Revealing of pack offs in RTDD

Abstract

Pack off is a major problem in the drilling industry today, and it will continue to be so until a solution to this problem is found. Being able to find pack offs and in addition to having an understanding of the mechanisms governing the causes of pack offs make it possible to prevent stuck pipe and or other incidences that may lead to non-productive time. The first part of this thesis will describe the rock mechanics of a formation and explains what stresses are involved at governing the wellbore instabilities such as hole collapse and fracture. Types of drilling mud as well as a description of equivalent circulation density and the general causes of pack offs encountered in a well are also discussed. The next part of this thesis is a case study of well 34/10-C-47 drilled in Gullfaks C which is located in the Norwegian North Sea. This was the main motivation for writing this thesis. The observations require knowledge about what caused that which is observed, the equipment and drilling fluid related to causes before the pack offs incidences are given in detail. Pack offs incidences are gathered into two groups based on the behavior of the SPP curve. Further, causes for the pack offs are explained as good as possible. Poor hole cleaning and wellbore instabilities such as swelling of shales and unconsolidated sands are the most likely causes for these pack offs. In the final part of this thesis two different models are described. The first model is applied for the automatic detecting of all sorts of pack offs, while the second method involves only those which is related to poor hole cleaning. It was created a matlab program based on the second model.