Mehdi Reza Poursoltani
Department of Geology, Mashhad Branch, Islamic Azad University
Iran
Title: Effect of diagenetic events on porosity: Early Cambrian sandstones, Lalun Formation as a potential reservoir, Iran
Biography
Biography: Mehdi Reza Poursoltani
Abstract
Across a large area of Central Iran, the Lalun Formation rests on older sedimentary rocks. Based on our study, three fluvial to shallow-marine facies associations of shale-sandstone and conglomerate are present. Elsewhere in the Middle East and North Africa, equivalent Cambrian clastic deposits contain hydrocarbon reservoirs, and this study presents the first analysis of porosity in strata of this age in Iran. The sandstones range from quartzarenite to arkose, feldspathic litharenite and rarely litharenite. Diagenetic events included compaction and pressure solution, cementation, grain fracturing, alteration, dissolution and replacement. Dissolution is prominent in the sandstones. The sandstones show variable degrees of compaction. Based on petrological and geochemical studies, we infer early, deep burial and late stages of diagenesis. A few porosity estimates from thin sections were high, and inspection shows that these more porous samples are either highly fractured or are unusually rich in partially dissolved feldspar. The bulk of the porosity appears to be secondary. Intragranular pores are prominent in feldspathic litharenites, especially as large spaces along cleavage planes and fractures. Intergranular pores are present locally where carbonate cements have been corroded; parts of these pores could be primary. Additional intercrystalline micropores are present between authigenic clay minerals and calcite and dolomite crystals. Microfractures are prominent within many grains. Those in quartz grains generally have been healed with silica, although some are filled with carbonate and iron oxides. Fractures form much of the porosity in some samples, and our assessment of porosity percent and type for these surface samples.