| 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. |
