Orientation load prediction method based on randomness/stochasticity of multi-source parameters in coiled tubing drilling

Abstract Well trajectory control is always the key point of directional drilling. Downhole parameters measurements and BHA (bottom hole assembly) configuration and adjustment have the vital and coupling effect on realizing effective and efficient trajectory control. However, error exists universally in both of these phases. Compared with previous fixed value prediction models on controlling parameters prediction, uncertainty analysis based method will make the prediction results more reasonable and meaningful to control the BHA performance. With the consideration of the randomness of downhole multi-source parameters in coiled tubing drilling, an uncertainty prediction method for orientation load at a certain confidence level is proposed. Based on the beam-column theory, the probability and statistics theory is introduced and the distribution forms of main parameters are counted statistically. The probability density function and cumulative probability function of the orientation load prediction model when pump off and pump on in coiled tubing drilling are derived. The lognormal distribution has better correlation with the probability function of the orientation load, and the analysis on the confidence interval of the orientation load is described. Then, several relevant validation experiments are carried out, and the prediction of uncertain orientation load in coiled tubing drilling is also made. Several conclusions are made regarding to the field trial results. The randomness of weight on bit, friction coefficient of the interfacial between drill string and borehole wall or drill string and casing and tool face angle are the principal factors affecting the uncertainty of orientation load in coiled tubing drilling. The orientation load predicted with the uncertainty method is not a single curve or a single value, but an interval with a certain confidence level. The width of interval window is determined by the accuracy and precision of parameters information. The higher the confidence level is, the wider the predicted interval of orientation load and the larger the uncertainty range become. Compared with the predicted results of the uncertainty method, an error exists in the result of traditional single-value calculation method. The error varies with the change of weight on bit and formations and can be positive or negative. Meanwhile, retrieving more accurate principal original dada, e.g. WOB, formation properties, will make the uncertainty of the prediction lower. This orientation load prediction method is helpful to improve the efficiency of directional drilling in coiled tubing drilling.