Application of crossplot and prestack seismic-based impedance inversion for discrimination of lithofacies and fluid prediction in an old producing field, Eastern Niger Delta Basin

Abstract

Abstract Lithofacies distributions and continuity are very important for proper reservoir development; and predicting the fluid types will also help in reducing uncertainties associated with characterizing hydrocarbon reservoirs. This study used Poisson impedance attributes and crossplots from prestack seismic inversion and well logs to discriminate and predict hydrocarbon-filled reservoirs in the Bumma Field, Greater Ughelli Depobelt, Niger Delta Basin. Seismic inversion and well log data were integrated to image and characterize lithofacies at reservoir zones of interest. A supervised model-based simultaneous inversion of Poisson impedance (PI) and crossplot was carried out on the prestack seismic data to understand the lithofacies classification and fluid types. Four classifications of lithofacies (clean sand, sandyshale, shaly-sand and shale) were discriminated based on the well log crossplot between gamma ray and Poisson impedance. The sand lithofacies shows low values of gamma ray ( 65 API) and PI (>− 100 ft/s*g/cc). Also, well log and inverted results from PI showed that values with less than − 100 ft/s*g/cc represent hydrocarbon-filled sand, whereas greater values represent brine and shale. These classifications provide better decision in predicting and discriminating lithofacies accurately. Furthermore, generated map revealed the presence of hydrocarbon-filled reservoirs in a northeast–southwest trending meandering channel. The successful application of crossplot and seismic-based impedance inversion will be helpful in discriminating lithofacies and predicts fluids for accurate location of new wells for optimum production from the field.

Keywords

• Acoustic impedance
• Cross-plot
• Lithofacies
• Poisson impedance
• Prestack seismic data
• Simultaneous inversion