Porosity Study of Paleocene Sandstone Reservoir Using Core and Petrography, Bintuni Basin (2011)



Natural gas reservoir sandstones of Paleocene interval in the Wiriagar Deep field, Bintuni Basin, Papua has very unique characteristics because in those intervals contained different porosity value. This research was conducted to identify the factors that affect the natural gas sandstones reservoir porosity in macroscopic scale and microscopic scale at the Paleocene reservoir and its influence to the porosity log value calculation. The core description method was used to determine vertical stratigraphic sequence of Paleocene interval. Petrographic analysis method was used to determine the mineralogy and rocks textures microscopically and correlated with the depositional environment to analyze the relationship between them and their influence to porosity. Paleocene interval at Wiriagar Deep field, Bintuni Basin, Papua based on its stratigraphy can be divided into 2members, there are Mud prone and Sand Prone. Sand Prone can be devided into 3 sub-members there are Upper Paleocene, Middle Paleocene and Lower Paleocene (Yoshino, 2000 in Marcou, J.A; Samsu, D., et al. 2004) and it has poor reservoir quality and heterogeneous turbidite sandstones reservoir (Kasim et al., 2000, and Yoshino et al., 2003 in Marcou, J.A; Samsu, D., et al. 2004). The Result from this research shows that the carbonate minerals domination was the most influential factor of the porosity value. All reservoirs in the Paleocene interval were dominated by carbonate cement, those were calcite and dolomite. Upper Paleocene and Lower Paleocene intervals had poor porosity value because it was
dominated by calcite cement and deposited in the distal submarine fan; while in the Middle Paleocene
interval was dominated by dolomite that was deposited on the proximal submarine fan.
Diagenesis had an important role to the presence of carbonate minerals in the sandstone and rocks dolomitization. According to porosity calculation from density log that had been calibrated with core porosity, then resulting the different formulation of the linear regression porosity equation due to different grain density.Equation for the Upper Paleocene {Φupper=-0,0146847+1,05586x(Φcore)}, Middle Paleocene {Φmiddle= 0,0329111+0,856568x(Φcore)}, Lower Paleocene {Φlower = 0,00809959+0,889382x (Φcore)}.
Keywords:Carbonate, Dolomitization, Paleocene,Porosity, Sandstone, Turbidite.


Author : Arief Satrio Prihanasto, Hadi Nugroho, Prakosa Rachwibowo