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The formation conditions and exploration fields of tight gas of Xujiahe Formation in Da'an exploration area, Sichuan Basin
LUO Yufeng, HOU Gangfu, LIU Zhanguo, XIONG Jiabei, WU Songlin, RUI Yun, CHEN Xingyu, YUAN Xiaojun, SONG Bing, WU Jin, LIU Shaozhi
Marine Origin Petroleum Geology ›› 2025, Vol. 30 ›› Issue (2) : 157-166.
PDF(10593 KB)
PDF(10593 KB)
The formation conditions and exploration fields of tight gas of Xujiahe Formation in Da'an exploration area, Sichuan Basin
In order to clarify the conditions for the formation of tight gas reservoirs in complex structural deformation zones and implement the next exploration areas, a systematic study is conducted on the hydrocarbon source rocks, sedimentary systems, tight sandstone reservoirs, and trap conditions of the Xujiahe Formation in Da'an exploration area of Sichuan Basin. The results show that: (1)The Xujiahe Formation in the Da'an exploration area has developed a shallow water delta sedimentary system, and the multi-stage sand bodies of the delta plain braided distributary channels in the 4th and 6th members are stacked and connected. Due to compaction and cementation, the reservoirs were generally dense, and later dissolution and fractures effectively improved the physical properties of the reservoirs. (2)The 3th and 5th members are the main source rock layers in the study area. The source rocks are thick, wide distribution in area, and have high organic matter content, mainly consisting of type Ⅲ and type Ⅱ2 kerogen. Currently, they are in the mature to high mature stage, laying a resource foundation for the formation of tight gas reservoirs in Da'an exploration area. (3)The tight sandstone reservoirs of the 4th and 6th members are interbedded with the source rocks of the 3th and 5th members in an uneven thickness in the vertical direction, forming a lower source-upper reservoir combination, which is conducive to the formation of structural gas reservoirs. The main source rock layers of the 3th and 5th members are developed with "mudstone wrapping sandstone" type meandering river channel sand bodies and tight sandstone reservoirs, forming a self generating and self storing combination, which is conducive to the formation of lens-shaped lithological gas reservoirs. The main part of Danfengchang anticline belt and the north, middle, and south wings of Linjiang syncline, as well as the east wing of Yunjin syncline are proposed as the key replacement areas of structural gas reservoir of the 4th and 6th members in Da'an exploration area. Of the Danfengchang anticline, the north of Laisu syncline, and the central part of Linjiang depression, the 3th and 5th members are integrated with source and reservoir, which is conducive to the formation of a "mudstone wrapping sandstone" type structural-lithological gas reservoir and is a potential exploration area for tight gas reservoirs in the next step.
shallow water delta / tight sandstone gas / accumulation model / exploration field / Xujiahe Formation / Da'an exploration area / Sichuan Basin
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Xujiahe Formation in central Sichuan Basin is characterized by large-area gas-bearing,low-degree charging,local-enrichment high-yield and complicated water-gas distribution.To verify the characteristics and the main controlling factors of natural-gas accumulation in Xujiahe Formation,comprehensive analyses have been carried out including the component and carbon isotope of natural gas,the light hydrocarbon of source rock adsorbed gas,the distribution of source rock,the physical property of reservoirs,the structural amplitude and the abnormal pressure.The results showed that natural gas in Xujiahe Formation was coal-derived gas featured with near-source and interbedded-accumulation.The source rocks owned large thickness in total but thin layer in single,and they were interbedded with sandstone which had low gas intensity and weak gas charging ability.Abnormal pressure provided charging dynamics for natural gas migration.Natural gas preferred to migrate into good-property sandbodies when gas-source was insufficient and the physical property took control of the charging degree of gas reservoirs.Local low-amplitude structure controlled the distribution pattern of gas reservoirs under slow structural background,and the higher the structure was,the more full the gas-water differentiation would be,and the easier the pure gas reservoir would develop.Overall,sandbodies inside source in Xujiahe Formation had a wonderful exploration prospect,and the northwestern,3<sup>rd</sup> member in the southwestern and 5<sup>th </sup>member in the central of Sichuan Basin were the favorable exploration target of gas reservoirs inside source.
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