气体钻井井壁稳定性评价方法分析

由于气体钻井技术在某些方面有着常规钻井液钻井不可比拟的优势，在国内得以大范围地试验应用。但是，作为一项新技术，气体钻井本身具有一定的局限性，其实用范围尚不完全清楚。因此，在现场试验过程中已经暴露出不少问题，井壁稳定性就是其中最为突出的问题之一。在常规钻井液钻井过程中，井筒与地层孔隙压力之间存在正压差，正压差对井壁起到一定的支撑作用，在一定程度上抑制了井壁坍塌，有利于井壁稳定。而在气体钻井中，这种支撑作用并不存在。为此，从气体钻井井壁岩石力学的基础着手，建立了气体钻井条件下井壁稳定性分析的评价方法，并结合实际工程地质特征，对川西特殊复杂地层没有流体产出情况下气体钻井井壁稳定性进行了定量评价，分析评价结果与现场施工情况吻合。

ANALYSIS ON THE METHODS USED TO EVALUATE THE WELLBORE STABILITY OF GAS DRILLING

Gas drilling technology has been experimentally applied in large areas in China due to some of its advantages compared with conventional drilling fluid drilling technology. However, as a novel technology, gas drilling still has some limits, its application scopes are still not fully known. Wellbore instability is one of many problems that have been encountered during field tests. During drilling by conventional drilling fluid, positive pressure difference exists between the wellbore pressure and the formation pore pressure, which provides some support to the wellbore and so inhibits the well caving in; but while during gas drilling, this kind of support is not available. This paper introduced the method set up to evaluate the wellbore stability of gas drilling based on the wellbore rock mechanics of gas drilling. And the actual geologic engineering properties are combined to make a quantitative evaluation of the wellbore stability during gas drilling without fluid production in West Sichuan formations. The evaluation results are similar to the engineering results on fields.