Page 130 - Handbook Of Multiphase Flow Assurance

126 5. Flow restrictions and blockages in operations

0 0
1 100
2 200
3 300
Pressure (MPa) 4 400 Depth (m)

500
5
6
700
7 CH 4 hydrate stability data 600
Geothermal profile T, K
8 800
9 900
10 1000

Temperature (K)
FIG. 5.20 Hydrate stability curve plotted together with the geothermal temperature profile shows where hydrate
can be stable in nature or in a producer or injector well.

Geothermal profile has to be measured for a specific well, or obtained from nearby wells.
In oil and gas wells the structure II hydrates are encountered most often, so the methane hy-
drate stability data should be substituted with structure II hydrate stability data for a specific
reservoir fluid. Each reservoir fluid is different, so the structure II hydrate stability will vary.
Typical depth for setting a SCSSV is between 2500 and 3000 ft. or 800 and 1000 m below
mudline in subsea oil and gas wells.
Existence of gas hydrate in nature had been proven experimentally in 1961 (Makogon).
Меssоyaha gas-hydrate deposit shown in Fig. 5.21 was discovered in 1967, with start of com-
mercial production оn 12/24/1969.
Several hypotheses exist about the effect of naturally occurring methane clathrate hydrate
deposits on the warming period known as Paleocene-Eocene Thermal Maximum. Besides earth,
hydrate may also exist in cosmic bodies and in comets as shown in Fig. 5.22 where gradual heat-
ing of surface by the sun causes gas and particles to erupt. Similar thermodynamic reasoning
applies to the hydrate accumulations in permafrost regions (Chuvilin and Davletshina, 2018)
and to the recently observed craters on the Yamal peninsula where hydrate may dissociate, upon
warming, below permafrost causing pneumatic eruptions (Makogon and Makogon, 2017).
The methods for estimating the water content in rock pore which is in equilibrium with
ice or gas hydrate in sediments was described by Istomin et al. (2017). The authors show that
the water content measured with via pore water potential by the dew point method was in
good agreement with direct contact measurements. The non-clathrate water content was es-
timated at 2–5% in contact with clay materials in the range of −20 to −2 °C hydrate formation
temperature shift. A modern overview of the worldwide gas hydrate deposits geology and
development was presented by Voronin (2017). To-date only two countries Japan and China
have achieved gas production from hydrate subsea. Flow assurance also plays an import-
ant role in these projects for commercial production of natural gas from subsea gas hydrate
deposits. Multiphase flow, subsea processing, artificial lift, rate and locations of phase tran-
sitions, and the distribution and effects of chemicals have been evaluated in the production
system design.