多种流体体系与砂岩水岩反应的实验研究

Experimental Study on Water-rock Reaction of Sandstone in Various Fluid Systems

针对珠江口盆地珠三坳陷文昌A凹陷渐新统珠海组砂岩次生孔隙成因问题,为确定不同流体对砂岩次生孔隙发育的影响,分别设置了草酸、乙酸、CO_2和大气淡水四种流体反应体系,对研究区珠海组二段、三段的砂岩岩心柱进行水岩反应观测。通过扫描电镜观察、离子浓度测量、反应液pH值测量、岩心孔隙度测量等实验,得出如下结论:(1)草酸体系的溶蚀速率最快,乙酸体系次之,碳酸体系(CO_2体系)最慢。(2)有机酸体系反应前后pH值变化较大,而CO_2体系基本无变化。(3)有机酸溶蚀最强的温度区间为90℃附近,长石大量溶蚀生成高岭石,同时引起孔隙度增加;CO_2体系在30～180℃区间内持续缓慢增孔,在150℃附近增孔明显。(4)草酸分解过量的CO_2,在反应过程中产生了碳酸钙的沉淀,而乙酸分解的CO_2,不足以产生碳酸盐矿物的沉淀。实验结果对碎屑岩溶蚀孔隙的成因和形成机理研究具有借鉴意义和参考价值。

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, CO_2 and meteoric water） were prepared and water-rock reaction of the sandstone core columns from the 2 nd and 3 rd 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（CO_2）.（2） The pH value of the organic acid system change greatly before and after the reaction, while the CO_2 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 CO_2 system continues to increase pores slowly in the range of 30～180℃ and increases observably at 150℃.（4） The excessive CO_2 decomposed by oxalic acid resulted the precipitation of calcium carbonate during the reaction process, but the CO_2 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.