Building 1D and 3D Mechanical Earth Models for Underground Gas Storage—A Case Study from the Molasse Basin, Southern Germany

Muhammad Zain-Ul-Abedin,Andreas Henk

doi:10.3390/en13215722

Abstract

Hydromechanical models of gas storage in porous media provide valuable information for various applications ranging from the prediction of ground surface displacements to the determination of maximum reservoir pressure and storage capacity to maintain fault stability and caprock integrity. A workflow to set up such models is presented and applied to a former gas field in southern Germany for which transformation to a gas storage site is considered. The workflow comprises 1D mechanical earth modeling (1D MEM) to calculate elastic properties as well as a first estimate for the vertical and horizontal stresses at well locations by using log data. This information is then used to populate a 3D finite element model (3D MEM) which has been built from seismic data and comprises not only the reservoir but the entire overburden up to the earth’s surface as well as part of the underburden. The size of this model is 30 × 24 × 5 km3. The pore pressure field has been derived from dynamic fluid flow simulation through history matching for the production and subsequent shut-in phase. The validated model is ready to be used for analyzing new wells for future field development and testing arbitrary injection-production schedules, among others.

Highlights

A thorough understanding of the pre-production stress state and its changes with time plays an important role for the safe and economic operation of hydrocarbon reservoirs and underground storage sites
3D finite element model (3D mechanical earth modeling (MEM)) which has been built from seismic data and comprises the reservoir but the entire overburden up to the earth’s surface as well as part of the underburden
We present a worked example on how to set up and populate a 3D hydromechanically coupled model of an underground gas storage site

Summary

Introduction

A thorough understanding of the pre-production stress state and its changes with time plays an important role for the safe and economic operation of hydrocarbon reservoirs and underground storage sites. Some regional information about at least one of the components of the stress tensor, i.e., the orientation of the maximum horizontal stress, can be gathered from the World Stress Map (WSM) [4]. On the scale of a reservoir both stress magnitudes and orientations can be quite variable due to lithological heterogeneities and structural complexities [5]. A tool is required which can provide a robust prognosis of the in situ stresses in space and time, i.e., the complete stress tensor and its changes during subsurface operations, honoring the specific conditions of the hydrocarbon reservoir and storage site, respectively

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Results

Conclusion