K.D. Nelson Lecture – Dr. Pedro Restrepo-Pace

The Department of Earth & Environmental Sciences in the College of Arts and Sciences presents the K.D. Nelson Lecture Series featuring guest speaker, Dr. Pedro Restrepo-Pace from Oil Search Ltd, Sydney Australia. His talk is titled: “Beyond Geometry: 2D structural thermo- kinematic models of the Papuan Fold and Thrust Belt”

The Papuan Fold Belt (PFB) exploration took off in 1986 with the Kutubu and immediately after with the Hides discoveries. About 7bboe later, it continues to deliver today with the Muruk discovery. Exploration has advanced on the back of extraordinary surface-related challenges, with an almost exclusively helicopter-supported operation. Mapping using remote sensing images calibrated by field geological campaigns and, to some extent, sparse 2D seismic data, delineated the first drilling targets. Surface information is hindered by topography, thick forest and heavy precipitation, making it very difficult to access. Seismic data in the fold belt continues to deliver mixed results in terms of subsurface imaging, which translates to problematic identification of subsurface traps.

The PFB depicts thin-skinned, thick-skinned and combined thick/thin-skinned related structural geometries generated by multiple detachments. The stratigraphic pile behaves mostly as a harmonic mechanical beam but recent discoveries and appraisal/development wells indicate strain partitioning occurs particularly at the Ieru Formation level. The implication of the latter is that in some instances surface structures do not directly relate to subsurface structural culminations. Furthermore, the linkage – geometric and kinematic – between the thick-skinned and thin-skinned structures continues to be an evolving matter of discussion amongst specialists. The kinematic story is faced with an additional obstacle: synkinematic sediments are rarely preserved in the fold belt. This discussion would be of academic interest if not for the fact that surface anticlines that involve our target reservoirs are being drilled-out and we are faced with finding hydrocarbons in deeper structural targets. We are relying on these deep targets to be the new frontier – not to mention the hinterland. Our more complex structures near or along the trend of a developed resource are ever more challenged in terms of defining them with our current seismic data and thus fall in the realm of “sound” structural interpretations or models. A compounding issue to the challenges previously mentioned relates to the economic viability of the discovered resource. There are two main drivers here: gas for LNG; and the geologic (and geographic) extent of the liquids “play” as it relates to existing facilities. There is a large uncertainty related to geological controls that yield gas-rich versus liquid-rich traps. This is where testing the thermo-kinematic history of our models and interpretations can provide insight into the controls of the hydrocarbon phase. Additionally, we could test alternate kinematic models, synkinematic/erosional models and these could be calibrated to known hydrocarbon discoveries. This presentation will illustrate the via calibrated and uncalibrated 2D case studies, the effect of structural evolution on maturation, charge and hydrocarbon phase in the PFB.