Successful application of spectral decomposition technology toward drilling of a key offshore development well

Abstract

The field of interest is one of ExxonMobil's development assets in offshore West Africa discovered in the late 90's. A main appraisal well was recently drilled to confirm the existence of reserves updip of existing well control within the Lower Miocene deepwater reservoir. The oil reservoir is a steeply dipping (20–45 degrees) deepwater channel complex located on a flank trap of a piercement salt diapir. The discovery well was drilled in late 90's by the “Well A” exploration well and possesses a class II DHI response. Poor seismic data quality prevented subsequent confident predictions of reservoir thickness and reservoir quality updip of the “Well A” well. The application of Spectral Decomposition allowed us to discriminate the most significant frequency content of the reservoir and thus optimize the seismic image quality for stratigraphic and DHI interpretation. Reservoir imaging was high‐graded by applying a bandpass filter to preserve the most significant frequencies of the reservoir reflections. The resultant dataset revealed the expected DHI response for a class II anomaly, showed clear reservoir amplitude conformance to structure, improved the stratigraphic details for higher confidence interpretation and ultimately supported the presence of thick high‐quality reservoir section updip from the “Well A” well. The “Well B” appraisal was drilled two years later to a target picked on the basis of the spectral decomposition analysis. The well penetrated over 154 meters measured depth (113 meters TVD) of net oil sands, confirming the presence of thick, high‐quality oil sands updip of the “Well A” well.