Predicting the Temperature of Hydrocarbon Expulsion from Oil Asphaltene Kinetics and Oil Source Correlation: A Case Study of South Cambay Basin, India*

Abstract

The oil asphaltene has structural similarity with parent kerogen. The kinetic data based on actual data from the reservoir oil is found to be a better method in reducing the risks associated with oil exploration and assessing the petroleum generation characteristics. An attempt has been made to assess the petroleum expulsion temperature/timing for predicting the kitchen in South Cambay Basin using oil asphaltene kinetics. The Gandhar field covers an area of about 800 km2 and is located on the rising northwestern flank of the Broach depression in the Jambusar-Broach block. The Olpad Formation was deposited during the Paleocene. The Eocene Cambay Shale, unconformably overlying the Olpad Formation, has excellent source rock characteristics. The Hazad Member of south Cambay Basin is a major hydrocarbon reservoir, and it consists of 12-individual sand units from GS-XII-GS-I. The oil asphaltene kinetic/expulsion temperature studies have been carried out on Rock Eval-6 instrument having Optikin and GENEX-1D software. The saturate/aromatic biomarkers data and fatty acid studies are also integrated with the present study. The Gandhar oils are placed into three groups. The group C oils (GS-XII & GS-XI) indicate that the temperature of expulsion from asphaltene kinetics (Tasph 90-112oC) corresponds to isothermal sequence of source rock from 2500 to 800m). Group B (GS- IX-IV) oils indicate that Tasph (119-132oC) corresponds to isothermal sequence of 2900 to 3200m, whereas Group A oils (GS-III-I) indicate that expulsion temperature (141-142oC) corresponds to the 3600-3800m sedimentary sequence. Asphaltene expulsion temperature data has shown positive correlation with biomarker maturity data and fatty acid distribution pattern and good matching with actual identified source rock units. The expulsion temperature determined by light hydrocarbons has no correlation with asphaltene expulsion temperature. This study will be very useful in fine-tuning the existing petroleum system where source rock data is not available.