Process for running scrapers for subsea lines

Abstract: A process for running a scraper through a line to be cleared of deposits consisting in lauching the scraper from a offshore platform through the line towards the wellhead on a step-by-step basis, this is, displacing the scraper along a given distance and returning it to the platform to bring back the deposits. The process proceeds by sending the scraper along successively longer distances, until it has swept the whole pipe section. In a second embodiment, the scraper is launched from a subsea chamber towards the platform cleaning the pipe in one pass. New scrapers are then sent through the clean pipe to the chamber an stored.

Description: This invention relates to a process for running scrapers for internal cleaning of petroleum piping or lines in petroleum extraction or exploration systems, consisting of either subsea launchers or those installed in a stationary production unit at the sea surface, for instance, in a platform. By means of launchers, the scrapers are run into the piping or lines of the petroleum extraction system and displaced by means of gas or fluid pressure. Thus the paraffin and other sediments accumulated on the lateral walls of the lines are removed. Reference made herein to scrapers is intended to relate to any device run into the lines with the purpose of removing incrustations deposited on their internal walls, particularly for paraffin removal. A particularly simple embodiment of known scrapers consists of spheres of diameter conforming to the inside diameter of the lines. In the usual terminology these scrapers are referred to as pigs. Processes of the type herein described are already known and utilized for the internal cleaning of petroleum exploration lines. One of the embodiments currently used consists of the so-called circulating pig. In this process the pig is launched from the surface through one line and returns to the surface through another, making a round trip. The pig may be launched through the production or production testing line and returned through the water or gas injection line or an auxiliary service line, or vice versa. One disadvantage of this known process is that when the launcher is located at the stationary production unit or platform, it is necessary for the launching lines and the return lines of the scrapers to the platform to have the same diameter, thus increasing the installation costs. Another known process consists of the utilization of a subsea launcher. However, this has the disadvantage of requiring the launcher to be periodically reloaded with scrapers, requiring the use of vessels for hoisting manoeuvres and re-installation of the launcher, thus increasing the installation costs and risks of accidents. The object of this invention is to provide a process which reduces the costs of installation, the costs of operation with periodical launcher reloading, and the risk of accidents. This invention is characterized by the features of claim 1. GB-A-1198461 discloses the use of a tool which passes in a first direction along a pipe string to be cleared, and is then returned to the downstream end of the pipe string by well flow pressure. The above stated object is thus met by the invention in that the scrapers are run into one line from a starting position and the return of scrapers back to said starting position is effected through the same line into which they were run, thus dispensing with the separate return lines which were required in the case of the circulating pig, and with expensive reloading operations which were required in the case of the subsea launcher. Thus the process for running a scraper includes the launching of the scraper, using a launcher installed at the stationary production unit or platform, through the line to be cleared. The scraper is displaced along a given section of the line and then returned to the platform by means of pressure applied either from the platform or from the production fluid iself; the scraper brings back the released residues. The cleaning operation proceeds by sending the scraper along successively longer sections, until the whole line has been swept. Once the cleaning of the line by the scraper has been completed, new scrapers are sent in the reverse direction along the clean line for storage in a subsea chamber installed in the subsea production system, until the next cleaning operation. One or more of these scrapers from the subsea chamber can then be released later to sweep the whole line in one pass. The pressure required for scraper displacement may originate either from the production fluid itself or from the platform, and one single subsea chamber may serve more than one line.

Claims: A process for clearing a subsea petroleum well line by running scrapers under fluid pressure propulsion from a stationary production unit at the sea surface out through the line to a subsea chamber; storing said scrapers in the subsea chamber until the cleaning operation; and clearing the line of deposits by returning a said stored scraper from the subsea chamber to the stationary production unit. A process according to claim 1, wherein the pressure required to displace the scraper originates from either the production fluid itself or the stationary production unit. A process according to any one of the preceding claims, wherein one single chamber may serve more than one line.

Inventors: CAPPLONCH RICARDO WAGNER, HERDEIRO MARCO ANTONIO NOGUEIR, MIRANDA LUIZ VICENTE AULER PAS, SILVA JOSE EDUARDO MENDONCA DA, CAPPLONCH, RICARDO WAGNER, HERDEIRO, MARCO ANTONIO NOGUEIRA, MIRANDA, LUIZ VICENTE AULER PASSOS, SILVA, JOSE EDUARDO MENDONCA DA, Silva, José Eduardo Mendonça da
Applicants: PETROLEO BRASILEIRO SA, PETROLEO BRASILEIRO S.A. - PETROBRAS
Application year: 1991
Main classification: E21B37
IPC codes: E21B37, B08B9