欠平衡钻井安全钻进控制参数评价

欠平衡钻进过程中，气体侵入井筒后，环空出现多相流动状态。由于气体具有可压缩性，环空压力场随着气体的侵入及侵入量的改变而呈现复杂的变化．整个井筒压力剖面将出现波动。、为使地层气体可控制地侵入井筒．需要及时调节控制回压和钻井液排量，保证井底压力在安全密度窗口内，维持合理的井底欠平衡状态，以实现安全钻进。、文中根据欠平衡钻进井筒压力平衡关系，建立了井底压力控制模型。通过分析影响井底压力的参数．建立了影响井底压力控制的安全钻进控制参数模型．并以控制回压为例给出了具体的求解流程。以新疆某井为例．说明控制参数对井底压力和环空压力场的影响、研究结果表明：地层出气后，能够通过增加控制回压，采用正常循环排出的方式，将侵入气体排出井筒，实现安全钻进；增加钻井液排量，气液混合速度增大，环空摩阻增大．导致井底压力增加。

Evaluation on safe drilling control parameters for underbalanced drilling

The mulliphase flow state appears in wellbore annular after gases invade into borehnle during underbalaneed drilling process. Transformation rule of the annulus pressure field is complex with the change of gas invasion he.cause of the gas compressibility and the wellbore pressure profile will fluetuate. In order to control gas intruding, it is necessary to adjusl control back pressure and mt,d flow timely, ensure the bottom hole pressure to be in the safe density window, maintain reasonably hottom hole underbalanced state and achieve drilling safely. According to the wellbore pressure balance of underbalanced drilling, this paper establishes the bottom hole pressure control model. Through the. analysis of influence parameters on the hottom hole pressure, the article sets up the safe drilling control parameter model influenced on the control of bottom hole pressure and gives the solving process taking the control hack pressure as an example. The eontrol parameters on the effee.t of hottom hole pressure and annular pressure fiehl are illustrated taking one well in Xinjiang as an example. The results show that the intrusive gas can be removed nnrmally when increasing the bacek pressure, ensuring safe drilling. Gas-liquid mixing speed increases as the increase of drilling fluid volume. The bottom hole pressure increases as the annular friction increases.