Wellbore stability and rock mechanics study on the Ula field

Abstract

In the years to come more challenging drilling conditions will occur when the last reserves need to be collected. More directional drilling will be used and good wellbore conditions will be necessary to make this possible. This means that good knowledge about the wellbore instability problems will be crucial. To get a good background of the field to make a good as possible model a lot of data was collected to get a good understanding of the Ula field. A geological overview was made to see the geological perspective of it all. All the historical instability problems and mud weight was collected from previously drilled wells which was then put into a three-dimensional model. This three-dimensional model gave a good understanding of how the field was behaving, and look at the wells as an overall picture and not just one by one. The objective of this study was to make a model that could be used to design a good mud program for the new injector wells that are going to be drilled on the Ula field in the near future. It is important that the mud program is designed such that the instability problems will be as low as possible and reduce non-productive time due to wellbore instability. From a calculated collapse curve it is possible to find the minimum recommended mud weight that could be used when drilling the new well. This study also uses the leak-off inversion technique to find the orientation of the stress field on Ula. The horizontal stress orientation was then mapped on a geological map of the field showing a good overview of how the stress is acting. The result of this test can be used to find the leak-off values of a new well that can help to avoid instability problems in the well.