Geology Reference
In-Depth Information
regionally include hard waters of the chlorine-calcium type. Individual
intervals on some structures locally contain infiltration meteoric waters
(sulphate- and hydrocarbonate-sodiumе, with rather low salinity of up to
3
5 g/l) (Table 2.14).
The major waterhead complexes are Cretaceous, Paleocene, Eocene,
Oligocene and Miocene. They are separated by regional barriers: the Upper
Cretaceous La Paz clays (Santonian, Maastrichtian), Upper Eocene Pauji
and Upper Miocene La Puerta.
he
Cretaceous complex
ground waters are produced from
Lower and
Upper Cretaceous carbonates (limestones of formations Apon, Copacho
and La Luna in the La Paz, Mara, La Concepcion, Sibucara, West Tarra
fields (the Western oil and gas area) and from sandstones of formation
Mito Juan (Upper Cretaceous-Danian) in the Lamar and Bolivar fields
(Bolivar-Falcon area). Their chemical composition is of the chlorine-
calcium type with the secondary salinity factor 31.9
−
58.6%-equiv. Total
salinity is in the range of 152.9 to 215.0 mg.-equiv. (43.7
−
61.4 g/l). The
sulphate-ion content reaches 3.9 mg.-equiv. (Lamar Field, flow interval
depth is 5,186 m). Metamorphism factor ranges between 0.42 and 0.71.
These parameters are minimal in the drilled sedimentary section of the
region. Waters of similar hydrochemical composition form the complex's
regional background.
The mostly clastic
Paleocene complex
(Husare, Catatumbo formations) is
distinct in the regional distribution of the hydrocarbonate-sodium waters
with salinity 52.8
−
−
58.2 mg.-equiv. (15.1
−
16.8 g/l) and primary alkalinity
factor 6.3
9.7%-equiv. (La Paz, Mara, Lamar, Lama and El Mene fields).
The sulphate concentration reaches 2.9 mg.-equiv. at 4,350 m (Lama).
In the fields, where the underlying Cretaceous complex is productive
and the overlying Paleocene deposits are oil-saturated (the Bolivar, Lamar,
La Paz, Mara and West Tarra zone), sporadic presence is recorded, within
the local structure areas with maximum hydrocarbon reserves densities, of
the chlorine-calcium varieties with elevated salinity (up to 150-170 mg-
equiv. - 42.1-48.6 g/l). In terms of this parameter, these waters approach
the Cretaceous interval waters. The secondary salinity factor in this case is
20.2-25%-equiv.
he
Eocene complex
(formations Los-Cuervos, Mirador, Carbonera,
Boscán and Los Flores, all components of the Concepcion Series) includes
all over the region hydrocarbonate-sodium-type waters with the salinity of
41.4-45.0 mg-equiv. (11.8-12.9 g/l) with the primary alkalinity factor 13.6-
46.3%-equiv. The sulphate content reaches 0.95-1.30 mg-equiv. (Boscán,
La Concepcion, Bochaquero-Bolivar zone, Lama and Lamar fields). Total
salinity values in the productive areas of the structures increase to 79-80
−
