Regulatory
Citation(s):
78.83b. Casing and cementing – lost circulation.
(a)
If cement used to permanently cement the surface or coal protective casing is
not circulated to the surface despite pumping a volume of cement equal to or
greater than 120% of the calculated annular space, the operator shall determine
the top of the cement, notify the Department, and meet one of the following
requirements as approved by the Department.
Question:
All the companies want to know if they can
calculate the cement top with the cement displacement pressure to comply with
78.83b.(a)?
Displacement methodology proposed (summarized
through discussions with operators):
·
Pressure
reading is acquired at the wellhead
·
Must
shut down prior to landing second wiper plug that isolates cement column from
chaser water and let pressure stabilize
·
Once
cement is pumped, a positive pressure will exist at the wellhead
·
Cement
will be in annular space, and water will be inside surface casing when pressure
reading is acquired
·
Back
pressure on cement head is measured once the column stabilizes – this is
essentially a hydrostatic calculation that considers cement density
·
Process
takes about 5 to 10 minutes (similar to mud balance determination process)
Response:
The
Department does not currently view this method as an acceptable means for
determining the top of cement in the event of lost circulation. Although there are scenarios where the method
could result in an accurate determination of the top of cement, there are also
many situations in which the calculation would not be sufficient for achieving
this end. The main issue arises as a
consequence of multiple fluids occurring in the annular space that are of
different densities, e.g., cement and a spacer or gel
water. Under such conditions, there are
many combinations of cement and the other fluids that could result in the same
pressure reading (see chart below). This
limits the ability of the operator to accurately estimate the column of cement
in the annular space based solely on a pressure measurement.