afety Performance
Review - Shallow Waterflows Can Pose Significant Hazards to Deepwater Drilling
This technical discussion is intended to
share information on an important safety issue.
Since 1987, operators have reported shallow waterflow (SWF)
events to the MMS, a phenomenon encountered in water depths
exceeding 600 feet. Reported waterflows are
between a few hundred feet to more than 4,000 feet below the seafloor.
Water flowing around the annulus will deposit
sand or silt on the seafloor within a few hundred feet of the wellhead.
Although in most cases there is no gas content
in the waterflow, in these water depths a stream of gas bubbles will form frozen
gas hydrates on flat surfaces of seafloor drilling equipment.
Abnormally pressured shallow sands may result
from either rapid slumping or rotating faults or from reworked cut-and-fill
channels sealed by impermeable mud or clay. Regional
mapping of these depositional facies will aid the shallow hazards reviewer in
identifying potential sources of SWF.
SWF
events can
cause additional expenditure
of time and money to allow the driller to control the well and resume drilling
and may end with the permanent plugging and abandonment of the well.
Losing time and
millions of dollars encouraged the major operators to study this phenomenon.
Video tapes from remotely operated vehicles (ROV)
document the flow at the seafloor. Electric
logs, temperature logs, pressure logs, and geotechnical data from test wells,
combined with high-resolution three dimensional seismic surveys (3D), or
two-dimensional (2D) high-resolution seismic with reprocessed conventional 3D
surveys, loaded on a workstation, can help to visualize the source of the
problem and refine the geologic model to determine the mechanism of waterflow.
MMS is compiling lists of location and
the potential cause
for each waterflow incident. The Deep Star
Consortium and Energy Research Clearing House previously compiled detailed
available information about SWF and made some of it available on CD disk.
MMS recently contacted major oil companies with
the most SWF incidents to update the SWF database. Most
of these companies provided additional data that formed the basis of this
updated report.
Six layout maps in JPEG format of the SWF
wells indicate severity by color code and depth below the mudline in feet.
This classification was suggested by British Petroleum’s geohazards
group and adopted by the MMS G & G analysis group. It
is based on the height of uncontrolled SWF flow above the wellhead monitored by ROV. Severity varies from minor to severe.
Texas A&M University (TAMU) and Geosciences
Earth and Marine Services (GEMS) used National Oceanic and Atmospheric Agency (NOAA)
swath bathymetry and digitized bathymetry in areas where there are no swath
bathymetry surveys to generate compact
disks and hard copy maps.
GEMS further enhanced this data using EARTHMAPER
software. MMS has purchased compact
disks from TAMU and received the enhanced version from GEMS. MMS annotated SWF wells on top
of the seafloor rendering maps using the ARCGIS mapping system.
Severity coded colors are severe (purple),
strong (red), moderate (orange), low (yellow), minor (light green) and
unreported severity shown in blue. MMS
geophysicists estimated the depth of SWF for unreported depth from 3D seismic.
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Map 1. Displays
SWF for Viosca Knoll and Mississippi
Canyon areas.
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Map
2. Displays SWF for
Atwater Valley area.
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Map 3. Displays
SWF for Green Canyon and Ewing Bank areas.
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Map
4. Displays SWF for Garden Banks
area.
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Map
5. Displays SWF for East Break area.
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Map 6. Displays
SWF for Alaminos Canyon and Port Isabel
In addition to the maps, three Excel files
present:
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Excel 1. This File
contains the data base including the integrity of SWF wells based on permanently
abandoned wells at shallow depth.
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Excel
2. Histogram displays wells count and
average SWF severity at each area.
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Excel
3. Histogram displays average water
depth and average SWF depth below the mudline in feet.
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PPT
1. This power point file displays SWF
severity, using a qualitative classification scheme for ROV. This
classification was adopted by MMS from BP with slight changes.
These maps and files will be updated in the
future to help operators take precautions in the proximity of potentially
hazardous areas.
SWF could threaten safety and the environment
and could cause serious economic loss if they were to occur on a
well-established production platform.
Contacts: Adnan A. Ahmed, Geophysicist (504-736-2501)
or Mike Smith, Geologist (504-736-2500).
G&G analysis unit, Technical Assessment & Operation Support Section, Field
Operations, GOM Region, MMS.