Characterization Of Thinly-Bedded Reservoirs: A New Approach In A Sparse Logged Area

Frass, N.I. (Schlumberger) | Coil, Carolina (Maraven) | Gamero, H. (Maraven) | Blyant, I. (Schlumberger-Doll Research Center)


The results of the high resolution logging throughout the Lagunillas Inferior reservoir, in the VLD- 1112 well in the Bloque IV area of Lake Maracaibo, Venezuela. are described in this work. Parts of the reservoir were previously overlooked due to the use of simple petrophysical evaluation using very sparse old logs ( SP. Or. Res. ) which show high water saturation''s ( Sw> 0. 5) and very low porosity''s (?<0. 1). In the intervals with thin laminations, the use of microresistivity images define the clean sands of the shaly section, where pressure tests were taken. With these logs, was possible to define local vertical permeability barriers, which separate the productive well known high permeability zones from other zones which could represent additional reserves. A new sedimentological model was defined using core information and the high resolution microresistivity images, subdividing the reservoir into 12 layers, replacing the old simple 3 layer model. Open hole evaluation of the new well and cased hole measurements using a saturation log indicate that gas has preferentially moved into high permeability zones, leading to bypassing of oil in moderate to low'' permeability layers. With this study the possible amount of oil which was overlooked by Maraven could be about 23% compared to the estimations derived from the simple petrophysical evaluation, in the shaly sands. which have a big impact in future completion programs. Finally these results were used to locate the first horizontal well in Bloque IV area.