Mr. Erik Milito - The House Committee on Natural Resources ...

ISOLATING POTENTIAL FLOW ZONES DURING WELL CONSTRUCTION 37
closed, the casing will expand as pressure increases. <strong>The</strong>n, when the pressure is released, a micro-annulus may be
created as the casing contracts, which could result in poor zonal isolation and SCP.
It is typically not advisable to trap pressure inside the cemented casing unless the float valves have malfunctioned
and are not holding pressure.
5.10 Post Cementing Operations
5.10.1 Maintaining a Full Hole and Cases for Applying Surface Pressure
In order to maintain maximum overbalance pressure, the fluid level should be maintained in the annulus. In addition to
maintaining the overbalance pressure, keeping the hole full will give an early warning if the well begins to flow. It also
provides a means for tracking fluid losses in the annulus.
If wellbore ballooning is occurring, the annulus should be closed and monitored until the cement has gained 50 psi of
compressive strength at the loss zone in order to prevent fluids lost to the formation from flowing back and
contaminating the unset cement.
Under some circumstances (see A.13), the controlled application, via pumping, of a constant pressure to the annulus
can be used to mitigate well control events such as kicks and reduce the risk of a LWC incident. This surface pressure
application increases pressure down the annulus to the source of the flow and helps create an overbalance across
the flowing zone to mitigate or stop the flow.
Some specialized applications such as foamed cementing or under-balanced operations may require that pressure
be held on the annulus during WOC time. Job-specific procedures should be consulted to determine a pressure and
time schedule for the annulus.
<strong>The</strong> characteristics of the well, including depth, fracture gradient and geometry can play a role in the success of the
above techniques. <strong>The</strong>y are intended only to supplement other techniques used for control of flow. To be effective, the
well should be rigged up and the technique started within a few minutes after bumping the top wiper plug which ends
pumping for the primary cementing job.
Care should be taken in washing out a riser, as this can reduce the hydrostatic pressure, leading to flow.
5.10.2 WOC
Operations on the well following cementing should be done in such a way that they will not disturb the cement and
damage the seal or cause the cement to set improperly.
Normally pipe movement to complete hanging the casing and activating seals should be finished before significant
gel strength has developed. If done after the cement has developed significant gel strength, such pipe movement
could cause a micro-annulus. <strong>The</strong>re is also danger of initiating flow if the pipe movement swabs the well in. In some
instances the pipe may be moved at a low-rate as a means to break gels until hydration starts.
If the casing is to be hung after cement strength is developed, as when intentionally increasing or decreasing the
landed tension in the casing, consideration should be given to the imposed forces on the cement and the cement
strength.
Regulations may require casing to be pressure tested. Preferably, pressure testing casing should be done before
significant gel strength has developed. However, such pressure testing will be limited by the pressure ratings of plugs,
floats, cementing heads and other equipment. Pressure testing can be done after the cement has set but this can
result in micro-annulus formation or damage to the cement sheath. <strong>The</strong> pressure should be held on the casing for the
shortest length of time required to accomplish the test. <strong>The</strong> effect of pressure testing will depend on the properties of
the cement, the pressure at which the casing is tested (and consequently the amount of enlargement of the casing)