深井固井水泥浆凝固阶段的传压效率时变规律

Change laws of pressure transferring efficiency over time in the setting stage of cement slurry in deep wells

随着油气井向深层超深层发展,地质条件愈加复杂,开采难度越来越大,尤其是高温高压、窄压力窗口地层是固井工程面临的突出难题。深层超深层压力敏感地层固井过程中,精确控制水泥浆柱压力是保障固井安全与水泥环层间封隔质量的关键。为探究凝固阶段水泥浆的失重规律和传压能力,建立了固井水泥浆静液柱压力评价装置和水泥浆传压效率评价方法,结合微量热仪和超声波静胶凝强度仪,测试了水泥浆水化过程不同厚度水泥浆的水化速率和静胶凝强度,最后分析了水泥浆失重和传压效率的时变规律。研究结果表明:①沉降稳定性良好的水泥浆体系,凝固阶段可根据其水化进程将失重分为水化诱导期的平稳阶段和水化加速期的快速降低阶段;②在水化诱导期内,悬浮分散结构的水泥浆静胶凝强度缓慢发展,其失重速率随厚度降低而加快,遵循胶凝悬挂理论,且该阶段液态水泥浆可高效、快速传递顶部压力,传压效率超过95%;③在水化加速期内,水泥浆变为凝胶网架结构,水化产物增强凝胶网架的强度及其与外界面胶结强度,转移固相重力和上部加压值至外界面,降低水泥浆静液柱压力和传压效率,最终使水泥浆丧失传压能力。结论认为,该规律认识可为压力敏感地层固井憋压候凝工艺的高效实施提供实验和理论支撑,为深层超深层油气的高效开发奠定坚实基础。

With the development of oil and gas wells to deep and ultra-deep strata,the geological conditions get more and more complicated,and the production gets more and more difficult.Particularly,the strata with high temperature,high pressure and narrow pressure window are the prominent difficulty in cementing engineering.In the process of cementing in deep and ultra-deep strata with pressure sensitivity,the accurate control of slurry column pressure is the key to ensure the cementing safety and the interlayer isolation quality of cement sheath.To explore the pressure loss laws and pressure transferring capacity of cement slurry in the setting stage,this paper establishes a hydrostatic column pressure evaluation device and a pressure transferring efficiency evaluation method for cement slurry.Then,the hydration rate and static gel strength of the cement slurry with different thicknesses in the process of slurry hydration are tested by using microcalorimeter and ultrasonic static gel strength tester.Finally,the change laws of slurry pressure loss and pressure transferring efficiency over time are analyzed.And the following research results are obtained.First,according to the hydration process,the pressure loss in the setting stage of the slurry system with good settlement stability can be divided into two stages,i.e.,the stable stage of hydration induction and the rapid reduction stage of hydration acceleration.Second,in the hydration induction period,the static gel strength of the cement slurry with suspension-dispersion structure develops slowly,and its pressure loss rate increases with the decrease of thickness,following the theory of gel suspension.In this period,the liquid slurry can transfer the top pressure efficiently and quickly with pressure transferring rate exceeding 95%.Third,in the hydration acceleration period,the microstructure of the slurry changes into the gelgrid structure,and the formation of hydration products enhances the strength of the gel grid and its bonding strength with external interface to transfer the solid gravity and the upper additional pressure to the external interface,reducing the hydrostatic column pressure and pressure transferring efficiency of the cement slurry,and eventually making the slurry free of pressure transferring ability.In conclusion,the research results can provide experimental and theoretical support for the efficient implementation of pressure holding and waiting in the cementing process in pressure-sensitive strata,and lay a solid foundation for the efficient development of deep and ultra-deep reservoirs.