A Method for Evaluating Drill String Fatigue Failure Risk

Abstract

The invention discloses a method for evaluating the fatigue failure risk of a drill string, which comprises the following steps: a. Obtaining or measuring the wellbore structure of the target well, the drilling tool assembly structure and the actual wellbore trajectory parameters; b. Establishing the limited dynamics of the drill string c) solve the buckling stress, dynamic bending stress and dynamic axial force of each joint section of the drill string in the whole well and correct the dynamic bending stress; d solve the fatigue frequency coefficient of each joint section of the drill string in the whole well; e. The relationship between the coefficient and the well depth is given, so as to evaluate whether the drill string has a high risk of fatigue failure, and determine the position with a high risk of fatigue failure of the drill string. The invention is not only applicable to the prediction of the fatigue failure risk of the drill string in the drilling design process, the optimization of the drill string structural parameters and drilling parameters, but also the assessment of the fatigue failure risk of the drill string in the actual drilling process, and the research on the fatigue failure of the drill string mechanism.

Description

technical field [0001] The invention belongs to the evaluation technology of the fatigue failure problem of the downhole drill string that often occurs in the exploration and development of oil and gas fields, in particular to an evaluation method for the fatigue failure risk of the drill string. Background technique [0002] The drill string is the main tool used to transmit power and transport drilling fluid, and plays an important role in the drilling process of oil and gas fields. In the process of oil well drilling, the drill string needs to work in the narrow and long borehole filled with drilling fluid for a long time, and the stress situation is very complicated. It bears a large stress mutation caused by alternating loads, and is prone to fatigue failure and drilling tool failure. Accidents often bring huge economic losses to oil fields. There are a large number of drill string failure accidents at home and abroad every year, among which drill string transition lea...

AI Technical Summary

Problems solved by technology

In 2013, 18 leak accidents occurred in a well in XX Oilfield, which seriously affected normal drilling operations and brought great hidden dangers to subsequent safe production

Therefore, neither the stress solved by the existing static finite element model nor the existing fatigue coefficient evaluation method can fully reflect the stress state of the drill string during actual drilling, and it is impossible to better evaluate the actual drill string fatigue. failure risk

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