Oligocene/Deep Targets in the North Malay Basin - The Challenges of HThp Exploration

Groot, Rob¹; Seerungphungsan, Songsak²; Phimthong, Suraphan²; Ponthanom, Piyanuch²; Krisadasima, Kanjana²; Kwaela, Chaiwat²
¹Bongkot Asset, Total E&P Thailand, Bangkok, Thailand.
²Bongkot Asset, PTTEP, Bangkok, Thailand.

In 1973 the first well in the area that was later to become the Greater Bongkot North (GBN) production license operated by PTTEP (Total and BG partners) in the Gulf of Thailand was spudded. This well penetrated dark grey thin bedded tight sandstones and shales in it's deepest sections. No oil or gas shows were associated to these reservoirs that were part of what was to be named Formation 0 (FM0). It took until 1994 to drill another FM0 penetration. This second deep well gave encouraging results and flowed significant volumes of gas from FM0. However, less successful follow up delineation wells and also cost and risk issues associated to high temperatures (>200degC) and overpressures slowed down the exploration and delineation pace for the deep Oligocene play. Today a total of only 4 exploration, 7 delineation and 2 dedicated development wells have reached the Oligocene FM0 in the Bongkot part of the North Malay Basin. Most of them only penetrated the uppermost part of FM0 where a relatively homogeneous stratigraphy similar to the one encountered by the first well described above was encountered. Only one recent well has reached deeper stratigraphic levels providing a much needed calibration point. The main challenges associated to the deep exploration are the following: 1) The high temperatures, typically above 200 degrees C but sometimes as high as 255 deg. C @TD, require special hardware and special tools for data acquisition (logging) and testing. This leads to significantly longer lead/preparation times, 2) Overpressures are observed. There appears to be an unexplained big difference between shale and reservoir pressures creating a potential drilling hazard, 3) The seismic data has not been processed for this deeper Oligocene interval, rather the overlying Miocene target interval, and as a result attribute maps leave a lot of room for interpretation, 4) Deep burial and compaction of the possible reservoirs as well as diagenetic processes and/or reservoir connectivity have possibly degraded permeability and productivity potential.

Bongkot is now a mature field at the Miocene levels; the exploration of the deep Oligocene play is risky and technically challenging, but it is well inscribed in the global strategy of the operator to fully explore and exploit hydrocarbon potential of the remaining plays in Bongkot.

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