Investigating Cap Rock Efficiency of Laffan Shale Formation in Sirri Oil Fields, Offshore Iran

Abstract

This study investigates the sealing efficiency of the Laffan Shale Formation as the caprock of the Sirri oil fields. Available information sources from Laffan Formation include drillhole core samples, daily drilling and geology reports and petrophysical logs of drilled wells. Type and quantity of minerals are determined by direct and indirect methods. In the next step in order to study the distribution of minerals and fabric of the shale samples SEM photomicrographs are taken. Petrophysical characterization by mercury porosimetry and laboratory experiments to measure total organic carbon and cation exchange capacity of samples are the next steps.  Pore pressure of Laffan Formation is determined by using data obtained from both acoustic and resistivity logs. Laffan Formation in Sirri oil fields is a shale formation comprising kaolinte clay mineral and calcite and quartz cement. It has a very low permeability. Laffan is a relatively thin and brittle formation but the presence of organic-rich layers and being buried at deeper depth has improved the chance of its lateral continuity and can be classified as a good seal. This study shows that similar results are obtained from direct and indirect methods in determining type of and mineralogy and also indicates that good correlations is achieved when taking into account of  permeability and total organic carbon. The next purpose of this paper is to provide a research process that can be applied in similar geological settings.

Key Word: Caprock-sealing efficiency; Shale formation; Clay mineral; X-ray diffraction; Scanning electron microscopy; Ductility; Total organic content