--> Oil Biodegradation Prediction: Applications of BDI Method in the Global Deepwater Areas, by Alan Z. Yu and Tim Huang; #90062 (2007)

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Oil Biodegradation Prediction: Applications of BDI Method in the Global Deepwater Areas

Alan Z. Yu and Tim Huang
BHPBilliton Petroleum, 1360 Post Oak Blvd., Houston, TX, 77056

Global drilling results highlight the vital economic importance of hydrocarbon fluid quality and biodegradation, particularly in the deepwater areas where drilling and development costs are high. Oil field data show a complex distribution of biodegraded oil occurrences in the deepwater areas. Some fields, in which the present-day reservoir temperature is as high as 80C, contain biodegraded oils; whereas in other fields, reservoirs which are cooler than 50C contain relatively fresh and unaltered oils.

It has been long recognized that temperature plays a key role in bio-degradation, as most biodegraded oils occur at temperatures of <80C. However, most studies have not integrated the burial and charge histories of the fields.

In 2001, Yu et al (World Oil, 2001) proposed the Bio-Degradation Index (BDI) approach to predict the biodegradation risk and fluid quality in the reservoir. Instead of using only the present day temperature, which can be misleading and usually overestimates biodegradation, BDI considers both the temperature history and residence time in the reservoir based on advanced basin modeling which define rock permeability and migration timing from source to reservoir. Using the temperature versus residence time plot generated from basin modeling, the area below the critical temperature (Tc), above which bacterial activity is not significant, indicates the bio-degradation risk.

This method has since been successfully applied in BHPBillition in the global pre-drill fluid prediction. The empirical relationships between BDI and oil API gravity have been refined based on more oil data. Furthermore, a three-dimensional BDI and oil API prediction module which allows predictions in any time and space for multiple reservoirs, was developed by BHPBillition this year. Application examples will be demonstrated in this paper.

AAPG Search and Discovery Article #90062©2006 AAPG Hedberg Research Conference, Veracruz, Mexico