Characterization of deeply buried heterolithic tidal reservoirs in the Smørbukk Field using inverted post-stack seismic acoustic impedance

Abstract

Deeply buried reservoirs in Smørbukk Field play an important role in oil production from the Halten Terrace hydrocarbon province (Mid-Norwegian shelf). These heterolithic reservoir sandstones are sedimentary systems for which estimation of reservoir properties is challenging. The main problem is to derive realistic models of the lateral changes of porosities and permeabilities in the inter-well space. There is a very significant upside potential in producible reserves if infill production wells can be placed and completed in an optimal position with respect to reservoir quality. In this paper reservoir characterization work, based on good quality seismic data, has been performed in order to predict porosity, net: gross ratio and permeability both qualitatively and quantitatively supported by reliable geological models. Essentially, Acoustic Impedance (AI) is correlated to porosity and inverted seismic data have been used to predict reservoir properties. Two different porosity modelling methods in the Tilje Formation are used: (1) by means of simple regression; (2) using geostatistical methods. Lateral changes in porosity follow a pattern that is sedimentologically plausible. A geostatistical workflow resulted in porosity maps that take into account both lack of vertical resolution in seismic data and poor lateral resolution in well data. This is considered to be the most optimal method for predicting geologically acceptable reservoir properties, because uncertainties in porosity modelling are measured. Porosity maps were used to update the reservoir simulation model and adjust targets for infill wells in the Smørbukk Field. Results were tested in two wells drilled after utilizing the seismic AI and showed an excellent match.