| Author's Name: ZHANG Yuangao1, PAN Wenqing1, TANG Yu2,3, ZHANG Junlong1, XIN Chaokun4,
CAO Yanqing1, CHAI Xubing4, QI Kunbo4, ZHANG Yunfeng2,3 |
| Pores are widely developed in the dolomite of the Lower Ordovician Penglaiba Formation-Yingshan Formation
in the Gucheng area, Tarim Basin, which are characterized by needle-like dissolution pores, ultra-grain pores,
intercrystalline micropores, etc., and are generally considered to be related to dolomitization. Based on data of core, thin
section, cathodoluminescence, inclusions, rare earth elements, carbon and oxygen isotopes, etc., the genesis, pore types and
genesis, pore evolution model of dolomite in the Lower Ordovician Penglaiba Formation-Yingshan Formation in Gucheng
area are analyzed. The results show that:(1) The dolomite is dominated by penecontemporaneous dolomitization, partially
superimposed by deep thermal fluid, and the dolomite filling in the fracture-vug is of hydrothermal origin. (2) The super
grain pores are macroscopically needle-like dissolution pores, which are developed in fine-medium crystalline dolomite
with original fabric as particles, mainly being medium-big pores, and are mostly developed in the middle and upper parts of
a single grain shoals cycle. They are intragranular dissolution pores, mold pores and intergranular dissolution pores formed
by selective dissolution of atmospheric fresh water in the penecontemporaneous period before dolomitization. The
intercrystalline micropores are isolated with poor connectivity and are formed by penecontemporaneous dolomitization.
Although the penecontemporaneous dolomitization did not directly produce a large number of pores, it provided a
framework that resisted compaction and hindered the later fluid precipitation, which was the key to the preservation of
pores. (3) The porous-type dolomite reservoir of Penglaiba Formation-the lower member of Yingshan Formation in
Gucheng area of Tarim Basin is characterized by multiple sets of thin layers. Its thickness and scale are affected by the
superposition of multi-stage granular shoals and their exposure degree. Exploration for this type of reservoir should be focus
on the high areas of paleogeomorphology where are conducive places to the development of dolomitization granular shoals. |
