Kuwait Energy
EL-12-211107
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is not aware of any activity on the Iranian side of the border. It is unlikely that unitisation
would be considered even if the field were to extend into Iran.
Raw wireline logs are available from all three wells. Conventional core analysis results
are available from Siba-3. Borehole rugosity is an issue in all three wells, with the caliper
logs in Siba-2 and Siba-3 indicating significantly enlarged boreholes in both wells. This
has an adverse effect on the quality of the density and neutron logs.
The primary gas reservoir is the Lower Cretaceous Yamama Formation (Figure 3.4). The
Yamama consists of a massive, heterogeneous, algal carbonate reservoir, deposited in a
restricted shelf marine environment, with an average gross thickness of about 650 ft
(200 m). Microfossils are abundant and secondary porosity is dominant as a result of
dissolution of the micro faunal skeletal remains. Subsequent diagenesis has resulted in
significant porosity occlusion by sparitic calcite cement. Micro-fractures are also present.
The porosity ranges from 6% to over 20% with permeability generally less than 10 mD.
Ten stacked reservoir zones within the Yamama Formation have been identified from the
well logs, referred to as Yamama Top and Yamama A to J, but the primary reservoir
targets are the Yamama A to D.
The top seal for the Yamama Formation is the Ratawi Formation, consisting of limestones
and shales.
KE has estimated GIIP using a Monte Carlo approach with inputs based on the
interpreted maps and petrophysical properties. The results are shown in Table 3.1.
There is a very significant uncertainty in the GIIP as a result of numerous factors
including:
Structural uncertainty due to the sparseness and poor to fair quality of the seismic
data combined with the relatively low structural relief;
Uncertainty in interpreted porosity, estimated by GCA to be ±1.5 porosity units
where hole conditions are optimum for logging, significantly greater elsewhere;
Uncertainty in interpreted water saturation, estimated by GCA to be ±15% due to
(a) the nature of the limestones which consist of a variety of porosity systems with
variable connectivity that are difficult to characterise in terms of the cementation
and saturation exponent inputs to Archie’s equation, and (b) the use of older
induction type resistivity logs which are not always reliable sources of true
resistivity in such lithologies;
Uncertainty in petrophysical properties away from the wells due to the
heterogeneous nature of the limestone formation, with the possibility of facies
changes over short distances;
Uncertainty in the gas-water contact depth in each reservoir: “gas down to” is
inferred from the production tests and the logs, while the maximum possible
contact depths in each reservoir are estimated from the inferred structural spill-
points; and
Uncertainty in fluid type in the untested formations.
However, in GCA’s view, KE has made appropriate allowances for these uncertainties in
estimating the range of possible GIIP values shown in Table 3.1. There is potential for
additional gas volumes to be present in other reservoirs (Yamama E to J) and also in the
second structural culmination around Siba-2, but further appraisal is needed to confirm it.
