Earth’s Magnetic Declination Error Influence on Wellbore Positioning in Pakistan Region and Norwegian Sea. Case Study

Abstract

The ultimate goal of petroleum industry is to perform their routine operations with minimal risks. Nevertheless, the possibilities of jeopardies for instance; blowout of a well always remains in the offering. This event normally occurs when all the well control barriers are failed in their functionality. Therefore, a contingency plan in the form of Relief well should always exist to tackle this acute risk associated event. In this study, two modeled well trajectories were designed in two different zones having different chorography. These regions are Pakistan and Norwegian Sea that are situated in lower and higher latitude regions respectively. The primary goal of this article is to study the influence of magnetic declination on wellbore positioning. During the initial phase of analysis, it was investigated from IGRF model that the internal geomagnetic field and the secular variations in Norwegian Sea are different than those in Pakistan. Upon further investigation, it was observed that in Norwegian Sea, the lower value of horizontal component of magnetic field of the Earth and higher values of dip angle results in increasing azimuthal uncertainty. Both of these components are part of weighting function of measurement while drilling, declination error source. This measurement while drilling model error source was then transformed in ellipses of uncertainty (EOUs). In Norwegian Sea almost 92% contribution in EOU size is from declination, whereas, in Pakistan this influence significantly drops to 35%. Furthermore, as EOUs size increases, the chance of premature collision also intensifies. This was experience in Norwegian Sea well, where the Relief well demonstrates separation factor less than 30 m before the desired depth, thus indicating an early intersection. Quite a reverse behavior was observed in Pakistan where the probability of premature collision with the Targeted well and the separation factor between the two wells before the desired depth are all in the desired range. Thus, it can be concluded that in Norwegian Sea, magnetic declination will have some serious consequences if not properly taken into consideration.