Grease injection system for riserless light well intervention

Abstract

A subsea lubricator system is disclosed which includes a lubricator tube adapted to be positioned subsea above a subsea well, a pressure control head adapted to be positioned above the lubricator tube, at least one pressure sensor adapted for sensing at least one of a pressure in the subsea well or an ambient seawater pressure proximate the pressure control head, and at least one pump that is adapted to be positioned subsea to inject a lubricant into the pressure control head at a pressure that is greater than the sensed pressure. A method of operating a subsea lubricator system positioned above a subsea well, the lubricator system including a pressure control head, is also disclosed which includes monitoring at least one of a pressure within the well and an ambient seawater pressure proximate the lubricator system, and injecting a lubricant into the pressure control head at a pressure that is greater than the monitored pressure.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a method for controlling grease injection to a subsea intervention system and an apparatus comprising a housing containing a control unit and a pump for grease.[0003]2. Description of the Related Art[0004]When performing intervention in a hydrocarbon well, it is necessary to isolate the well from the environment. Intervention is often carried out using wireline techniques (braided wire, composite cable or slickline). To contain the pressure in the well during operations and avoid hydrocarbons escaping to the environment, intervention operations involve the use of a stuffing box which is part of a pressure control head (PCH). The PCH provides a dynamic seal between the cable and the wellbore enclosures to maintain pressure control and prevent wellbore fluids from leaking into the environment. However, because of its braided (wire rope like) exterior, the cable has a bumpy, crevice-filled surface ...

AI Technical Summary

Benefits of technology

[0012]The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

[0013]The present subject matter is generally directed to a method and a device for controlling grease injection to a subsea intervention system, where there is provided an at site pressure compensated system for providing the grease at a pressure higher than the outside pre

Problems solved by technology

However, because of its braided (wire rope like) exterior, the cable has a bumpy, crevice-filled surface which is difficult for the PCH to seal around as the cable passes through the PCH as it travels into and out of the well.

This operation gets complicated when performing this practice subsea on a subsea well.

For RLWI, the PCH 113 is now remote and difficult to monitor; making it difficult to determine when and how much grease needs to be injected.

Furthermore, as the stack is run in deeper water, the length of the grease supply line feeding the PCH 113 grows longer, making it increasingly difficult to pump viscous grease down to the PCH 113 at a reasonable surface pressure or pump rate.

The long grease lines and viscous grease becomes more problematic as deeper colder environments are encountered.

In subsea situations, the pumping pressure is exacerbated by the length of the grease line going down to the subsea PCH 113 and the rate is often a pure guess, often resulting in sending too much grease down to conservatively compensate for the unknown conditions.

There is also a more subtle problem associated with grease injection to a subsea PCH 113, namely, water ingress.

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