Mathematical modeling and prediction of drill string stability region

Knowledge of the allowed stability region of drill pipes and collars is the first step to having an optimal design of drill string in specified conditions of wellbore. With lack of sufficient knowledge of drill string stability region may be used pipes with more resistance for more safety. Hence drilling cost will increase. This paper describes software designed to predict the drill string stability region across the entire length of the drill string. All mathematical equations have coded by using MATLAB software. Drilling depths have classified to n-elements in this MATLAB code. Calculations perform for the elements from surface to a certain depth or from a certain point to the next desired depth. Then the number of n-functions of axial stress and compression force create versus depth. Then the software substitutes the desired depths and gives to the user graphical and digital form of outputs. Data statistical analysis method has been used for programming this software to remove unwanted members. The user will be able to observe string stability region as point-to-point. So the users will have more accurate in choosing the appropriate size and type of pipes and collars. Also the field studies have done for several wells of southwestern Iranian fields. We have shown that in drilling some of them could be used proper lighter pipes to decrease drilling costs.