低渗透油藏中油包水乳液的生成及其扩大波及体积的作用

Transition from O/W to W/O and its action on improving sweep efficiency in low permeability reservoirs

针对低渗透水驱波及效率低的问题,研究了具有扩大波及体积作用的油包水乳液的形成及对驱油效果的影响。乳化剂浓度、油水比以及岩心渗透率是影响水包油乳液向油包水乳液的转变的重要因素。在高浓度条件下(0.5%和0.3%),乳化剂TC-6和原油形成的分散体系以水包油乳液为主。随着浓度降低,水包油乳液转变为油包水乳液并伴随着分散体系粘度的升高。相同浓度条件下,油水比升高也会引起水包油乳液向油包水乳液的转变。质量浓度0.3%条件下,油水比<6∶4时,分散体系以水包油为主;油水比>7∶3时,水包油乳液转变为高粘度油包水乳液。乳化剂浓度,油水比渗透率低于50.1 m D时,水包油乳液不稳定,容易发生反相形成油包水乳液。低渗透岩心实验表明,具有扩大波及体积功能的乳化剂能够在水驱基础上提高采收率8.9%,明显高于超低界面张力表面活性剂体系提高采收率效果。同时,乳化剂分子量小、粘度低,本身不存在注入性的问题,因此对于低渗透油藏水驱后扩大波及体积、提高原油采收率具有重要意义。

Investigations on transition from O/W emulsions to W/O emulsions and its action on oil recovery were carried out by phase appearance, viscosity, morphology and core flooding experiment. At high concentrations （0.5% and 0.3% ）, the dispersions are major in O/W emulsions. Decreasing the concentration will induce the O/W emulsions transferring into W/O emulsions with high viscosity. At mass con- centration of 0.3 %, the dispersions behave as O/W emulsions when volume ratio of oil to water is below 6： 4. Above 7 ： 3, increasing volume ratio leads to the O/W emulsions transferring into W/O emulsions with high viscosity. At low permeability conditions, O/W emulsions become unstable which are prone to transfer into W/O emulsions. Simulated flooding experiments show that emulsifier fluids will make an im- provement of oil recovery by 8.9%. The research may provide a new method to improve sweep efficiency without environmental damage in low permeability reservoir exploit.