流体pH值对致密砂岩储层渗透率的影响

地层流体pH值一般分布在4～9范围，一旦侵入储层的流体pH值过高或过低，将引发外来流体与储层流体、储层矿物不配伍的问题，必然造成储层损害。文章以川中香溪群致密砂岩气层为例，开展流体pH值逐级升高和pH值逐级降低对储层渗透率改变的综合评价实验。实验表明，储层具有强碱敏、强的HCl酸敏感性。研究指出，高pH值流体条件诱发粘土矿物微结构的破坏，导致伊利石、绿泥石等粘土矿物溶解、脱落、分散（运移），渗透率大幅度下降；低pH值流体破坏绿泥石的晶体结构，使结构中的Fe²⁺、Fe³⁺、Mg²⁺等离子析出，产生Fe(OH)₃以及Mg(OH)₂沉淀，堵塞喉道。

INFLUENCE OF FLUID pH ON THE PERMEABILITY OF TIGHT SANDSTONE RESERVOIR

The rang of stratum fluid pH is from 4 to 9 in general. Once the pH of the fluid invading reservoir is too high or too low, it is inevitably happened that invasion fluid not matches with reservoir fluid and mineral so as to cause reservoir damage. Taking the tight sandstone reservoir of Xianxiqun Formation as an example, the comprehensive evaluation experiment of changing the reservoir permeability by gradually increasing or decreasing fluid pH is carried out and the result shows the clay mineral microstructure damage caused by high pH makes the clay minerals such as illite and chlorite etc. dissolve, disperse, migrate and decrease the permeability; low pH fluid can destroy the crystal microstructure of chlorite, which makes the Fe 2 + , Fe 3+ , Mg 2+ within the structure separate to cause Fe(OH)_3 and Mg(OH)_2 deposit and plug up pore throat.