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Safety 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 water flow (SWF) events to the MMS, a phenomenon encountered in water depths exceeding 600 feet.  Reported water flows 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 water flow, 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.

In rare cases hydrates below the mud line could be a source of SWF by melting down hydrates during oil production.

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 water flow.

MMS is compiling lists of location and the potential cause for each water flow 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 contacted major oil companies with the most SWF incidents to update the SWF database.

Since 2004 MMS created a WEB environment e-Well which enables the operators to report any significant well problems including SWF.  See latest list of last five years count of SWF is in EXCEL 4.  Most of these companies provided additional data that formed the basis of this updated report.

Six layout maps in PDF format of the SWF wells indicate severity by color code and depth below the mud line 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.  Shallow water flow depth displayed in the maps are in feet with a red color.  SWF block number are in blue.  Bathymetry are in meters with white color.

• Map 1.  Displays SWF for Viosca  Knoll and Mississippi Canyon areas.  
• Map 2.  Displays SWF for Atwater Valley area. 
• Map 3.  Displays SWF for Green Canyon and Ewing Bank areas.  
• Map 4.  Displays SWF for Garden Banks area.  
• Map 5.  Displays SWF for East Break area. 
• Map 6.  Displays SWF for Alaminos Canyon and Port Isabel  

In addition to the maps, four Excel files present:

• Excel 1.  This File contains the data base including the integrity of SWF wells based on permanently abandoned wells at shallow depth.
• Excel 2.  Histogram displays wells count and average SWF severity at each area.
• Excel 3.  Histogram displays average water depth and average SWF depth below the mudline in feet.
• Excel 4.  List of last five year incidents of SWF reported in WAR (weekly activity reports) and block diagram of reported significant events in five years from January first 2005 to January first 2009.
• 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) Regional Analyses Unit, Resource Studies Section, Resource Evaluation Office Region, Gulf of Mexico OCS Region, MMS.