Studi Diagenesis Batupasir Formasi Kerek pada Daerah Kaliputih dan Sekitarnya, Kecamatan Singorojo, Kabupaten Kendal, Jawa Tengah

Abstract

The forming of sedimentary rock is always associated with the process of diagenesis, which affected by the 3 main process of physical, chemical, and biological. This process is profoundly influence the characteristic of sedimentary rock, including the structure, texture, cementation type, pore fluid, and mineral composition. Hence, it is so important to know or learn the stage of sandstone diagenesis, especially in the Kerek Formation to mark the correlation between diagenesis and petrophysical sandstone, and to identify potential significant diagenesis in the effectiveness of the exploration and exploitation sandstone reservoir. The purpose of this research is to identify the stage of diagenesis, the type of cementation, diagenesis environment and the relationship between diagenesis stage and sandstone porosity. The methods used in this research are survey method and data analysis method. The survey method includes the making of cross-sectional measured stratigraphy and data analysis method includes petrographic and scanning electron microscopy (SEM). The sedimentary structures found in the carbonate sandstones are burrows, convolute ripple lamination, graded bedding, parallel lamination, cross lamination, current ripple lamination; which are features of turbidity deposition (Bouma sequence). Based on the petrography analysis results for sample P 01 and P 02 experienced compaction, cementation, dissolution, and bioturbation, with a porosity value of 1 %. Sample P 03 experienced compaction, cementation, dissolution, and bioturbation, with a porosity value of 7 %. Sample P 04 experienced compaction, cementation, and dissolution, with a porosity value of 1 %. Sample P 06 experienced compaction, cementation, dissolution and replacement, with a porosity value of 5 %. Sample P 07 experienced compaction, and cementation, with a porosity value of 30 %. The Litology type in the research area was calcarenite (the dominant shell fragments), the litology names are packed biomicrite (Folks, 1959; in Nichols, 1999), and packstone (Dunham, 1962; in Nichols, 1999). Carbonate sandstones predominantly feldspar and quartz minerals and the litology names are carbonate quartz wackes (Pettijhon, 1975; in Nichols, 1999), and carbonate feldspathic arenite (Pettijhon, 1975; in Nichols, 1999). There are three minerals type of cement in carbonate sandstones which are calcite cement, chlorite cement and pyrite cement. Thus, it can be concluded that the diagenesis stages carbonate sandstones experienced in the research area are cementation, dissolution, replacement bioturbation, and compaction, so that the more stages of diagenesis that occurs in carbonate sandstones will result in reduced porosity and progressively up at for formation stratigraphy excelsior sediment rock assess his porosity that is equal to 1%, 5%, 7% and 15%. The type of cement minerals in the carbonate sandstone influence porosity, especially in carbonate sandstone which there are chlorite cement that have small porosity value of 1%, 5% and 7%. The environment of diagenesis in carbonate sandstones that is phreatic and burial experienced of eogenesis process, mesogenesis process and telogenesis process.