The Distribution of Cementation and Dissolution Processes in Relation to Sedimentary Facies and Disconformity Surfaces of the Sarvak Formation in One of Hydrocarbon Fields in Southwest of Iran

This study has been focused on the relationship between cementation and dissolution processes with depositional facies and unconformity surfaces of upper part of the Sarvak Formation (Cenomanian-Turonian and mid-Turonian unconformity surfaces), using core and thin section data from a key well. Based on petrographic studies, six facies related to lagoon, slope and open marine sub-environments were identified. The results of this study indicate that the dissolution and cementation processes have been occurred in several diagenetic stages. Dissolution of unstable skeletal grains under the effect of eogenetic diagenesis created extensive vuggy porosity. In addition, during the telogenetic diagenesis and in relation to unconformity surfaces, vuggy pore types within the grains and rock matrix have been developed. The distribution of calcite cement within the reservoir shows a close relationship with initial mineralogy of the skeletal grains, size of dissolution vugs as well as density and the width of the factures. Calcite cement occurs as drusy and blocky forms and with meteoric and burial source within the dissolution vugs and microfractues. Within the Turonian interval that has been situated below the mid-Turonian unconformity, due to the mud-dominated nature of lagoon and open marine facies, dissolution and cementation have insignificant distribution, and calcite cement is mostly observed in relation to fractures. In contrast, in the interval below the Cenomanian-Turonian boundary, these processes have more distribution due to the frequency of grain-dominated facies. The results of this study show that the nature of depositional facies has significant role on distribution of cementation and dissolution processes within the Sarvak Formation.