Geochemical, Palynofacies Evaluation and 1D modeling of the Galhak and Al Renk Formations in Miyan Field, Melut Basin South Sudan

Abstract

ABSTRACT

This research concerns the study of the source rocks in Miyan Field, Melut Basin

South Sudan. The main objectives of this work are to investigate the organic matter

(the Kerogen types) as characterization of potentially source rock and hydrocarbon

effective source rock, using maturation study for determining oil and gas window, and

the expulsion timing of the hydrocarbons.

Geochemical and palynofacies analyses indicate that kerogens types are dominated

by amorphous organic matter and classified as kerogen type II, a few samples

showing kerogen type III. Kerogen Type I is rarely, restricted to the deepest parts of

the basin. The organic matter is composed of variable proportions of algal, terrestrial

and bacterial remains. Galhak Formation shows rapid vertical and lateral variation in

the organic richness, probably reflecting the changing environments of the lacustrine

system which have been identified within the studied sections. The richest organic

facies found within Al Renk small interval in two wells.

The Upper Cretaceous lacustrine Galhak and Al Renk Formations of the Melut

Basin generally contain rich to very rich source rocks and display total organic carbon

(TOC) values ( average TOC in Galhak Formation about 3.20 wt% up to 7.0%), and

average TOC in Al Renk about 2.2 wt% and may reach about 3.4. % and hydrogen

index (HI) values range between 242 and 531 mg HC/g TOC (mean 378) in Galhak,

for Al Renk the maximum HI value about 180 mg HC/g TOC. Galhak Formation

(Campanian –Maastrichtian), is very much thicker and more widely distributed it

shows good to very good oil potential in most parts, but the top most part is

organically leaner and shows potential for dry gas only. The Al Renk Formation

(Campanian –Maastrichtian) of well MiyanS-1 shows good oil potential S2 up to 7.

The Galhak and Al Renk source rock Formations inter the maturity at about 1850 m.

Miadol, Jimidi and Adar Formations are other source in the area but not contributed

as hydrocarbon producing due to low maturity.

Based on the 1D basin modeling, the expulsion of the hydrocarbon for Galhak

Formation started about 45 Ma while Al Renk Formation expelled earlier.

The heat flow is variable in space and time, the maximum heat flow (HF) predicted

about 60 mW/m 2 during the second rifting period. The present study confirmed that

there have been at least three rifting phases controlling the deposition and

sedimentation of the source rock linked to deposition of sedimentary cycles.