Directive 065: Resources Applications for Oil and Gas Reservoirs ...

Requirements
date of the test or the analysis used to
estimate the pressures, and if there are
pressure differences between pools and
coal and shale zones proposed for
commingling, evaluations of
a) the potential for cross-flow of reservoir
fluids between the pools and zones,
particularly when the well is shut in,
and
b) why the pressure differences will not
result in any adverse impacts if
commingling is permitted.
17) If the application has been filed because the
reservoir pressure of a pool or zone
proposed for commingling exceeds 90 per
cent of the lesser of the closure or
breakdown fracture pressure of one of the
other pools or zones proposed for
commingling,
a) calculations to demonstrate that the
reservoir pressure of a pool or interval
proposed for commingling exceeds either
• 90 per cent of the fracture closure
pressure of a shallower zone that has
been fracture stimulated, or
• 90 per cent of the fracture breakdown
pressure of a shallower zone that has
not been fracture stimulated,
b) confirmation that the shallow pool or
zone will be segregated during periods
that the well is shut in, including a
wellbore schematic showing the actual
or proposed completion to ensure
segregation, and
c) pressure decline analysis to demonstrate
the length of production time needed for
the pressure of the higher-pressured
pool or zone to decline so that
segregation is not required during
periods the well is shut in.
Comments
Pressure differences between pools/zones
raises the possibility that commingling of
production may result in the cross-flow of
reservoir fluids between pools. The crossflow
may contaminate a non-saline water
zone or result in an adverse impact on the
recovery of hydrocarbons from a pool/zone
involved. For example, recovery may be
adversely impacted by cross-flow of fluids
by gas entrapment behind perforations, by
precipitate formation resulting from
incompatible reservoir fluids, or by the
movement of fine particles. In addition, a
water-sensitive formation may be damaged
by the cross-flow of water.
Closure pressure is the pressure needed to
open and/or extend a fracture resulting from
previous stimulation operations. Breakdown
pressure is the pressure needed to initially
fracture a reservoir during stimulation
operations.
Having extreme pressure differences between
pools/zones proposed for commingling raises
a safety issue in that wellbore control may be
jeopardized if fluid from a high-pressured
reservoir flows into a lower-pressured
reservoir that has a well completion or
wellhead equipment not designed for such
high pressures. Another concern about the
commingling of production from pools/zones
with extreme pressure differences arises
when a new well is drilled into a pool/zone
that has an unusually high pressure due to
cross-flow from a commingled completion;
this raises a safety issue in that the party
drilling nearby may not anticipate the higher
pressure.
3-28 • ERCB Directive 065: Resources Applications / Commingled Production (October 2011)