The Mananda Anticline, Papua New Guinea: A Third Oil Discovery, Appraisal Programme and Deep Potential

Abstract

The Mananda Anticline is one of the larger structures in the Papuan Fold Belt at 40 km long, 15 km wide and up to 2000m high. It is >20 km from the nearest road and airstrip, is deeply karstified, covered in equatorial jungle and is regularly in the clouds. The stratigraphy comprises 1 km of Miocene limestone, above 1 km of Cretaceous shale seal overlying earliest Cretaceous Toro and Digimu sandstone reservoirs and inferred Jurassic source rocks. The size of the structure suggests basement inversion and hence deep sub-thrust plays, but wells to date have been confined to the hangingwall where they have encountered thin-skinned structures and transported old normal faults. Since 1971, nine wells had been drilled along the topographic crest, including the SE Mananda-1 oil and gas discovery in 1991. Between 2000 and 2005, six moderate-quality seismic lines were acquired as well as additional field data, including Sr isotope dating of the surface limestone. The seismic, surface dips, Sr dates and structural dips in the Mananda 3X/4X wells all indicated that the structural crest was SE of the topographic crest. In 2010–11 the Mananda 5 well was drilled 1.5 km south of Mananda 3X and tested oil and gas in the Toro sandstone reservoirs, which were 400mTVD higher than in Mananda-3 and probably separated by an old normal fault. The Mananda 6 well was drilled in 2013 as an appraisal well to the Mananda 5 discovery and discovered the third separate field on the Mananda Anticline, with 2 new oil columns intersected down dip of the Mananda 5 block discovery. In 2013/2014, the Mananda 7 appraisal well was planned to appraise the Mananda 6 discovery and de-risk the major structural, fault seal and compartmentalisation uncertainties. The resulting 5 boreholes, including 3 geological sidetracks, achieved the appraisal objectives and significantly increased knowledge of the trap geometry and structural evolution of the Mananda Anticline. The future of the Mananda Anticline remains bright with 3 discoveries to date, further untested hangingwall fairway prospects and potentially large sub-thrust, footwall targets. This paper will examine the exploration and appraisal phases of the Mananda Anticline, focusing on the geological and operational challenges faced in the 43 year history.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015