The Influence of Drilling Rig and Riser System Selection on Wellhead Fatigue Loading

2012 ◽  
Author(s):  
John F. Greene ◽  
Dara Williams
Keyword(s):  
Fatigue Life ◽  
Shallow Water ◽  
Deep Water ◽  
Fatigue Loading ◽  
Careful Consideration ◽  
Drilling Rig ◽  
Drilling System ◽  
Drilling Rigs ◽  
Water Depths ◽  
Selection Of

With drilling and exploration activity currently high in both deep and shallow water regions rig availability and selection is an issue for operators to consider in order to achieve the desired exploration schedule. At present the industry focus is on the development of 6th generation drilling rigs with the capacity to operate in increasing deep water. However despite the focus on deepwater exploration and the associated demand for deepwater drilling rigs there still exists demand for drilling rigs that can operate in shallow to moderate water depths (100m–500m). In addition, certain field development scenarios may exist where planned water depths for drilling activities vary significantly and therefore a drilling rig and riser system is required that can operate satisfactorily in both shallow and deep water depths. For a given drill site, rig availability or well location, may be such that an operator may have to select a modern deepwater 6th generation rig for shallow water activities where a 3rd generation rig would appear to provide a better solution. Other considerations such as vessel station keeping requirements may lead to selection of a 6th generation rig over a 3rd generation rig, as the former tend to have improved DP thrusters capacity. However it is also important to note that while the 6th generation rigs may have been proven to be robust systems for operation in deep water, the response of a 6th generation drilling system in shallow water depths can be very different to that of an older 3rd generation rig and drilling riser system. Thus careful consideration must be made by the operator when considering the selection of drilling vessels for shallow to moderate water depths. Fatigue life of the wellhead is shown to be affected when one compares the response of the 6th generation and 3rd generation drilling systems in shallow to moderate depths. This also needs to be accounted for when selecting rigs for workover or intervention operations on older infrastructure. This paper presents a discussion on the various parameters such as BOP stack size, riser, flex joint and vessel design that influence the response of the drilling system in shallow to moderate water depths (100m–500m). A number of case studies and parametric studies have been carried out and the results of these are presented in order to compare the wellhead fatigue damage from the older 3rd generation systems with the 6thgeneration systems and also to identify the critical drivers for this fatigue life reduction.

Optimisation of Conductor System Design to Minimise Wellhead Fatigue Issues

2013 ◽  
Author(s):  
Dara Williams ◽  
Kevin Purcell
Keyword(s):  
System Design ◽  
Shallow Water ◽  
Water Depth ◽  
Fatigue Loading ◽  
Recent Experience ◽  
Water Wells ◽  
Increased Risk ◽  
Main Driver ◽  
Drilling Rigs ◽  
Water Depths

Current market trends in the construction of newbuild drilling rigs indicate that the market is driven by demand for ultra-deepwater capacity semi-submersible rigs and drillships. These drilling vessels have capacity to drill in water depths of up to 12,000ft and possibly beyond in the near future. With increase in water depth capacity, more complex and heavier BOP stacks are required. Many modern drilling vessels are now incorporating BOPs with capacities of 20ksi pressure and up to 7 shear/seal rams incorporated. This leads to increased height and weight in the BOP. Whilst newbuild drilling vessels will be required to operate in water depths from 1,500ft to 12,000ft whilst on DP mode, deepwater semi-submersible drilling rigs will also have capability for operation in water depths <1,500ft using conventional mooring. Recent experience with modern deepwater rigs with large BOP stacks in water depth of 1,500ft or less suggests increased risk of fatigue when compared to 3rd generation rigs. If future trends continue with larger BOP stacks being designed then the problem of wellhead fatigue with modern deepwater drilling vessels is likely to become more acute. As noted in previous studies the water depth at drillsite has a major impact on the level of fatigue accumulated in the wellhead system. The main driver for this has been found to be the height and weight of the BOP. With requirements for newbuild drilling rigs for 12,000ft water depth capacity being the industry norm, and with increased requirements for BOP functionality, the gap between wellhead loading from 3rd generation and 6th generation rigs is widening. Given that many 3rd generation rigs will likely be decommissioned in the coming years then the usage of 6th generation rigs for shallow water operations will only become more commonplace due to rig availability. Thus, unless market conditions dictate the construction of smaller and lighter BOP stacks, the design of shallow water wells will be critical to ensure fatigue loading on the wellhead and conductor is kept to a minimum. This paper presents a summary of the results of a series of parameter studies carried out to assess a range of options for optimisation of casing and conductor design for 6th generation rigs in shallow water. Various recommendations are made as part of this study as to the addition of supplemental casing and conductor strings of varying sizes and wall thickness to ensure a robust conductor system design for fatigue performance.

Operational Challenges for Drilling Shallow Water Wells With Dynamically Positioned Rigs

2020 ◽  
Author(s):  
Rohit Vaidya ◽  
Mahesh Sonawane
Keyword(s):  
Shallow Water ◽  
Weak Link ◽  
Mitigation Options ◽  
Drilling Rig ◽  
Water Wells ◽  
Fatigue Monitoring ◽  
Drilling Operations ◽  
Drilling Rigs ◽  
New Generation ◽  
Selection Of

Abstract Traditionally, shallow water wells have been drilled from fixed platforms, jack-ups or moored drilling rigs. Recently there has been increased interest in performing operations on these wells using new generation of Dynamically Positioned (DP) rigs, driven by available capacity of these rigs and environmental regulations that restrict laying anchors on the seabed. Shallow water offshore drilling operations present a set of unique challenges and these challenges are further amplified when operations are performed on older wells with legacy conductor hardware with newer DP vessels and larger BOPs. The objective of the paper is to present challenges that occur during drilling in shallow water and discuss mitigation options to make these operations feasible through a series of case studies. Key challenges to optimizing riser operability and rig uptime are discussed. Potential modifications to the upper riser stack-up and rig deck structure for maximizing operational uptime are discussed. Riser system weak point assessment is presented along with solutions for mitigating risks in case the wellhead or conductor structural pipe is identified as the weak link. Selection of the drilling rig can have significant impact on wellhead fatigue response. Some criteria for rig selection based on drilling riser and wellhead system performance is presented with the objective of optimizing the fatigue performance of the wellhead and conductor system. Wellhead fatigue monitoring solutions in combination with physical fatigue mitigation options are presented to enable operations for fatigue critical wells.

Deep Water Scientific Drilling in Lake Malawi, Africa

2006 ◽  
Vol 40 (1) ◽  
pp. 29-35
Author(s):  
K. Moran ◽  
M. Paulson ◽  
M. Lengkeek ◽  
P. Jeffery ◽  
A. Frazer
Keyword(s):  
Deep Water ◽  
Lake Malawi ◽  
Design Work ◽  
Scientific Drilling ◽  
Drilling Rig ◽  
Core Recovery ◽  
Lake Floor ◽  
Drilling System ◽  
Rift Valley Lakes ◽  
First Time

A new deep water drilling system was developed and applied to recover deeply buried sediments for scientific analyses in one of the deep rift valley lakes of Africa—Malawi. This approach overcame the difficulty of maintaining position over a drill site in a remotely located, large, deep lake. Environmental conditions in Lake Malawi are similar to deep water marine settings and, as such, a marine approach was adopted for the Lake Malawi Drilling Project (LMDP). In February and March 2005, the modified pontoon, Viphya, successfully completed a scientific drilling expedition in Lake Malawi. This expedition recovered core at depths greater than 380 m below lake-floor in water depths as great as 600 m. The major refit of Viphya included installation of a moonpool, bridge, crew accommodations, mess, washroom, power system, dynamic positioning, and a drilling system. These major modifications required early pontoon surveys and naval architectural analyses and design work prior to their commencement. The expedition also used modified scientific coring tools with a marine geotechnical drilling rig for the first time, resulting in excellent core recovery and quality.

Numerical Simulations of Ocean Drilling System Behavior With a Surface or a Subsea BOP in Waves and Current

2008 ◽  
Author(s):  
Celso K. Morooka ◽  
Raphael I. Tsukada ◽  
Dustin M. Brandt
Keyword(s):  
System Behavior ◽  
Traditional System ◽  
Drilling Rig ◽  
Advantages And Disadvantages ◽  
Ocean Drilling ◽  
Sea Bottom ◽  
Drilling System ◽  
Drilling Rigs ◽  
High Level ◽  
Drilling Bit

Subsea equipment such as the drilling riser and the subsea Blow-Out Preventer (BOP) are mandatory in traditional systems used in deep sea drilling for ocean floor research and petroleum wellbore construction. The drilling riser is the vertical steel pipe that transfers and guides the drill column and attached drilling bit into a wellbore at the sea bottom. The BOP is used to protect the wellbore against uncontrolled well pressures during the offshore drilling operation. Presently, there is a high level of drilling activity worldwide and in particular in deeper and ultra-deeper waters. This shift in depth necessitates not only faster drilling systems but drilling rigs upgraded with a capacity to drill in the deep water. In this scenario, two general drilling systems are today considered as alternatives: the traditional system with the subsea BOP and the alternate system with the surface BOP. In the present paper, the two systems are initially described in detail, and a numerical simulation in time domain to estimate the system behavior is presented. Simulations of a floating drilling rig coupled with the subsea and surface BOP in waves and current are carried out for a comparison between the two methods. Results are shown for riser and BOP displacements. Critical riser issues for the systems are discussed, comparing results from both drilling system calculations. Conclusions are addressed showing advantages and disadvantages of each drilling system, and indicating how to correct the problems detected on each system.

Environmental Forces on Offshore LNG Terminals: The Complications of Shallow Water

2004 ◽  
Author(s):  
George Z. Forrsitall
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Field Measurements ◽  
Review Of The Literature ◽  
Water Demands ◽  
Local Measurements ◽  
Wave Heights ◽  
Overall Reliability ◽  
Water Depths ◽  
Water Bottom

Construction of large and expensive facilities in relatively shallow water demands that additional effort be paid to the extreme environmental conditions expected there. A review of the literature on waves in shallow water shows that many processes must be considered there which are not important in deep water. Bottom friction under waves depends on the detailed bottom conditions and parameterizing it properly may require calibration to local measurements. The limits on wave heights over the nearly flat bottoms that are common in water depths of 10–30 m are poorly known. Additional laboratory and field measurements appear to be necessary before depth limited waves can be confidently specified. The structures often respond differently to wave from different directions, so directional criteria could be useful. Commonly used methods of specifying directional criteria are un-conservative, but it is possible to adjust them so that the overall reliability of the structure is preserved.

Subsea Tree Fatigue Mitigation Solutions For Shallow Water Drilling

2021 ◽  
Author(s):  
Mahesh Sonawane ◽  
Michael Ge ◽  
Steven Johnson ◽  
Mike Campbell
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
High Stress ◽  
Fatigue Loading ◽  
Fatigue Performance ◽  
Hydrodynamic Damping ◽  
Industry Study ◽  
Blowout Preventer ◽  
Significant Length ◽  
Fatigue Evaluation

Abstract The offshore drilling industry is advancing technologies to extend deep water drilling technologies and attain feasibility of operations at deeper depths and higher pressures. However, shallow water operations themselves pose a certain unique set of challenges that need to be addressed with customized and innovative solutions. While shallow water poses certain benefits and conveniences to the operations, like ease of retrieval and better access to wells, there are significant challenges in terms of operational down time caused by limited operability and poor drilling riser and subsea hardware fatigue performance. Shallow water operations do not have the advantage of deep water drilling where the motions and loads imparted to the subsea blowout preventer (BOP) are relatively decoupled and damped out by hydrodynamic damping from the significant length of the water column. Thus, the vessel motions and wave hydrodynamic loads imparted on the riser are transferred to the wellhead and subsea hardware. In this paper the fatigue challenges encountered for drilling wells in 530 ft water depth from a sixth generation moored semi-submersible rig are explored. The fatigue loading is critical for the subsea tree connector which is characterized by a high stress amplification factor (SAF). Multiple riser space-out solutions were evaluated including fairings, helically-grooved buoyancy, joints with rope, and modifications to the telescopic joint each of which will be presented in the paper along with combination of different damping parameters to optimize the fatigue performance. The paper will present the subsea tree connector fatigue performance for different riser space-out options and make recommendations for future operations with similar conditions. Other challenges encountered in fatigue evaluation will be discussed. This will highlight the current assumptions and unknowns in data that can form the subject of evaluation for a future joint industry study.

Nonlinear effects in the response of a floating ice plate to a moving load

2002 ◽  
Vol 460 ◽  
pp. 281-305 ◽  
Author(s):  
EMILIAN PĂRĂU ◽  
FREDERIC DIAS
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Critical Speed ◽  
Moving Load ◽  
Ice Sheet ◽  
Phase Speed ◽  
Nonlinear Effects ◽  
Line Load ◽  
Weakly Nonlinear ◽  
Water Depths

The steady response of an infinite unbroken floating ice sheet to a moving load is considered. It is assumed that the ice sheet is supported below by water of finite uniform depth. For a concentrated line load, earlier studies based on the linearization of the problem have shown that there are two ‘critical’ load speeds near which the steady deflection is unbounded. These two speeds are the speed c0 of gravity waves on shallow water and the minimum phase speed cmin. Since deflections cannot become infinite as the load speed approaches a critical speed, Nevel (1970) suggested nonlinear effects, dissipation or inhomogeneity of the ice, as possible explanations. The present study is restricted to the effects of nonlinearity when the load speed is close to cmin. A weakly nonlinear analysis, based on dynamical systems theory and on normal forms, is performed. The difference between the critical speed cmin and the load speed U is taken as the bifurcation parameter. The resulting normal form reduces at leading order to a forced nonlinear Schrödinger equation, which can be integrated exactly. It is shown that the water depth plays a role in the effects of nonlinearity. For large enough water depths, ice deflections in the form of solitary waves exist for all speeds up to (and including) cmin. For small enough water depths, steady bounded deflections exist only for speeds up to U*, with U* < cmin. The weakly nonlinear results are validated by comparison with numerical results based on the full governing equations. The model is validated by comparison with experimental results in Antarctica (deep water) and in a lake in Japan (relatively shallow water). Finally, nonlinear effects are compared with dissipation effects. Our main conclusion is that nonlinear effects play a role in the response of a floating ice plate to a load moving at a speed slightly smaller than cmin. In deep water, they are a possible explanation for the persistence of bounded ice deflections for load speeds up to cmin. In shallow water, there seems to be an apparent contradiction, since bounded ice deflections have been observed for speeds up to cmin while the theoretical results predict bounded ice deflection only for speeds up to U* < cmin. But in practice the value of U* is so close to the value of cmin that it is difficult to distinguish between these two values.

CIDS: A Mobile Concrete Island Drilling System for Arctic Offshore Operations

1984 ◽  
Vol 21 (01) ◽  
pp. 1-11
Author(s):  
Sherman B. Wetmore ◽  
Harold D. Ramsden
Keyword(s):  
The Arctic ◽  
Structural System ◽  
Drilling Rig ◽  
Gravity Load ◽  
Unique System ◽  
Landfast Ice ◽  
Drilling Operations ◽  
Drilling System ◽  
Key Features ◽  
Water Depths

This paper describes a unique system that can provide an alternative to gravel islands as a means of supporting drilling operations in shallow Arctic waters. The Concrete Island Drilling System (CIDS) is composed of modular concrete "bricks" stacked one on top of the other which, in turn, support a barge-mounted drilling rig. Sequentially stacking these modules provides a great deal of flexibility in siting the modules in water depths of 18 to 52 ft. The modules incorporate an efficient concrete "honeycomb" structural system that offers inherent longitudinal, transverse and torsional strength. The superior strength of the CIDS, coupled with its massive ballasted weight, enables it to withstand the ice pressures prevalent in the landfast ice areas of the Arctic. Several key features of the CIDS make it a unique and economically advantageous exploratory drilling platform. Because it is modular, the CIDS reduces construction and transportation problems and allows the use of various configurations that can be modified to suit the water depth requirement. No dredging or gravel-hauling activity is associated with the CIDS since the gravity load is achieved by merely ballasting the modules with seawater. The entire system, with the drilling rig intact, can be relocated by pumping out the saltwater ballast and towing the CIDS to a new site. No rig demobilization or "under-dredging" of caisson fill is required. The use of concrete insures a long-lived structure that can be reused on many wells.

Global Design and Analysis of Umbilical in Offshore Applications

2009 ◽  
Author(s):  
Weiyong Qiu ◽  
Qiang Cao ◽  
Filippo Librino ◽  
Guillermo Hahn ◽  
Paul Stanton
Keyword(s):  
West Africa ◽  
Gulf Of Mexico ◽  
Shallow Water ◽  
Deep Water ◽  
Steel Tube ◽  
Bottom Current ◽  
Global Configuration ◽  
Motion Characteristics ◽  
Vessel Motion ◽  
Selection Of

An umbilical is an assembly of fluid conduits (thermoplastic hoses and steel tubes), cables (electrical and fibre optic), and power cores, joined together for flexibility and over-sheathed, with or without armouring, for mechanical strength and stability. The emphasis of this paper is on the global configuration design and analysis of offshore umbilicals. The extreme and interference analysis methodologies are presented. One example is given for the application of very small OD electrical umbilical in shallow water in West Africa. The proposed global configurations are presented. Another example is presented for the application of a hydraulic umbilical in deep water in the Gulf of Mexico. The selection of the global umbilical configuration in deep water depends on the host vessel. In other words, the vessel motion characteristics may dominate the umbilical configuration selection for the deep water application. This paper also deals with the influence of the bottom current on the global design of the umbilical in deep water. It can be concluded that an optimized umbilical global configuration, which meets the strength and interference design criteria, can be achieved for the application of a small OD electrical umbilical in shallow water in West Africa as well as for a steel tube designed hydraulic umbilical in deep water in the Gulf of Mexico.

MAPPING TIDAL CURRENTS AND RESIDUAL CURRENTS BY USE OF COASTAL ACOUSTIC TOMOGRAPHY

2017 ◽  
Author(s):  
Xiao-Hua Zhu ◽  
Xiao-Hua Zhu ◽  
Ze-Nan Zhu ◽  
Ze-Nan Zhu ◽  
Xinyu Guo ◽  
...  
Keyword(s):  
Shallow Water ◽  
Shallow Water Equations ◽  
Mean Amplitude ◽  
Momentum Equation ◽  
Tidal Currents ◽  
Acoustic Tomography ◽  
Mean Values ◽  
Residual Currents ◽  
Water Depths ◽  
Deep Area

A coastal acoustic tomography (CAT) experiment for mapping the tidal currents in the Zhitouyang Bay was successfully carried out with seven acoustic stations during July 12 to 13, 2009. The horizontal distributions of tidal current in the tomography domain are calculated by the inverse analysis in which the travel time differences for sound traveling reciprocally are used as data. Spatial mean amplitude ratios M2 : M4 : M6 are 1.00 : 0.15 : 0.11. The shallow-water equations are used to analyze the generation mechanisms of M4 and M6. In the deep area, velocity amplitudes of M4 measured by CAT agree well with those of M4 predicted by the advection terms in the shallow water equations, indicating that M4 in the deep area where water depths are larger than 60 m is predominantly generated by the advection terms. M6 measured by CAT and M6 predicted by the nonlinear quadratic bottom friction terms agree well in the area where water depths are less than 20 m, indicating that friction mechanisms are predominant for generating M6 in the shallow area. Dynamic analysis of the residual currents using the tidally averaged momentum equation shows that spatial mean values of the horizontal pressure gradient due to residual sea level and of the advection of residual currents together contribute about 75% of the spatial mean values of the advection by the tidal currents, indicating that residual currents in this bay are induced mainly by the nonlinear effects of tidal currents.

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