Division and evaluation of oil-gas prolific zones for litho-stratigraphic reservoirs in the Nanpu Sag

Abstract

The Nanpu Sag is a typical lacustrine downfaulted hydrocarbon-rich depression. Some litho-stratigraphic reservoirs have been discovered in recent years. Based on “Sag-wide Oil-Bearing Theory” and petroleum system, the concept of “play” is used as a unit for the division and evaluation of oil-gas prolific zones in this paper. The overlaying technique of “four maps”, which are the fault structure map, the sedimentary facies, the major effective source-rock distribution map, and the current exploratory situation map, is applied to the comprehensive evaluation of oil-gas prolific zones. The Nanpu Sag in vertical is divided into three first-order plays, namely, above-source play, in-source play, and below-source play, and each of them can be subdivided into second-order plays. The above-source play is divided into eight oil-gas prolific zones and four favorable areas are evaluated. The in-source play is divided into five oil-gas prolific zones and four favorable areas are evaluated. The below-source play is divided into two parts with ten oil-gas prolific zones and five favorable areas are evaluated. Key words: Nanpu Sag, litho-stratigraphic reservoir, play, zone division: zone evaluation