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GEOLOGICAL AND ENGINEERING DATA ON SP-2 (1300m) AND C-3
(5000m) PROSPECT WELLS DRILLING PROJECTON
THE TERRITORY OF REBUPLIC OF MAURITANIA
( prospecting block 11 )
1. GENERAL DATA ON THE AREA OF OPERATIONS
The wells designed for drilling are located in the Islamic Republic of Mauritania,
situated on the Atlantic coast, between Maghreb states (Arabian West – Morocco, Algiers)
and West African states (Senegal, Mali).
The country’s territory constitutes 1 025 520 km2; it stretches from North to South
for nearly 1500 km, and from West to East – for more than 1000 km.
From the administrational point of view, the country is divided into 12 regions and 1
metropolitan district. The capital and major seaport – the city of Nouakchott (population
550,000). The second seaport town – Nuadibu (population 70,000). Other most prominent
towns – Zuerash, Kaedi, Atar, Rosso and Boge. The country’s population is 2,274,000 (as of
1995).
The country has a desert climate, dry and hot, excluding the coastal zone and southernmost region in the valley of the Senegal River.
The yearly amount of precipitation fluctuates from 100 mm in the country’s north to
1000 mm in the Senegal River area.
Major seaports located in the towns of Nouakchott and Nuadibu provide practically
all the country’s cargo turn-over (about 13 mln tons per year).
The main country’s water artery is the navigable Senegal River, flowing on the south
of the land. Though the water level and the river bed are changeful, which causes difficulties
for the navigation.
The length of motorways exceeds 9,000 km, from which 4,700 km are usable for
round the year transportation. About 2,000 km of them have asphalt covering.
The single country’s rail-road connects iron ore open pits of Zuerash area with the
seaport of Nuadibu (652 km).
2. GEOLOGIC AND GEOPHYSICAL STRUCTURE,
TECTONICS, OIL AND GAS CONTENT OF THE OPERATION AREA
The survey of the coastal basin of Mauritania to discover the hydrocarbon potential
began in the 60-s of the last century. Many well-known companies, such as AMOCO, TEXACO и BEICIP, participated in this process, but their efforts were generally focused on surveys in the shelf zone. By results of previous works, the shelf zone was characterized by airborne geophysical survey data, 2D seismic survey results and data on drilling of about twenty exploration wells (‘Geologic-geophysical study scheme’). In close proximity to Block 11,
on the west, in the shelf zone, seismic surveys were performed by AMOCO, 1968, and CGG,
1982. Land seismic surveys were done only from the southern side of Block 11, by OXOCO
in 1984. The costal zone, including Block 11, was characterized only by airborne magnetic
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survey and gravimetric survey, per the license for exploration works belonging to IPG SA.
Currently, thanks to IPG SA efforts, direct information is obtained on the geological structure of Block 11, including the results of a detailed aeromagnetic survey, 2D seismic survey,
data on TANIT-1 deep well drilling and recently drilled SP-1, SP-6 and SP-9 structuralparametric wells.
The area under consideration is situated in the northern part of MauritanianSenegalese coastal sedimentary basin, open westward in the direction of the Atlantic Ocean,
and having sharp boundaries in the east, north and south, with emergencies of rocks, sedimentary cover and crystalline basement. The geological structure of the given region includes the rocks of Archaean- Proterozoic basement and sedimentary cover in the volume of
Palaeozoic, Mezozoic and Cainozoic deposits (‘Generalized lithologic and stratigraphic
cross-section’). The data on the stratigraphic lines position by the wells, drilled by IPG SA,
are given in the table titled ‘Marks of the main stratigraphic horizons by Block 11 wells’.
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Geologic-geophysical survey layout
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Generalized lithologic and stratigraphic cross-section
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Main stratigraphic elevations by Block 11 wells
Well
SP-1
SP-6
SP-9
TANIT-1
Horizon
P3
(2-nd Oligocene carb. member roof, seismic ОГ II )
P3-2
( Eocene carbon roof, seismic
ОГ III)
P2 ( inside Paleocene deposits
?)
P2-1 (inside Paleocene deposits? )
KV
(Cretaceous deposits roof ? )
PZ
(Palaeozoic, deposits roof,
seismic ОГ Pz )
P3
P3-2
KV
PZ
P3
P3-2
P2
P2-1
KV
PZ ( ? )
N1
( Neogene deposits
?)
P3
P3-2
P2
P2-1
P1
( Paleocene deposits roof ? )
K2 (Inside Cretaceous deposits? )
K1
(Inside Cretaceous deposits?)
Depth, m
Actual elevation, m
259.6
-249.6
409.14
-399.14
465.26
-455.26
474.39
-464.39
544.86
-534.86
557.01
122.9
253.82
307.96
323.65
301.07
570.4
660.14
678.43
1061.79
1064.93
-547.01
-79.1
-210.02
-264.16
-279.85
-291.07
-560.4
-650.14
-668.43
-1051.79
-1054.93
386.08
522.84
842.48
987.15
1062.28
-378.75
-515.51
-835.15
-979.82
-1054.95
1376.29
-1368.96
1595.17
-1587.84
2906.86
-2899.53
Archaean – Proterozoic deposits (AR-Pr).
Pre-Cambrian basement deposits crop out north-easterly of the territory considered, on
Reguibat upland (500-600 km from Block 11). By the lithologic description of outcroppings,
basement rocks are represented by metamorphic (phyllites, gneisses, migmatites) and volcanic rocks; ferruginous quartzite are also met at times. In the exploration area, Pre-Cambrian
age rocks are open-up by Idini, El-Adress and Aleg wells, located in the south and south-east
of Block 11, at the depths of 481 m, 170 m, 105 m correspondingly. In deep wells on the
shelf, and also in TANIT-1, basement rocks are not open-up to the depth of 4,300 m.
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Paleozoic deposits (PZ).
Paleozoic deposits outcroppings are registered along the whole perimeter of Mauritanian-Senegalese coastal basin land. To the east of the investigated territory, in Mauritanides
mountains (50-100 km from Block 11), in the east of Bova basin (Guinea-Bissau) and in the
north, in Aaiun-Tarfaia and Tindouf basins in Western Sahara.
Silurian (S) deposits are described in Bova basin (Senegal). These are clay slates with
high organics content, which are most probable parent rocks for all hydrocarbon accumulations of this coastal basin.
Devonian (D) deposits are described in the north, in Western Sahara; represented by
sandstones and clays; and in the south, in Senegal, where sands of quarts composition are
met, possessing high collecting properties.
Coal (C) deposits represented by arkosic sandstone, are met in Mauritanides mountains; and in the lower horizons of TANIT-1 well sandstones are met with similar composition, but redeposited in the later Cretaceous period.
Permian (P) deposits are not described individually; they are united with overlying
formations in a single Permian- Triassic - Lower Jurassic complex, in correspondence with
the tectonic development of this region; they are lithologically represented by terrigenous
and evaporite rocks.
Mezozoic deposits (MZ). Divided into two complexes: syn-rift and post-rift:
Triassic (T) and Lower Jurassic (J1) deposits are part of the syn-rift Upper Paleozoic –
Lower Mezozoic terrigenous-evaporite complex, formed idiogenously with development of
Permian-Triassic rift and opening-up of the North-Atlantic Ocean. This complex includes the
salt deposits, over the domes of which oil fields are discovered on Mauritania shelf. The
overlying complex of Mezozoic deposits was formed in the sea and fore-shore & sea conditions.
Upper-Middle-Jurassic (J2-3) and Lower Cretaceous (K1) deposits are rather manifold by the lithologic composition. They can be represented by carbonate rocks formed in the
shallow shelf conditions (opened-up by Loup de Mer-1 well), or terrigenous rocks, essentially by sand-rocks formed in coal continental conditions, as in TANIT-1 well. Moreover, in the
deep-sea wells of the shelf, AK-1A и RB-1, Lower Cretaceous deposits are represented by
turbidites of clay-aleurolitic composition.
Upper Cretaceous (K2) deposits were formed in the period of large transgression of
the sea, and are represented mainly by deep-sea clays. Deep-sea clays are open-up by V1,
OCT-1B и MTO-2 wells; their thickness reaches 150 m; they have medium and high organics content, and they are the second priority parental rocks of this region, after Silurian slates.
Cainozoic deposits (KZ). Paleogene deposits (P) close the cycle of transgressionregression of the sea, which started in the Upper Cretaceous period. Lithologically they are
represented by interlaying of clays and sandstones in the upper part with continental genesis
sandstones, partially degraded during Upper Miocene. Neogene deposits (N) were formed in
the sea and fore-shore & sea conditions; represented by interlaying of clays and sands of various thickness with separate thin veins of clay-stone and limestone; they occur in Upper Cretaceous and Paleogene deposits with pronounced non-conformity.
The considered region is tectonically located in the passive part of the marginal rift
zone. That is why the following main tectonic development phases of this region tectonic development are being determined: pre-rift, syn-rift and post-rift. The pre-rift complex of the
sedimentary sediment rocks of the early and medium-paleozoic age, is substantially complicated by the folds and abnormalities during Hercynian orogeny, which lead to formation of
Mauritanides massif in the east of the basin. During the rift (syn-rift) phase of the territory
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development, in the late-paleozoic – early mezozoic period, the sedimentation of the terrigenous-evaporite rocks complex occured. The salt deposits of this complex were the reason
of the diapirismа and appearance of the salt-dome tectonics in the overlying formations.
Basement movement at the rift forming and opening-up lead to the occurrence of faults in the
sedimentary cover of the shelf zone, up to the neogene age deposites. In the final post-rift
phase of this region development, continuing up to now, the tectonic processes are connected
in the first place with the phenomenon of salt diapirism, but also, the possibility of faults
growth from the syn-rift phase to neogene deposits is not excluded. Besides that, the phenomena of landslides and turbidite flows are possible on the margin of the shallow and deepsea shelf.
The industrial oil & gas content of this region is proved by discovering the oil fields of
Chinguetti and Banda, Tiof oil & gas field, and also Pelikan gas field on Mauritanian shelf,
across from Blocks 10 and 11. In the southern part of the considered basin, on the territory of
Senegal, Gadiadja field and Diam Niadio gas & oil were discovered on the land, and also oil
fields on the shelf – Dom Flor and Dom Dji.
Several horizons are being productive deposits. Most high-bedded are Miocene sands
of the Neogene in the fields of Chinguetti, Tiof and Banda, possessing very high collective
properties and field performance. Hydrocarbons flow rates reach 1800 m3/day of oil.
In Pelikan field productive are the sandstones of the later Cretaceous or earlier Paleogene age; unfortunately, there is no information on the flow rate amount. The upper Cretaceous deposits are also productive in Senegal, in Gadiadja field, where the gas flow rate
reaches 283,000. m3/day, and Diam Niadio, where the inflow jointly amounted to 56 m3/day
of oil and 57,000. m3/day of gas.
In the shelf fields of Senegal, Dom Flor and Dom Dji, low-gravity oil accumulations
are discovered in carbonate sedimentations of Paleogene; and high-gravity oil accumulations
– in the upper Cretaceous terrigenous deposits.
Besides the discovered hydrocarbon fields, a lot of oil & gas showings at drilling, and
also hydrocarbon traces in the drilling mud are known. For instance, in AK-1 well drilled in
1969, vivid oil showings are marked in the lower Miocene; gas indications in Oligocene and
lower Miocene. Multiple oil & gas showings are marked in all the open-up interval of Mezozoic deposits. In V-1 (1974) well, the aggregate gas indications in the Eocene and Paleocene
interval reach 10-20 %. In OCT-2 (1972) well, at drilling the Cretaceous deposits, high gas
indications are registered, and luminescent glow of the sludge is marked. Moreover, traces of
oil & gas are marked in one of the intervals of Neocomian deposits; but at testing this interval, salty water influx resulted (85000 ppm by NaCl). In MTO-1 well (1970) oil & gas showings are marked in upper Paleocene, and gas showings are encountered in thin alternations of
Miocene. MTO-2 well (1970) is featured by traces of hydrocarbon gas in Mezozoic deposits
and upper Paleocene. In LDM-1 well (1991) insignificant gas showings were marked in
Paleogene deposits, and also insignificant gas & oil indications in the Cretaceous age rocks.
Rare traces of hydrocarbons are marked in Autruche-1 well (1989) in the lower Cretaceous
formations. On the territory of Senegal, in the single land well covered by data, in TB-1
(1961) gas showings are marked in the sands of the lower Cretaceous.
3. GOALS OF THE DESIGNED PROSPECTIVE DRILLING
The survey of the deep lying deposits of Mezozoic and Paleozoic mantles of Mauritanian-Senegalese coastal basin with further determination of their oil & gas content prospects.
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4. MAJOR TECHNICAL & ECONOMIC DATA OF THE DESIGN
#
Item
Meaning
1
2
11
1
Block number
2
Well
3
Drilling goal and well designation
4
Design
5
Designed depth, m
6
7
8
Number of test sites
7
in open-up shaft with
formation tester
in extracting colulmn
Well type
Core recovery
#1 (SP2), №2 (С3)
prospective
Neocomian assize
Well #1 – SP2 – 1300 m
Well #2 – C3 - 5000 m
Yes, possible, in case of detecting oil indications.
Yes, in case of detecting oil indications.
vertical
Well #1 – SP2 – 1300 m
22 m (boring head 215,9mm) isolated core
Well #2 – C3 - 5000 m
110 м (boring head 215,9mm) isolated core
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Drilling mud purification system
Four-stage
10
Drilling method
Turbine-rotor
11
Assembly type
Primary
12
Drilling rig (DR) type
Rated capacity no less than 300 tons
13
Top drive availability
Yes
14
Power supply
Diesel power plant included in DR
15
Water supply
16
17
Preparing the cluster foundation and
sludge pit
Motorways
Blowing well with salt water density up to 1,16
g/cm3.
Contractor shall test the water by solutions to determine the possibility of its usage for preparing drilling
mud.
In case of operating with fresh water, delivery of the
water for technical and amenity needs by autotransport shall be envisaged.
Depending on the drilling rig type.
In case of site location on moors (sepkha) foundation
pour under drilling rig shall be provided.
Round the year passage from the city of Nouakchott
to wells #1 and #2.
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18
19
20
21
22
GTI along the whole well shaft. Gas logging in the
Geological & technical investigations
intervals agreed with the Customer geological survey
(GTI), gas logging.
to be envisaged.
Casing string
Casing string is supplied by the Contractor.
Prior to commencement of works, the drilling
Preparation of the drilling program
contractor shall prepare and agree with the Customer
the well drilling program
Well construction scheme
‘Turnkey’
First the well depth 1300m is drilled, then the well
Construction sequence
depth 5000m.