| Author's Name: XIAO Kunye, ZHAO Ning, CHEN Yajing, LIN Zimo, SUO Xiaofei,
MA Xueying, ZHOU Hongpu, OU Yafei |
| Large carbonate hydrocarbon fields have long been a global research focus. Statistical analysis of HIS data
reveals that Africa's giant carbonate oil and gas fields are mainly distributed in five basins: the Sirte, Pelagian, and
Eratosthenes basins in North Africa, and the Lower Congo and Kwanza basins in West Africa. Among them, Sirte Basin
accounts for 48.2% of Africa's total carbonate oil and gas reserves, making it the most prolific. Through detailed analysis
of 19 large carbonate oil and gas fields, the conclusions are drawn as following: (1) The passive-margin marine
transgressions associated with the Late Cretaceous-Eocene opening of the Neo-Tethys Ocean and South Atlantic are
prerequisites for large-scale hydrocarbon accumulation in carbonate rocks, with the main reservoirs developed in the
Cretaceous, Paleocene, and Eocene strata. (2) Unlike deep-water carbonate rocks, the shallow marine sedimentary
environment and low latitude warm and humid climate after the breakup of Gondwana continent control the scale
distribution of reservoirs and source rocks, forming various types of reservoirs mainly composed of bioclastic limestone,
with dolomite, foraminifera limestone, oolitic limestone, and reef limestone as secondary reservoirs, and high-quality
source rocks mainly composed of shallow marine shale. (3) During the base-level rise period (lowstand to transgressive
system tracts), multiple sets of marine shale (source)-carbonate rock (reservoir)-shale (cap) combinations tend to develop.
Subsequently, through sedimentary burial and tectonic processes, structural traps and stratigraphic-lithologic traps are
primarily formed, leading to hydrocarbon accumulation. (4) The widely developed limestones, grainstones, and dolomites,
along with diagenetic processes, governs the effective reservoirs and physical properties of large carbonate oil and gas
fields. Large oil reservoirs are characterized by moderate to high porosity and moderate to low permeability, whereas large
gas reservoirs typically exhibit moderate to low porosity and moderate to high permeability. From the distribution of
recoverable oil and gas reserves in African carbonate rocks, there is still a huge exploration space, and the mature
theoretical techniques in the genesis and characterization of carbonate reservoirs in China are worthy of further
referencing. |
