Distribution and geochemical significance of dibenzofurans,phenyldibenzofurans and benzo[b]naphthofurans in source rock extracts from Niger Delta basin, Nigeria

The distribution and geochemical significance of dibenzofurans,phenyldibenzofurans and benzo[b]napthofurans in source rocks from Niger Delta basin,Nigeria,were investigated by Rock-Eval pyrolysis and gas chromatography-mass spectrometry(GC-MS).The data obtained from the source rocks evaluation showed that the rock samples contained type Ⅱ/Ⅲ kerogen capable of generating oil and gas and were within immature to early mature stage.The relative abundance of the C-,C-and C-dibenzofurans range from 1.75% to 29.82%,27.60% to 40.52% and 29.66% to 68.89%,respectively.The dibenzofurans were dominated by C-dibenzofurans.Among the C-dibenzofurans,2-+3-methyldibenzofuran was the most abundant in the rock samples while 1-methyldibenzofuran appeared to be the least.The relative abundance of benzo[b]naphtho[1,2-d]furan([1,2]BNF),benzo[b]naphtha[2,1-d]furan([2,1]BNF) and benzo[b]naphtha[2,3-d]furan([2,3]BNF) in the rock extracts range from 12.01% to 52.58%,32.61% to 75.21% and 10.27% to 52.43%.The wide range of values recorded for the three isomers of benzo [b]napthofurans in the samples suggest source rocks formed from mixed organic matter.Among the phenyldibenzofuran isomers,4-phenyldibenzofuran was the most abundant while 1-phenyldibenzofuran was the least.Phenyldibenzofuran ratio-1(PhFR-1) and phenyldibenzofuran ratio-2(PhFR-2) values range from 0.13 to 1.20 and 0.11 to 2.11,respectively.The results showed that the relative abundance of PhFR-1 and PhFR-2 increase gradually with increasing burial depth and maturity(VR≤0.77%,MPI-1≤0.62,T≤443℃),and have a good correlations with calculated vitrinite reflectance,MPI-1 and maximum Temperature(T).This range of values suggested immature to early mature source rocks.The source rocks were found to have shale and coal lithologies and deposited in a lacustrine/fluvial/deltaic settings within immature to early mature stages based on the distribution of dibenzofurans,phenyldibenzofurans and benzo[b]naphthofurans in the source rocks.This study showed that dibenzofurans,phenyldibenzofurans and benzo[b]naphthofurans were effective in determining the origin,depositional environment and thermal maturity of source rocks in Niger Delta basin,Nigeria.