Petroleum system analysis in the Persian Gulf region: geochemistry and numerical basin modeling

Baniasad, Alireza; Littke, Ralf (Thesis advisor); Sachsenhofer, Reinhard (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The Persian Gulf region on the northeastern Arabian Plate is the world energy heartland with a history of modern exploration and production activities back to the early 20th century. A set of analytical organic geochemistry and numerical basin modeling studies is presented and partly combined in this thesis to enhance our understanding of the basin evolution and petroleum systems in the region and to facilitate future exploration decision-making. The associated uncertainties in each part were identified and investigated. An integrated geochemical study of Jurassic-Tertiary reservoir oils was completed based on a large dataset to analyze active petroleum systems in a regional context in the Persian Gulf region. The dataset consists of different physical, bulk and molecular geochemical parameters as well as stable carbon isotope data of more than 500 oil samples collected from 11 different reservoirs in 112 oil fields. It was compiled from literature and reevaluated geochemical and isotopic data and was further augmented by new analyses. The primary intent was to document the geochemical characteristics of the oil samples and identify the geochemical trends in the region which can be used as a guideline in future studies. Exploration of the distinct genetic oil families based on the biomarker ratios and multivariate statistical-based modeling, i.e. chemometrics led to classification of oil samples into 2 clans, 6 oil families and 10 subfamilies. Families/subfamilies with possible mixed origin from multiple source rocks were identified qualitatively using the chemometric analysis. The age, lithology, depositional setting and organic matter type of the respective source rocks for each family/subfamily was inferred from its geochemical fingerprints. The regional extension of different families was used to evaluate charge access as well as migration directions and migration pathways. The results of this organic geochemical study were further applied in the context of numerical basin modeling to physically explain the findings. The basin modeling study focused on the northwestern part of the Persian Gulf, offshore southwest Iran, in an area of about 20,000 km2 incorporating the southern Mesopotamian Basin. This region represents arguably one of the most complicated petroleum systems of the northeastern Arabian Plate. A 3D conceptual model bounded by the base-Triassic and the present-day sea-floor was constructed based on the interpretation of 2700 km of 2D seismic lines. Depth and thickness maps were created tied to data from 20 wells. The thermal model was calibrated using bottom-hole temperature and vitrinite reflectance data from ten wells, taking into account the main phases of erosion/non-deposition and the variable temporal and spatial heat flow histories. Changes in sediment supply and depocentre migration through time and their relationship with tectonic setting evolution were studied in detail. The modeling results indicate the major role of the Zagros orogeny on controlling burial and thermal evolution as well as hydrocarbon migration and accumulation. The Binak Trough and Northern Depression, a continuation of the southern Iraq depression, were identified as local hydrocarbon generation kitchens. Early oil window maturities for two important source rocks, i.e. the Neocomian and Albian were reached between the Late Cretaceous (90 Ma) and the Early Miocene (18 Ma) at different locations in the kitchen areas within the southern Mesopotamian Basin. Hydrocarbon generation may continue at the present-day. Fluid flow modeling revealed further information regarding migration patterns and their variability in the region. The direction of hydrocarbon migration and accumulation is mainly controlled by the kinematics of the structural highs. During the Late Cretaceous to Miocene, southward deepening of the basin directed most hydrocarbon migration towards the northern part. The latest phase of the tectonic activity during the Miocene and tilting and deepening of the horizons towards the northeast resulted in a change of the main direction of hydrocarbon migration towards the south. The results further support the simultaneous presence of two principal time-related migration/accumulation processes, i.e. classical migration following (structural) trap formation and re-migration from former reservoirs into later, newly formed structures. Understanding the timing of migration events can greatly help to explain both hydrocarbon accumulation and exploration failures. The findings in this thesis provide a large-scale picture of different petroleum systems and their extension in the region of the Persian Gulf and explain different processes controlling the distribution of oil families. The results can reduce future charge-related exploration risks in the region, especially for the stratigraphic and combined structural-stratigraphic traps. This study also provides some hints for future successful hydrocarbon exploration.

Institutions

• Division of Earth Sciences and Geography [530000]
• Institute for Geology and Geochemistry of Petroleum and Coal [532410]