Accurate placement of a horizontal well within a reservoir can be complicated and with uncertainties (McLennan, 2006). That was the case for the 8.5-in. horizontal well in the study being reported. Uncertainty in the structural geology existed due to distance from the closest well (~500 m) and also the vast number of faults identified on the seismic data.
With the well supposedly landed in the reservoir, the expectation on start drilling sand was not met upon drilling out the casing shoe. Approximately 180 m MD of shale was encountered before making a decision to use the well for appraising the upper seismic reflector. The section was subsequently abandoned for a sidetrack that aimed at producing the upper sand lobe.
From the original casing shoe of the landing point, to access the upper sand lobe with the shortest shale section possible, a strong build in inclination to >90° would be required upon exiting the shoe. Once the wellbore entered the reservoir sand package through the base, a change in trajectory was immediately required to avoid exiting through the top of the thin sand. The sooner the well entered the sand, the greater the success of the well because drilling more than 410 m MD would intersect the drainage radius of another producing well; hence, creating undesired production interference.
A new model was developed and the well plan was executed. Based on the model, approximately 140 m MD of shale was expected before intersecting the base of the reservoir; however, in actuality, 167 m MD of shale was drilled prior to intersecting the reservoir entrance. Within 20 m MD inside of the reservoir, an indication of the top of the reservoir was observed on the distance-to-boundary inversion. As a result, the trajectory was adjusted accordingly to prevent exiting the reservoir that resulted in achieving 60% of reservoir sand.
This case study will highlight how the combination of real-time distance-to-boundary mapping technology and proactive steering decisions aided in eliminating a second consecutive sidetrack of the horizontal section.