Visual Analysis Of The Rub-impact And It's Induced Wear Characteristics Of Drill String On Casing

Oil and gas are indispensable strategic resource for a country.With the decrease of shallow oil and gas resources in China,it has become an inevitable trend to explore and develop the oil and gas resources in deep formation and deep sea.But with the increase of well depth,the integrity of wellbore becomes more and more serious.Casing wear is one of the key factors affecting wellbore integrity.The study of casing wear is of great significance for understanding casing string working condition and improving wellbore integrity.Casing wear is mainly caused by continuous contact or rub-impact action between drill string and casing,and many research works have been done on the former and little on the latter.Field data reveals that the impact and rubbing caused by the whirling of drill string can is an important cause of uneven and random casing wear.In view of this problem,this paper analyzes the rub-impact characteristics of the drill string against the casing on the basis of the study of the dynamic characteristics of the drill string.A 3D visualization method is established to study the rub-impact and its induced casing wear characteristics.The main research work is as follows:Firstly,a full investigation of both domestic and international research works was made,including rub-impact against the wellbore,casing wear evaluation method,logging technology and finite element modeling method of drill string dynamics.The feasibility of the rub-impact characteristics simulated by drill string dynamics finite element model was analyzed.Secondly,taking into consideration of the geometric and contact nonlinearity,bitrock interaction together with the damping of drilling fluid,a drill string dynamic finite element model was established and solved.On this basis,a simulation program of drill string dynamics was developed and verified.Thirdly,the lateral motion of drill string and the rub-impact characteristics on the casing were simulated by the program.The influences of key parameters such as the surface rotary speed,the weight on bit and drilling fluid density on the lateral motion characteristics of drill string were analyzed.Fourthly,a 3D visualization method was proposed to evaluate the casing wear induced by the impact and rubbing.On this basis,the wear characteristics and the influence of key parameters on it were studied visually.Finally,according to the actual hole trajectory of the vertical well,both the rubimpact and wear characteristics of the casing were studied.The influence of hole curvature on casing wear was also analyzed.