INBIGS, ONGC Ltd., A&AA Basin, Jorhat stumah_pahari@rediffmail.com P-224 Evaluation of Hydrocarbon Prospectivityby Non-seismicMicrobial Anomalies Method in Khubal Area of Tripura, India S. Pahari*, R.Tripathi, Ashok Kumar and Subir Kumar, ONGC Summary Geomicrobial hydrocarbon prospecting methods which involves quantification and distribution of hydrocarbon utilizing bacteria (HUB) in surface sediment has become a cost effective and new methods of the modern petroleum exploration that enhances exploration success and reduces finding costs. It offers more effective way of hydrocarbon finding and improving discovery rates in integration with other geophysical and geological exploration techniques. Evaluation of hydrocarbon prospectivity has been carried out in this present work for prioritizing leads and prospects on the basis of microbial anomalies in Khubal area of Tripura and understanding the genesis of the anomaly and its relationship with oil and gas accumulations by non- seismic microbial anomalies method. A total of 20 no.s microbial anomalies, potential hydrocarbon migration indicator have been delineated in study area which may be considered as potential hydrocarbon migration pathways /seepage. Microbial anomalies found in study area have been integrated with geological structure map in time which discloses the presence of microbial anomaly in the vicinity of faults. Possible hydrocarbon sources could be in the distant northern part of study area and hydrocarbon migration /seepage occurs primarily through various faults and cross faults. Microbial anomalies are found to be concentrated on both side of cross fault-2 (CF2) and mostly terminated within cross fault-6 (CF6) which indicates possibly maximum hydrocarbon migrations around both side of cross fault-2 (CF2). Only minor anomalies/ migrations could have been observed in the south east part of study area crossing CF2. However no anomalies have been observed in the south and south west part of study area crossing CF2. Therefore, areas on either side of CF2 seem to have good hydrocarbon prospectivity but south and south west part of study area are seem to be poor hydrocarbon prospectivity. Occurrence of delineated microbial anomaly in the vicinity of faults show authentication of this non seismic technique with Geophysical and geological exploration techniques and hydrocarbon migration in the study area seem to be driven by folding and faulting. Keywords: Geomicrobial hydrocarbon prospecting, Non seismic method Introduction In petroleum exploration, various useful techniques involving geology, geophysics, geochemistry and geomicrobial studies are employed to get various indirect information regarding presence/absence of hydrocarbons in sub-surface. Geo-microbial hydrocarbon prospecting is an indirect, economical and reliable method for evaluating exploration leads and prospects based on the principles that lighter hydrocarbons existing below the sub- surface, escape to the earth’s surface due to micro/macro seepages from the reservoirs and create favorable conditions for microorganisms to grow and develop at the surface. It helps us to define individual prospects and also evaluate remote exploration areas based on direct and positive relation between hydrocarbon concentration in soil and spread of hydrocarbon utilizing bacteria (HUB) which feed on light hydrocarbons in surface soil samples can be measurable and reproducible. It offers more effective way of hydrocarbon finding and improving discovery rates in integration with other exploration techniques. Evaluation of hydrocarbon prospectivity has been carried out in this present work for prioritizing leads and prospects on the basis of microbial