Kuwait Energy
EL-12-211107
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quality is poor to fair for structural mapping and poor for stratigraphic, lithologic and fluid
interpretation. The vertical resolution is estimated to be about ±160 ft (50 m) at reservoir
depth.
All four wells were logged with conventional, Western-style, wireline log suites between
1979 and 1990. Cores were recovered from all the wells.
Mansuriya is a double plunging anticline striking northwest-southeast. It is about 25 km
long, extending outside the license area at both ends, by 6 km wide. It is the result of
compression forces associated with movement of the Arabian plate. Five northwest-
southeast faults are currently mapped but more probably exist, including thrust faults with
repeat sections within the core of the anticline.
The main reservoir is the Lower Miocene-aged Jeribe Formation (Figure 3.6). It is a
massive, recrystallized limestone with dolomitized marls and chalks and minor anhydrites.
These carbonates are interbedded with evaporites and salt. The environment of
deposition is lagoonal, reefal and back reef in a shallow marine environment. The Jeribe
Formation lies conformably above the Dhiban Formation and below the Lower Fars
(Fatha) Formation. Gross thickness of the Jeribe Formation ranges from 180 ft (56 m) to
240 ft (73 m). There are four principal reservoir units, which have different petrophysical
properties. The seals are provided by the interbedded Middle Miocene evaporites.
The secondary reservoir is the Middle Miocene-aged Transition Bed of the Lower Fars
(Fatha) Formation. It is conformable with the underlying Jeribe Formation and the
overlying Upper Fars Formation. The reservoirs here are thin, fractured dolomitic
limestones interbedded with evaporite, marls and siltstones. The overall thickness varies
from 650 ft (200 m) to nearly 3.000 ft (900 m). The environment of deposition is shallow
marine and evaporite basin. Seals are provided by the interbedded anhydrites. Although
there are 11 possible reservoirs, TB4 and TB8 are the best zones with porosities ranging
from 15% to 20%.
KE has estimated GIIP by building a reservoir model using the Petrel software (the static
model). This model was also used as the basis for a compositional reservoir simulation
model run with the Eclipse-300 software (the dynamic model). KE’s low, best and high
case dynamic models have GIIP of 1.83, 2.49 and 3.78 Tscf respectively.
GCA reviewed the inputs to KE’s static and dynamic models at end 2010 and found them
to be reasonable. GCA is not aware of any updates since that time. Uncertainty in GIIP
arises principally from uncertainty in the average petrophysical properties and in the
depth of the gas-water or gas-oil contacts.
As a result of the heterogeneous dolomitic fabric of the Jeribe Formation and the
Transition Beds, grain density is variable and difficult to constrain, resulting in uncertainty
in the determination of porosity from the bulk density log. Neutron porosity log values are
affected by a variable amount by the presence of gas.
In the Jeribe Formation, uncertainty in porosity from the log data alone is estimated by
GCA to be ±2.5 porosity units where hole conditions are optimum for logging, significantly
greater elsewhere. Uncertainty in interpreted water saturation is estimated to be ±20%
due to 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. It is also not clear how well the salinity of
the formation water is known.
