Vertical distribution characteristics of light hydrocarbon components in Well SK-2 and its implications for deep oil and gas

With the maturation of oil and gas exploration and development in Songliao basin, it is urgent to expand strategic replacement areas for oil and gas storage and production. In this task, deep oil and gas seem to be an important direction. Roof gas logging with continuous sampling in the whole well section of Well SK-2 obtained 6042 groups of light hydrocarbon composition data containing 103 monomers, and fully demonstrated vertical variation characteristics of light hydrocarbon components in the deep part of Well SK-2, which shows obvious segmentation. As a whole, it can be divided into 6 sections:section Ⅰ (470-1000 m in well section), which has a small peak area, a small number of peak outfalls, and a low heavy hydrocarbon content, showing the characteristics of shallow and low-mature oil and gas; Section Ⅱ (well section 1000-2800 m) has a large peak area, a large number of peaks and a high heavy hydrocarbon content. It is a mature type Ⅰ source rock and a conventional oil and gas section dominated by oil generation; Section Ⅲ (2800-3320 m in well section) has fewer and scattered peaks, low content of heavy hydrocarbon and no hydrocarbon source rocks, which are characteristic of reservoirs; Section Ⅳ (3320-5940 m in well section) is the upper unconventional gas section of Shahezi Formation, with a large peak area and a large number of peak outputs, high content of heavy hydrocarbon, being Type Ⅲ source rocks with large thickness in the maturation-over-maturation stage, and sandstone interbeds can form various types of unconventional natural gas, suggesting an important section for future exploration; Section Ⅴ (5940-6200 m in well section) is the lower part of Shahezi Formation and Huoshiling Formation, and the peak area and peak number of roof gas are scattered within the section which is considered to be in the stage of over-maturation; Section Ⅵ (6200-7108 m in well section) is volcanic rock and basement segment, and the peak area and number of peaks are generally low. However, the peak area of top gas in 7000-7100 m well segment shows that the light hydrocarbon parameters are different from those of section Ⅴ, and it is inferred that there may be gas sources of type Ⅱ-Ⅲ organic matter in the deep part. These characteristics show that the vertical distribution of light hydrocarbon components reflects the different characteristics among Jurassic, Cretaceous and the basal formations in oil and gas formation, maturation, gas content and oil and gas sources. The results obtained by the authors reveal the potential of deep unconventional gas resource, and provide an important foundation for Songliao Basin's exploration shift from conventional oil and gas exploration and tight conglomerate gas exploration at the edge of fault depression to deep trough zone for the exploration and expansion of unconventional natural gas.