The regulator for drilling off the coast of Newfoundland (C-NLOPB) provides guidance in the form of the Drilling and Production Guidelines (March 31, 2011) which can be found at the following web address: http://www.cnlopb.ca/pdfs/guidelines/drill_prod_guide.pdf
When investigating procedures for well decommissioning, Husky’s primary objective is to observe the regulations and guidelines of the C-NLOPB, more specifically Part 6 of the “Drilling and Production Guidelines”. As a secondary objective, the requirements of NORSOK D-010 and the recommendations of Oil & Gas UK (http://oilandgasuk.co.uk/) are evaluated and observed where practicable.
With respect to different reservoir sections within a well, the C-NLOPB does not provide much guidance. The regulator simply states the following:
56 Suspension or Abandonment
The operator shall ensure that every well that is suspended or abandoned can be readily located and left in a condition that
a) Provides for isolation of all hydrocarbon bearing zones and discrete pressures zones
b) Prevents any formation fluid from flowing through or escaping from the well-bore.
Per NORSOK D-010, Section 9.6.2, assuming that the reservoir sections are in the same “pressure regime” they can be abandoned with a primary/secondary plug set above the uppermost formation fluid-bearing section – see figure below.
Cement Plug Length
NORSOK indicates that a 100m (330ft) cement plug is sufficient as a combination barrier solution when cement bond logs are not available for well – this requirement exceeds those of the CNLOPB (60m if set within casing).
The O&G UK Guidelines for the Suspension and Abandonment of Wells recommends 240m (800ft) to serve as a combination barrier solution – see barrier diagram below. The guideline specifies “good cement” in the annulus which implies that cement bond logs are available.
Verification of Barriers
NORSOK D-010 states that tagging a cement plug is a required method of verification even when pumped on top of pressure tested mechanical plug.
The recommendations of the O&G UK Guidelines for the Suspension and Abandonment of Wells vary from NORSOK stating the following:
The C-NLOPB is aligned with the O&G UK Guidelines, stating the following in the “Drilling and Production Guidelines”, Section 59.4, m):
Any cement plug that is not supported by a bridge plug (or the bottom of the well) should be confirmed to be in place by either tagging the plug or by using some other appropriate means to confirm the presence of the plug.
With respect to the intermediate casing, the CNLOPB, “Drilling and Production Guidelines”, Section 59.4, i) requires that the stump of any cut and recovered casing strings be plugged with cement.
Hope this helps!
Completions Engineer, Husky Energy