Deep Water?
In the oil and gas world, the
term deepwater can mean different things depending on the discipline. Geologists
generally define deepwater with regards to the depositional environment (Slatt
2013). In drilling and well construction, water depths greater than 500m is
generally considered as deepwater because the technology requirements above
this depth changes (Cuviller et al. 2000). There have been other
sub-classifications of deepwater referring to deepwater as depths between 500m
and 2000m and Ultra-deep water as depths greater than 2000m.
Deepwater Potential
The potential of deeepwater
reserves has been widely recognised. According to the International Energy
Agency (IEA) (2013), it is believed that deepwater reserves harbour about a
quarter or 300 billion boe of the remaining recoverable conventional oil in
offshore fields. Table 1 shows the ultimate recoverable resources for the major
producing deepwater regions.
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Table 1 Deepwater Resources for Major Producing Deepwater Regions |
Deepwater Reservoirs
Deepwater reservoirs are typically
comprised of loose unconsolidated sands depending on age, depth of burial and
lithology (Ostermeier 1995). Majority of these reservoirs are relatively young
geologically and belong to class of formations known as turbidites (Total
2014). Due to their relatively young geological age, deepwater reservoirs
generally have good porosities and can be prolific hydrocarbon producers. The
nature of deposition of turbidites (Figure 1) results in layers of relatively
uniform sands and hence good permeability (Research Triangle Energy Consortium
2010).
Deepwater Challenges
These deepwater fields can be
challenging in various regards, from the economics to the technological
aspects, to HSE. Some of these challenges are highlighted below.
- They require large investments
- Large volumes of hydrocarbon producing at high rates are required to offset the large investments
- Early sand production due to the poorly consolidated nature of turbidite reservoirs
- Well Intervention is expensive due to high rig costs.
- Reservoir compaction can occur due to the poor consolidation as the reservoir is depleted.
- Observations and data acquisition have to be done remotely.
- The HSE risks are exacerbated due to remoteness from land.
References
CUVILLER, G. et al., 2000. Solving Deepwater Well-Construction
Problems. Oilfield Review
INTERNATIONAL
ENERGY AGENCY, 2013. Resources to Reserves. International Energy Agency.
NILSEN, T. et al., 2007. Atlas of
deep-water outcrops: AAPG Studies in Geology 56.
OSTERMEIER, R.M., 1995. Deepwater Gulf
of Mexico Turbidites - Compaction Effects on Porosity and Permeability.
RESEARCH TRIANGLE ENERGY CONSORTIUM,
2010. Deep water completions urgently need innovation. [online] North Carolina:
Research Triangle Energy Consortium. Available from:
http://rtec-rtp.org/2010/01/25/deep-water-completions-urgently-need-innovation
SLATT, R.M., 2013. Deepwater Deposits
and Reservoirs-Chapter 11. Developments in Petroleum Science, 61, pp. 475-552
TOTAL, 2014. Understanding deepwater
reservoirs. [online] Paris, France: Total. Available from:
http://www.total.com/en/energies-expertise/oil-gas/exploration-production/strategic-sectors/deep-offshore/expertise/understanding-deepwater-reservoirs
