| In order to confirm the formation of secondary pores of sandstone in Zhuhai Formation in Wenchang A Sag of Pearl River Mouth Basin, and to determine the influence of different fluids on the secondary pore of sandstone, four fluid reaction systems (oxalic acid, acetic acid, CO2 and meteoric water) were prepared and water-rock reaction of the sandstone core columns from the 2nd and 3rd members of Zhuhai Formation in the Oligocene of the study area was conducted. By SEM observation, ion concentration measurement, reaction fluid pH measurement and core porosity measurement, the following conclusions are drawn: (1) Oxalic acid has the fastest dissolution rate, followed by acetic acid and carbon dioxide(CO2). (2) The pH value of the organic acid system change greatly before and after the reaction, while the CO2 system doesn’t change almost. (3) The temperature range occuring organic acid dissolution strongestly is around 90℃, and the porosity increase due to the dissolution of feldspar. The sandstone in CO2 system continues to increase pores slowly in the range of 30~180℃ and increases observably at 150℃. (4) The excessive CO2 decomposed by oxalic acid resulted the precipitation of calcium carbonate during the reaction process, but the CO2 decomposed by acetic acid are not enough to produce the precipitation. The water-rock reaction experiment of sandstone in various fluid systems has a reference value for the study on the dissolution pore types and formation mechanism of the clastic rock. |
