| Author's Name: TONG Kaijun1, LI Zongze2, CAO Shuchun1, TANG Jiawei1, LIU Yilong1,
LIU Sibing2, FAN Yunjie2, FU Meiyan2 |
| The Asmari Formation in Iraq B Oilfield was deposited in a remnant ocean basin environment formed during
the closure process of the Neo-Tethys Ocean. Influenced by the intermittent uplift of the Arabian Shield from the
Oligocene to Miocene, the study area developed a multi-stage terrigenous clastic supply system. Under the depositional
background of a gentle slope, frequent sea-level fluctuations have led to complex mixed sedimentary characteristics of
sandstone, dolomite, limestone, and mixed rocks in vertical and planar distributions, whose lithological distribution laws
remain to be further clarified. This study takes Iraq B Oilfield as the research object, and systematically reveals the main
controlling factors of complex lithology development under the gentle slope background through detailed core
observation, thin-section microscopic analysis, and comprehensive interpretation of drilling and logging data. The
research has achieved the following understandings: (1) The lithologies of the Asmari Formation can be scientifically
classified into three major categories: carbonate rocks, mixed rocks, and terrigenous clastic rocks. Among them, mixed
rocks are further subdivided into 8 types based on the 50% ternary classification nomenclature; seven typical lithofacies
combination sequences are identified through the coupling analysis of petrological characteristics and logging responses. (2) The spatial distribution of lithofacies shows significant zonation: the northwestern and southeastern regions of the
study area are dominated by carbonate facies, the proportion of clastic facies in the central part increases significantly, and
the mixed rock facies account for a large proportion in the remaining transition zones. (3) The paleogeomorphology of the
study area presents a gentle slope pattern of "low in the northwest and southeast parts and high in the central part". The
comprehensive tectonic-sedimentary analysis shows that terrigenous clastic sediments are mainly developed in the paleouplift area, carbonate sediments are developed in the paleo-depression area, and mixed sediments are dominant in the
transitional slope zone. Finally, a development model of complex lithology controlled by three factors of
"paleogeomorphic form—sea-level fluctuation—material source supply" under the gentle slope background is established. |
