Drilling on Target: Saving Rig Time While Maximising Reservoir Exposure in a Horizontal Well

Abstract

Abstract A pilot hole is a commonly used method to reduce uncertainties while drilling a horizontal well, but it is a costly procedure. Thus, there is high demand in the industry to have alternative solutions to reduce total well cost but still achieve the well objectives. This paper presents a case study of a horizontal well in the Malay basin that was landed accurately in the target oil reservoir without any pilot hole and drilled optimally in the target layer with improved reservoir thickness evaluation. The well target was a sand layer with average thickness of 3 to 5 m and variation in quality. Unlike the other target reservoirs in the field, there was no concern over fluid contacts within this sand; thus, options to eliminate a pilot hole were considered feasible. The main challenges were the structure determination, formation dips, and thin-sand thickness that would cause significant impact to landing accurately and achieving a minimum of 300-m lateral length inside the reservoir. A full suite of logging-while-drilling (LWD) measurements, combined with a model-compare-update well-placement method, were used during landing to address these challenges. For the lateral section, an additional deep-directional resistivity measurement was used for boundary detection, which enabled proactive geosteering to avoid premature exit. As a result, the horizontal well was landed accurately in the target reservoir layer without the need for a pilot hole; thus, significantly reducing the well cost. Furthermore, a 500-m lateral section was maintained 100% inside the target reservoir, which exceeded the initial objective. A post-drilling analysis was performed using density image dip-picking and bed-boundary mapping results. The drilling polarity along the lateral section could then be determined and the true stratigraphic thickness of the target reservoir extracted, which resulted in a more accurate reservoir thickness evaluation. The methods and processes used in this case study yielded best practices and recommendations for drilling and evaluating similar reservoir conditions elsewhere.