气体正循环钻井压力模型

气体钻井是一种与传统钻井方式相比有着很大区别的欠平衡钻井。为了合理预测井内流体的流动特性，有必要推导出统一适用的理论公式。气体体积流量是保证欠平衡钻井施工的关键，由于采用具有极大压缩性的气体作为循环介质，其循环系统的体积流量与压力变化密切相关，因此气体钻井压力计算成为研究重点。按照气量从钻柱内注入沿环空上返的顺序，分别对钻柱和环空处压力公式进行了推导，建立压力随深度和温度变化的计算模型，并以空气钻井为例求解各处方程通解。根据边界条件确定常数，就可获得压力随温度和井深变化的规律，进一步计算即可确定体积流量，为合理选择空压机等配套设备，确定钻进方法提供理论依据。

Pressure Model of Air Normal Circulation Drilling

Air drilling，as a member of under balance pressure drilling family，is different from conventional drilling methods.In order to predict the flow characteristics，it is necessary to derive the unified applicable theoretical formula，which can provide basis for choosing compressor and determining drilling methods.The air volumetric flow is the key to guarantee the construction of under balance drilling.Owning to air drilling taking the compressed air as circulated fluid，the circulation system volume flow is closely related to pressure variation，so the pressure calculation becomes the major research emphasis.According to the order of air injection，the pressure formula derivation of drill string and annulus were respectively studied，and took the air drilling as an example to solve the generic solution.According to the boundary condition to ascertain the constant，the law of pressure variation changing with the temperature and depth could be gained.To further compute the air volume flow could provide the solid basis for compressor.