CO_2气驱封窜用改性凝胶体系的研制与室内评价

Development and Laboratory Evaluation of A Modified Gel System for Channeling Blocking in CO_2 Flooding

开发了一种CO2气驱封窜用改性凝胶封窜剂。凝胶稳定性试验表明,二价阳离子浓度以及酸碱度对该改性凝胶封窜剂的稳定性有明显影响,随着Mg2+或Ca2+浓度的增加,凝胶强度呈先上升后下降的趋势,改性凝胶体系中Mg2+的适宜浓度在0～1500mg/L,Ca2+适宜浓度在0～1000mg/L。适宜pH值范围5～9。单岩心与并联岩心封堵试验均表明,选择的改性凝胶体系在渗透性高的岩心有良好的注入性,而在低渗岩心注入性很差,即可以减少改性凝胶在低渗岩心的注入量,从而选择性地封堵高渗岩心。在并联岩心CO2驱封窜试验过程中,气驱压力0.15MPa与模拟温度65℃条件下,低渗岩心先有流体流出,而高渗岩心则在注气压力升到0.2MPa后才有流体流出,说明改性凝胶体系进入高渗岩心后,在65℃温度下可以成胶,并能有效地封堵高渗岩心,使后续CO2驱时气体转向进入低渗岩心,从而驱出低渗岩心中的原油。并联岩心在改性凝胶封堵后再进行CO2驱时,低渗岩心能提高采收率4.8%,高渗岩心提高采收率为5.4%。

A modified gelling agent for gas-channeling blocking in CO2 flooding was developed.The gelling stability tests showed that the divalent cationic ion concentration and pH had significant effect on the stability of the modified gel.With the increase of Mg2+or Ca2+ concentrations,the gel strength increased firstly and then decreased.For modified gel system,the optimum concentrations of Mg2+ and Ca2+ were 0~1500mg/L and 0~1000mg/L respectively,and the optimum pH range was from 5 to 9.Sealing tests using single core and parallel cores showed that the modified gel system had good performace of injection in the high permeability cores and it had poor injection in low permeability cores.That was the injection volume could be reduced in the low permeability cores,by which selective blocking could be chosen in high permeability cores.In the CO2 flooding experiments using parallel cores,the fluid firstly flowed from the low permeability cores under 0.15MPa(gas displacement pressure) and 65 ℃(simulation temperature).Compared with the low permeability cores,the fluid did not flow from the high permeability cores until the injection pressure was raised to 0.2 MPa.The above experiments showed that the modified gel was gelatinized at 65 ℃ after it flowed into the high permeability core,and could effectively block the high permeability core,which turned the CO2 flooding into the low permeability core,thus drove the crude oil out from the low permeability cores.After the modified gel is injected into the parallel cores,the oil recovery of the low permeability core and the high permeability core could be enhanced by 4.8% and 5.4% respectively in the CO2 flooding.