WELLBORE STABILITY OF DIRECTIONAL WELLS ALONG DEPLETED ZONES OF GACHSARAN FIELD

Maintaining a stable wellbore is of primary importance during drilling and production of oil and gas wells. The shape and direction of the hole must be controlled during drilling, and also, hole collapse and solid particle influx must be prevented during production. Wellbore stability requires a proper balance between productions. Wellbore stability requires a proper balance between the uncontrollable factors of earth stresses, rock strength, and pore pressure, and the controllable factors of wellbore fluid pore pressure, and the controllable factors of wellbore fluid pressure, mud chemical composition, mud pressure and mud chemical composition. Wellbore instabilities can take several forms. Hole size reduction can occur when plastic rock is squeezed into the hole, and hole enlargement can be caused by caving shales or hard rock spallings. If the wellbore fluid pressure is too high, lost circulation can occur as a result of unintentional hydraulic fracturing of the formation; but if it is too low, the hole may collapse. Excessive production rates can lead to solid particle influx. The hole instability can cause stuck drill pipe as well as casing or liner collapse. These problems can result in side tracked holes and abandoned wells. Since 1940 considerable effort has been directed toward solving rock mechanics problems associated with wellbore instabilities, and much progress has been made during the past 10 years toward providing predictive analytical methods. Some of the literature representative of this work is discussed in this paper. Emphasis here is on understanding factors that influence wellbore stability in open holes, prediction of wellbore failures, and applications of rock mechanics concepts to control wellbore stability. In addition, in this paper, a brief historical overview is followed by discussion of various types of wellbore instabilities and descriptions of studies of field wellbore stability problems.

کلیدواژه ها:

Collapse gradient ، Fracture gradient ، Wellbore stability ، Horizontal stresses ، Mud window