Integration of sequence stratigraphy and geostatistics in 3-D reservoir modeling: a case study of Otumara field, onshore Niger Delta

Abstract

Sequence stratigraphic concepts for continental settings were assessed to analyze depositional systems of the formations penetrated by wells in the Otumara field. Identification and delineation of five sequences and their bounding surfaces was carried out using well logs. Reservoir sands A to D were mapped using conventional 3-D seismic interpretation techniques. Geostatistical simulation was carried out to provide equiprobable representations of the reservoirs, and the distribution of reservoir parameters and system tracts delineated from the stratigraphic framework. The modeled reservoir properties resulted in an improved description of reservoir distribution and connectivity. Reservoir sands A and B have the highest distribution of both highstand systems tract (HST) and lowstand systems tract (LST) deposits, while reservoir sands C and D have the lowest. Since reservoir sands C and D are from deeper depth, the results indicate that HST and LST decrease with depth while transgressive systems tract (TST) increases with depth. Correlating the 3-D geostatistical model with structures shows prospects with low and high hydrocarbon saturation. Crossplot of porosity and permeability for all reservoirs yielded good correlation. The crossplot of systems tract and hydrocarbon saturation with lithofacies as Z value shows a strong correlation of 0.89. The result also indicates that high hydrocarbon saturation is related to sandy facies of lowstand systems tract. Thus, the LST has the highest hydrocarbon potential. The models resulting from this study can be used to improve reservoir management and well placement, and to predict reservoir performance in Otumara field.