Loss circulation refers the phenomenon of drilling fluid inside wellbore leaking into formation pores,cracks and other spaces during drilling.
It is a common phenomenon during drilling process,most wellbore have different degrees of loss circulation.Serious loss circulation lead to decrease the wellbore stabilization,effect drilling speed,occur blow out and even threaten operator’s personal safety.
According to different degrees of lose circulation,it can divided to four types loss circulation:
Penetration loss circulation : mostly occur in high permeability formation and the main reason is the high permeability of layer.The rate of loss circulation is slow.
Crack loss circulation: causes by fractures,which include natural fractures and induced fractures.the rate of loss circulation is fast.
Cavernous loss circulation: caused by the cavernous formed in the formation, generally only appear in the limestone formation, the rate is extremely fast.
Rupture leakage: caused by formation rupture or depleted, the leakage rate changes greatly.
The reason of lose circulation can be divided into five categories:
The pressure of the drilling fluid is greater than the pore pressure of the formation.
The formation has large liquid-accommodating pores (such as cracks, cavernous), has loss circulation channels and good permeability.
The diameter of the loss circulation channel is greater than the size of the solid particles in the drilling fluid.
Improper drilling process measures cause loss circulation ,open the pump is too fast or too fast drilling speed can cause lose circulation.
Improperly oil--well structured.
