Wells – Submerged well – Testing
Reexamination Certificate
2001-02-02
2003-02-04
Dang, Hoang (Department: 3672)
Wells
Submerged well
Testing
C166S250070, C166S337000, C166S066000
Reexamination Certificate
active
06513596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains generally to wells for production of petroleum products and more specifically concerns wells located in a subsea environment where the pressure containing integrity of wells is of particular concern from the standpoint of environmental protection and for protection of workers and equipment from the hazards of pressure leakage from wells. More particularly, the present invention provides a non-intrusive method for monitoring pressure in well casing annuli without compromising the pressure containing integrity of the well system in any way, and thus permitting excessive pressure in typically inaccessible annuli to be detected, and corrective actions taken before a hazardous event can occur that might impact human life, the environment or property.
2. Description of the Prior Art
While the present invention has application to petroleum producing wells other than subsea well systems, for purposes of simplicity and to facilitate ready understanding of the invention by others, the present invention is described herein particularly as it relates to subsea wells.
The Minerals Management Service (MMS) recently revised its policy on Sustained Casinghead Pressure (SCP) for the Gulf of Mexico Outer Continental Shelf Region (GOMR). The MMS issued a proposed Notice to Lessees and Operators (NTL) to define changes that are forthcoming to its current policy. Current (previous) policy is defined in a Jan. 13, 1994 Letter to Lessees (LTL).
SCP occurs when one or more leaks develop in the barriers designed to achieve and maintain pressure control of wells. SCP is defined as:
1. A pressure measurable at the casinghead of a casing annulus that rebuilds when bled down;
2. A pressure that is not due solely to temperature fluctuations; and
3. A pressure that has not been deliberately applied.
It is thus considered desirable to monitor all casing annuli for SCP on all subsea trees to ensure early detection of pressure buildup in any of the various annuli thereof.
The Jan. 13, 1994 LTL required all annuli on offshore producing wells to be monitored for SCP. However, this regulation is written primarily for wells on conventional, fixed platforms and departures have been granted for subsea wells. The accepted requirement for subsea wells is to monitor only the annulus between the production tubing and production casing strings (the “A” annulus) since it can be monitored by pressure sensing lines passing through the wellhead, without any need for penetrating the outer pressure containing housing or wall which isolates annulus pressure from the seawater or other environment. The conventional method for monitoring the “A” annulus is to provide an annulus monitor line in the tree's production control umbilical and/or to provide an electronic pressure sensor in the tree's annulus flowpath. The control line and/or pressure sensor can be isolated from the production annulus of the well by one or more valve closures on the subsea tree. Wells with SCP in the “A” annulus that is less than 20% of the minimum internal yield pressure (MIYP) of the affected casing can be produced on a “self approved” basis, provided the annulus pressure can be bled to zero through a ½″ needle valve in 24 hours or less. Criteria is also established to determine unsustained casing pressure that is typically caused by thermal Ad effects during well start up.
Surface wellhead systems, used on land and on offshore platforms, provide pressure containing side outlets in the casing and tubing heads, from which annulus pressure can be monitored. API Specification 17D does not permit body penetrations in high pressure subsea wellhead housings. Even if penetrations were allowed in subsea wellhead, housings, the overall safety of the well would be at higher-risk because each wellhead penetration creates a potential leak point. Obviously when a wellhead is located at or near the seabed leakage or a body penetration connection would be difficult to detect until a major problem has occurred.
In 1995, a laboratory demonstration was provided for a non-intrusive wellhead casing monitoring system to the Deepstar Joint Industry Project. This non-intrusive annulus pressure monitoring system uses strain gauges on the outside of the wellhead housing. The elevation of the strain gauges on the wellhead corresponds to the annular areas between the casing hanger packoffs inside the wellhead housing. Pressure is monitored by correlating the strain measured on the outside of the wellhead housing to the pressure applied between the packoffs inside the wellhead housing. The strain gauge method has not progressed beyond the laboratory stage due to technical concerns about implementing the method for the subsea environment.
U.S. Pat. No. 5,544,707, dated Aug. 13, 1996, covers an adjustable seal sleeve mechanism that can be installed in the place of a normal packoff assembly on the production casing hanger to provide access to the annulus around the outside of the production casing (the “B” annulus). The position of the sleeve is adjusted mechanically by a running tool prior to installing the tree. When the tree is installed, pressure in the “B” annulus can be monitored separately from pressure in the production tubing annulus (the “A” annulus) through a side outlet in the tree body. Monitoring of the “B” annulus is achieved by conventional means, in the same manner as described above under current practice for the “A” annulus. The adjustable-sleeve approach only enables pressure to be monitored in the innermost two annuli of a well. Some subsea wells with extensive casing programs may have up to six annuli. The seals and ports on the adjustable sleeve are potential leak points that increase the overall safety risk for the well.
U.S. Pat. No. 4,887,672 covers a method that uses hydraulic couplers between the top of wellhead housing and the tree connector. The couplers enable ports in the wellhead and tree to communicate with each other when the tree is locked to the wellhead. A long vertical hole drilled from the coupler location in the top of the wellhead communicates with a short, internal, horizontal hole in the wellhead housing. The elevation of the internal hole exposes the annular area between casing hanger packoffs to the monitoring port. One coupler/port combination is used for each annulus to be monitored. The ports can be monitored through a line in the production umbilical and/or by an electronic pressure sensor, per current practice. The hydraulic coupler method is not believed to have been installed in the field. Orientation of the couplers prior to tree/wellhead makeup is critical and the couplers are subject to damage. Each port is a potential leak point that increases the overall safety risk for the well.
The Minerals and Management Service (MMS) of the U.S. Department of the Interior has proposed that wells with subsea trees will need to have all casing annuli monitored for sustained casing pressure, beginning with trees installed after Jan. 1, 2005. This requirement may present a safety risk to subsea wells, because the most straightforward method of accessing an annulus for pressure monitoring is to make a pressure containing penetration through the body of the pressure vessel. Since it is well known that all penetrations through the outer pressure containing housing of wellheads are potential leak points which add sealing risk, and thus safety risk, to the well system pressure monitoring in all well annuli will not be practical unless a safe system for doing so becomes commercially available. A further complication is that API Specification 17D for Subsea Wellhead and Christmas Tree Equipment explicitly prohibits body penetrations in high pressure subsea wellhead housings. Therefore, the recommended method for monitoring pressure in multiple annuli is by non-intrusive means, which does not exist according to current practice. It is to this need that the present invention is addressed.
The GOMR will not grant departures to allow pressure on t
Andrews & Kurth LLP
Dang Hoang
FMC Technologies Inc.
Jackson James L.
LandOfFree
Non-intrusive pressure measurement device for subsea well... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-intrusive pressure measurement device for subsea well..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-intrusive pressure measurement device for subsea well... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3127491