气体介质钻井条件下测井响应特征与判别方法

气体介质条件下钻井技术是一项新型欠平衡钻井技术，该技术对减小钻进过程中对地层的污染、及时发现低压、低孔低渗油气层非常有效。但是，气体介质钻井时，井内没有钻井液，使得井壁垮塌现象比较严重，井身质量较差，多项测井技术的测井响应受到严重影响，导致气体介质条件下的测井资料质量变差，给储层测井评价增加了许多不确定与不利因素。而另一方面，井筒内的气体介质虽然导致测井资料质量变差，但地层不受常规钻井液侵入污染影响，为部分测井方法凸显气、水层测井响应的差异提供了有利条件。文章以川中川南过渡带区3口井资料为例，分析了气体介质条件与常规钻井液条件下的测井响应特征与差异，且进一步探讨了气体钻井条件下测井资料气水判别方法及其适应性。

Characteristics of Log Response and Identification of Gas and Water Layers under Gas-drilling Medium Conditions

Drilling under gas medium conditions, a new underbalanced drilling technology, can effectively alleviate formation damage and timely identify oil and gas layers with low pressure, low porosity and low permeability in the process of drilling operation. However, when gas medium is used in drilling, there is no drilling fluid in the borehole, so borehole wall sloughing is serious and wellbore quality is relatively low. The log responses of several well logging technologies are severely influenced and the quality of logging data is low, resulting in many uncertain and adverse factors in logging evaluation of reservoirs. On the other hand, no formation damage from conventional drilling fluid occur when drilling with gas medium, providing favorable conditions for highlighting the log response difference between gas and water layers. Taking the data of 3 wells in the transitional zone between the southern and the central Sichuan as examples, the characteristics and differences of log responses under gas drilling medium and conventional drilling fluid are analyzed, and the methods and their applicability of discriminating gas and water layers with logging data acquired under gas-drilling medium conditions are further discussed.