A Novel QI Screening Technique for Identifying Deep-Water AVO False Positive: Learnings from Well X

Abstract The quest for hydrocarbon has led explorationist to investigate amplitude anomalies popularly known as direct hydrocarbon indicators (DHI) from seismic data. Although DHI technology has proven to be a reliable tool in reducing exploration risk leading to many discoveries, it is not infallible and therefore can lead to disappointing outcomes of drilling into water bearing reservoirs that are classed as false positives which were characterized at predrill phase as hydrocarbon bearing sands. Hence the effectiveness of DHI's should properly be ranked particularly on the backdrop of sound geological and geophysical models. This paper presents a study from a deep-water field where an integrated QI workflow has revealed a distinction between false positives and conventional hydrocarbon bearing sands. An Exploration well - Well X was recently drilled targeting Body X sand - a channelized lobe displaying high amplitude anomaly and Class II/III AVO signature. The well turned out to be a 78ft thick brine sand with 32% porosity and 100% net-to-gross. A post-mortem rock physics analysis of this sand and other false positives that were previously encountered in the field indicate that false positives show a distinct behavior compared to conventional oil and brine bearing sands. Two elastic properties; - LambdaRho, a fluid indicator and MuRho - a proxy for lithology, formed the basis of this analysis. From the rock physics cross plot, false positives are observed to be more rigid with higher MuRho values compared to conventional hydrocarbon and brine filled sands. LambdaRho and MuRho deterministic seismic inversion attributes were generated directly from broadband angle stacks that highlighted the high rigidity values of the false positives in line with the rock physics cross plot. This technique therefore serves as a first pass screening tool for identifying false positives that could improve our predrill prediction and future risking of potential hydrocarbon opportunities in Nigeria Deep-water operations.