井中永置式套管外三分量光纤MEMS地震检波器研究

Development of three-component fiber MEMS geophone:an external instrument for permanent downhole microseismic monitoring

针对非常规油气井套管外永置式微振动监测,研制了一种基于光纤法布里帕罗(F-P)干涉原理和微机电(MEMS)技术的三分量光纤MEMS地震检波器,将微地震信号转化为F-P腔长的变化,通过超快光谱探测技术和动态白光干涉解调技术实现高速解调。设计并理论仿真了μm/g量级的高灵敏度MEMS加速度芯片,突破大深度双面套刻工艺完成芯片样品制造。采用高集成度小型化结构设计、无胶封装工艺设计和陶瓷微加工工艺实现25 mm微型外径,满足套管外永置式安装要求,提高了高温检测精度。在实验室完成了检波器与标准电学加速度计的性能对比测试,结果表明:检波器可耐受175 MPa高压和180℃高温,灵敏度分别为1.2382,1.2590,1.0862μm/g,工作频带为0~350 Hz,量程为±5 g,线性度误差<0.01%,抗横向串扰能力<5%。研制的检波器耐高温高压、尺寸小巧、灵敏度高、线性度良好,在非常规油气井储层压裂改造和采油气生产过程中,永置式套管外的三分量光纤MEMS地震检波器可以发挥重要的监测作用。

For permanent downhole microseismic monitoring of unconventional hydrocarbon reservoirs,we develop a type of three-component fiber MEMS geophone installed outside the casing pipe based on the Fabry-Pérot(F-P)interference principle and micro-electro mechanical system(MEMS).The instrument converts microseismic signals into F-P cavity length variations,and fast demodulation is accomplished using ultrafast spectroscopy and dynamic white light interferometry.We design and theoretically simulate MEMS accelerometer chip with the sensitivity of μm/g-scale,the samples of which are fabricated using double-side exposure process.The external diameter of 25 mm is achieved through highly integrated miniature structure design,non-gel encapsulation technology,and ceramic micro-machining for permanent installation outside the casing pipe and high-precision detection at high temperatures.According to performance testing conducted using the new geophone and standard electronic accelerometer in the lab,the new geophone shows resistance to high pressure of 175 MPa and high temperature of 180℃,sensitivities of 1.2382,1.2590,and 1.0862μm/g,respectively,operating band of 0~350 Hz,measuring range of±5 g,linearity error<0.01%,and transverse crosstalk resistance<5%.Owing to good performance of high temperature and high pressure resistance,small size,high sensitivity,and good linearity,the new geophone will play an important role in fracturing stimulation of unconventional reservoirs and hydrocarbon production.