Accurate geological placement of a lateral in the sweetest portion of the reservoir plays a major role in optimizing production rates and increasing recovery from horizontal wells, particularly for complex reservoirs with heterogeneous features. Horizontal wells have thus been routinely steered both geologically and geometrically using evaluation measurements from conventional bottom hole assemblies with sensor points some 50 feet away from the bit. This implies that correction runs and it’s effective response time and footage will be dependent on directional drilling personnel proficiency and tool performance relative to formation type. It is not surprising thus, that a sizeable part of the reservoir is drilled sub-optimally, and in some cases the eventual well bore undulation has caused impossible completions, developed water sumps and have also given birth to speedy breakthroughs of gas and water. All of these have impacted production negatively, and caused unnecessary oil deferment, early work-over and associated cost overrun on budget.
The ideal option would thus be to minimize the undulation while geo-steering the lateral along the sweetest portion of the reservoir in an attempt to minimize attendant production problems and hence allow efficient and early completions.
A tool has been developed which measures well bore inclination 1 foot away from the drilling bit. Shell West Nigeria introduced the At bit Inclination measurement tool to horizontal well drilling on the Opukushi 26 well in March 99. This was to complement multiple depth propagation resistivity and quadrant density-neutron measurements while drilling utilized in horizontal evaluation, to enable full wellbore geologic steering with optimized response time for correcting changes in the desired direction. The result is a significant improvement in the ratio between actual versus predicted production figures as compared to previously drilled wells executed without the combination measurement. It also aided geosteering decision, improved directional performance and enhanced delivery of better quality well.
This paper therefore reviews the SPDC horizontal wells experience in identifying the impact of deviation profiles and lateral placement with respect to production performance, and how the use of the near bit inclination tool along with the formation evaluation measurements has resulted in noticeable improvement.