超细“G”级油井水泥低温低密度水泥浆研究

Study on Ultra-fine "G" Grade Oilwell Cement with Low-temperature and Low-density Slurry

针对海洋深水低温、破裂压力低等特点,通常要采用低密度水泥浆来封固深水表层;低温环境下普通"G"级油井水泥水化速度缓慢或几乎不进行水化反应,水泥石早期抗压强度低且发展缓慢。为有效降低现场候凝时间,节约深水作业成本,开发了一套适用于深水表层固井用超细"G"级水泥用低温低密度水泥浆。对水泥浆体系的设计原理与水泥浆组分进行了论述,并对该水泥浆体系在深水环境下的性能进行了评价,和中海油服现场在用的普通"G"级油井硅酸盐水泥浆体系进行了对比。结果表明,超细"G"级水泥低温低密度水泥浆体系在低温环境下具有较高早期强度、低失水量以及良好的流变性和稠化性能,其中密度为1.40g/cm^3及1.44g/cm^3的水泥浆在10~13℃温度下的稠化时间≥8hr,API失水<70m L,1.40g/cm^3水泥石在10℃及13℃温度下养护24h后的抗压强度可达到3.9MPa及5.4MPa;1.44g/cm^3水泥石在10℃及13℃温度下养护24h后的抗压强度可达到5.8MPa及8.3MPa。同等水泥石密度及温度下,超细"G"级水泥石24h强度较中海油服在用的普通"G"级油井硅酸盐水泥石强度提高40%以上。

In condition of deepwater with the characteristics of low temperature and low fracture pressure, low-density cementing slurry is commonly used to seal and strengthen the deep-water surface layer.In low-temperature environments,ordinary "G" grade oil well cement presents a slow hydration rate or hardly undergoes hydration process,resulting in slow strength development and low compressive strength of hardened cement paste at early curing age.In order to effectively reduce the on-site setting time and save the cost of deep-water operations,with the characteristics of low hydration temperature and low density,a set of cementing slurry prepared with ultra-fine "G" grade cement for deep-water surface enhancement has been developed.The design principle and composition of the cementing slurry system are discussed,and the performance of the cementing slurry system in deep water environment is evaluated,compared with the performance of the ordinary G-grade oil well Portland cement used at COSL.The results show that the designed ultra-fine "G" grade cementing slurry presents higher early strength,lower water loss,and better rheological and thickening properties in a low temperature environment than or ordinary "G" grade cement.The thickening times of the cementing slurry with a density of1.40 g/cm^3 and 1.44 g/cm^3 at the temperatures of 10 and 13℃ are longer than 8 hours,and the API losses of water are both less than 70 mL.The compressive strength of hardened cement paste with the density of1.40 g/cm^3 reaches 3.9 MPa and 5.4 MPa after curing for 24 hours at the temperatures of 10℃ and 13℃.The compressive strength of hardened cement paste with the density of 1.44 g/cm^3 can reaches 5.8 MPa and 8.3 MPa after curing the temperatures of 10℃ and 13℃ for 24 hours.At the same condition of density,temperature and curing age,the strength of ultra-fine "G" grade hardened cement paste presents 40% higher compressive strengths than those of ordinary "G" grade oil well hardened cement paste used at COSL.