Influência dos processos diagenéticos na porosidade dos arenitos da formação iborepi, bacia de lavras da mangabeira, estado do Ceará

Abstract

Analyzes of diagenetic processes that acted on the sandstones of the Iborepi Formation were performed on samples of rocks from the Lavras da Mangabeira Basin. The petrology and the diagenesis of these sandstones is little known, mainly regarding the diagenetic processes that acted on the original porosity of these rocks that can be studied as analogues of oil basin reservoirs. Petrological and petrographic studies were carried

out on nine slides in order to assess the diagenetic processes that impacted the original porosity of Iborepi sandstones. The processes found were: clay infiltrated as cuticles involving grains and interstitial microcrystalline aggregates; compaction generating fractures in grains, pseudomatrix in ductile lithoclasts, bent micas, and dissolution of grains resulting in concave-convex and sutured contacts; growth precipitation secundary (overgrowths) and projections of quartz (outgrowths), kaolinite, smectite and chlorite; alteration and replacement of potassium, muscovite and biotic feldspar by kaolinite, illite and chlorite. The porosity of these rocks is predominantly intergranular, with an average of 14%, but secondary porosity occurs due to fracture and dissolution of primary grains and shrinkage of clay. In general, the primary porosity of Iborepi sandstones was reduced mainly by clay cementation,  mechanical and chemical compaction, and clay infiltration, impacting its quality as a hydrocarbon reservoir.

Keywords: Sandstones, porosity, reservoir.