Page 31 - Fundamentals of Gas Shale Reservoirs

DATA ASSESSMENT 11
a passive margin during the Carboniferous and Jurassic, 1.6 DATA ASSESSMENT
respectively.
The Northern Petroleum System (NPS) seems most This section presents some statistics and discussion on the
favorable, with the target at shallow depths (4800 ft), having distribution, geological characteristics, and general features
high organic content (average of 5.8%), reasonable average of the shale gas plays based on the data collated.
thickness (150 ft), and maturity in the wet to dry gas window
(average Ro 1.4%). However, it is thought to be associated 1.6.1 Distribution
with high clay content.
The Southern Petroleum System is minor by comparison, The relative and absolute distribution of an estimated shale
and also much less favorable in terms of depth (13,500 ft), gas TRR across different regions and countries is depicted in
organic content (average of 2.4% TOC), and thermal matu­ Figures 1.4 and 1.5. However, the following should be con­
rity (Ro 1.15%). sidered in this context:
Recent exploration activity seems to have validated the
shale gas potential of the Northern Petroleum System (BBC, • Shale maps published by the SPE (2012, 2013) define
2013), with Caudrilla Resources suggesting that there may many large shale basins that are not included in any of
be 20 Tcf of TRR based on drilling. the source studies, and hence are not reflected in the
values noted. For example, the Sao Francisco Basin in
Brazil covers approximately 750,000 mi , hence could
2
1.5.20 Northern South America
greatly impact the TRR estimate for South America.
Northern South America has a total estimated TTR of 30 Tcf • The significance that shale gas in any particular region
shale gas, with 11 Tcf within the Venezuelan Maracaibo is not simply a function of the absolute volume of
Basin and 19 Tcf within the Colombian Catatumbo Subbasin. resources. Factors, such as the availability of other
Of the three prospective shales identified, all are in the wet domestic sources of natural gas and the current demand
to dry gas window, have moderate thickness (~200 ft), have for energy, influence significance considerably.
medium clay content, and are age equivalent to the Eagle
Ford Shale play in the United States.
The Colombian La Luna Formation within the Catatumbo 1.6.2 Basin Type
Basin seems to be the most favorable, with both high average Based on the data sources available, an assessment of the
organic content (4.5% TOC) and a relatively shallow depth basin type has been made. The type noted refers to
(6600 ft). The other two prospective shales are either of the architecture of the basin at the time of deposition of
relatively low organic content (average of 1.3%), or relatively the prospective shale. The basin types allocated to each
deep (13,500 ft). play are passive margin basin, foreland basin, rift basin,
Both prospective basins are associated with significant
conventional gas, which is considered a geologically com­
plex region. Conventional exploration does suggest there is Shale gas TRR by region (Tcf)
gas potential, although the shale gas potential has not yet
been validated. Russia, 162 E. Europe, 252
Middle East, W. Europe, 372
153
1.5.21 Turkey
Australia, 396
Turkey has an estimated TRR of 15 Tcf within the Anatolian
(9 Tcf) and Thrace Basins (6 Tcf). All the prospective shales Asia, 1389
are of marine origin. The shale gas characteristics seem rea­
sonable in all the prospective shales. However, the Anatolian
Basin shale occurs at the shallowest depths (8000 ft), whilst
still having reasonable net thickness (150 ft), high organic North America,
richness (5.5%), and a degree of maturity (predominately Africa, 1042 1820
wet gas, Ro 1.1%). The Thrace Basin has two target shales,
one of which is very deep (14,000 ft), whilst the other has
only moderate organic richness (2.5% TOC) and marginal South America,
maturity (Ro 1.1%). 1225
The Anatolian Basin has active conventional oil produc­
tion, but shale gas exploration is still only in the leasing FIGURE 1.4 Chart illustrating the relative abundance of shale
stage, with no specific plans for exploration yet. gas across different regions.