EP0470883B1 - Installation and method for the exploitation of small offshore reservoirs - Google Patents

Description

The present invention relates to a method and an installation suitable for the exploitation of small oil fields.

The present invention makes it possible in particular to exploit at low cost hydrocarbon fields hitherto economically inaccessible. This is possible due to the use of a flexible method which uses light and standardized materials, and which involves low investments compared to the structures usually used.

Floating platforms installed on the seabed, floating production systems consisting of a semi-submersible type platform or ships carrying the usual installations for the separation and treatment of petroleum effluents are extremely expensive to carry out. and maintain. The discovery in recent years of petroleum deposits whose recoverable reserves are limited, has led to the consideration of a production method and system which can be amortized under acceptable economic conditions over the total quantity of effluents extracted from small deposits. It is this system and this method which are the subject of the present invention.

In addition, the invention avoids costly withdrawal operations from already existing platforms when main deposits have become unusable, by reusing these platforms for the exploitation of one or more small deposits located near the latter. .

We take advantage of the facilities located on an already existing main platform located near small deposits to be exploited to increase the profitability of the production of these small deposits.

This is possible due to the overcapacity of processing the isntallations of the main platform when the production rate of the main deposit exploited begins to decrease. Using an underwater pipeline, the unused capacity of the main platform is used to process the production of neighboring secondary fields. Thus, a daily production capacity is planned for the system from 5 to 30.10³ bbl (0.78 to 4.77 10³ m3), while the main platform is equipped for production of the order of 50 to 150.10 ³ bbl per day (7.85 to 23.85 10³ m3).

All of the effluent from marginal deposits is treated at the main platform.

However, this economical method of exploiting small deposits remains of an application limited by the constraint of distance between the deposit and the main platform. The pressure losses in the pipes require the secondary deposits to be located at distances between 10 and 15 kilometers from the main platform.

Thus, the secondary well exploitation area from a main platform is relatively small. As a result, the number of exploitable secondary wells is also low and the economic profitability precarious.

In addition, most of the devices making up such systems are not standardized, which means having a larger number of devices, each one dedicated to the exploitation of one type of well and being unable to turn the devices in their use without discrimination of the type of deposit exploited.

The aim of the present invention is to propose a new method of exploiting at least one secondary submerged (or offshore) oil deposit distant from a main exploitation platform and not justifying the construction of a platform. conventional operating form, as well as an installation for its implementation.

The operating method is automatically controlled from the main platform. Thus, at least one essential function for the implementation of the proposed method is controlled by remote control means.

The aim of the present invention is also to propose an installation the structure of which allows the possible recovery of the elements used, once the operation operation has ended and, on the other hand, which allows rotation of use on all the small deposits making up the oil field or other petroleum fields due to the standardization of its equipment.

• on positionne une station flottante temporaire à une distance donnée de la plateforme principale d'exploitation et à proximité d'au moins un gisement pétrolier ayant une faible capacité individuelle de production,
• on connecte ladite station flottante à au moins une tête de puits du gisement pétrolier,
• on remonte les effluents pétroliers provenant d'au moins une tête de puits et on transfert lesdits effluents à l'aide de moyens de pompage situés sur la structure flottante et sans séparation desdits effluents jusqu'à la plateforme principale,
• lorsque la production desdits effluents provenant du gisement pétrolier est terminée, on retire ladite station flottante, et
• on repositionne ladite station flottante à proximité d'au moins un autre gisement pétrolier situé à une distance donnée de ladite plateforme principale afin d'exploiter ce nouveau gisement.

To achieve this objective of reducing the operating costs of such deposits as much as possible, the operating method allowing the exploitation of petroleum deposits located under a layer of water from a main exploitation platform to be extended includes the following steps :

• a temporary floating station is positioned at a given distance from the main operating platform and near at least one oil field having a low individual production capacity,
• said floating station is connected to at least one wellhead of the oil deposit,
• the petroleum effluents from at least one wellhead are raised and said effluents are transferred using pumping means located on the floating structure and without separation of said effluents to the main platform,
• when the production of said effluents from the oil deposit is finished, said floating station is removed, and
• said floating station is repositioned near at least one other oil deposit located at a given distance from said main platform in order to exploit this new deposit.

The floating station can be positioned near at least one wellhead using flexible anchoring means attached to the floating station and extending like a catenary to a portable anchor on the seabed .

The floating station can also be positioned near at least one wellhead when the production of wellheads from the primary deposit located near the main platform has decreased enough to allow the facilities of the main platform to treat multiphase effluents from at least one wellhead.

• 1) On ancre au moins un système composé d'une structure flottante et de ses équipements, à l'aide de moyens d'ancrage, au-dessus ou au voisinage de puits de production communiquant avec un desdits gisements situés à proximité d'une installation principale,
• 2) On remonte les effluents dudit gisement vers ladite structure flottante à travers des premiers moyens de transfert,
• 3) On transfère lesdits effluents vers la plate-forme principale à l'aide de moyens de pompage situés sur ladite structure flottante, et de seconds moyens de transfert, sans séparation de leur constituants, et
• 4) En fin d'exploitation du gisement, on retire ledit système et on le transfère sur un autre gisement pour son exploitation.

Another way for the exploitation of petroleum deposits under a layer of water located near an exploitation platform whose individual production capacities do not justify the construction for each of an operating platform comprising the following stages:

• 1) At least one system composed of a floating structure and its equipment is anchored, using anchoring means, above or in the vicinity of production wells communicating with one of said deposits located near a main installation,
• 2) the effluents from said deposit are raised to said floating structure through first transfer means,
• 3) said effluents are transferred to the main platform using pumping means located on said floating structure, and second transfer means, without separation of their constituents, and
• 4) At the end of exploitation of the deposit, the said system is removed and it is transferred to another deposit for its exploitation.

According to one embodiment of the operating method, preferably at least one essential function for the exploitation of the deposit is controlled by a submerged material transmission link connecting the main platform and the floating structure.

In this way, the minimum proper functioning of the operation is ensured reliably and in all circumstances.

The hardware link can be multifunction ensuring the supply of electrical energy and the remote control signals necessary for the operation of the various items of equipment in the floating structure, of control installations and of means necessary for operating the well.

The floating structure can be immersed between two shallow waters.

A buoy can be used as a floating structure.

The floating structure can be fitted with a porous element acting as a shock absorber, or with an anti-heaving device, as described in patent application FR 90 / 15,749.

The anchoring means are preferably of the funicular or catenary type, more suitable than the taut line anchors in the context of the operating method according to the invention.

In fact, the equipment used during the installation of systems with taut vertical lines in most cases uses rigid steel pipes that are difficult to recover once installed and more expensive. Funicular systems on the other hand use hoses such as those manufactured by the company Coflexip, for example, whose recovery is easy.

In the context of applications according to the invention, the funicular systems have qualities of reliability and sufficient flexibility. They also offer the advantage of using standard, standardized materials.

Another advantage which emerges from the use of funicular or catenary type systems is the possibility of recovering the elements which make it possible to anchor the floating structure at the bottom of the sea, which is not possible when using a platform with taut vertical lines, this operation being much heavier to perform. Indeed, the anchor points put in place with the latter are much more complex than those used in catenary type structures which mainly use anchors, and in fact, the anchor elements can be easily recovered. This structure therefore allows rotating use of the installation described in the present invention, that is to say the possibility of moving it to different deposits and sites by eliminating or minimizing as much as possible the risks of incompatibility with respect to the different deposits. to exploit.

In the context of applications according to the invention, the anchoring of the catenary or funicular type is less expensive, more mobile and much less complex than the vertical anchoring with taut lines.

Thus, the anchoring means can, for example, comprise chains, cables or any other means having the qualities required for an anchoring usually used in funicular systems or of catenary type. In all cases, these means will preferably be standardized. In this way, the system can be used "universally" for different types of deposits, at least the deposits located in the same basin.

One or more pumps can be used as pumping means, each associated with a drive device, at least one of these pumps is a multiphase pump, in particular in the case of petroleum effluents, this pump being associated with a buffer tank intended to regulate the respective flow rates of the gaseous and liquid phases of the effluent.

An electric motor or a diesel engine with its fuel tank, or a gas turbine with its ancillary equipment can be used as a driving device to use the gas produced by the wells.

The method makes it possible to transfer the effluents from the floating structure to the main platform over distances preferably between 10 and 80 km. The recovery of effluents being easier and faster, it is possible to exploit in an economically profitable way relatively close deposits, between 10 and 30 km for example.

The method according to the invention making it possible to transfer the effluents from the well to the main platform without separation of their constituents and over great distances, it is possible to inject a compound serving to reduce the formation of hydrates or to disperse them.

The transfer of all the effluents to the main platform without separation of their phases is advantageous. The gas phase can be used to generate energy on the main platform. It can be reinjected into a depleting deposit to maintain its pressure. It can also be transferred to shore and distributed if the main platform is connected to a distribution network.

It is also possible to send cleaning or measuring scraper tools into the second means for transferring the effluents from the floating structure to the main platform.

The present invention also relates to an installation or device making it possible to implement the method and to carry out the various operations that make it up.

The device or installation according to the invention comprises in combination a main operating platform equipped with production means suitable for the exploitation of underwater deposits, at least one system composed of a floating structure and its equipment, anchoring means, connecting the floating structure to the bottom of the sea so that it is in the vicinity of production wells communicating with one of said deposits, first effluent transfer means allowing the transfer of effluents from the deposit to the floating structure, pumping means installed on said floating structure, these means allowing the transfer of petroleum effluents from said deposits without separation between its various constituents or phases, from the floating structure to the main platform, and second transfer means ensuring the transfer of effluents from the floating structure to the main platform.

The installation comprises at least one submerged material transmission link between the main platform and the floating structure.

The material link can be submerged between two waters.

The material link can be placed at the bottom of the water.

The hardware link can be a multifunction link attached to the production line.

The anchoring means are preferably of the funicular or catenary type.

The anchoring means may comprise chains or cables or any other anchoring means having characteristics which allow the anchoring of funicular or catenary type systems.

The anchoring means may include anchors which have, among other things, the advantage of carrying out the setting up and removal operations with a certain ease.

The first transfer means include, for example, flexible pipes which can go directly from the floating structure to the bottom of the sea or be supported by an intermediate element, thus giving them an "S" shape which in particular enables them to avoid damage. due to the heaving coming from the swell movements.

The pumping means can consist of one or more pumps each associated with a drive device, at least one of these pumps being a multiphase pump, this pump being associated with a buffer tank intended to regulate the respective flow rates of the gas phases and liquids.

The pump drive device can be an electric motor or a diesel engine fitted with its fuel tank or a gas turbine with its ancillary equipment for using a gas phase produced by the wells.

The pumping means have sufficient power to allow the transfer of the effluents without separation of their constituents from the floating structure to the main platform over a distance preferably between 10 and 80 km.

The second transfer means may include a pipe connecting the floating structure to the main platform.

The pipeline can be a flexible or rigid, or partially rigid or flexible pipe resting on the seabed.

The floating structure may in particular include control means and means necessary for the operation of the well.

Said floating structure can be provided with equipment allowing the injection of a compound making it possible to reduce the production of hydrates or to disperse them.

Said floating structure can be equipped with a device making it possible to send scraper tools for cleaning and / or measuring in the second means for transferring the effluents to the main platform.

• la figure 1 est une vue montrant une application de l'invention pour l'équipement et l'exploitation d'un champ de production comprenant plusieurs gisements,
• la figure 2 est un mode de réalisation possible de l'invention dans le cas où l'on utilise une plate-forme principale équipée d'une source d'énergie électrique.
• les figures 3A et 3B montrent un système d'ancrage de mise en place et de retrait relativement aisé, ainsi qu'une ancre,
• la figure 4 décrit un mode de mise en oeuvre de l'installation pour l'exploitation d'un champ pétrolier comportant différents gisements secondaires, et
• la figure 5 montre une variante du mode de réalisation de l'invention dans le cas où la structure flottante est équipée de moyens de contrôle et de moyens nécessaires à l'exploitation de gisements pétroliers.

Other characteristics and advantages of the present invention will appear more clearly on reading the description below of a non-limiting example of embodiment of the invention, made with reference to the appended drawings in which:

• FIG. 1 is a view showing an application of the invention for equipping and operating a production field comprising several deposits,
• Figure 2 is a possible embodiment of the invention in the case where a main platform equipped with a source of electrical energy is used.
• FIGS. 3A and 3B show a relatively easy positioning and removal anchoring system, as well as an anchor,
• FIG. 4 describes an embodiment of the installation for the exploitation of an oil field comprising different secondary deposits, and
• FIG. 5 shows a variant of the embodiment of the invention in the case where the floating structure is equipped with control means and means necessary for the exploitation of petroleum deposits.

FIG. 1 shows one of the implementations of the invention for operating a production field comprising several production units 1.

Anchoring means 2 preferably of catenary or funicular type and comprising for example cables or flexible lines F and anchors A (Fig. 2), keep anchored each production unit 1 above or near the well or wells to bring the deposit into production. Each production unit 1 comprises a floating structure 3 such as a buoy, supporting pumping means 4, 5 which are connected to the head of each well by first transfer means 6. By second transfer means 7 comprising at at least one pipe, the pumping means 4, 5 convey the effluents from the floating structure to a main platform 8. During the exploitation of small deposits, the usual treatment and exploitation equipment equipping the main platform 8 schematically represented in FIG. 2 by the functional block 9. Usually, the production ascent pipe runs along one of the legs of the platform, FIG. 2 representing it in the center, for reasons of clarity. the figure.

The distance between the production units and the main platform is arbitrary, but preferably located in the interval 10.80 km.

• 1) A l'aide de moyens d'ancrage 2, par exemple un câble ou ligne flexible F et une ancre A, on ancre la structure flottante 3, au-dessus ou à proximité du ou des puits de production du gisement. Cette structure flottante étant considérée comme un satellite vis à vis de la plate-forme principale, pourra être désignée dans le texte en tant que satellite de traitement.
• 2) on remonte les effluents pétroliers jusqu'à la bouée à travers des premiers moyens de transfert 6, par exemple des risers flexibles,
• 3) on transfère lesdits effluents, sans séparation de leurs constituants en utilisant les moyens de pompage 4, 5 situés sur la bouée, vers la plate-forme principale 8 à travers des seconds moyens de transfert 7, par exemple une canalisation, et
• 4) on déplace la bouée en exerçant simplement une traction verticale sur le flexible F, vers un autre gisement à exploiter si on considère que l'exploitation du gisement cesse d'être rentable ou si, par exemple, on a besoin ponctuellement du système d'exploitation sur un autre gisement.

One of the possibilities for putting a multiple deposit into operation according to the invention comprises, for example (FIG. 2), the following steps:

• 1) Using anchoring means 2, for example a flexible cable or line F and an anchor A, the floating structure 3 is anchored, above or near the well or wells producing the deposit. This floating structure being considered as a satellite with respect to the main platform, could be designated in the text as a processing satellite.
• 2) the petroleum effluents are brought up to the buoy through the first transfer means 6, for example flexible risers,
• 3) said effluents are transferred, without separation of their constituents using the pumping means 4, 5 located on the buoy, to the main platform 8 through second transfer means 7, for example a pipe, and
• 4) the buoy is moved by simply exerting vertical traction on the flexible F, towards another deposit to be exploited if it is considered that the exploitation of the deposit ceases to be profitable or if, for example, the system d is needed from time to time on another deposit.

During the exploitation of the deposit, various checks are made on the operation of the pump and the production wells.

Thus the operations control and measurement operations are carried out automatically and provide the platform with an indication allowing the latter to react using remote control means on the equipment located on the floating structure.

The remote control signals are sent, for example, from the main platform 8 to the floating structure 3 by a hardware link 10.

The hardware link 10 can be multifunctional and ensure the transfer of the remote control signals as well as the energy necessary for the operation of the various satellite structures.

A buoy is used whose flotation characteristics are such that a part of its body is immersed, the other emerging sufficiently above the surface of the sea 11, so as to install the operating equipment there. The buoy can be equipped with a porous element acting as a shock absorber such as that described in application FR 90/15749, this in order to minimize all the heaving movements due in part to the swell.

The technical data necessary for determining the buoyancy characteristics of the buoy and of the pump suitable for the described application can be calculated by known methods.

One can use as buoy, a big buoy of the type of those used to moor at sea oil tankers. The typical dimensions of the latter in diameter can be between 20 and 30 meters, in height between 5 and 15 meters. We can also consider the use of a pencil type buoy.

The anchoring means may advantageously comprise at least one flexible cable or line F and one anchor A or any other available means which make it possible to anchor the production unit 1 securely, such as systems of the catenary or funicular type.

Line 6 being flexible, it can follow the local drift of the buoy. The position of the anchor points 12 and the length of the anchor chains or flexible lines F are determined so that the pipe 6 is always under tension.

The flexible pipe can optionally be supported by an intermediate element SI (FIG. 1), the latter then taking the form of an S. This arrangement makes it possible, for example, to reduce the repercussions of pounding movements on the flexible.

The pumping means 4, 5 located on the floating structure 3 can comprise at least one multiphase pump 4 and its drive device 5 comprising, for example, an electric motor.

Thus, for example, a multiphase pump of the type described in patents FR-2,333,139 and FR2,471,501 is used, equipped with its buffer tank intended to regulate the respective flow rates of the gaseous and liquid phases.

The position of the buoy at a distance of, for example, between 15 and 80 km from an already existing platform, allows the buoy to be equipped with an electric motor if the main platform has electrical energy, l energy then being supplied by the cable 10. In the case where the platform has no electrical energy, a diesel engine is used, the buoy then comprising a fuel storage means.

A chemical additive can be injected into line 7 so as to avoid the formation of hydrates or to disperse them. This pipe 7 is connected to one end of the production unit 1, the other being attached to the main platform 8. The pipe 7 is partially rigid and flexible. It includes, for example, a downward pipe extended by a horizontal section resting on the seabed and ending with a vertical upward pipe, the latter being attached to the main platform 8. The friction of the pipe with the seabed limits its possible drift. The pipes can have a J shape.

The pipe 7 and the cable 10 can be included in the same sheath.

FIGS. 3A and 3B describe more precisely an anchoring method using anchoring lines used in funicular or catenary type systems and an anchor capable of being used. The present method offers the advantage of easy installation and lifting and therefore of making the system more mobile than those comprising platforms with taut lines.

FIG. 3A shows a way of positioning such a type of anchor line F. The tension in the line F is chosen to be sufficiently low so that the line rests on the seabed over a length L necessary for the anchoring of the anchor in the seabed 13 in the vicinity of the anchor point 12 and so that it thus presents a chain configuration.

An anchor such as that described in patent FR-2,519,310 can be used.

FIG. 3B describes a possibility for installing an anchor A which comprises at least one plate 21 to which is attached at least one anchoring line F at at least one point by a flexible connection not introducing substantially any moment of rotation at attachment point P. The point of application of the tensile force on the plate is fixed and located in front of the barycenter G of the bearing surface of this plate, if we consider the direction of movement of the latter in the seabed during its establishment. The process of penetration of the plate into the ground is made easier by combining a sufficient weight for the anchor with members arranged so as to keep the end of the anchor inclined towards the seabed relative to the seabed, or angle i not exceeding 30 °. A simple pull on the line is enough for the plate to penetrate the seabed.

The anchoring is obtained by the progressive insertion of the anchor A which slides in the ground under the effect of the force applied by the chain or taut line F.

To remove the anchor, simply pull the anchor line F vertically or backwards, possibly with another cable attached to the back of the anchor so that it slides in the opposite direction .

This example is by no means limiting. Any other anchoring means or method having similar characteristics of ease of anchoring or removal can be used, in particular the anchoring device described in patent FR-2,519,310.

FIG. 4 represents one of the possible modes of implementation of the method previously described for the exploitation of marginal deposits.

• P est le gisement principal,
• P1, P3 sont des gisements anciennement exploités,
• P2 est un gisement qui se situe à une distance de 10 km de la plate-forme principale et donc suffisamment proche pour être exploité sans avoir recours à une bouée satellite,
• P4, P5, P6 sont des gisements secondaires situés respectivement à des distances de 50 km, 30 km, 70 km de la plate-forme principale. Dans ce type de configuration, ils sont équipés de bouées satellites de traitement. Les distances citées sont données à titre indicatif pour montrer une des possibilités de positionnement des gisements par rapport à la plate-forme principale, et
• P7 est un puits découvert et non encore exploité.

In the configuration shown, the oil field to be exploited comprises several deposits P1 to P7 distributed in the vicinity, for example within 100 km of a platform 8. In FIG. 4 for example:

• P is the main deposit,
• P1, P3 are formerly exploited deposits,
• P2 is a deposit located at a distance of 10 km from the main platform and therefore close enough to be exploited without using a satellite buoy,
• P4, P5, P6 are secondary deposits located respectively at distances of 50 km, 30 km, 70 km from the main platform. In this type of configuration, they are equipped with satellite processing buoys. The quoted distances are given as an indication to show one of the possibilities of positioning the deposits relative to the main platform, and
• P7 is an discovered well that has not yet been exploited.

The operating scheme can be as follows.

At time T0, only the main deposit is exploited, the processing capacities C of the main platform are fully used.

When the production of the main well begins to decrease, part d of the processing capacity C of the platform becomes unused. The processing capacity used on the platform is therefore: C - d.

où les CPi (i = 1 à 4) correspondent aux capacités de production de la plate-forme nécessaires pour l'exploitation des puits Pi (i = 1 à 4).The wells P1 to P4 are then put into operation. The processing capacity of the platform used is then equal to: $$\text{Ct = C - d + CP1 + CP2 + CP3 + CP4}$$

where the CPi (i = 1 to 4) correspond to the production capacities of the platform necessary for the exploitation of the Pi wells (i = 1 to 4).

At T0 + t2, the production of well P3 is close to zero. We then disconnect the satellite buoy equipping this deposit and move it to well P5.

At T0 + t3, the production of well P1 drops to zero and in the same way, the satellite buoy equipping this well is moved towards P6, thus allowing the well to be put into operation.

This mode of implementation of the device is only a particular example of the possibilities offered by the device according to the invention for the exploitation of at least one deposit located near a main equipped platform. It is understood that the movements of the satellite buoys from one well to another are made taking into account the length of the pipes and so as to move the pipes already in place as little as possible.

The use of hoses such as those manufactured by the Coflexip firm makes it easy to adapt the length of the pipe either by cutting or abutting different sections to obtain the necessary length.

FIG. 5 schematically illustrates a routing and production control system which implements the use of several multiphase pumps. With reference to FIG. 5, four wells are used, the multiphase or effluent fluid to be transferred arriving from the different wellheads, via lines 61, 62, 63, 64.

The effluent arrival systems from the well to the floating structure are identical for all the wells. Line 61, for example, is connected by a safety valve V11 controlled automatically or manually. Two remotely controlled valves V21 and V21 ′ allow the effluent to be conveyed either to a COP production collector or to a TOC test collector.

The safety valves associated with lines 62 to 64 are designated by V12, V13 and V14 respectively. Likewise, V22, V22 ′ are designated; V23, V23 ′; V24, V24 ′ the valve couples for lines 62 to 64, analogs to the previous V21, V21 ′ couple.

All of the effluents are collected, coming from the various wells in the COP production collector, the valves V21, V22, V23, V24 being open, the valves V21 ′, V22 ′, V23 ′, V24 ′ being closed.

All of the effluents are then sent to a buffer tank T via a line L1. The multiphase fluid regulated by its passage in the buffer tank T, is transmitted by a line L2 to a first pumping stage. In our example, this first pumping stage includes two pumps MP1 and MP1 ′ and the fluid reaches them through pipes L3 and L4. The first pumping stage can consist of several pumps placed in parallel. Parallel mounting is a special case suitable when the flow of the entire production is too high to arrive on a single pump.

The number of pumping stages and the number of pumps per stage depend on each particular application case, and more precisely on the pressure increase to be carried out, on the mass and volume flow rates of the different phases to be pumped.

By passing through this first stage, the pressure of each of the parts of the multiphase fluid is increased.

The outputs of the pumps MP1, MP1 ′ of the first stage communicate by valves V31, V31 ′ with a pipe L5, which is connected via a valve V32 with the inlet of a second compression stage constituted, by example, of an MP2 pump. The output of this communicates by a valve V33 with a pipe L6. A D1 bypass comprising a VD1 valve, allows the L5 and L6 lines to communicate directly. Valves V31 and V31 ′ are fitted with a non-return valve to prevent possible passage of the multiphase fluid from pump MP1 to pump MP1 ′, and from pump MP1 ′, to pump MP1.

Line L6 communicates via two valves V4 and V5 with line 7 connecting the floating structure to the main platform.

During the operation illustrated in FIG. 5, it is necessary to have suitable control and security functions. In the present case, each line 61, 62, 63, 64 coming from the wells, is equipped with a safety valve V11, V12, V13, V14 for example an electro-pneumatic valve, which allows their closing in the event of problems. .

The buffer tank T is equipped with a pressure sensor CP1 and a means for detecting the level of liquid NL1. Depending on the pressure and liquid level values, action is taken by remote control means T1 on the flow rate of the wells, this by a line TP1, which can be an electric or electro-pneumatic line or any other line allowing to transmit the information to the wellhead.

The T1 remote control means also allow lines CM1, CM1 ′ and CM2 to act on the control of the motors M1, M1 ′ and M2, respectively actuating the pumps MP1, MP1 ′ and MP2 for example to control their starting or their stop.

In the event of a deterioration in the operation of one of the pumps, for example the pump MP1, the valve V3 is closed so as to continue to operate the wells in degraded mode with only the pump MP1 ′.

If the problem is at the second stage, in our example on the MP2 pump, we close the valve V32, we open the valve VD1 of bypass line D1. In this way, the fluid is diverted, having undergone the pressure increase in the first stage, in the line L6.

The CP sensors located after the pumps allow control of the fluid pressure after passage through the pump and therefore give information on the operation of each of the pumps.

The method described above also makes it possible to carry out an occasional control of the different characteristics of the fluids coming from the wells, for example, the measurement of the total flow rate of the effluent produced by the well, and of the different phases constituting the effluent. It is possible, for example, to carry out a count for each flow well of the gas, water and oil constituting the effluent, plot the pressure curve as a function of the flow and with this indication, regulate the production by through the tubes fitted to the well heads.

To carry out these checks, we use, for example, a boat equipped with a test separator of the type used on drilling systems and a hose through which we connect to the TOC test collector. During this operation, the valves V21, V22, V23 and V24 are closed, the valves V21 ′, V22 ′, V23 ′ and V24 ′ are opened on the operator's order via lines TV1 and T01.

The method also makes it possible to inject a compound, such as a chemical additive to avoid the formation of hydrates during a transfer of the effluents or reduce them in their dispersed form in order to facilitate the transfer of the effluent from the satellite to the platform. - main form.

Another possibility offered by the method is to allow the cleaning of the pipe 7 by which the fluid is conveyed from the floating structure to the main platform 8, which makes it possible to eliminate any deposit hindering the circulation of the fluid in the pipe. such as paraffins etc.

During this operation, a means is used to scrape the pipe via the input E1 of an airlock S, for example, a scraper usually used on production fields, the valve V4 is closed, and the valve is opened. valves V6 and V7. The fluid then pushes the scraper in the pipe 7.

It is understood that it would not depart from the scope of the invention if certain modifications were made in the equipment of the system, for example in a non-exhaustive manner, if the buoy was replaced by a large equipped barge.

At least one of the multiphase pumps previously described can be of the helical type. This type of pump is particularly well suited for this kind of application. Indeed, the pump can be used over a fairly wide range of variation in the ratio of the quantity of GLR liquid (in English Gas Liquid Ratio), which leads to a reduction in the installations to be placed on the buoy. In particular, such a pump makes it possible to avoid the separation of the effluent in several phases and therefore a single pipe is used for the transfer of the constituents between the buoy and the platform.

In the case of exploitation of gas fields, the pumping system can use a simple pump or compressor, and its drive device.

The drive device can be a diesel engine with its fuel tank, a gas turbine with its ancillary or other equipment.

the petroleum effluent can be sent directly to the platform in the case where the deposit has sufficient natural pressure.

It would also not depart from the scope of the invention if the floating structure and its pumping equipment were connected to wells located at a relatively short distance from a main installation when the natural pressure of this well becomes insufficient. In this way, the operating life of an oil field is extended. We accelerate and we also increase the recovery of crude.

The method can also be used temporarily to test the production capacities of a still poorly understood deposit. In this case, a test is carried out using the method described above and the floating structure is replaced, if the test is positive, by an operating device better suited to the capacity of the deposit. It thus avoids investing in a fixed platform and expensive while the production capacities of this deposit are uncertain.

The floating structure may include a means of injecting chemical additives, serving to protect the pipes from corrosion.

The floating structure used for the exploitation of the deposit can be equipped with all the means necessary for the exploitation or the well test without modification on the bottom of the proposed system. In addition, the usual equipment for floating units can be placed there, namely a manifold allowing the production of products from different wells to be grouped together.

The floating structure may include a basic emergency accommodation and possibly a light bridge for helicopters.

Thus, it appears that the present invention avoids the use of amphibious ("submarine" or submerged) pumping means and therefore expensive.

We will not go beyond the scope of the present invention if instead of considering using a main submarine platform, we directly send the production of deposits to a coastal installation.

It is preferable to stabilize each floating structure by anchoring means of the funicular type for their ease of use. In some cases, however, stretch lines may be used if the circumstances allow.

It is also preferred for safety reasons, to use a physical link between the main platform and each floating structure. However, this cannot exclude the use of any other sufficiently secure means of connection in the context of the proposed operation.

Claims (32)

1. A method allowing exploitation from a central platform to be extended to oil deposits located under a layer of water comprising the following steps:

   - a temporary floating station (3) is positioned at a given distance from the main exploitation platform (8) and close to at least one oil deposit having a low individual production capacity,

   - the floating station (3) has at least one well head at this oil deposit,

   - the petroleum effluent is brought up to at least one of the well heads and the effluent is transferred by pumping means (4, 5) located on this floating structure (3) to the central platform (8) without separation of the effluent,

   - when effluent production from the oil deposit has been completed, the floating station (3) is withdrawn, and

   - the floating station is repositioned close to at least one other oil deposit located at a given distance from the central platform (8) in order to exploit at least this new deposit.
2. A method as claimed in claim 1, characterised in that the floating station (3) is positioned close to at least one well head using flexible anchoring means (F) which are attached to the floating station (3) and which extend as a chain to a portable anchor (A).
3. A method as claimed in claim 1, characterised in that the floating station (3) is positioned close to at least one well head when production at the well heads of the primary deposit located close to the central operating platform (8) has decreased sufficiently to allow the installations on the central platform to process additional multi-phase effluent from at least one well head.
4. A method for exploiting oil deposits under a layer of water located close to an operating platform whose individual production capacities do not justify the construction of an operating platform for each of them, characterised in that it comprises the following steps:

   - at least one structure comprising a floating structure (3) and its equipment is anchored by anchoring means (2) above small deposits or in the vicinity of a production well communicating with one of the deposits located close to a main installation (8),

   - the effluent is brought up from the deposit to the floating structure (3) though first transfer means (6),

   - this effluent is transferred to the central platform (8) using pumping means (4, 5) located on the floating structure (3) and by second transfer means (7) without separating the constituents,

   - when exploitation of the deposit has been completed, the system is withdrawn and transferred to another deposit in readiness for exploitation.
5. A method as claimed in claim 4, characterised in that at least one function essential to controlling exploitation of the deposit is controlled by a submersed, physical transmission link running between the main platform and the floating structure.
6. A method as claimed in claim 5, characterised in that the physical link is a multi-purpose link capable of handling the transfer of electrical power and remotely controlled signals.
7. A method as claimed in claim 4, characterised in that the floating structure is submersed between two stretches of water.
8. A method as claimed in claim 4, characterised in that a buoy is used as the floating structure.
9. A method as claimed in claim 4, characterised in that the floating structure is fitted with a porous element serving as an absorber.
10. A method as claimed in claim 4, characterised in that anchoring means of the cable or chain type are used, comprising chains or cables and appropriate anchors.
11. A method as claimed in claim 4, characterised in that one or several pumps and their respective drive devices are used as pumping means.
12. A method as claimed in claim 11, characterised in that the pumping means comprise at least one multi-phase pump (MP) connected to a buffer tank (T) designed to control the respective flows of the gaseous and liquid phases.
13. A method as claimed in claim 11, characterised in that production from the floating structure is transferred to the central platform over distances preferably ranging between 35 and 80 km.
14. A method as claimed in claim 4, characterised in that a compound is injected to prevent the formation of hydrates or disperse them.
15. A method as claimed in claim 4, characterised in that means are used which enable cleaning scraper tools and/or measuring instruments to be conveyed in the second transfer means.
16. An installation designed for the exploitation of oil deposits under a layer of water (or offshore) and communicating with the bed of the layer of water by means of production wells, characterised in that it comprises in combination: a main operating platform (8) equipped with production means (9) designed for the exploitation of sub-sea deposits, at least one floating structure (3), anchoring means (2) to connect the floating structure to the sea bed so that it is in the vicinity of production wells communicating with one of these deposits, first transfer means (6) for the effluent, these first means enabling production from at least one production well to be transferred to the floating structure, pumping means (4, 5) installed on this floating structure, these pumping means enabling the transfer of petroleum effluent from these deposits without separating its different constituents or phases, and second transfer means (7) for the transfer of the effluent from the floating structure (3) to the central platform (8).
17. An installation as claimed in claim 16, characterised in that it comprises at least one physical transmission link submersed between the main platform and the floating structure.
18. An installation as claimed in claim 17, characterised in that the physical link is submersed between two stretches of water.
19. An installation as claimed in claim 17, characterised in that the physical link is positioned on the sea bed.
20. An installation as claimed in claim 17, characterised in that the physical link is a multi-purpose link connected to the production line.
21. An installation as claimed in claim 16, characterised in that the anchoring means are of the cable or chain type.
22. An installation as claimed in claim 16, characterised in that the first transfer means are flexible pipes.
23. An installation as claimed in claim 22, characterised in that the flexible pipes link the floating structure directly to the sea bed.
24. An installation as claimed in claim 22, characterised in that the flexible pipes are supported by an intermediate support element (SI) between the production wells and the floating structure.
25. An installation as claimed in claim 16, characterised in that the pumping means comprise one or several pumps and their respective drive devices, at least one being a multi-phase pump connected to a buffer tank designed to regulate the respective flows of the gaseous and liquid phases.
26. An installation as claimed in claim 25, characterised in that the drive device is an electric motor or a diesel engine equipped with its fuel tank or a gas turbine with its respective equipment to use a gaseous phase produced by the wells.
27. An installation as claimed in claim 25, characterised in that the pumping means have sufficient power to transfer the production from the floating structure to the main platform without separating its constituents preferably over a distance ranging by preference between 35 and 80 km.
28. An installation as claimed in claim 16, characterised in that the second transfer means (7) comprise a pipeline linking the floating structure to the main platform (8).
29. An installation as claimed in claim 28, characterised in that the pipeline is a flexible or rigid pipe or is partially rigid or flexible.
30. An installation as claimed in claim 16, characterised in that the floating structure has control means and means necessary to exploit the well.
31. An installation as claimed in claim 16, characterised in that the floating structure (3) is equipped with means for injecting a compound intended to prevent the formation of hydrates or to disperse them.
32. An installation as claimed in claim 16, characterised in that the floating structure is equipped with a device enabling scraping tools to be carried in order to clean the second transfer means.

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