Study On Foamed Cement For High Temperature Geothermal Wells

In the high temperature geothermal wells, the characters such as high temperature, low formation pressure, and broken formation are common. And these would cause problems such as lost circulation.The environment with high temperature and low formation pressure will cause to the recession of compressive strength, reduce of slurry thickening time, increasing of filter loss, and the variation of stability. These problems have a serious influence in construction safety and the cementing quality. To ensure the quality of geothermal well cementing, we will develop high temperature resistance and low density cement.It is usually added hollow microsphere and foaming agent to cement to reduce the density of well cement. To balance the low formation pressure in the wells and obtain needed compressive strength, the objective of this paper is to designing high temperature resistance and low density foamed cement with density ranging from 1.00 g/cm3 to 1.25 g/cm3 and compressive strength is over than 6.9MPa after 24 h in 200℃.On the basis of detailed literatures review, I have done the following experiments, the evaluation of anionic surfactants, amphoteric surfactants and their compounded system under room temperature and 180℃ for 3h in the quantity and half-life of foams. Through these experiments, the anion/zwitterionic surfactant compounded system SLES + CAO + CAB is selected as the foam agent for foamed cement. After preliminary experiment evaluation, I determine the foamed cement with API class G oil well cement as: API class G oil well cement + 35% silicon powder + water + foam agent+ foam stabilizer, and foamed cement with slag/fly ash: slag/fly ash(80/20) + 6% sodium silicate + water + foam agent. I have studied on the influence on its density of different amount of foam agent and different water cement ratio for foamed cement with API class G oil well cement and foamed cement with slag/fly ash, then choose one whose density is less than 1.25g/cm3.To design low density foam cement system, this paper have fitting curve on the relationship of water cement ratio and the amount of foaming agent. Finally, it is convenient to design foamed cement with API class G oil well cement and foamed cement with slag/fly ash according to the fitting curve, and determining the water cement ratio and foaming agent. According to the characteristics of the high temperature resistance foamed cement, it is required to estimate the density of foam cement system, setting time under different temperature, compressive strength after high temperature curing, free liquid and the stability of the foam cement slurry. After these experements, foamed cement with API class G oil well cement and foamed cement with slag/fly ash which are conformed to normal performance is optimized.The results showed that compressive strength of foamed cement with API class G oil well cement and foamed cement with slag/fly ash after 24 h curing in high temperature is morer than 6.9 MPa. The density is less than 1.25 g/cm3. The setting time is more than 90 minutes at 30℃, 60℃, 90℃. The stability of slurry is good, the maximum density difference of the slurry is less than 0.04 g/cm3 after standing for 2h, free liquid content is less than 1.0%. It is all conformed to the requirements of the high temperature geothermal well cementing.