R. Eschard1, A. Aayub2, E. Albouy1, F. Gaumet1
(1) Institut Français du Pétrole, 92852 Rueil Malmaison Cedex, France
(2) Premier Oil Pakistan, Pakistan
ABSTRACT: Stratigraphic Architecture of Amalgamated Turbiditic Channel Complexes in a Passive Margin Setting : the Pab Range Outcrops (Mastrichtian), S.W. Pakistan
The Pab Formation is one of the most prolific reservoirs in Pakistan. In S.W. Pakistan, the Pab deltaic system, well developed in a platform setting eastward, passes westwards to slope deposits then to a thick turbiditic system. The margin, which is fully preserved in outcrops, provides a unique opportunity to understand the sequential evolution and the reservoir architecture of basin-floor fans in passive margin settings.
The growth-faulted margin architecture has been reconstructed in an outcrop profile 100 km long. The 1000 m thick turbiditic system completely pinched out southwards over the margin. Three types of turbiditic systems can be distinguished, from base to top : 1) massive amalgamated turbiditic channels corresponding to an initial relative sea-level drop, 2) channel-levee systems, time-equivalent to a regional transgression, and 3) a prograding system of lobes and channels, forming sand-sheets of great lateral extension, probably deposited during the delta progradation on the platform.
Excellent 3D outcrops allow the detailed reconstruction of the reservoir architecture in each of these turbiditic systems. Of particular interest is the architecture of the basal turbiditic channel complexes, which consisted of three main stacked channel belts. Each of these, 50m thick and around 10 km wide, resulted from the amalgamation of tens of sand-rich turbiditic channels. A single channel shows a basal erosional and by-pass surface, then a multistorey infill phase of coarse-grained material, and finally, a construction phase with the development of sandy levees. The abandonment of the channel was then marked by hemipelagite draping.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado