Khatatba Formation as an active source rock for hydrocarbons in the northeast Abu Gharadig Basin, north Western Desert, Egypt

Abstract

Rock samples and a suite of oil samples collected from wells drilled in the northeastern part of the Abu Gharadig Basin were studied to determine the petroleum potential of the Middle to Late Jurassic Khatatba Formation as a source rock for oil produced in the basin. Twenty-four cuttings and two cores in addition to three oil samples from the Riviera-1, Swag-2, and Spyglass-1 wells retrieved from the Upper Cretaceous reservoirs were analyzed. Analyses include total organic carbon (TOC), Rock-Eval pyrolysis, and vitrinite reflectance for rock samples and biomarker analyses for liquid hydrocarbons. Results reveal that the Khatatba Formation is an organic-rich source rock with TOC ranging from 1 to 5 wt%, locally exceeding 21 wt% due to the presence of coal interbeds in the depth interval 4,386–4,388 m. Rock-Eval pyrolysis data show that the Khatatba Formation is dominated by algal type II and mixed type II/III kerogens, but type III and type I kerogens also occur. The Khatatba shales and carbonaceous shales have entered the peak-mature stage of the oil generation window. Tmax for the samples ranges from 436 to 449 °C and vitrinite reflectance measurements between 0.76 and 0.92 %Ro. Geochemical analyses reveal that all analyzed oils were generated from thermally mature and organic-rich shale and carbonaceous shale belonging to Middle–Upper Jurassic and Lower Cretaceous source rocks during early and peak stages of the oil window. The correlation between oil samples from NE Abu Gharadig Basin shows that these oils are quite similar and were generated from mixed marine–terrigenous organic matter formed under suboxic–oxic depositional paleoenvironments. However, the differences in bulk and biomarker properties and light-end content of the oil samples can be attributed to thermal maturation, source rock facies variations, or secondary reservoir transformation, such as evaporative fractionation.