| Abstract：Based on the innovative practice of exploration, discovery and evaluation of Taiyang shallow shale gas field in
Zhaotong Demonstration Area, the basic geological characteristics and enrichment law of mountainous shallow shale gas
field in strong reconstruction and complex structural area are systematically summarized. It is pointed out that 30-40 m
thick high-quality shale is developed in O3w(Wufeng Formation) - S1l11-1(first sublayer of Longmaxi Submember 11) of
Taiyang shallow shale gas field. The geochemical characteristics show that the TOC of high-quality shale is generally
greater than 2.0%, the type of organic matter is II1, and the macerals are mainly sapropelic. The maturity of organic matter
(Ro) is among 1.65%-3.11%, with an average of 2.54%, belonging to the dry gas generation stage of over mature, which
provides a good material basis for the generation of a large amount of shale gas. The reservoir conditions are superior, and
various types of pores are developed, with porosity ranging from 2.04% to 10.06%. The pores dominated by organic
matter pores and clay mineral interlayer fractures provide a large amount of reservoir space for shale gas. The gas content
of the target layer generally increases with the increase of depth. The average adsorbed gas content of shale in O3w-S1l11-1
measured by methane adsorption experiment is 1.92 m3 / t, which proves that the adsorbed gas accounts for a large
proportion of shallow shale gas. Moreover, the trace strength of structural transformation is generally weak, which is
conducive to the formation of a complete three dimensional sealed box system with the characteristics of roof and floor
with good vertical sealing performance, reverse fault with good lateral sealing performance and shale reservoir with strong
self-sealing performance. Therefore, the overall preservation conditions of the target layer are good, with high gas content
and atmospheric pressure to micro overpressure system. Shale has high content of brittle minerals and small horizontal
stress difference in anticline structure area, which is easy to be transformed by volume fracturing. S1l11-1-lower S1l11-2and
S1l11-3 are double favorable targets, which can be developed in volume of small well spacing and three-dimensional
staggered layer. The innovative understanding of the geological theory of shale gas accumulation and occurrence and the
economic efficiency progress of geological-engineering integrated technology are the key to the exploration breakthrough
and efficient evaluation of Taiyang shallow shale gas field. The successful exploration experience of Taiyang shallow
shale gas field has important reference and guiding significance for shallow shale gas exploration in complex structural
areas in southern China. |
