Digital Rock Approaches to Estimate the Impact of Early Quartz Cementation in Miocene Deepwater Sands Niger Delta Basin, Nigeria

Abstract

Quartz cement forming as syntaxial overgrowths is one of the most abundant cement type in sandstones. The rim and occluding cements develop around the surfaces of frame work grains and fill up pore spaces with no preferred orientation with grain surfaces. Imaging the various forms of quartz cement generation and development in 3D as it increases through time will help in further evaluation and better understanding of a reservoir in deep water sands in Niger Delta Basin.Petrographic analysis was performed on 10 Samples with micron resolutions of 0.675 and 0.337 per pixel. Scanning Electron Microscopy (SEM) using the Cathoduluminiscence (CL) and Back Scattered Electron (BSE) was employed in delineating the detrital quartz from the syntaxial quartz cements. Image J Software and Scandium Software were employed in binarizing the BSE image samples and study the iteration porosity, final porosity and permeability. 3DSlicer software was employed to produce 3D images for better understanding of the impact of early cement in the deep water sands. Two Phase Flow Models was also generated for each samples to outlines the effect of cementation.Quartz cement reduces porosity and peremability significantly at early stages of quartz cementation. Small local quartz overgrowths do join and link together with increasing cement precipitation hence gradually impeding porosity and drastically reducing permeability. Modelled results showed similar trends and this is an indication that when analysing a top reservoir unit, once the cementation is more than 6% the possibility of it being a good reservoir is relatively low.