SUMMARY

Quantifying anomalies detected on seismic-generated attributes is critical to evaluate carbonate reservoir heterogeneities prior to planning and designing CO2 enhanced oil recovery operations. In this study, facies-based pre-stack inversionmethodisappliedtoa3Dcompressionalwaveseismic survey to characterize the Ordovician Red River U4 dolomitic reservoir. The facies-based inversion technique is able to delineate reservoir and non-reservoir facies and quantify porosity from inverted elastic volumes and the developed rock physics model.

INTRODUCTION

The target reservoir is unit 4 of the Red River Formation at approximately 9,000 feet below the surface. The field is located in the Williston Basin and will undergo carbon dioxide (CO2) enhanced oil recovery operations (EOR) in the near future. The objective of this reservoir characterization study includes understanding the heterogeneity within the reservoir and its potential influence on the CO2 flood. Available data consist of a 2014 3D compressional wave seismic survey and borehole measurements from 17 wells existing within, or in close proximity to, the study area (Figure 1). Figure 2 shows interpreted events across the seismic survey. TheRedRiverreservoirsaretypicallysubdividedintoA,B,C and D units(from youngest to oldest). Theyrepresentaperiod of 6 million years of cyclic depositional packages that grade from highly burrowed, open marine limestones through laminated dolomite mudstone into bedded anhydrites (Longman and Haidl, 1996). Red River U4 (RRU4) petrophysical unit is the study reservoir interval and corresponds to the dolomitic B zone in literature. In this paper, reservoir heterogeneity is characterized from the inverted elastic volumes using a facies-based pre-stack inversion method applied to the seismic dataset. At the request of the operator, the field’s name and location are omitted for confidentiality. Seismic surface extractions are limited to the field unit and edge effects are present where field unit reaches seismic survey limit. This study is the first published application of the facies-based inversion method on a deep and thin carbonate reservoir