This paper reports the results of laboratory tests made on materials used to prevent loss of circulation of drilling mud. In this study, the well and formation model are used to evaluate the lostcirculation materials. The well model is made of double pipe to test under the circulating of drilling mud.
In the formation model, various size beads and wedge-shaped slots are used respectively to represent increasing permeabilities of formation and opening size of fissure. A bentonite mud is used to suspend 5 to 60 grams per liter of each material tested. Mud tested is circulated through the well and formation model by pump. Following conclutions are obtained.
1) Forty- five of lost-circulation material per liter of mud is the optimum.
2) It is necessary to consider the seal depth to evaluate effect of lost-circulation material in permeable fomation.
3) In granular lost-circulation material, maximum size of particls is equivalent to the size of the openings to be sealed.