Integrated analysis of a mixed carbonate-siliciclastic reservoir in the Iranian Asmari intra-shelf Basin: Insights from well data, seismic profiles, and outcrops

Abstract

A multidisciplinary approach (facies analysis, biostratigraphy, cyclostratigraphy, and seismic stratigraphy) was employed in this case study to assess the depositional geometry and sequence stratigraphic architecture of a mixed carbonate-siliciclastic reservoir in the Oligo-Miocene Asmari intra-shelf basin (SW Iran). The integration of both the surface and subsurface datasets provides an excellent opportunity for this analysis. Previously, this reservoir was assumed to consist of flat-lying strata with no significant gradient, primarily because of the emphasis on the lithostratigraphy correlation technique and, to some extent, biostratigraphy resolution. However, these aspects have been discussed and improved in this study. Subsurface data, including well data and seismic data, correspond to the southern flank of the Asmari Basin (Kupal Oil Field), which was compared with the exposed sections (Lar and Dashtak anticlines), exceptionally found in its northern counterpart. The Oligo-Miocene rock successions studied here are Chattian-Burdigalian in age and comprise 14 sedimentary facies distributed along different settings of a depositional profile, ranging from deep-water basin (F.1, F.2) and shallow-water carbonate platform (F.3 to 13) to continental settings (F.14). Using cyclostratigraphy, 19 significant timelines were identified along the oil field and calibrated with age dating and seismic data. The integration of well-to-seismic data ties and outcrop observations allowed for the identification of five seismic facies and four seismic packages. Consequently, the combination of these techniques and methods established a sequence stratigraphy architecture comprising four 3rd-order depositional sequences (sequence. I, II, III, IV). The transgressive system tract (TST) and highstand system tract (HST) are the main packages identified within these sequences. Due to the resolution of seismic data and the spatial position of the Oligo-Miocene depositional setting in the Kupal Oil Field, Lowstand system tract (LST) can only be observed in the sequence. I. within this sequence, three 4th-order depositional sequences (cycles. I-a, I-b, I-c) were hierarchically nested into the HST package.