Sequence Stratigraphy and its relationship with Reservoir Quality at Sarvak Formation in one of Zagros Basin oil fields

Abstract

In order to investigate sequential stratigraphy and its influence on the reservoir quality of the Sarvak Formation (Sarvak Formation), some 3 wells which were drilled in one of oil fields in the Abadan Plain have were in this work. On the basis of evidences like palaeosoil, brecciation, meteoric porosity and karstification, 4 discontinuities were identified in the wells as: Lower Cenomanian discontinuity, Middle Cenomanian discontinuity, Cenomanian-Turonian and Middle Turonian discontinuities. With respect to the identified facies, discontinuities, gamma log diagram and core samples, 4 sedimentary sequences of 3rd order were identified in the wells as: The 1st sequence of Upper Albian, Lower Cenomanian age, the 2nd sequences of Middle Cenomanian age, the 3rd sequences of Upper Cenomanian age, the 4th sequences of through Middle Turonian age. The entire sequential boundaries are of SBI type as per the identified discontinuities, exclusive of the lower boundary of the 1st sequence which is of SB2 type. The facies which belong with the TST portion of the 1st and 2nd sequences are of low reservoir quality, whilst the TST of the 3rd and 4th sequences have good to high reservoir quality (owing to the presence of grain-supported rudistic facies). The HST of the 3rd and 4th sequences has the greatest reservoir quality in the study formation. In sub-discontinuities, notably in those of Upper Cenomanian and Cenomanian-Turonian boundary, reservoir quality has markedly risen due to the development of meteoric diagenetic processes, viz. karstification, moldic porosity and widespread and large vuggy solutions.