Maturity modeling of the basal Qusaiba source rock, northwestern Saudi Arabia

Abstract EN

Integration of source rock data and measured maturity information, together with time/stratigraphic data based on geological reconstructions is used to construct burial history and thermal maturity models of sedimentary basins.

Regional geochemical trends can be mapped to determine the location of the hydrocarbon kitchen and to show potential migration routes for use in the exploration of a frontier basin.

This paper presents the results of such an exercise from the northern part of Saudi Arabia.

The most likely source rock of the region is the lowermost black shale unit of the Qusaiba Member of the lower Silurian Qalibah Formation.

The gamma-ray "hot” part of the lower Qusaiba attains a thickness >175 feet (53 m), has excellent organic richness, and is oil-prone.

Regional maturity trends, based on well information and seismic data, indicate that the deepest burial occurred in the northeast part of the study area.

This region has attained dry gas maturity, and most generation and expulsion occurred about 360 million years ago (Ma), before the Hercynian uplift event.

Burial was shallowest to the west around the margin of the Arabian shield.

The source rock in this location is immature and/or early mature.

Present maturity was probably attained about 360 Ma and was "frozen" during the Hercynian uplift event.

Two other areas, the northern Jawf Graben and the southeastern part of the Nafud Basin, may have attained high enough temperatures during Mesozoic and Tertiary burial to have re-initiated further maturation of the source rock.

Both these areas probably achieved early mature to oil expulsion maturities during the Devonian followed by expulsion of lighter oil through gas phases during the Mesozoic.

Several migration pathways for the expelled hydrocarbons were determined using the present-day structural configuration for the basal Qusaiba shale.