Modeling and mechanism analyzing of casing running with pick-up and release technique

Abstract

The pick-up and release technique is a most frequently used and accessible method when casing string is hindered by high friction force during casing running process. However, its application is mainly based on working experience in drilling field and lacks of mechanism analysis and theoretical guidance. Thus an analysis model of the technique is established to reveal the mechanism. Then a simulation model of the technique in actual wellbores is built to predict the trip-in ability of casing strings, which combines with soft string model and buckling theory. And the simulation model is also used to research the influence regularities that how factors can affect the trip-in ability, such as frictional coefficient, axial force, tensile force of wellhead, the release way, displacement-vertical ratio and wellbore quality. The mechanism shows that the elastic energy is accumulated during the pick-up process and converts to stress wave during the release process. Then the friction force decreases for the propagation of stress wave in casing strings, so that the original axial force can push casing strings forward even though it is smaller than the total friction force. The researches show that there is a negative correlation between frictional coefficient and trip-in ability while positive correlations between axial force, tensile force and trip-in ability with the technique. Meanwhile, the trip-in ability with a rapidly release way, small displacement-vertical ratio or high quality wellbores is much better. Through model field data verification, the model prediction results are proved to match well with actual field data. Therefore, the proposed models and relevant conclusions can provide necessarily theoretical guidance for application the technique during casing running operation in oil/gas industry.