Mineralogical studies of tertiary shales from k-well Akiri field, Niger delta

Abstract

Shale cuttings from the K-Well (Akiri) in the Niger Delta have been analysed for their mineralogical and geochemical compositions. Analysis of the 2m portion from the 2183, to 3,720m stratigraphic period was performed using X-ray diffraction, inductively coupled plasma optical emission (ICP-OES), and mass spectrometry (ICP-MS). Many types of clay minerals exist, although kaolinite and chlorite predominate. From 3250-3720m in altitude, the illite/smectite composition shifts from a phase with 32% illite layers to a phase with 82% illite layers. Shallow shales had a drop in kaolinite concentration (from 22-16%) whereas deep shales saw a decline (from 29-22%). Unlike chlorite and feldspar, whose abundance do not rise with depth, but quartz does. In all samples, calcite may be found in minute quantities. In this case, the pore water is the source of the potassium. Total organic carbon (TOC) readings obtained from the shale samples demonstrate a high concentration of organic matter in the rock.