Investigating the relationship between the Khami reservoir horizon in the Chilingar and Garangan oilfields in the Southern Dezful Embayment using surface geochemistry
Abstract Understanding reservoir connectivity is critical for reducing exploration risk and optimizing field development. This study uses surface geochemistry techniques to investigate the relationship between the Khami reservoir horizon in the Chilingar and Garangan oilfields, located in the Southe...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
University of Isfahan
2025-09-01
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| Series: | Journal of Stratigraphy and Sedimentology Researches |
| Subjects: | |
| Online Access: | https://jssr.ui.ac.ir/article_29537_037e8325b42cc60dc37a7e98d1c4c315.pdf |
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| Summary: | Abstract Understanding reservoir connectivity is critical for reducing exploration risk and optimizing field development. This study uses surface geochemistry techniques to investigate the relationship between the Khami reservoir horizon in the Chilingar and Garangan oilfields, located in the Southern Dezful Embayment. A total of 154 surface soil samples were collected from the field closures and the inter-field area. These samples were analyzed using acid extraction and fluorescence analysis to evaluate hydrocarbon migration, identify geochemical anomalies, and assess potential reservoir connections. Hydrocarbon gas ratios (C1/C2, C2/C3, and C1/(C2+C3) vs. C2/(C3+C4)) revealed that surface hydrocarbons are primarily oil-derived. The composition and ratios of samples from the inter-field area closely matched those from the closures, suggesting a shared source. Fluorescence analysis provided R1 ratios (three-ring to two-ring aromatics) and inferred an average API gravity of 36˚, indicating high-quality, light oil consistent with field samples. Geochemical anomaly maps revealed similar hydrocarbon compositions and quality between the two fields, supporting a likely connection through a saddle structure. These findings demonstrate the effectiveness of surface geochemistry in assessing reservoir connectivity and reducing exploration risks.Keywords: Surface geochemistry, Reservoir connectivity, Chilingar and Garangan oilfields, Acid extraction, Fluorescence analysis IntroductionDiscovering new hydrocarbon resources and enhancing the production efficiency of existing fields remain critical challenges for global oil and gas producers. Until the 1940s, oil drilling was primarily based on visible surface hydrocarbon seeps (Link 1952; McGregor 1993). Hydrocarbon seeps refer to the surface or near-surface accumulation of light or high molecular weight hydrocarbons, often indicating the presence of subsurface reservoirs. The global demand for energy in the 20th century pushed oil exploration from empirical methods toward more scientific approaches. Surface geochemistry, introduced in the 1930s, became a significant tool for oil exploration, examining direct and indirect hydrocarbon seepage linked to deep reservoirs (Tedesco 2017). In Iran, surface geochemistry was initiated in 2014 by the Energy Researchers Ariana (ERA) company. After decades of oil production in the Zagros Basin, better reservoir management is crucial to maximizing efficiency. The Chilingar and Garangan oilfields, located in the southern Dezful Embayment, are closely situated and separated by a saddle structure. Reservoir studies show connectivity between the lower and upper Khami reservoirs in these oilfields. Understanding this connection is vital for planning field development and identifying weakly connected reservoir zones. This study uses the soil gas method, a direct surface geochemistry technique, to analyze reservoir connectivity and hydrocarbon-rich zones. The findings aim to guide efficient production management, reduce drilling risks, and advance field development strategies at lower exploration costs.Materials & MethodsThis study utilized direct geochemical techniques, including acid extraction and fluorescence analysis, to detect subsurface hydrocarbon reservoirs. Surface prospecting relies on vertical hydrocarbon migration, which creates detectable seeps and geochemical anomalies. Sampling followed pre-existing geophysical lines, with 154 soil samples collected across 35 lines. Acid extraction analysis measured light hydrocarbons (C₁–C₅) released via a hydrochloric acid reaction, while fluorescence analysis quantified polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) and UV excitation. Both methods identified surface anomalies linked to potential subsurface accumulations, underscoring their utility in hydrocarbon exploration (Schumacher 1996). Discussion of Results & ConclusionsThis study focused on the Chilingar and Garangan oilfields, located in the southern Dezful Embayment, using surface geochemistry to investigate hydrocarbon seepage and assess reservoir connectivity between the two fields. Hydrocarbons typically migrate vertically due to high subsurface pressure, with stratigraphic layers, faults, and fractures facilitating this movement. In oil and gas reserve areas, light hydrocarbons in sediments indicate a potential reservoir, with higher concentrations suggesting economically viable accumulations. If anomalies between the two fields match those over the anticline, it supports the hypothesis of a hydrocarbon connection. To determine hydrocarbon content, soil samples were analyzed using acid extraction (AE) and fluorescence methods. Acid extraction showed that methane-to-ethane (C1/C2) and ethane-to-propane (C2/C3) ratios point to oil-associated hydrocarbons (Pixler 1969). The area between the two fields displayed similar hydrocarbon concentrations to those above the fields. Standard ratio charts, such as C1/(C2+C3) vs. C2/(C3+C4), confirmed an oil origin for most hydrocarbons, with anomalies indicating high concentrations between the fields. Fluorescence analysis revealed that inferred API gravity and aromatic hydrocarbon ratios (R1) suggest high-quality hydrocarbons, including oil and gas condensates. The changes in the interpolated parameters reveal the presence of major faults in the region and the influence of the north-south trending fault in the western part of the Garangan oilfield. Areas surrounding the old wells in the Chilingar field exhibit a lower value of the inferred API index in the interpolated map, due to reservoir pressure depletion caused by prolonged production. The results of both methods strongly indicate the presence of liquid hydrocarbons between the fields, supporting the likelihood of a reservoir connection through a saddle structure. These findings are crucial for efficient exploration, reducing risks, and guiding field development. |
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| ISSN: | 2008-7888 2423-8007 |