Exploration in Thrust Belt Area, "A Case Study from Jairampur, Arunachal Pradesh, India"

Borthakur, Ajoya N.; Bordoloi, Amitav
NEF Project, OIL INDIA LIMITED, Dibrugarh, India

The Assam Shelf, Naga Schuppen belt and the Assam-Arakan Fold belt are the prime geological feature of Assam-Arakan shelf-slope basinal system. Exploration history of the Upper Assam and fold belt areas dates back to late nineteenth century (1856-1889) when Asia's first commercial oil fields were discovered by the Burma Oil Company in Digboi and Makum. The Jairampur area is situated at the Himalayan foot hills in the eastern fringe of Arunachal Pradesh of NE part of India and lies within a zone of regional NE-ENE structural trends immediately north of the strongly deformed "Schuppen" zone.

The geological importance of the Jairampur area is the exposure of Barail Group of rocks (which is hydrocarbon prolific in entire Assam-Arakan basin) and has come up due to the thrusting near to the Indo-Burmese plate margin. Several oil fields have already been established in and around the study area. Presence of Oil (32.60 API) was reported from a shallow well (364 m) drilled over an antiform by Geological Survey of India (GSI) in 1986.

During19th centuries no of shallow wells (around 300m) were drilled in Digboi area and produced from Tipam Sands using Clayey-water based mud and slotted liner completion for production. During 1998 Oil India Limited (OIL), drilled it's first well, Jairampur#1. However, due to bad hole condition owing to the geological complexities, the well could not be tested properly. In 2009, Mineral Exploration Corporation Ltd (MECL) drilled a shallow well (335m) from the same plinth mainly to evaluate shale-oil prospectivity of the area and encountered two gas kicks at a shallow depth (154m and 162m). Analysis of Gas samples and core samples confirmed the gas to be thermogenic in nature. Encouraged from this results, coupled with the afresh log interpretation of well Jairampur#1, in 2010,OIL drilled a shallow well of 700m from the same plinth of well Jairampur#1 using the conventional drilling and completion methods to probe the supra thrust hydrocarbon prospectivity of the area, but commercial hydrocarbon discovery could not be established.

Detailed log interpretation of the shallow well including FMI log interpretation opens up few facts with regards to the adopted drilling and completion technology in thrust-fold belt areas. This paper attempts to technically analyze and suggests the selection of drilling and completion technology for successful drilling and testing of wells in thrust-fold belt areas in future.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012