due to the complexities of the models, simplified assumptions were made in order to undertake the investigation by using staggered approach. The results were compared with the experimental and simulation data from the open literature. It was found that the maximum displacement with negative damping occurs at low frequency and rotation speed.

The analysis on coupling vibration of drill string and marine riser in deep-water drilling

During drilling in the deep water, the system including marine riser and drill string over the wellhead exits strong dynamic response because of the motion of platform. The contact-collision problem between the drill string and marine riser under platform swaying is a highly non-linear dynamics problem, drill string and marine riser contact-collision position along the axis of marine riser is randomly distributed, and that there exits friction. In this paper, by using the method of finite element, the model of dynamical behavior of the system is set up, the state of contact between marine riser and drill string shows randomness. The rule of free lateral coupling vibration of drill string and marine riser has been obtained; the result shows the situation of random contact between drill string and marine rising. By case analysis the result shows that the platform swaying has great effect to the system of marine riser and drill string.

Simulation of parachute FSI using the front tracking method

We use the front tracking method on a spring system to model the dynamic evolution of parachute canopy and risers. The canopy surface and the riser string chord of a parachute are represented by a triangulated surface mesh with preset equilibrium length on each side of the simplices. The stretching and wrinkling of the canopy and its supporting string chords (risers) are modeled by the spring system. The spring constants of the canopy and the risers are chosen based on the analysis of Young's surface modulus for the canopy fabric and Young's string modulus of the string chord. Damping is added to dissipate the excessive spring internal energy. The current model does not have radial reinforcement cables and has not taken into account the canopy porosity. This mechanical structure is coupled with the incompressible Navier–Stokes solver through the “Impulse Method”. We analyzed the numerical stability of the spring system and used this computational module to simulate the flow pattern around a static parachute canopy and the dynamic evolution during the parachute inflation process. The numerical solutions have been compared with the available experimental data and there are good agreements in the terminal descent velocity and breathing frequency of the parachute.

大水深掘削ライザーの技術課題と展望 ２，０００ｍ水深における掘削ライザーシステムの構築

A joint study has been created for the development and the operation of a deep water drilling riser in Japan. For the realization of the project, innovative and advanced technologies are required. This paper provides a description of the project and its goals.The current world record of 2, 328m for deep water riser drilling was established in 1988 in the Gulf of Mexico. As only five wells have been drilled deeper than 2, 000m, riser drilling operations in these water depths cannot yet be considered an established technology.Four primary new research areas are required.The first is the development of a new deep water riser analysis program that will include the effects of liquid inside the riser and the vibration caused by vortex shedding.The second is a control optimization program using thrusters installed on the riser string. This will be effective for both the drilling mode and reentry mode. The program will account for and control, using both the riser and the vessel motions, helping to shorten operational downtime.The third is the research and development of new materials for the riser. Titanium, hybrid materials, and composites will be each studied to optimize the vesel and the drilling riser equipment.Fourth, for the safety of the operation personnel and the preservation of the vessel in extreme weather conditions, the concept of a near surface disconnectable riser system will be studied.The joint study, conducted by the Technology Research Center of the Japan National Oil Corporation, includes the Japan Drilling Company, Mitsui Engineering & Shipbuilding, and Mitsubishi Heavy Industries. The research and development will continue over a period of six years, with the ultimate goal of serving oil companies, drilling contractors, and related industries.

Upper Ball Joint Force Variations due to Riser Tensioner and Vessel Motions—Part I: Derivation of General Equations

General equation for the tensioner cable forces and for the forces exerted on the riser upper ball joint by the ship joint-tensioner system are derived. An analysis of the variation of forces acting on the upper ball joint of a riser string due to drill ship motion and riser tensioner dynamic has been conducted. The analysis includes the effect of breakaway torque on the tensioner sheaves while assuming vessel and upper ball joint motion to be independent.

Upper Ball Joint Force Variations due to Riser Tensioner and Vessel Motions—Part II: Analysis and Computer Simulation

An analysis of the variation of forces acting on the upper ball joint of a riser string due to the drill ship motion and riser tensioner dynamic has been conducted. The analysis includes the effect of breakaway torque on the tensioner sheaves while assuming vessel and upper ball joint motion to be independent. General equation for the tensioner cable forces and for the forces exerted on the riser upper ball joint by the ship joint-tensioner system derived in Part I are solved. The variation in the tensioner cable forces is compared to data generated in field operation.

Riser Tensioner Force Variations

Original manuscript received in Society of Petroleum Engineers office Feb. 24, 1976. Paper accepted for publication June 14, 1977. Revised manuscript received Aug. 21, 1978. Paper (SPE 6309, OTC 2648) first presented at the Eighth Annual Offshore Technical Conference, held in presented at the Eighth Annual Offshore Technical Conference, held in Houston, May 3-6, 1976. Abstract Excessive riser-force variation on the upper joint in a riser string can lead to buckling and excessive fatigue. This variation is caused by two components of the riser support system - the riser tensioning system and the telescopic, or slip, joint. Using specific examples, two conclusions are reached. First, the force variation at the top of the riser string may be much greater than that indicated by monitoring the tensioner system's air-tank pressure. Second, a major contribution to this pressure. Second, a major contribution to this variation can be pressure drop in the air valves. Introduction The riser tensioners and slip joint (Fig. 1) form the support system for the riser string used in floating drilling operations. Although tensioners are the primary support mechanism, their forces are transmitted through the slip joint to the upper joint in the riser string. In many deep-water drilling operations, the riser string is isolated in bending by an upper ball joint from the more massive telescopic joint. This upper ball joint interacts directly with the riser string; therefore, the forces seen at that joint become riser-string forces because of the tensioner support system. Ideally, the tensioner support-system forces at the upper ball joint should provide a net axial load on the riser string and should be constant in magnitude as well as direction. However, the nonideal behavior of the riser tensioners - as well as the inertia and geometrical effects associated with vessel, slip joint, and riser-string motions - result in load variations. Generally, the upper ball-joint force vector depends on time. No limits as yet have been determined for allowable variations of the riser-string forces resulting from the riser support mechanism. Nevertheless, measuring these variations analytically and qualitatively is important when assessing the effectiveness of the support mechanism or when providing important information about the boundary providing important information about the boundary conditions necessary to analyze the riser string. Our paper has two purposes. First, to emphasize by numerical examples the strong dependence of riser-tensioner force variations on the character of the assumed losses (pressure chop) in the tensioner-system air valves. Second, to present an analytical expression and numerical results for the tensioner-system force variations at the upper ball joint, thereby emphasizing the strong effects of vessel motion on riser-string force. TENSIONER ANALYSIS The typical drilling riser tensioner is a hydropneumatic mechanical system (Fig. 2) that provides tension in the cable attached to and supporting the outer barrel of the slip joint. Kozik studied the cable tensioner variation (r) resulting from cable motion. A convenient form for his equation is .....................(1) SPEJ P. 399