Target-Hitting Probability Prediction of Landing Point for a Horizontal Well

Abstract

Summary The uncertainties of the reservoir depth and wellbore position derived from the measurement error of the well trajectory means that entering the landing point of a horizontal well is challenging. In many cases for horizontal well trajectory control, the influence of depth error on the target probability is not considered because methods of analyzing the effects of position uncertainty quantitatively are lacking. This study considers the effects of uncertainty of the wellbore position and that of the vertical depth of the reservoir on the horizontal well in terms of hitting a target. We assume that the wellbore position and target depth conform to the law of normal distribution. Accordingly, a horizontal well target-hitting probability prediction model is established. With the four aspects of random, system, well-by-well and global errors considered, 14 error sources and error weight functions that affect the measurement depth are first determined. The error theory is then used to establish a calculation model for the error of measurement depth as well as a method for predicting the probability of hitting the landing point in a horizontal well. This method not only can be used to predict the target-hitting probability of the landing point, but it can also be used to analyze various factors that affect the target entry in the horizontal well. This research also provides a theoretical basis for selecting marker beds and conducting well trajectory design to effectively improve the target-hitting probability in horizontal wells.