Abstract
Focusing on Xujiaweizi fault depression, the geological conditions and geochemical characteristics of deep natural gas formation in the north of Songliao basin are evaluated, the natural gas resources are estimated, and the favorable areas are optimized. Shahezi Formation shale is a set of coal bearing sediments with high organic matter abundance (TOC is 1%～12%), high over maturity (Ro is 1%～4%) and shore shallow lake facies, which are mainly distributed in Xujiaweizi fault depression, Gulong-Lindian fault depression and Yingshan fault depression. The thickness, TOC, Ro and hydrocarbon generation of four thirdorder sequences with different lithology (mudstone and coal) are carefully evaluated for the Shahezi Formation shale in the deep layer of Songbei. The comprehensive evaluation shows that the mudstone thickness of Es4 member in Anda and Xuzhong areas of Xujiaweizi fault depression is large (150 ~ 525m), TOC is high (1% ~ 4%), thermal evolution degree is high (Ro is 1.2% ~ 3.4%), and gas generation intensity is high (20 ~ 815) × 108m3 / t), moderate buried depth (3000~4500m) and overlapping area of 756km2. It is a favorable exploration area for natural gas and shale gas in Daqing Oilfield.
Highlights
The deep strata in the north of Songliao Basin mainly include lower Cretaceous Huoshiling formation, Shahezi formation, Yingcheng formation and Denglouku formation from bottom to top
The coal mudstone of Shahezi formation dominated by shore shallow lake facies is thick, with good hydrocarbon generation conditions and great resource potential
The results show that three cycles of high-quality source rocks can be developed in each sequence set of Shahezi Formation, in which the TOC value of Shahezi Formation source rocks in the north of Xujiaweizi fault depression is mainly 1% ~ 3%, and the TOC value of some wells is greater than 3%
Summary
The deep strata in the north of Songliao Basin mainly include lower Cretaceous Huoshiling formation, Shahezi formation, Yingcheng formation and Denglouku formation from bottom to top. The basement is Carboniferous Permian (Fig. 1), belonging to volcanic eruption and clastic rock coal bearing deposition in fault depression period. The coal mudstone of Shahezi Formation dominated by shore shallow lake facies is thick, with good hydrocarbon generation conditions and great resource potential. Xujiaweizi has discovered the Xushen gas field in the volcanic rocks of the Yingcheng formation, and has obtained industrial gasflow in several sets of formations such as Shahezi and Denglouku formations. There are many exploratory wells that have seen oil and gasd in Gulong-Lindian fault depression in the west and the Yingshan fault depression in the east [1,2,3]
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