Preparation of microemulsion and its in-situ oil removal performance on oily sludge from shale gas drilling platforms

Shale gas extraction produces a lot of solid waste in the process of drilling and exploitation， and oily sludge has been listed as hazardous waste. The complex composition of oily sludge and a variety of harmful compounds make the treatment of oily sludge difficult. Microemulsion is made by mixing a certain proportion of oil， water， salt， surfactant， and cosurfactant. The microemulsion method has advantages， such as low energy consumption， low cost， no heating needed， high oil removal efficiency， and can realize the ability to recover crude oil resources， etc.， so it is suitable for the in-situ oil removal for oily sludge. At present， it is necessary to explore a kind of composite microemulsion， which can improve the elution ability of microemulsion on oily sludge and have better recycling performance. In this paper， Na2SiO3 was proposed to be used to compound single microemulsion （SDS-Na2SiO3 type， AOS-Na2SiO3 type）， and its dispersion performance was utilized to form a composite microemulsion with higher oil removal efficiency. Firstly， by studying the phase change rule and oil removal efficiency of the microemulsion configured with a single surfactant， the preparation， phase change rule， and recycling frequency of the microemulsion configured with Na2SiO3 composite surfactant were studied. On this basis， SDS and AOS were used to prepare the composite microemulsion with sodium silicate （Na2SiO3）， and the phase variation of the microemulsion was studied. The removal rate of SDS microemulsion was 86.33%. The optimal formula was SDS∶ alcohol∶ NaCl=2.72%∶ 13.21%∶ 2.17% （mass ratio）. The removal rate of AOS microemulsion was 87.45%， and the optimal formula was SDS∶ Alcohol∶ NaCl=2.72%∶ 15.41%∶ 2.17% （mass ratio）. The effect of SDS microemulsion on eluting oily sludge was slightly lower than that of AOS microemulsion， but SDS microemulsion had a better effect on preparation and phase stability. The salt resistance of AOS-Na2SiO3 composite microemulsion was better than that of SDS-Na2SiO3 composite microemulsion， but the alcohol resistance was opposite. The oil removal efficiency of SDS-Na2SiO3 composite microemulsion was 92.47%， better than that of the single microemulsion. On the basis of reaching the national secondary utilization standard， the compound microemulsion can be reused for 5 times. This study，provides a new idea and technical support for in-situ treatment of oily sludge.