CALCULATION MODEL OF CASING RUNNING SURGE PRESSURE AND INFLUENCE FACTORS ANALYSIS

Casing running surge pressure may induce weak formation leakage and cause downhole problem. According to this problem, the calculation model of casing running surge pressure was established based on flat plate laminar flow model. The effect of drilling fluid property, annular clearance, casing depth on surge pressure was analyzed by using numerical calculation. The results showed that drilling fluid rheological and gelling structure were closely related with surge pressure, drilling fluid circulation before casing entering open hole could reduce drilling fluid thixotropy which was favour of reducing surge pressure; the smaller the annular clearance was, the bigger the surge pressure was; Casing running velocity should be controlled even the casing was in the upper casing, because running casing quickly may cause mud loss for narrow density window well.