WO2011041860A1 - Hydrodynamic damper for catenary riser - Google Patents

Abstract

The present invention relates to the use of hydrodynamic dampers (1) in at least a given segment of a riser (R). The main feature of the hydrodynamic damper (1) is that it stops the propagation of a compression wave (O) in the riser (R), inducing a controlled and expected buckling, at a certain distance from the touch down point (P) of the riser (R) at the sea bottom. The hydrodynamic damper according to the invention can have different configurations that can be combined in various ways.

Description

 HYDRODYNAMIC DAMPER FOR UPPER PIPE

 IN CATENARY

FIELD OF INVENTION

 The present invention is in the field of components of an subsea oil production system. More particularly, this component is a free overhead catenary riser that carries hydrocarbons and other fluids involved in this oil production process. More specifically, it deals with devices in the form of overcoating sections that are applied to segments along the riser to modify their dynamic response and prevent buckling in the region where it touches the underwater ground.

BACKGROUND OF THE INVENTION

 The exploration and production of oil is being conducted every day, being conducted in deeper water depths, already exceeding 2,500 meters deep.

 Typically, a floating drilling unit is used to create a well. Once the well has been completed, a floating production unit which may be a semi-submersible platform, a float or a production vessel known to the experts as Floating Production Storage and Offloading (FPSO) is installed on site for production to be completed. wells can be drained and processed.

The main component for raising oil from the subsea below-ground reservoir to the floating production unit is a pipeline that transports hydrocarbons, water and other fluids used in the oil production process, also known as the riser and, by the term risef term by which it will be referenced hereinafter throughout this report. The riser is also used for the transport of hydrocarbons between two platforms or between a platform and an earth drain. Risers have various types of construction and can take various shapes and configurations.

 The simplest and most commonly adopted configuration is the so-called free catenary. In this configuration the risers can be flexible or rigid.

 Rigid risers are usually referred to by the technique as "SCR" (Steel Catenary Riser) and are generally made up of a plurality of welded steel tubes that provide simplicity of installation operation, no intermediate connections and reasonable compliance. against the movements that the floating unit of production may suffer because of the environment.

 When extreme environmental events such as very large waves and very strong winds hit a floating unit of production, they induce to this floating unit of production movements that normally have a large amplitude. Since the top of the riser is connected to this floating production unit, the large amplitude movements performed by the floating production unit are immediately transmitted to the riser.

 The movements in the riser generate a compression wave that propagates from the top to the point where the formed catenary touches the undersea ground, known to the experts as "TDP" (Touch Down Point). Once the TDP is reached, the compression wave encounters an obstacle to its propagation which is the soil itself. Evoking the principle of action and reaction, marine soil tends to reflect the back compression wave, further increasing the compression level in this region.

If the compressive loads, both action and reaction, reach a critical limit, the riser structure releases all compressive energy through a geometric instability known by the term buckling, which subjects the riser construction structure to very high stress levels and can lead to structural collapse. Attempts at solution involve placing float devices along the riser length in order to reduce the weight of the riser or even to modify the way it descends to the underwater floor away from the free catenary descent configuration.

 Another natural cause that can structurally affect a riser is the incidence of marine currents. When passing around a riser, behind the so-called attack surface (which is the part of the riser's cylindrical surface that is directly directed against the current direction), seawater vortices are created at a frequency that is proportional to the current velocity. maritime If the current velocity is too strong, the frequency of vortex creation can reach critical values; As a result, the riser begins to vibrate in accordance with a phenomenon known to experts as "VIV" (Vorticity Induced Vibrations).

 These vibrations bring particularly damaging consequences to the material that makes up the riser and drastically reduce the life of the riser, resulting in the call of fatigue.

 In order for this phenomenon to be prevented, devices known as vortex suppressors have been created and are installed along the length of the riser to guide the passage of the marine current through the riser in a non-turbulent manner.

 Although vortex suppressors are employed and function in their various constructive forms known in the art, these devices end up generating too much of the riser's final cost, due not only to the cost of the device itself, but also to the time it takes to install it on top of it. the riser.

Until then, state-of-the-art solutions for eliminating or at least suppressing the critical motion effects on riser TDP have been rooted in the decoupling of floating unit of production of the region of contact of the riser with the submarine soil.

 Examples of such solutions include Riser Lazy Wave, Riser Lazy-S, Riser Pliant-Wave, Riser Self-supporting Hybrid and Subsurface Buoy. However, the configurations using these solutions are very complex, with application that demands a lot of logistics, time and disadvantages related to the high cost involved.

RELATED TECHNIQUE

 The specialized technical literature and various patent documents cite as an example compositions which have become widespread.

 US 4,400,110 (Pierre A. Beynet), incorporated herein by reference, describes a floating production system for oil and gas producing wells that employs a subsurface float to decrease stress on a flexible ripper used to connect a production pipe to a floating unit. The subsurface float uses a cradle mount with a drag balancing device to counteract the torsion moments applied to the cradle by the effect of marine currents.

 US 4,567,842 (Peter R. Gibb), incorporated herein by reference, discloses a description of an offshore hydrocarbon mooring and transfer system for a production vessel using a weight-compensated riser system installed on the ship. The riser is attached to the ship at one end of a rocker arm to compensate for the vertical loads imposed on the ripper by the vertical movements of the ship. In this way the high load effects that lead to fatigue the structure of the riser are minimized reducing its useful life.

US 6,824,330 (Avie Max Grobe), inserted herein as Reference, presents a catenary riser system that includes a tensioning mechanism in a floating structure that applies a substantially constant and controlled tension to the riser, which is coupled to the floating structure by a flexible conduit. More specifically, the upper portion of the riser is above the water surface and is connected to the tensioning mechanism by means of a rope, cable, chain or wire. Hydraulically the top of the riser is connected to a flexible conduit that carries fluids from inside the riser to the floating structure. Constant tensioning of the tensioning mechanism is intended to minimize the effects of riser fatigue by extending its life and avoiding fixed connection arrangements known in the art.

 WO 2007/017574 (Roberto Jourdan de Aquino et al.), Incorporated herein by reference, discloses a curvature limiter for a subsea hydrocarbon transfer system, characterized in that it comprises a flexible tubular member where an intermediate portion of this flexible tube comprises a plurality of successive substantially circular sections pivotally mounted relative to each other defining a median plane such that the flexible tube forms a moderate curvature equal to the radius of curvature of this median plane. The objective is to keep the intermediate portion of the flexible tube in suspension between the underwater floor and the floating structure.

 WO 2009/063163 (Zhimin Tan et al.), Incorporated herein by reference, discloses a flexible pipe support system in which a number of adapted supports on the flexible pipe, which serve to maintain the pipe at a certain height from the underwater floor. , print controlled buoyancy to a stretch of hose and be adaptable and compliant with the conditions under which hose can experience under the influence of the medium.

The technique still resents an alternative to avoid the reduced service life, particularly in SCR-type risers, in an efficient and straightforward manner.

SUMMARY OF THE INVENTION

 Objectives of the present invention are: reducing the buckling phenomenon at the point where an SCR-type riser in a free catenary configuration touches the underwater floor, reducing its apparent weight and reducing the fatigue-damaging material of which it is used. The riser is formed, whether these problems are caused by movements from the floating unit to which it is attached, or by the passage of marine currents around the riser.

 These objectives are achieved by applying hydrodynamic dampers to at least one particular riser segment.

 The main characteristic of the hydrodynamic damper is eminently functional, that is, the hydrodynamic damper has the function of stopping the propagation of a compressive wave by the riser, inducing a controlled and expected buckling at a certain distance from the riser touch point with the riser. undersea soil.

 A minor, but no less important benefit is the increased life due to Vortex Induced Vibration Fatigue (VIV). Hydrodynamic dampers modify the dynamic response of the riser and the results of numerical simulations point to the possibility of reducing or even eliminating the need for the use of vortex suppressors.

 There is also a reduction in the apparent weight of the riser because it is the hydrodynamic damper made of low density material, which can reduce the loads in the production unit.

The hydrodynamic damper of the present invention has a plurality of possible and scenario-dependent embodiments, but the feature common to all One embodiment is the conformation of an overcoat with easy adaptation and keeping the riser in the free catenary configuration.

BRIEF DESCRIPTION OF THE FIGURES

 The characteristics of the catenary riser hydrodynamic damper of the present invention will be better understood from the following detailed description, by way of example only, associated with the drawings referenced below, which are an integral part of this report.

 Figures 1A, 1B, 1C and 1D are representations of some possible embodiments for the hydrodynamic damper of the present invention installed on a SCR type riser.

 Figure 2 is a representation of the application of the hydrodynamic damper of the present invention on only one segment of the SCR and without hydrodynamic load.

 Figure 3 is a representation of the application of the hydrodynamic damper of Figure 2 where this damper is in the deformed configuration due to the action of hydrodynamic loads.

 Figure 4 is a representation of the application of the hydrodynamic damper of the present invention to more than one segment of the SCR also showing its deformed configuration.

DETAILED DESCRIPTION OF THE INVENTION

 The detailed description of the catenary hydrodynamic shock absorber, object of the present invention, will be made according to the identification of the components that form them, based on the Figures described above.

It is an object of the present invention to reduce the buckling phenomenon at the point where a ridge in a free catenary configuration touches the underwater ground, to reduce its apparent weight and to reduce the damage caused by VIV due to the effects of hydrodynamic loading being imposed upon the rísis by the conditions environment, whether these conditions are due to the induction of movement by the floating unit to which it is attached, or these conditions due to the passage of marine currents around the.

 By way of clarity, the word riser will hereinafter be used as a designation for specifying an SCR {Steel Catenary Riser) riser.

 As discussed earlier, the current technique has not yet found an effective solution to prevent buckling in the TDP (Touch Down Point) region in free catenary risers. In practical application, to overcome this problem, other types of risers are employed in configurations that decouple movements relative to the floating unit of the riser contact point with the ground. However, these solutions greatly increase the costs involved.

 A first experiment in finding a solution to the buckling problem involved the use of a lightweight stretch at the point where the riser touches the undersea ground, taking into consideration as a floating unit an anchored FPSO-type vessel. multipoint, receiving the incidence of extreme waves in an ultra deep water depth, was negative in relation to the efficiency in reducing extreme stresses in the riser.

 The objectives of the present invention have been achieved by applying one or more lightweight patches over riser segments that lie along the suspended length rather than just in the TDP region (P).

Hydrodynamic dampers (1) of the present invention are characterized by interrupting the propagation of a compressive wave (O) by the riser (R) by inducing a calculated and controlled buckling in a portion of the suspended length of the riser (R) at a certain distance from the touch point (P) of the riser (R) with the submarine ground, ie the TDP region.

 Figures 1A, 1B, 1C and 1D show possible, but not limiting embodiments for the hydrodynamic damper, object of the present invention.

 In Figure 1A, in a first embodiment, the hydrodynamic damper (1) comprises a single lightweight, constant diameter stretch (11) applied over at least one suspended length segment of a riser (R).

 In Figure 1B, in a second embodiment, the hydrodynamic damper (1) comprises a larger diameter stretch (12) of light coating applied over at least one suspended length segment of a riser (R) and at least at least one light-lined stretch (11) installed near at least one end of the larger diameter stretch (12), stretch (11) intermediate diameter between the riser diameter and the largest diameter stretch (12).

 In Figure 1C, in a third embodiment, the hydrodynamic damper (1) comprises a larger diameter stretch (12) of light coating applied over at least one suspended length segment of at least one riser (R). a lightweight transitional section (13) installed near at least one end of the larger diameter section (12) and at least one lightweight section (11) installed near at least one , one end of the transition stretch (13), which has an intermediate diameter between the riser diameter (R) and the stretch diameter of (11)

In Figure 1D, in a fourth embodiment, the hydrodynamic damper (1) comprises a light-coated segment (16) of variable diameter, where this diameter continuously increases from its ends (E1, E2) in diameter close to the diameter of the riser (R), to a maximum diameter (Dm), segment (16) which is applied over at least one segment of the suspended length of the riser (R).

 The use of the stretch (11) in relation to the ends of the larger diameter stretch (12) has a positioning that can be chosen from: at one end, and at both ends.

 When employed more than one unit, the portion 11 may be chosen from: having same length, having different lengths, having same diameters and having different diameters from each other.

 The use of both the transition section (13) and the

(11) in relation to the ends of the larger diameter section (12) has a position which can be chosen from: being asymmetric with different sections (11, 13), with more than one section (11, 13) at one end and, at least one element at the other end and sections (11, 13) at only one end.

 The hydrodynamic damper (1) employs as its constituent common liner material which simultaneously meets the mechanical strength and low density requirements. A typical example of this material is the commonly used commercially available riser (R) thermal coatings.

 The use of low density material reduces the apparent weight of the riser (R) segment where it is installed, making it more compliant. Increasing the riser hydrodynamic diameter (R) by adapting the hydrodynamic damper (1) makes it more susceptible to hydrodynamic loading (CH).

Figure 2 shows a hydrodynamic damper in one possible embodiment applied to a suspended length segment of the riser (R) away from the TDP region (P) and in a hydrodynamically load (CH) free situation. Figure 3 shows a hydrodynamic damper (1) under the propagation action of a compressive wave (O) and hydrodynamic loads (CH).

 It can be observed that when the floating unit (U) moves by surface waves, the vertical movement (V) that the unit performs is transmitted directly to the top of the riser (R). This movement generates a vertical load in the riser (R) compression direction that propagates toward the underwater floor. In addition, the riser (R) also moves generating hydrodynamic loads (CH) perpendicular to the wall due to the presence of external fluid (seawater) (hatched detail in Figure 3).

 The diameter of the riser (R) becomes larger in the segment where the hydrodynamic damper is applied. The loads perpendicular to the riser wall (R) are proportional to its hydrodynamic diameter. Due to this, the hydrodynamic loads in this segment will also be higher.

 The resulting stresses on the riser segment (R) and the damper cause the latter to bend controllably in response to requests and stop the propagation of the compressive wave (O) from the top of the riser (R).

 The control of the riser segment curvature (R) as a function of the magnitude of the load request can be obtained by controlling parameters that include: the segment length, the material specific weight and the hydrodynamic damper thickness (1).

Figure 4 illustrates a situation where more than one riser segment (R) is equipped with a hydrodynamic damper, which increases the efficiency in stopping compressive wave propagation (O) and solving the buckling problem in the region (P ) of the TDP. In the hatched detail of this Figure 4, the hydrodynamic dampers (1) can be observed in a situation of deformation due to the fact that they are subjected to hydrodynamic (CH) and compression loads.

 The hydrodynamic damper riser segment (R) when flexing under load, prevents compression loads from the motions imposed on the top of riser (R) from buckling in the TDP region (P) where this riser (R) touches the undersea soil.

 In order to study the feasibility of using SCR risers (R) coupled to FPSO floating units, numerical simulations were performed based on data from a scenario located in the Santos Basin, Brazil, presented here as mere example.

 The simulations were made considering a riser (R) without the hydrodynamic damper and with hydrodynamic damper. The numerical results obtained showed that the riser (R) with the hydrodynamic damper of the present invention eliminated buckling in the region (P) where the riser (R) touches the undersea ground and, even when simulating extreme level loading situations, the level of stress imposed on the riser (R) showed reductions of up to 60%.

 The use of hydrodynamic shock absorbers opens the possibility of using free catenary steel risers (R), which is still the simplest and most robust riser (R) concept without the high cost of applying vortex suppressors, and eliminating problems with the use of SCR due to extreme events.

Although the present invention has been described in its preferred embodiment, the main concept underlying the present invention, which is a hydrodynamic damper (1) which has the function of stopping the propagation of a compressive wave (O) by a riser ( R) inducing buckling in a controlled and expected manner at a certain distance from the riser touch region (P) with the submarine ground remains preserved in its innovative character, where those usually employed in the art may envision and practice appropriate variations, modifications, alterations, adaptations and equivalents to the working environment in question, without, however, departing from the scope and scope of the present invention. , which are represented by the following claims.

Claims

CATENARY UPPER HYDRODYNAMIC DAMPER, characterized in that it comprises at least one lightweight, constant diameter stretch (11) applied over at least one suspended length segment of a riser (R) to stop the spread of a compressive wave (O) by the riser (R) by inducing a calculated and controlled buckling at a portion of the suspended length of the riser (R) at a certain distance from the touch point of the riser (R) with the undersea soil.  CATENARY UPPER PIPE HYDRODYNAMIC DAMPER according to claim 1, characterized in that it optionally comprises at least one larger diameter section (12) of light coating applied over the light coating section (11).  CATENARY UPPER PIPE HYDRODYNAMIC DAMPER according to claim 1, characterized in that it optionally comprises at least one larger diameter stretch (12) of light coating applied by at least one first light coating transition element (13) installed on it. at least one end of the larger diameter stretch (12), and the latter is applied over the lightly coated stretch 11. CATENARY UPPER HYDRODYNAMIC DAMPER, characterized in that it comprises at least one lightweight, variable diameter segment (16), where this diameter continuously increases from its ends (E1, E2) in diameter close to the diameter of the riser (R) to a maximum diameter (Dm), said segment (16) being applied over at least one segment of the suspended length of the riser (R)  Upstream CATHYDRAIN CUBE HYDRODYNAMIC DAMPER according to claim 1, characterized in that the resulting stresses on the riser segment (R) and the hydrodynamic damper (1) cause said riser segments (R ) bend controllably in response to requests, and stop the propagation of the compressive wave (O) from the top of the riser (R).  6. CATENARY UPHOLDER HYDRODYNAMIC DAMPER according to claim 1, characterized in that the control of the riser segment curvature (R) due to the magnitude of the load request is a function of the segment length, specific material weight of the hydrodynamic damper coating and thickness (1). 7. Catenary ascending pipe hydrodynamic damper according to claim 1, characterized in that the riser segment (R) with hydrodynamic damper when flexing under load maintains the riser (R) in a free catenary without any movement. that cause buckling in the region (P) where this riser (R) touches the submarine ground.  A CATHENARY UPPER PIPE HYDRODYNAMIC DAMPER according to claim 1, characterized in that the section (11) can be positioned between: at one end only and at both ends with respect to the end of the section. of larger diameter (2). CATENARY UPPER HYDRODYNAMIC DAMPER, according to claim 1, characterized in that it is possible to apply more than one unit over a riser segment (R) and that the transition sections are chosen from: having the same length, having different lengths. . A CATHENARY UPPER PIPE HYDRODYNAMIC DAMPER, according to claim 1, characterized in • because the sections (11) and transition (13) in relation to the ends of the largest diameter section (12) can have their positioning chosen from: being asymmetric with different sections (11, 13), having more than one section (11) 13) at one end and at least one element at the other end; and have sections (11, 13) at one end only.