Probabilistic Well-Time Estimation Revisited: Five Years On

Abstract

Summary In 2010, Adams et al. published a paper on well-time estimation, which for the first time allowed accurate calculation of probabilistic duration for noncritical wells. The present paper extends the method and data coverage to high stepout and high-pressure–high-temperature (HP/HT) wells. The method has now been in use for 5 years. Actual and predicted durations are given for each year's drilling, showing that the accuracy is historically within 2 to 3% for stable trainwreck rates. The historical well database upon which the statistics are based now stands at 211 wells, 93 more than the previous paper. To the authors’ knowledge, it remains the only large-sample timings database published in the open literature. To allow others to use the method, the updated activity timings, mechanical nonproductive time (NPT), and waiting-on-weather (WOW) data for semisubmersible-drilled wells are given in full. It is shown that the commonly used distributed trainwrecks model has too high a sampling uncertainty for accurate time estimation. The lumped trainwrecks approach presented here does not suffer from this limitation, and is therefore (to the authors’ knowledge) the only published method that delivers the required accuracy for practical data-set sizes.