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A GLOBAL OUTLOOK ON METHANE GAS HYDRATES
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3.4.4
Well completion
Well completion is the final step in well construction prior
to production. Well completion includes design and installa-
tion of the production casing, measures to access the forma-
tion and to control near-wellbore interactions, placement of
downhole production equipment (production tubing, down-
hole pumps, etc.), and installation of equipment to allow in-
tervention during production should unexpected operational
issues arise or should it be desirable to further stimulate
production from the reservoir. Advances in completion tech-
nologies have substantially improved the efficiency of oil and
gas recovery and enabled cost-effective production in reser-
voirs that would not have been considered economic even a
few decades ago.
The major elements of a typical well completion for a produc-
tion well using the pressure drawdown technique are shown
in Figure 3.5. Completion considerations for gas hydrate pro-
duction will likely include:
• Measures, such as sand screens or gravel packs, to con-
trol sand inflow to the wellbore due to loss of sediment
strength upon dissociation of in situ gas hydrates in un-
consolidated media;
• Custom-designed downhole pumps and/or downhole
heaters and/or chemical flow lines, depending on the gas
hydrate production method utilized;
• Equipment to lift or pump produced gas and water to the
surface;
• Completions that enable concurrent production of multi-
ple gas hydrate layers from the same well; and
• Provisions for smart completions that allow real-time
monitoring of the formation response and manipulation
of downhole pressure and temperature to optimize gas hy-
drate production.
3.4.5
Managing and monitoring a
producing gas hydrate field
Production operations for a typical gas hydrate field would
likely extend over a decade or more. Experience to date sug-
gests that the technologies used for sand-dominated reser-
voirs will be based on production equipment and procedures
already employed in conventional oil and gas fields. How-
ever, as commercial production of gas hydrate is still hypo-
thetical, it is challenging to establish a reliable basis for the
prediction of the long-term production response of a gas hy-
drate reservoir. For a conventional gas field, such predictions
are normally accomplished through sophisticated numerical
reservoir simulations that enable the estimation of flow re-
sponses and evolving changes in critical reservoir properties
over the anticipated production life of the field.
Given the importance of reliable field predictions, considera-
ble effort is underway, worldwide, to develop and/or improve
reservoir simulators to accommodate the unique properties
and behaviours of gas hydrates. However, the task is complex.
While some progress has been made in verifying the models
through short-term formation pressure tests (Anderson
et
al.
2010; Wilder
et al.
2008) and the Mallik 2008 full-scale
test (Kurihara
et al.
2012; Udden
et al.
2012; Wright 2011),
results remain speculative. Rutqvist
et al.
(2009), Moridis
Horizontal completion
Surface casing
Subsurface
safety valve
Production
casing
Gas lift
Production packer
Gas hydrate
bearing strata
Underburden sediment
Pump and gas separator
Slotted liner with screens
or gravel pack
Sea oor
Sur cial
sediment
Overburden/
cap sediment
Intermediate casing
Chemical injection
mandrel and lines
Sub sea tree
with control lines
Vertical completion
Figure 3.5:
Well completion for gas hydrate production. Well
schematics show possible horizontal and vertical well completions
for a gas hydrate production well employing the depressurization
technique. Modified after Hancock
et al.
(2010).