Saturday, February 12, 2011

Concerns related to marcellus shale well construction - Even after Regulatory Changes

The following are my primary concerns related to the construction of the Marcellus Shale Wells

1. String Placement and Design - needs to take into consideration the geology and hydrology for the site - the simple statement of 50 feet below freshwater, but not more than 200 feet is not adequate.

String Placement - Needs to be Standardized - but Site Specific.


1. First String - should prevent the circulation of mud, cuttings, and gas migration to the wells within the first 500 feet from the well. Casing needs centralizers every 2 lengths of casing and the cement needs to be filled from base and returned to surface. This will likely need the installation of an extra casing that extends to a depth of 300 to 500 feet.
2. Second String - should extend into the first confining layer below the freshwater aquifer and should separate the freshwater from saline water - This will likely need to be in the depth range of 750 to 1200 feet.
3. The third string need to separate the saline from brine water and should be placed within a confining layer.  This will likely need to be between 1200 to 2000 feet
4. Fourth String may be needed to separate saline and brine water aquifers - especially if shallow gas is present.  This may need to extend to about 2500 feet
5. Typically the kick off point is 500 feet above the Target Formation - then the horizontal leg is completed, the production casing is then cemented to 500 to 1000 feet above the kick off point or to the surface. 

Potential Problem - Depending on the string layout - it is possible that there could be a 1000 to 2000 foot zone beneath the final or deepest string and the production casing that has zero cement.  This seems to be a potential problem.  It would be best if the annulus above the production casing was cemented to the surface or at least cemented to 100 feet inside the lowest string. 

6. Cement bonding testing - this has been implemented.
7. Installing on-site monitoring wells to a depth to the lowest portion of the freshwater aquifer.

This would should help with the potential problem of gas migration and the interconnection or exposure of the casing to corrosive fluids and gases.

Keys -we need to make sure we have recreated the confining layers in the formations, good cement bonding, and limit the potential for migration of gases, liquids, and muds.

This is a work in progress.

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