| The Gonghe Basin is located in the southeastern part of the Qaidam Basin and is an important replacement field for potential oil-gas resources in the northwestern part of China.The previous oil-gas exploration work has revealed good prospects for exploration in Gonghe and Guide.The study on source rocks and reservoirs has important guiding significance for the search for oil-gas resources.However,there is little cognition of the source rocks and reservoirs in Guide Depression of Gonghe Basin,which has restricted the further oil-gas exploration work in this area.In this paper,through a series of technical means,such as the field profile observation,gravity and magnetic data analysis and geochemical experiments,combined with the characteristics of sedimentary facies,the source rocks and reservoir conditions of the Cretaceous in Guide Depression of Gonghe Basin are preliminarily determined,contributing to the further oil-gas exploration work.The study shows that the Cretaceous source rocks in Guide Depression of Gonghe Basin are mainly developed in the sub-facies of the shore shallow lake and the semi-deep lake.The lithology is dominated by gray-green calcareous mudstone,mudstone and gray-black mudstone and shale.The hydrocarbon generation ability of the former is poor,while the latter has a strong hydrocarbon generation capacity.The TOC distribution of the mud shale is 0.04%?2.18%,and the average value is 0.62%;the kerogen type is mainly type I and type II1;the Ro is in the range of 0.68%?1.22%,and the average value is 0.89%;individual gray-green calcareous mudstones,mudstones and most gray-black mudstones and shale achieve good source rock standards.Among them,gray-black mudstone and shale near Zhihai village have large sedimentary thickness,high organic matter abundance,good organic matter type and are in the mature stage,which are potential high-quality source rocks.The lithology of the Cretaceous reservoirs in Guide Depression of Gonghe Basin is mainly lithic feldspar sandstone of the delta front subaqueous distributary channel,with strong carbonate cementation and dense reservoirs.The reservoir space type is dominated by intergranular dissolved pores and fractures,and the porosity distribution is 2.8%?13.1%,the average value is 6.4%;the permeability is in the range of0.03×10-3?m2?1.78×10-3?m2,and the average value is 0.39×10-3?m2,which is generally characterized by low porosity and low permeability.The oil-gas infiltration is observed in both pores and fractures of the reservoir,showing good oil-bearing properties.The source-reservoir-caprock assemblage includes self-sourcing and self-reservoiring type and upper-sourcing and lower-reservoiring type and lower-sourcing and upper-reservoiring type.And the structural traps can be seen in the field. |
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