Abstract:
The present research study is dealt with the Late Paleocene-Early Eocene Lockhart
Formation for detailed sedimentological investigations and reservoir characteristics in
Kotal Pass section of Kohat sub-basin. A total of 25 samples were collected out of which
20 samples were thin sectioned and were studied for the petrographic investigations and
diagenetic imprints. Based on the allochems to matrix ratio, a total of four microfacies are
identified; Bioclastic foraminiferal wacke-packstone (KLL-1), Miscellanea wackepackstone (KLL-2), Foraminiferal wackestone (KLL-3) and Lockhartia rich wacksetone
(KLL-4). Based on the faunal assemblages and depositional fabrics, these microfacies of
the Lockhart Formation are interpreted to be deposited the in an open ramp/inner lagoon
of Inner ramp to proximal open marine middle ramp settings of the homoclinal carbonate
ramp environment. The faunal assemblage of the Lockhart Formation includes the larger
benthic foraminifera (LBF) species of Miscellanea (Miscellanea miscella, Miscellanea
juliettae other species of Miscellanea), Lockhartia (Lockhartia haimei, Lockhartia
conditi, Lochkartia tipperi), Rotalia. Milliolid and very rare Ranikothalia sp.
(Ranikothalia sindensis) along with the invertebrate fauna like echinoderm and
dasycladales algae. Based on these index fossil of species of Lockhartia, Miscellanea and
Ranikothalia sindensis, the Thanatian age of Late Paleocene is assigned to the Lockhart
Formation. Among the diagenetic fabrics, the secondary porosities generated by
dissolution (in the form of molds, vuggs) and microfractures (channel porosity) have
played the pivotal role which enhance the reservoir characteristics of the formation
envisaging the carbonates of the Lockhart Formation could be an acceptable reservoir.
Based on the SEM analysis, among the identified microporosities, vuggy, dissolution and
intergranular are the dominant porosities that can play effective roles to act the Lockhart
Formation as a good reservoir. Based on the petorphysical analysis, a zone of interest
between 2687m to 2710 m having thickness of 23m is marked in Maramzai-02 well. This
zone is typified by low values of Gamma ray log and shale volume with average porosity
and effective porosity values ranging from 7-9% and 4-6% respectively. This zone has
low Sw which is 26.40% and relatively fair to good effective porosities of 4 to 6% with
permeability in range of is 1-3md envisaging that the Lockhart Formation in Maramzai -
02 bears fair to acceptable reservoir properties.
