徐深气田空气钻井转换雾化钻井最佳时机确定

针对空气钻井地层出水后，岩屑易形成泥环造成环空循环不畅等问题，需要确定转化为雾化钻井的时机，开展了临界地层出水量及最佳转化时机研究与试验。通过使用烘干的采集于空气钻井不同层位的岩样，开展了气体雾化水、岩屑吸水、岩心吸水及岩屑吸水形态变化地面试验，得到了岩屑吸水后形态变化情况，得出岩屑聚团是气体钻井出水后危险的状态。同时以空气钻井裸眼段长度1 000 m为例，经过对试验数据分析，当排砂管线内有自由水出现，地层出水量为0.51 m3/h时，空气钻井应及时转换成雾化钻井。现场试验表明，通过试验手段得到空气钻井转化成雾化钻井转化时机能够有效地指导徐深气田空气钻井安全施工。

Determination of optimal conversion time from air drilling to mist drilling in Xushen Gasfield

When air drilling is adopted, mud rings tend to be formed from debris, hindering the circulation in annulus after formation water breakthrough. To deal with these problems, it is necessary to determine the conversion time from air drilling to mist drilling. Therefore, the critical formation water production and the optimal conversion time were investigated and tested. A series of ground experiments were carried out on the dried rock samples taken from different horizons during air drilling, and they are air atomized water experiment, debris water absorption experiment, core water absorption experiment and morphological change experiment after debris water absorption. And accordingly, the morphological change after the debris were absorbed with water was understood. It is indicated that debris agglomeration is the dangerous state of air drilling after water breakthrough. Finally, a case study was performed on an open hole interval of 1 000 m long where air drilling was carried out. Experimental data analysis results show that the air drilling shall be converted into mist drilling as soon as the formation water production rate reaches 0.51 m3/h after free water occurs in clearance pipelines. Field tests indicate that the conversion time from air drilling to mist drilling determined by means of experiments can be used as the effective guidance for safe air drilling in Xushen Gasfield.