| The tidal flat dolomite reservoir of the Middle Triassic Leikoupo Member 4 in Chuanxi Gasfield, Western
Sichuan Basin is characterized by the development of a large number of fabric selective dissolution pores. The reservoir is
distributed in a large area on the plane, but the high-quality reservoir is characterized by longitudinal thin and transverse
discontinuous distribution, and the spatial distribution law is unclear, which directly affects the deployment of highly
deviated horizontal wells in Chuanxi Gasfield. By observing the rock structure and pore characteristics of the reservoir
through cores and thin sections, and using the test data of rock carbon and oxygen isotopes and cathodoluminescence,
combined with the analysis of the vertical sequence characteristics of high-frequency sedimentary cycles of tidal flat
facies, the penecontemporaneous dissolution characteristics, the controlling factors of dissolution intensity and the
influence of penecontemporaneous dissolution on the distribution of high-quality reservoirs in Leikoupo Member 4 of
Chuanxi Gasfield are studied. The results show that: (1) Penecontemporaneous dissolution characterized by the development
of seepage bean particles, calcium crusts and layered pane pores is the key controlling factor for the distribution of highquality
reservoirs in Leikoupo Formation. (2) Controlled by the high-frequency sedimentary cycle due to frequent sea-level
changes in the tidal flat environment, penecontemporaneous dissolution is characterized by short single-stage exposure and
dissolution time, large area and multi-stage superimposed exposure and dissolution. The penecontemporaneous dissolution
intensity is controlled by the vertical sequence characteristics of sedimentary cycles and the thickness of a single sedimentary
cycle. (3) Four types of sedimentary cycles are mainly developed in Chuanxi Gasfield, among which the high-frequency
sedimentary cycle formed in the upper intertidal-supratidal zone is the most conducive to the occurrence of
penecontemporaneous dissolution. From bottom to top in a single sedimentary cycle, the closer to the exposed surface, the
pores are more developed, the slightly lower the carbon and oxygen isotopic composition value, the higher the logging GR
value, and the lower the deep and shallow resistivity. The penecontemporaneous dissolution in the middle and upper part of a
single cycle is the strongest, which is easy to form high-quality reservoirs. When the thickness of a single cycle is less than 5 m,
the high-quality reservoirs is relatively concentrated in the vertical direction and continuous in the horizontal direction. |
