Oil and gas pools in weathering crusts on the sedimentary basin basement

Weathering crusts of the sedimentary basin basement are collectors in several regions of the world. They enclose huge reserves of oil and gas. The paper considers the geochemical, mineral, and petrophysical heterogeneities of weathering crusts that should be taken into consideration in the prospecting, exploration, and development of hydrocarbon raw material therein. Areal and linear-fissure types of weathering crust are defined. They were formed before the overlapping of basement by rocks of the sedimentary cover. Areal crusts are pervasive at the basement roof, whereas linear-fissure crusts are formed along fractures. A complete weathering crust profile includes the following zones (from the bottom to top): disintegration, leaching and hydration, hydrolysis, and final hydrolysis. Rocks of the lower two zones represent the cavernous-fissure collector, while rocks of the upper zones are impermeable. In the arches of uplifted blocks of the basement, weathering crusts are subjected to erosion during marine transgressions. In such places, the roof is composed of rocks of the lower permeable zones that often make up a single heterogeneous natural reservoir overlapped by sandy collectors of sedimentary sequences. Linear-fissure weathering crusts show zonal distribution with good filtration-capacity properties. Several large oil and gas pools have been discovered in them.