科研之友
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摘要
The tight sandstone reservoir in 8th member of the Permian Shihezi Formation in the Ordos Basin has undergone intense dissolution and transformation, forming a wide range of secondary pores. However, the dissolution process and reservoir effect of feldspar minerals and calcite cement in sandstone under geological conditions have yet to be further studied. In this paper, the method that temperature and pressure co-controlled the dissolution simulation experiment under closed system was adopted, and the dissolution law of calcium-bearing litharenite and feldspathic litharenite in acetic acid solution was studied under different temperature and pressure conditions by means of test and analysis of inductively coupled plasma emission spectrometer, X-ray diffractometer, polarizing light microscope and scanning electron microscope. The experimental results show that the temperature increases the dissolution rate and the dissolution amount of feldspar, but the amount of Al3+ migration first increases and then decreases, so it is difficult for Al3+ to be migrated out of the deep sandstone. Calcite dissolves much faster than feldspar and contributes more to the pore formation. As the temperature increases, the calcite dissolution first increases and then decreases, and the pressure inhibits calcite dissolution and has a greater effect than temperature. Calcite and feldspar of He 8 Member dissolved in the Late Triassic to the early cretaceous, which was the main period of secondary pore formation. After the Middle Cretaceous, the reservoir uplifted and the temperature and pressure decreased continuously, and caused some calcite to dissolve away.
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