Heterogeneity of High Temperature Dolomite (HTD) Reservoirs in the Sarvak Formation, Anaran Anticline, Ilam, Islamic Republic

Spectacular outcrops of dolomite of hydrothermal origin are described from the Anaran Anticline, in the Simply Folded Belt of the Zagros Mountains, Ilam province, SW Iran. Dolomite replaces Cretaceous carbonates of the Upper and Lower Sarvak formation (Albian to Turonian). The typical paragenetic association includes a matrix replacing dolomite phase followed by a void-filling saddle dolomite. Both are interpreted to be of hydrothermal origin. The contact between dolomite and precursor lithology is typically sharp on the scale of the outcrop, with contacts being both stratigraphically, structurally and diagenetically (reaction front) controlled. Dolomite bodies in both the Lower Sarvak and Upper Sarvak have been described and sampled systematically in order to constrain lateral and vertical textural and poro-perm variations. Systematic collection of structural data has also been undertaken to evaluate the possible control of fractures (joints + faults) on fluid flow, and to place constraint on the timing of the dolomitisation event within the geological evolution of the Zagros Mountain belt. Comparison between fracture pattern inside and outside the dolomite bodies is taken into account to evaluate a possible impact on reservoir modelling.