Production Risers Research Articles

The lifetime dynamics of a deep water riser design

This paper discusses the dynamics of a hybrid production riser designed for a water depth of 1500 m in the harsh environment west of Shetland where one of the main design drivers is offshore installation time. To minimise installation time, a free standing riser was developed comprising a carrier pipe, top and bottom taper sections and an integral subsurface buoy connected by flexibles to the moored FPSO. The paper discusses the different dynamic characteristics of the structure during tow out, upending, connection and when installed. The simulation methods used, the design drivers, design compromises and parameter sensitivities are also discussed. It is concluded from extensive dynamic analysis and structural design that the proposed design is feasible and the estimated on-site installation time is 2–3 weeks.

Comparative Risk Assessment of Alternative TLP Systems: Structure and Foundation Aspects

Abstract Offshore operators can choose from a wide variety of alternative production systems including those based on fixed platforms, tension leg platforms (TLPs), compliant towers, floating production systems, and remote subsea systems. These systems involve varying degrees of technical innovation and technological risk. Life cycle costs, including initial costs and operating costs over the life of the project, need to be carefully considered to define systems that will minimize cost and maximize return on investment. The life cycle includes all stages of the project, including design, construction, operation, and decommissioning. To address decision-making issues in the selection of alternative systems, eighteen sponsoring organizations under the leadership of Amoco helped define the Methodologies for Comparison of Alternative Production Systems (MCAPS) project. Conducted during a two-year period (1988-1990), this project developed and illustrated an engineering procedure to assist the process of making rational comparisons among design alternatives for offshore production systems. The example developed to illustrate application of MCAPS was a TLP concept designed for Gulf of Mexico conditions. Four TLP alternatives were analyzed and compared; these involved three production riser alternatives and two tendon system alternatives. This paper addresses the structural and foundation aspects of the two tendon system alternatives. A companion paper (Stahl et al., 1991) addresses the production riser alternative, the alternative system economic evaluations, and the comparison processes. The structure aspects addressed in this paper include both first-phase coarse qualitative and quantitative evaluations, and second-phase detailed quantitative evaluations. The detailed quantitative evaluation is illustrated with structural damage in extreme conditions, including potential overloading of the hull, tendons, and the foundation piles. The paper concludes that MCAPS is not a simple process. It is an intensive interdisciplinary process requiring good teamwork and extensive familiarity with the system being analyzed. The judgmental elements of the process are considerable. The potential benefits of the process include: an improved understanding, qualitatively and quantitatively of risk mechanisms; identification and mitigation of hazards; improved cost-effectiveness of designs; and improved safety. The specific risk numbers generated are less important than the design improvement insights that are developed; these numbers can only serve as a guide to focus attention on those aspects of the project which generate the most risk and to indicate where cost-effective risk reduction measures can be implemented.

Composite Risers for Deepwater Applications

This paper is devoted to the high performance composite tubes developed by the Institut Francais du Petrole (IFP) and Aerospatiale for deepwater risers applications. The design principles of the tubes are first presented, along with results of preliminary work carried out as part of the initial feasibility study. Applications of composite tubes to drilling riser Kill and Choke lines and to TLP production risers, both of which have been studied in detail, are then described. Technical and operational advantages obtained from such applications are discussed.

Three-Dimensional Analytical Simulation of Flexible Pipe Wall Structure

A three-dimensional analytical model of the mechanical response of a bonded layered flexible pipeline section to a general set of loads and pressures is presented. Stiffness relations for isotropic, orthotropic and helically wound armoring layers are developed and combined to form a total section stiffness equation incorporating inter-layer pressures and radial deformations. These layers may be used to model the mechanical responses of flexible pipelines including any number and order of layers. Typical loads are taken from a three-dimensional analysis of a flexible production riser in a steep-wave configuration in 310 m water depth. An illustrative pipe section with five layers, including an inner steel tube, two contrawound steel cable layers and two modeled with rubber matrix materials, is subjected to this three-dimensional load set. Computations show the dominant influence of the steel strands in carrying the ambient loads and also gives an accurate picture of the radial distribution of inter-layer pressures across the pipe thickness. The analytical model is designed to give a detailed assessment of deformations and stresses in the various layers such that estimates may be made of critical parameters including wear, slip, rupture, debonding and other related aspects of flexible pipe performance.

Model Tests on Multi-Tube Production Risers

Abstract Model tests carried out at 1/14.5 scale on two production risers in a towing tank are described. One of the risers considered is modeled on that used in the Buchan field, while the other has a compact low drag configuration of the same production capacity. The tensioning system was carefully modeled, and vessel surge motions were accurately represented in both regular and irregular waves. Current was represented by carriage motion. Some results are presented for bending moments and displacements for both models and comparisons are made with computer simulations to deduce appropriate values for hydrodynamic coefficients.

Remotely Operated Guideposts Reduce Drilling Time and Costs

Summary Remotely operated guideposts were successfully used to establish, release, and re-establish guidelines for a template installation in 1,758 ft [536 m] ofwater in the Gulf of Mexico. The guideposts were used to reduce thedrilling-template weight, to improve accessibility of the remotely operatedvehicle (ROV) around the well slots, and to reposition the blowout preventer(BOP) stack on a new well without tripping the stack to the surface. Beforefield installation, procedures were developed and the guideposts and runningtools were function tested. Wet tests verified the reliability of the ROV andguidepost interface. This testing contributed to the successful use ofguideposts. Drilling-template costs dropped significantly. The approach helpedsave about 36 days of drilling time. The guideposts were also used to tie backthe tendons and production risers for the tension-leg well production risersfor the tension-leg well platform (TLWP). platform (TLWP). Introduction The Jolliet Project has been under development since June 1987 in 1,758 ft[536 m] of water in Green Canyon Block 184 of the Gulf of Mexico. Drillingthrough a template in this depth requires safe, cost-effective subsea-guidelineanchoring techniques. Therefore, guideposts and associated equipment weredesigned to be used with an unmanned ROV. The guideposts were used to install the template well pod and to positionthe BOP stack (Fig. 1). Because of the importance of reliable procedures andequipment, especially in a deepwater environment, contingency planning wasemphasized. This included operational testing before field use. This paper discusses objectives for guidepost use, the remotely installedguidepost, guidepost running tools, and equipment testing. It also presentsfield performance results, conclusions, and performance results, conclusions, and recommendations for future applications. Objective and Results Use of removable guideposts improved drilling-template design and optimizedprocedures. The elimination of permanent procedures. The elimination ofpermanent guideposts reduced the template weight and decreased the materialcosts because only four primary and four backup guideposts were required. Italso provided an uncluttered template work area. This increased the ROV'spossible work scope while reducing the complexity of its operations. Procedures that allowed the BOP stack to be kept on bottom for 90 days bymoving from well to well were simplified by a topaccess guidepost design. Stackrepositioning, including raising and relatching, was completed in about 9hours, which saved 1.8 days/well. With minor modifications, the guideposts were also used to optimize twoother operations (Fig. 2). When the production riser is run, special shearbolts that break with a reduced tensile load on the guidepost are used. Toassist in the installation of the tendons for the TLWP, the guidepost wasfitted with an outer sleeve that has a sheave Fig. 3). Equipment Guideposts. Skeels and Landeis described the design of the remotely operatedguidepost (Fig. 4). The post has an 8.62-in. [219-mm] -diameter outer body witha latching profile on top and a landing ring near the bottom that lands in thefunnel receptacles on the template. Two spring-loaded, outwardly biased latchdogs at the bottom of the post anchor the guidepost to the receptacle. Theguidepost has an inner sleeve and cam mechanism so that a top-access tool canretract the latch dogs and release the post. A backup release mode is providedby four shear bolts. The tensile force to shear the bolts is applied byattaching a strong wire rope to the guidepost or latching onto the guidepostwith a steel drillpipe tool. Tools. Two types of guidepost tools can be used to release a guidepost fromits funnel receptacle. Both types have a collet that slips over the latchingprofile at the top of a post. Hydraulic cylinders in the tool move a ring downover the collet to lock the tool to the post (Fig. 5). Continued movement ofthe post (Fig. 5). Continued movement of the ring depresses the guidepost innersleeve, which causes the cam mechanism in the guidepost to retract the latchdogs for release of the post from its funnel receptacle. The steel version of the tool is run on drillpipe with two hydraulic linesconnecting it to a 3,000-psi [21-MPa] hydraulic pump on the rig. TheROV-compatible version of the tool was made for this project by usinglightweight materials and adding flotation elements. The ROV positions the tooland then supplies the hydraulics to operate it. Ancillary tools, such as guideframes and remote cable anchors, allowflexibility in procedures. To re-establish a guideline, for procedures. Tore-establish a guideline, for example, the remote cable anchor can be latchedto a guidepost with the guidepost tool. Equipment Testing Guideposts and tools of this basic design were developed and tested in 1985and successfully used in 1,400 ft [427 m] of water in the Gulf of Mexico. Additional testing was needed for the Jolliet Project because of the concernfor ROV dependability and use of prototype ROV tool designs. P. 272

The Highlander Field - One Year's Operating Experience

Summary In 1985 the Highlander field was brought on stream from one of the first generation of advanced remote-controlled subsea production facilities in the North Sea only 15 months after the U. K. Dept. of Energy approved development. The successful development of the Highlander field was made possible by a combination of innovative ideas and the advancement of existing technology. This paper describes the problems and successes during 1 year of operating experience. Introduction The Highlander field is located in Block 14/20, 8 miles [12.9 km] northwest of the Tartan platform in 420 ft [128 m] of water (Fig. 1). Because "stand-alone"-type developments were seen as uneconomical, the decision was made to develop the field with a remote-controlled subsea production and water-injection facility would be controlled by and produced to the Tartan platform. The development was completed in two phases, a procedure that substantially reduced the time from project approval to first oil being produced. Phase 1 consisted of running well completions in predrilled, offtemplate wells and connecting these wells to the Tartan platform through two 8-in. [200-mm] service lines. During Phase 2, the template and slug catchers were installed; the wells were reconnected to the template; and the template, test and bulk production pipelines, slug catchers, and risers were commissioned. These two phases are described more fully by Smith and Batcheler. This paper deals with the operating experience of Phase 2. The development originally consisted of four wells-Wells HS12, HS13, HS14, and HS15-previously drilled and suspended between 1980 and 1983. In 1985, these wells were completed and tied into a subsea template that has 12 additional slots for future wells. Since then, three wells (Wells H1, H2, and H3) have been drilled successfully through the template. All wells and services are interconnected by manifolds on the template. Production to the Tartan platform is through 12-in. [300-mm] bulk and 8-in. [200-mm] test multiphase pipelines. The pipelines are connected into two subsea slug catchers at the base of the Tartan platform. These slug catchers are designed to eliminate slugging before oil is pumped up to the platform through two 7-in. [180-mm] casing strings. Gas is separated out of the crude at the slug catchers and routed to the platform through the 18 5/8x7-in. [470X180-mm] riser annuli. The template is also connected to the Tartan platform by 8-in. [200-mm] waterinjection, 8-in. [200-mm] gas-lift, and 4-in. [100-mm] utility flowlines. Umbilicals provide hydraulic and electrical power and chemical injection to the template. Maintenance is by diver intervention during well servicing, and workovers require a diving support vessel or semisubmersible drilling rig. A new subsea wireline technique, successfully tested on Well HS14 in Nov. 1987, allows routine well work to be carried out from either a diving support vessel or a semisubmersible drilling rig simultaneously with the drilling of new wells. This will substantially reduce well-servicing costs.

Improving Wellhead Performance With Programmed Cement Shortfall

Summary Subsea wellheads can be subjected to extreme external loads when a drilling or production riser remains connected during storm or vessel drive-off conditions. In addition, vortex shedding from high currents and wave action on drilling and production risers can subject the wellhead to high-cycle fatigue loads. These extreme external and high-cycle fatigue loads can cause failure of the wellhead system when a fully cemented annulus between the 30-in. [76-cm] structural conductor pipe and 20-in. [51-cm] surface casing is not achieved. This effect of cement shortfall is most damaging when the cement level is just below the wellhead-body/conductor-housing region. Purposefully setting the cement level far below the mudline can be a cost-effective solution to the unintentional cement-shortfall problem.

Development of Buoyancy for Flexible Production Riser System for North Sea Sun Oil Balmoral Field

This paper covers the design, manufacture and hydrostatic pressure testing at the maximum working depth, of some of the largest buoyancy units ever considered in syntactic foam. Finite element analysis and evaluation of individual polymer material and bond to steel properties, were key elements in the design of these units, which have now been in service in the North Sea for over 2 years of their 20 year life guarantee.

4735267 Flexible production riser assembly and installation method

4735267 Flexible production riser assembly and installation method

Static, dynamic and eigen analysis of non-integral production risers

A mathematical model of static, dynamic and eigen analysis of non-integral production risers, based on a small deformation, two dimensional, structurally linear and hydrodynamically nonlinear single riser model, is developed. It takes into consideration guide arms which connect and hold apart individual component-risers. Algorithms are developed based on contact, substructuring and condensation techniques which handle efficiently constraints imposed by guide arms. The static and dynamic algorithms require only solution of the corresponding problems of all component-risers and equilibrium of guide arms. The eigen analysis algorithm solves a problem with number of degrees of freedom equal to those of the entire system reduced only by the number of those constrained by guide arms. Its solution reveals the dependence of the eigen solution on the distribution of guide arms. Simple problems are solved to verify computer programs implementing the three algorithms. Typical non-integral production riser problems are solved and results are compared to those of single risers.

4704050 J-configured offshore oil production riser

4704050 J-configured offshore oil production riser

Drilling and Producing Operations Utilizing a Tension-Leg Platform

Summary The Hutton field, discovered in 1973, is located in U.K. Block 211/28 about 275 miles [440 km] off the Shetland Islands in 485 ft [148 m] of water. The 1979 decision to proceed with field development was significant because the structure selected would become the world's first commercial tension-leg platform (TLP). This operational review covers the predrilling and completion of the first 10 wells from a semisubmersible drilling rig, their subsequent tieback to the TLP, and the startup activity from an integrated-deck philosophy with production operations from a platform with moving trees, flexible flowlines, and production riser tensioners.

Computer control of a complex block-loading test

This paper describes the rig used for the full-scale fatigue testing of an oilfield production riser connection. The complex block-loading spectrum and the need to co-ordinate data acquisition with the loading made a real-time, computer-based control system an attractive, perhaps an essential, solution. It is seen that in the integrated system of electronics, servohydraulics and rig hardware, the computer functioned as a man/machine interface. Aspects of safety to which the computer contributed are highlighted, but the importance of electro-mechanical devices is also recognized. It was found that a multiple checking technique was a valuable tool in avoiding nuisance tripping of the safety circuit. Finally, the main advantages of the computer-based control system are summarized.

Large deformation three-dimensional static analysis of deep water marine risers

The problem of static three-dimensional, nonlinear, large deformation response of a marine riser is formulated within small strain theory and solved numerically. This type of analysis is necessary, for the new generation of drilling and production risers. The mathematical model takes properly into account the effects of internal and external pressure and the complete nonlinear boundary conditions, without linearizing the follower forces. The extensibility or inextensibility condition is used as the constitutive relation in the tangential direction. Torsion and bending are coupled. The external load and the boundary conditions are deformation dependent. A solution method is developed based on an incremental finite element algorithm, which involves a prediction-correction scheme. In the correction phase deformation dependent quantities are updated. The extensibility or inextensibility condition is used to reduce the degrees of freedom of the system. The numerical results of the developed computer code compare very well with available semi-analytical and numerical solutions. Three numerical applications are used to demonstrate the importance of large deformation, nonlinear and three-dimensional analyses.

Hydrodynamic Forces on Multitube Production Risers Exposed to Currents and Waves

This paper presents the experimental results of a joint industry riser test program. Over a five-year period, an extensive experimental investigation of hydrodynamic loads acting on various production risers was carried out. The program included the laboratory testing of many multitube riser configurations as well as a single cylinder. Several major oil companies sponsored the project. The tests were made with rather large-scale models which were: 1) held stationary in steady current, 2) moved at constant speed or constant acceleration through a quiescent fluid or through a moving fluid, and 3) held stationary in oscillating flow or in steady current superimposed on oscillating flow. The primary objective of this investigation was to establish an accurate measurement of the hydrodynamic forces on bundle-type risers. The findings from this study will be presented in two papers. In the first, we shall present the hydrodynamic force coefficients for some marine risers consisting of one or more cylinders interacting either only with currents or oscillatory flow separately. In a companion paper, the pertinent data for the joint presence of the oscillatory flow and currents will be discussed. Among the results outlined here are the drag, inertia, and lift coefficients for various composite risers as a function of the Reynolds and Keulegan-Carpenter numbers. An analysis and synthesis of the test data are also presented.

Deepwater Production Riser

The design of a deepwater production riser is described. The compliant riser design consists of a lower rigid section terminated about 200 ft (60 m) below the sea surface with a tensioning buoy assembly and a flexible upper section made of a bundle of flexible pipes. It is designed to be compliant to waves, currents, and vessel motions and applicable to both mild and severe environments. Design, analysis, testing, and installation are discussed.

Finite-element analysis of the marine riser

A two-dimensional finite-element computational method is presented for determining marine riser displacements and stresses due to self-weight, buoyancy, internal and external pressures, surface vessel motions and environmental forces arising from currents and waves. A dynamic analysis is performed in the frequency domain for regular waves by linearizing the hydrodynamic damping term. A fully nonlinear time step integration of the equations of motion using the Newmark constant acceleration method is also presented. Extensive use is made of a substructuring technique in the dynamicv analysis to reduce the number of degrees of freedom and, therefore, achieve a substantial reduction in computer time and storage without a discernible performance penalty. A number of test cases are presented to compare the linearized and nonlinear dynamic analyses and to highlight the performance of this method in relation to other marine riser analysis techniques. The application of this finite-element method to multitube production risers with complex cross-sections is discussed.

Subsea riser manifold with structural spanning member for supporting production riser : Assigned to mobil oil corp, New York, N.Y. USA US Patent 4 398 846 (16 Aug 1983)

Subsea riser manifold with structural spanning member for supporting production riser : Assigned to mobil oil corp, New York, N.Y. USA US Patent 4 398 846 (16 Aug 1983)

Buckling of Columns With Nonmovable Boundaries

The global buckling problem of slender tubular columns subject to distributed load is studied. The load consists of the column weight, tension/compression exerted at the top of the column, and internal and external variable static pressure forces due to fluids in gravity field. Nonmovable supports at the upper and lower column ends define the boundary conditions. The resulting nondimensionalized eigenvalue problem is general, and applicable to columns, tubes, pipelines, marine drilling and production risers, mining risers and legs of tension leg platforms. The eigenvalue problem consists of a linear, fourth order differential equation with variable coefficients and four homogeneous boundary conditions. The exact solution is derived in terms of Airy functions of the first and second kind. A power series solution is presented as well. Both methods are numerically implemented and become unstable only for high values of the loading variables. The combined results of the two methods cover the entire domain of practical interest. The critical curves are plotted in the space of the two loading variables for the first six modes. Their asymptotic behavior and its dependence on the boundary conditions is revealed.