Introduction

Several deepwater drilling-related and environmental issues have dictated a need for the development of a Subsea Rotating Control Head (RCH). Such a tool may also be referred to as a Subsea Rotating Control Diverter. It's purpose is to effect more precise pressure management by enabling annulus returns containment, diversion, and/or backpressure to be applied on the wellbore in a subsea environment.

Practical applications of such a tool generally fit within the IADC definition of Managed Pressure Drilling (MPD) and include:

  1. Alternatative technology to current industry practice of Pumping and Dumping sometimes huge quantities of a heavy viscous mud to the seafloor as a means of overbalancing relatively shallow-to-the-mudline geohazards (abnormally pressured aquifers, gas) when establishing subsea top holes, drilling without a marine riser.

  2. For the practice of dual gradient riserless drilling where mud and cuttings may be returned to the rig, this were a subsea RCH diverts returns to a subsea pump.

  3. For cost effective riserless drilled exploratory "throw-a-way" or "punch & go"" wellbores. Here a subsea RCH with ROV operated choke enables greater wellbore pressure than the mud gradient itself would impart. More precise pressure management is achieved with the pre-selected drilling fluid, resulting in a simplified casing program and deeper open hole.

  4. As a component required in a proposed Rierless Top Hole Drilling Package for casing less wellbores when collecting scientific cores in deep water.

  5. And, when deployed within a subsea BOP, marine riser, or riser gas handler, function as a subsea annulus barrier, enabling the practice of several variations of dual gradient deepwater drilling.

Given the importance of reliability of subsea equipment in general, shop tests that mimic subsea conditions are warranted. Such test results confirm or otherwise quantify a design's fitness-for-purpose.

This paper speaks to shop test criteria and results of a Subsea Rotating Control Head prototype design.

Subsea RCH Test Parameters

Intended applications as described in the Introduction indicate a subsea RCH Bearing and Annular Seal design would require the following subsea "fit-for-purpose" capabilities:

  1. Function without maintenance for one week at a depth of 7500' seawater.

  2. Easily deployed and retrieved.

  3. 2,000 psi dynamic, 4000 psi static, wellbore annulus to subsea gradient differential pressure capability.

  4. Drill string rotation of 150 RPM nominal, 195 RPM intermittent.

  5. Annular seals (stripper rubbers) capable of stripping 28,000' of 6 5/8" drill pipe with Tool Joints.

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