钻孔体应变与面应变观测井孔耦合系数的计算

钻孔应变观测系统（岩石、 膨胀水泥和应变仪钢筒）存在显著的井孔耦合效应，只有确定这一耦合系数，才能得到地壳岩石的真实应变值，从而实现不同测点数据的可比性．本文根据双衬套理论及弹性力学理论，建立了三维空间应力作用下体应变与面应变观测力学模型，并进一步推导各自井孔耦合系数计算式，发现两组系数与井孔的受力状况密切相关，分别与不同力源引起的应变信号相对应．亦即应力比（钻孔轴向应力与平面应力之比）不同，耦合系数也不一样，体应变随应力比的增大而下降，面应变则上升. 本文结果还表明平面应力作用下的耦合系数与外加应力无关，只与观测系统本身有关，故数值保持恒定. 此外，文中对其影响因素也进行了分析，结果表明，体应变和面应变的井孔耦合系数均随岩石弹性模量和泊松系数的增大而增大，且前者的幅度较大，井孔耦合材料水泥对二者影响均很小． 

Calculation of borehole coupling coefficient based on borehole volume strain and area strain observation

Obvious borehole coupling effect exists in the borehole strain observation system (rock, expansive cement and strainmeter steel tube).The real strain of rock in the crust can be obtained by determinng the coupling coefficient, so that comparativity of the data measured at the different points can be improved. According to the double bushing theory and elastic mechanics model, this paper establishes the mechanical models of volume strain and area strain observation under the action of three-dimensional stress. Then we deduced the borehole coupling coefficient formula at different observatories, from which we found that the coefficient was closely related to stress in the holes. The different strain signals can be correspondently attributed to different sources. That is to say, the stress ratio (the ratio of axial stress of drilling to plane stress) is different, the coupling coefficient is not the same. The volume strain decreased with the stress ratio increasing, and area strain increased. In addition, the coupling coefficients under plane stress had nothing to do with the additional stress, but only with the observation system as shown by the constant measurements. Finally, the affecting factors were analyzed. The results show that borehole coupling coefficient of volume strain and area strain increased with the rock elastic modulus and Poisson’s coefficient increasing, and the change in the former is larger, effect of borehole coupling material of cement on the two quantities is small.