Abstract
The maintenance of wellbore stability remains one of the major sources of Non-Productive Time in the oil industry.During drilling process,the drill string vibration cyclic loads which are applied on the wellbore progressively affect the initial parameters of the fractured formation(such as its length and width),finally resulting into wellbore instability.In this research,a three-dimensional poro elasto plastic finite element model was built using a non-linear finite element software ABAQUS purposely to investigate the effect of drill string vibration cyclic loads on the wellbore natural fracture growth.The main conclusions exhibited that the dependency of the fracture width profiles with the time followed an oscillating comportment analogous to the vibration cyclic loads profiles.For distinct cyclic load magnitudes and constant number of cyclic loads,the biggest percentage augmentation of the fracture width after integration of cyclic loads was 64.77%.Interestingly,the aperture of the fracture increased with the length of the fracture in the region neighboring the wellbore while it globally declined when going farther aside the wellbore.But for constant magnitude of cyclic load and distinct cyclic loads number,the highest rate of fracture aperture augmentation after incorporation of cyclic loads was moderately smaller representing 63.12% while the sinusoidal period of the fracture aperture grew with the number of cyclic loads number.The alternate studies demonstrated that the vibration cyclic loads were approximately unrelated to the fracture length development and the bottom hole pressure evolution.However,the fracture aperture and the loss circulation rate were significantly influenced by the vibration and the biggest percentage augmentation of the loss circulation rate after implementation of cyclic loads was 14.3%.This study broadens the understanding of the coupling between the drill string vibration cyclic loads and the wellbore natural fracture rock development which is a thematic that has been seldom examined in the literature.
NSTL