3D Static Modeling of Complex Fluvial / Tidal Channels and Log based Sequence Stratigraphic Framework for Pab Sandstone and Lower Ranikot in Loti Field

Abdul Rauf Mirza¹, Nasir Hamim¹, Agha Hassan Akram² Muhammad Nawaz Bugti², and Ammar Ahmad²
¹Oil and Gas Development Company Limited
²Schlumberger

The Pab Sandstone in Loti Field has been interpreted to represent near shelf fluvial systems which may transit to slope channels further west of Loti Field. The logged interval of Pab Sandstone shows a lower heterolithic succession i.e. Pab Sandstone 2 and more homogenous channelized sands in the upper interval of Pab Sandstone 1. The two classified levels of Pab Sandstone show single stacked (isolated) channels in Pab Sandstone2 while Pab Sandstone 1 shows multi stacked / amalgamated channelized sands. The amalgamated channelized sands in Pab Sandstone 1 show an aggradational profile on the basis of GR and have been interpreted to represent most likely a Highstand Systems Tract (HST), with a possible Sequence Boundary (SB) on top whereas the isolated poorly connected channel sands in Pab Sandstone 2 represent most likely transgressive sands in a Transgressive Systems Tract (TST), this also shows high intensity of floodplain events may act as localized barriers to fluid flow / heterogeneity. Loti 3 and 7 are the only wells which show the maximum thickness and amalgamation of channelized sands, this localized event pinches sharply in the neighboring wells has been interpreted to represent a localized incised valley.

The Lower Ranikot represents tidal channel setting for the Loti Field, with one amalgamated channel unit i.e. Tidal Multi Stacked (TMS) which represents Highstand Systems Tract (HST) is the main producer from the Lower Ranikot in Loti Field. It is important to mention here that the Lower Ranikot shows a paleo reversal for the sediment flow direction after the Late Cretaceous sediments of Pab Sandstone. The influence of Tidal / Tide dominated shelf let to the formation of tidal inlets with a possible tide direction of SW to NE.

Realistic 3D geological modeling of complex Pab Sandstone and Lower Ranikot channels was achieved by adopting high intensity layering scheme which captured the heterogeneity at a 2m scale in the fine model.

The complex fluvial / tidal channels of Pab Sandstone and Lower Ranikot were modeled in an innovative way using Sequential Indicator Simulation where the major and minor directions of variograms were selected in a way which captured the true geomorphology of the fluvial / tidal channels, in terms of channel thickness, width and meander belt widths.

AAPG Search and Discovery Article #90160©2012 PAPG/SPE Annual Technical Conference, 3-5 December 2012, Islamabad, Pakistan.