CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase filing under 35 U.S.C. § 371 of International Application No. PCT/BR2019/050383, filed Sep. 10, 2019 and claims priority to Brazilian Application No. BR 10 2018 068428 0, filed Sep. 12, 2018. The entire contents of the prior applications are incorporated herein by reference in their entity.

FIELD OF THE INVENTION

The present invention relates to technologies for pumping and discharge of oil from subsea wells. More particularly, the present invention relates to systems for depressurizing subsea apparatus and lines.

BACKGROUND OF THE INVENTION

The present invention relates to the field of systems for production of oil and hydrocarbons in general, in deep water, which use methods to guarantee flow to prevent or remove blockage by hydrates.

In this connection, to increase offshore oil production or make it viable, mainly in deep water, various systems and apparatus have been developed in the prior art. Said apparatus is generally installed on the sea bed in various positions, between the wellhead up to the foot of the riser, such as, for example, on a wet Christmas tree, pumping units, manifolds, subsea lines, among others.

In general, the oil production obtained from each subsea well is discharged, individually or combined with the production from other wells, through subsea lines and risers to a production unit, such as an FPSO (Floating Production Storage Offloading).

However, in the case of deepwater oil production there is a risk of hydrate formation, the result of direct contact of gas and water, in certain conditions of high pressure and low temperature, for example: 20 kg/cm2and 4° C.

Despite the advent of various techniques for oil production and prevention of hydrate, at times it is still necessary to use naval resources, such as sophisticated vessels or rigs, classified and approved for receiving hydrocarbons on board, for carrying out operations for remedying blocking with hydrates.

Besides the high cost involved in the use of these naval resources, it is necessary to wait for them to become available and to be moved, and tens of days may pass until it becomes possible to carry out these operations. Thus, interruption of production may be very damaging for the industry.

Some documents of the prior art already deal with various ways of combating hydrate formation in subsea apparatus, as will be presented hereunder.

Document US20100051279A1 discloses a method for preventing hydrate formation in a subsea pipeline, which involves heating a volume of water to a high temperature and increasing the flow of water in the line. It is also described that an ROV is used for heating a volume of seawater and pumping this heated water into a subsea line at the point where hydrate formation is identified.

Document WO2012149620A1 discloses a system for depressurizing fluid and subsea apparatus that comprises a pump outlet or a hydraulic pump, which is operated remotely in the ascending direction by a remotely operated vehicle (ROV). This document further envisages that the system comprises a WCT cap with a depressurizing system, implemented by an electric pump supplied electrically by a power cable from the PU. It is also described that the valves allow a suction point to be selected, which may be on the: production line, annulus line or production string. The valves also allow a discharge point to be selected, which may be in the: production line, annulus line or production string.

Thus, document WO2012149620A1 basically describes a depressurizing system resident on the subsea apparatus, which has the advantage that it can be operated quickly and remotely from the production unit, without being dependent on a vessel and ROV.

However, the fact that the system is resident presents the disadvantage of adding a number of new elements to the subsea apparatus where hydrate formation is to be combated, which increases the complexity of the operation, besides significantly increasing the costs of the system. In addition, the system disclosed in WO2012149620A1 requires mobilization of an offshore rig for installing and dismantling the subsea apparatus, which also increases the final cost of the operation.

Thus, the present invention aims to solve the problems of the prior art by providing a system for combating hydrate formation in subsea apparatus for exploration for petroleum and hydrocarbons, which is nonresident, and depends exclusively on the mobilization of a vessel with ROV for operation thereof.

Accordingly, it is clear that in the state of the art there is still space for the development and use of systems and tools operated by subsea robots of the ROV (Remotely Operated Vehicle) or AUV (Autonomous Underwater Vehicle) type, which perform operations of depressurization of lines and apparatus without the need to return hydrocarbons to support vessels.

As will be presented in greater detail hereunder, the present invention aims to solve the problems of the prior art described above in a practical and efficient manner.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a system that performs operations of depressurization of lines and apparatus without the need to return hydrocarbons to support vessels, in which the system is nonresident (with respect to the subsea apparatus), and depends exclusively on the mobilization of a vessel with ROV for its operation.

In order to achieve the aims described above, the present invention provides a nonresident system for depressurizing subsea apparatus and lines comprising a depressurizing tool adapted for being coupled to an ROV interface of a subsea apparatus, in which the depressurizing tool is coupled to an ROV, wherein: the one ROV interface comprises a first connecting pipeline to a first hydrocarbon transport line, a second connecting pipeline to a second hydrocarbon transport line, and a connection mandrel; and the depressurizing tool comprises a suction line adapted for being connected to the first connecting pipeline to the first hydrocarbon transport line; a discharge line adapted for being connected to the second connecting pipeline to the second hydrocarbon transport line; a pump; and a connector adapted for connecting the connection mandrel of the ROV interface.

The present invention further provides a method for depressurizing subsea apparatus and lines, comprising the steps of: removing a blind cap from an ROV interface with the aid of an ROV; coupling a depressurizing tool to the ROV interface of a subsea apparatus; suction and removal of fluid from a first hydrocarbon transport line, wherein the first hydrocarbon transport line comprises hydrate formation; and pressurizing and reinjecting the fluid into a second hydrocarbon transport line.

