Field-wide reservoir compressibility estimation through inversion of subsidence data above the Groningen gas field

Rob M.H.E Van Eijs,Onno Van Der Wal

doi:10.1017/njg.2017.30

Abstract

AbstractNot long after discovery of the Groningen field, gas-production-induced compaction and consequent land subsidence was recognised to be a potential threat to groundwater management in the province of Groningen, in addition to the fact that parts of the province lie below sea level. More recently, NAM's seismological model also pointed to a correlation between reservoir compaction and the observed induced seismicity above the field. In addition to the already existing requirement for accurate subsidence predictions, this demanded a more accurate description of the expected spatial and temporal development of compaction.Since the start of production in 1963, multiple levelling campaigns have gathered a unique set of deformation measurements used to calibrate geomechanical models. In this paper we present a methodology to model compaction and subsidence, combining results from rock mechanics experiments and surface deformation measurements. Besides the optical spirit-levelling data, InSAR data are also used for inversion to compaction and calibration of compaction models. Residual analysis, i.e. analysis of the difference between measurement and model output, provides confidence in the model results used for subsidence forecasting and as input to seismological models.

Highlights

The Groningen field was discovered in 1959 and gas production started in 1963
The Slochteren Sandstone reservoir consists of a quartz-rich cemented sandstone that is part of the Permian Rotliegend Group, a reservoir layer situated at a depth of around 2900 m
The subsidence and compaction models presented in this paper are fully calibrated to the geodetic data, but we will demonstrate that the applied uniaxial compaction coefficients in the calibration still fall within the range of measured Cm values from the core tests

Summary

Introduction

The Groningen field was discovered in 1959 and gas production started in 1963. Globally, the field is one of the top ten largest gas fields, and subsidence was recognised, even before production began, as a threat to groundwater levels. Doornhof (1992) provides an overview of data and subsidence models up to 1992 and provides a detailed description of the shallow and deep compaction measurements above the Groningen field.

Results

Conclusion