FROZEN HEAT | Volume 2

3.4.4 Well completion

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

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

Horizontal completion

Vertical completion

Sub sea tree with control lines

Sea oor

Surface casing

Sur cial sediment

Intermediate casing

Subsurface safety valve

Chemical injection mandrel and lines

Overburden/ cap sediment

Production casing

Gas lift

Production packer

Slotted liner with screens or gravel pack

Gas hydrate bearing strata Underburden sediment

Pump and gas separator

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).

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 73