IPTC-11191-MS-P

IPTC 11191 The Control of Fracturing and Dolomitisation on 3D Reservoir Property Distribution of the Asmari Formation (Oligocene-Lower Miocene), Dezful Embayment, SW Iran Adnan A.M. Aqrawi and Ole Petter Wennberg, Statoil Copyright 2007, International Petroleum Technology Conference This paper was prepared for presentation at the International Petroleum Technology Conference held in Dubai, U.A.E., 4–6 December 2007. This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor Society Committees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, IPTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abstract The Asmari Formation (Oligocene-early Miocene) is the most important reservoir in the oilfields in the Zagros foreland of the Dezful Embayment of SW Iran. The carbonate reservoirs of the Asmari Formation are characterized by low matrix permeability, and effective drainage is dependent on the occurrence of open fractures. The fractures have been formed during the Zagros Orogeny since late Miocene, which is also responsible for the geometry and formation of NW-SE trending anticlinal traps. Dolomitisation is another factor controlling reservoir qualities as dolostones in general have higher porosities than limestones.

stratigraphic cycles deposited during early transgression, and these have better reservoir quality, particularly if leached or coarsely crystallined. General Geology The Dezful Embayment of SW Iran is one of the rich oil provinces in Middle East, see Fig. 1. The structural and stratigraphic features of Dezful Embayment have been investigated continuously since mid-last century (e.g. Haynes and McQuillan, 1974; McQuillan, 1985; Blanc et al., 2003, Wennberg et al. 2006 & 2007, Ehrenberg et al 2007). Most oilfields in this region are asymmetric anticlines having NWSE trend as in Fig. 1. 49

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The fractures are typically stratabound and sub-perpendicular to bedding. The density and dimension of fractures are controlled by the mechanical stratigraphy, which is controlled by the depositional environment and cycles. In the platform top sequence, the Dunham’s (1962) texture classification appears to be the most important factor controlling the Fracture Intensity (FI) rather than the mechanical layer thickness. Mud supported textures (mudstone and wackestone) have higher FI than grain supported (packstone and grainstone). The fracture density is high in the vicinity of faults. Two main types of dolomite fabric are recognised; finely crystalline pervasive dolomite (