Petroleum source-rock potential and thermal maturity of Zarama 10 and Zarama 11 oil wells in the Niger Delta, Nigeria

Abstract

ABSTRACTDrilling cuttings and drilling mud samples were collected from Zarama 10 and Zarama 11 oil wells in the Niger Delta at various depths in order to characterize the extractable organic matter and biomarkers distribution patterns. The total organic carbon contents of the samples were determined using Walkley Black method. The distribution of n-alkanes, pristane, phytane, phenanthrene, and its alkylated derivatives were studied by gas chromatography-mass spectrometry. The total organic carbon values show that the samples satisfy the minimum amount of 0.5 wt% organic matter required to serve as a potential source-rock of petroleum. The distribution of n-alkanes and alkylated phenanthrenes shows that the samples contain admixture (marine and terrestrial) of organic matter. The pristane/phytane ratio (1.25–2.25) indicates sub-oxic depositional environment for the organic matter of the samples. Equivalent vitrinile reflectance values calculated from methyl phenanthrene index (MPI-1) were in the range of 1.23–1.38% for the well studied. The maturity parameters obtained were used to assess maturity, which revealed high maturity level of the two wells. Further, calculated vitrinite reflectance (Rc) confirmed that the sediments have a range of maturity within the “oil window.”