Abstract

The production stage of oil and gas wells is drilled by using drilling mud with a sufficient density which achieves pressure exceeding  the formation pressure in about (5-12%) for preventing blowouts. When circulation of drilling fluid is stopping the drilling fluid must have gelling characteristics which will prevent drill cuttings from settling down over the bit . At the reason of increasing the gel strength, a part  of clay suspense is placed on well walls. This matter leads to decrease the density of mud, consequently, formation pressure is to be become more the hydrostatic pressure of drilling mud which allows the formation fluids to blow out of the well.

Studying  the factors  affecting the hydrostatic pressure of drilling mud enables controling the time, required for decreasing hydrostatic pressure of drilling mud to values of formation pressure ( balanced time ), then  the production  stage will be drilled  without problems .  

    In This  research we will study the effect of the diameter and the length  of the well model on  the balanced time of the mud column