相对湿度对盐膏岩蠕变规律影响的机理研究

Mechanism of Effect of Relative Humidity on Creep Behavior of Gypsum Rock

马跃 陈勉 金衍 侯冰 杨沛

Ma Yue Chen Mian Jin Yan Hou Bing Yang Pei

油气资源与探测国家重点实验室(中国石油大学(北京)), 北京 102249; 中国石油塔里木油田分公司油气工程研究院, 新疆库尔勒 841000

State Key Laboratory of Petroleum Resources and Prospecting(China University of Petroleum(Beijing)), Beijing, 102249, China; Institute of Oil and Gas Engineering, Tarim Oilfield Company, PetroChina, Korla, Xinjiang, 841000, China

为了弄清盐膏岩在井下环境下的蠕变规律,对盐膏岩蠕变规律影响机理进行了研究。采用调节盐溶液中含盐量的方法来控制岩样周围环境的相对湿度值,并在相对湿度为35%,65%,95%的条件下,进行围压分别为0,2,5 MPa的三轴短期压缩试验和单轴应力为10 MPa的蠕变试验。相对湿度从35%增加到95%,盐膏岩岩样强度由38.2 MPa降至35.2 MPa;弹性模量和泊松比变化量小。相对湿度为95%时,盐膏岩岩样产生负向的体积应变(膨胀);相对湿度为35%时,盐膏岩岩样产生正向体积应变(收缩)。研究结果表明,盐膏岩的强度对于相对湿度的变化不很敏感;结合Heard模型,利用蠕变激活能可以解释相对湿度对体应变速率的影响;晶体到毛细管空间的水分子相互运移的机械化学机制,可以解释相对湿度对体应变的影响。研究得到盐膏岩井下真实的蠕变规律,为盐膏层安全钻井提供了理论依据。

In order to find out the creep behavior of salt-gypsum under the down hole conditions,the mechanism affecting salt-gypsum creep was studied.By adjusting the concentration of salt in the salt solution to control the relative humidity around the rock samples,the uni-axial compression test was carried out at 10 MPa and tri-axial compression tests were carried out at confining pressures of 0,2 and 5 MPa under relative humidity of 35%,65% and 95% respectively.It was found that in a short-term test of salt-gypsum rock,the rock strength displays a downward trend from 38.2 MPa to 35.2 MPa with the increase of relative humidity from 30% to 90%,the change in Young’s modulus and Poisson’s ratio is small.When the relative humidity is 95%,the sample generates negative volumetric strain (expansion) and when the relative humidity is 35%,the sample generates positive volumetric strain (shrinkage).The study shows the strength of salt-gypsum is not highly sensitive to the change of relative humidity;and combined with the Heard model,the impact of relative humidity on the volumetric strain rate can be explained by the theory of creep activation energy;and the influence of relative humidity on the volumetric strain can be explained by the mechanical-chemical mechanisms of mutual migration of water molecules between the crystal and capillary spaces.The creep behavior of salt-gypsum rock underground revealed by the study can provide theoretical basis for safe drilling in this kind of formations.

国家重点基础研究发展计划("973"计划)项目"深井复杂地层安全高效钻井基础研究"(编号:2010CB226701);国家自然科学"深部应力敏感裂缝性地层漏失封堵力学机理研究"(编号:51204195)部分研究内容。

https://doi.org/10.3969/j.issn.1001-0890.2013.04.005