Challenges on Building Representative 3D Static Models under Subsurface Uncertainties for a Giant Carbonate Field in Central Luconia, Offshore Sarawak

Abstract

This paper focuses on the challenges in building representative 3D static models under all subsurface uncertainties for a green field. The case study is based on a giant carbonate gas field, appraised with a few partially penetrated wells in Central Luconia province, offshore Sarawak, Malaysia. With very limited hard data for reservoir characterization, knowledge from Central Luconia literature and nearby field analogues had to be used together with the 3D seismic data. Standard geostatistical methodology was used to integrate the subsurface interpretations and to capture the identified subsurface uncertainties, i.e., structural framework, fluid contacts, facies distribution, petrophysical interpretations, saturation function, permeability prediction etc. Some of the key challenges, findings and results are listed below; How to quantify a long list of subsurface uncertainties with a manageable number of 3D static models? Full factorial design was used together with expert knowledge to limit the total number of uncertainties. How to quantify the structural uncertainty and the challenge in building geocellular grid for carbonate platform and pinnacle buildup? Even with very limited core data, the lithofacies interpretation was completed and incorporate 3D seismic data as representative 3D trend for distributing the expected carbonate facies. It is a massive challenge in characterizing the petrophysical properties for carbonate reservoirs, as heterogeneity (both primary and secondary processes) can be difficult to predict. Similar porosity seen in seismic inversion might have different flow behavior in permeability. Sub-seismic geological features like flooding surfaces might be acting as vertical baffles, which must be modelled as an important element of the geostatistical models. Reservoir characterization and uncertainty quantification will allow an improved understanding of the reservoir, and the results will guide the data acquisition program in subsequent appraisal campaign. This case study will enrich the knowledge within the Central Luconia carbonate province, and a discovery in a mature basin is still a massive challenge for reservoir characterization under uncertainties.