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Not 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.

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This paper was selected for presentation by an SPE Program Conmitfee following review of information mnfained in an abstract subrnffed by the author(s). Contents ot the paper, aspresented, have not been reviewed by the society of Pelroleum Engineers and are subj.xf to mrrecfion by the author(s). The material, as presented, dces not necessarily reflect any postion of !he Sc$iefy of Petroleum Engineers, its officers, or metiers. Papers presented at SPS meetings are subpct 10 publ,cat!on rewew by Editorial Comuffees of the Society of Petroleum Engineers. Stectronic reproduction, distribution, o: storage of any part of thw paper for mnnmrcial purposes wthout the wrtfen consenl of the Society of Petroleum Engineers is pmhibted. Perrnssion to reprcduce m print $s restricted to an abstract of not mare than 300 words; illustrations may not b mpled. The abstract must contain conspicuous aclmovdedgm-mt of where and by Mom Ihe paper was presented. Write Lrbranan, SPE, P.O. Box S3SS3S. Richardson. TX TSOS3-3S436,U. S.A., fax 01.972.952.9435. AbstrsctA predictive in-situ stress model has been built using finiteelernem techniques for salt enclosed stringers located in the South Oman Salt Basin, The stringers comprise silicilyte reservofr and shale formation layers, in a semi-thrustlike configuration. The model provides input and support to the fracture distribution and the compaction assessment of the silicilyte reservoirs. The model has been build based on seismic, gravity and well data.Before building the in-situ stress model, two series of sensitivity analyses have been carried out concerning the geometrical parameters that influence the stress distribution and stability of in salt enclosed stringers. In the first anatysis, the dominating parameters in an environment with an active rising salt dome (halokinesis) have been investigated. This analysis improved the motivation for the kinematic and geological development of the structures. In a second analysis, the stability of a single dipping stringer in a stationary salt body was investigated. The latter configuration is concordant with the current situation in the South Oman Sat Basin. The outcome of this anafysis provided insight into the stress distribution of sinking stringers encased in salt, The insights obtained from these analyses were incorporated into the in-situ stress model. AcknowledgementAll finite-element analyses for the studies described in this report were conducted using the DIANA finite-element system at the Netherlands Institute for Applied Geoscience TNO in Delft supported by Mrs. J. Siermartn and I. Schrijnemaekers and under super-vision of Mr. W Zijl,

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