A series of palaeolandslides is described in eastern Belgium, with geophysical investigations, trench analysis and a number of 14 C dates complementing the field description. The proposed sliding mechanism stresses the importance of initial liquefaction of the upper Cretaceous Aachen sands underlying the~30-m-thick Vaals Clay Formation, in which all landslides are developed. Slope-stability analyses support the hypothesis of sudden landsliding and yield further useful information to discuss their origin. A main difficulty in determining the landslide trigger arises from insufficient absolute dates. Assuming that all landslides occurred simultaneously, we weigh the probabilities, respectively, of a climatic and a seismic trigger. Although the 150 a.d. possible date of landslide initiation falls close to one of the wettest periods of the Holocene, the spatial distribution of the deep slides and their proposed mechanism strongly suggest a seismic origin in connection with a rupture of the nearby Ostend segment of the active Hockai fault zone. However, considering that the nearby 1692, Verviers earthquake apparently caused no ground failure, it is probable that both the climatic and seismic triggers were jointly needed to provoke such deep and extended landsliding on moderate, generally stable slopes.

hi. SPE/lSRM 47587 Water/chalk (or collapsible soil) interaction: Part Il. Results of tests performed in laboratory on Lixhe chalk to calibrate water/chalk models Ch. Schroed&, University of Lkge, A-P. Bois SPE, SIMECSOL, V. Maury SPE, ELF-EP and G. Halle, Elf Petroleum Norge m! 1*. q-of POtrO&IM Engi'wers, Inc. This paper was prepared for pmsentatkm al ttw SPEflSRM Eur.xk '9S held in Trc+xlheim, Nmway, 3-10 July t99B This paper was selected for paemlafion w an SPE Program Committee following review of lnfornmti~ccolah?ed in an abstract submitted by the aulhor(s). Conlenls of the paper, as pmsew6d, have not been mviewad by the society ot Petroleum Engineers and are subject to WTdhI~th. WthO@) 7h0 fIWtWid,~S pf9S-811tWf dW6 ITOt IVB3SSWIV Wfkd any P@fim d the SociMy d Petroleum Engineers, ifs officers, or nwmbsrs. Papers presented at SPE meetings am subject to rwbikation review ty Editorial Committees of Ihe Society of Petroleum Engineers, Electrcfdc reproduction. distribution, or stomgs of any part of this paper for commercial purposes without the witkin ccfwent of the society of Petroleum Engineers is prohibited. Pwmission to reprod.ica In prtnt IS restricted to an abstract oi not more lhan 300 e Olustmtlons may net be copied. The abstract must wmlmn .YXWp!cuaus 8c4amwledgnmnt d w4'18Mand ty~cm me paper was presented. Write Librarian, SF%, P.O. 60X 8SS8S6, Riiardsm, 7X 750S34836, U. S.A., iaX 01-972-952-9435 AbstractEkof~k, Valhall and other North Sea reservoirs are made of water sensitive rocks such as pure high porosity chalk. Production of these fields implying water-flooding leads in several cases to compaction and subsidence. In order to perform reliable predictions of compaction and subsidence when water-flooding such reservoirs, it is necessary to take into account not only the deformations that come from depletion in the compressible reservoir rocks but also to inciude additional deformations induced by water saturation (WS) increase.These additional deformations may eventually be determined by performing water-injection (WI) tests in laboratory.This paper presents additional tests that have been performed in laboratory in order to understand the mechanical behavior of chalk at the water-front.It shows the existence of a degree of WS above which chalks mechanically behaves as if it is fully saturated, while chalk with a lower WS looks stronger than if the degree is higher). Greater the WS is, smaHer the consolidation pressure P co .

No abstract

hi. SPE/lSRM 47587 Water/chalk (or collapsible soil) interaction: Part Il. Results of tests performed in laboratory on Lixhe chalk to calibrate water/chalk models Ch. Schroed&, University of Lkge, A-P. Bois SPE, SIMECSOL, V. Maury SPE, ELF-EP and G. Halle, Elf Petroleum Norge m! 1*. q-of POtrO&IM Engi'wers, Inc. This paper was prepared for pmsentatkm al ttw SPEflSRM Eur.xk '9S held in Trc+xlheim, Nmway, 3-10 July t99B This paper was selected for paemlafion w an SPE Program Committee following review of lnfornmti~ccolah?ed in an abstract submitted by the aulhor(s). Conlenls of the paper, as pmsew6d, have not been mviewad by the society ot Petroleum Engineers and are subject to WTdhI~th. WthO@) 7h0 fIWtWid,~S pf9S-811tWf dW6 ITOt IVB3SSWIV Wfkd any P@fim d the SociMy d Petroleum Engineers, ifs officers, or nwmbsrs. Papers presented at SPE meetings am subject to rwbikation review ty Editorial Committees of Ihe Society of Petroleum Engineers, Electrcfdc reproduction. distribution, or stomgs of any part of this paper for commercial purposes without the witkin ccfwent of the society of Petroleum Engineers is prohibited. Pwmission to reprod.ica In prtnt IS restricted to an abstract oi not more lhan 300 e Olustmtlons may net be copied. The abstract must wmlmn .YXWp!cuaus 8c4amwledgnmnt d w4'18Mand ty~cm me paper was presented. Write Librarian, SF%, P.O. 60X 8SS8S6, Riiardsm, 7X 750S34836, U. S.A., iaX 01-972-952-9435 AbstractEkof~k, Valhall and other North Sea reservoirs are made of water sensitive rocks such as pure high porosity chalk. Production of these fields implying water-flooding leads in several cases to compaction and subsidence. In order to perform reliable predictions of compaction and subsidence when water-flooding such reservoirs, it is necessary to take into account not only the deformations that come from depletion in the compressible reservoir rocks but also to inciude additional deformations induced by water saturation (WS) increase.These additional deformations may eventually be determined by performing water-injection (WI) tests in laboratory.This paper presents additional tests that have been performed in laboratory in order to understand the mechanical behavior of chalk at the water-front.It shows the existence of a degree of WS above which chalks mechanically behaves as if it is fully saturated, while chalk with a lower WS looks stronger than if the degree is higher). Greater the WS is, smaHer the consolidation pressure P co .

According to many experimental investigations of porous chalk an elastoplastic model with two yield surfaces is proposed. The physical meaning of the parameters of the model and the method used for their determination are explained. Some laboratory tests are then simulated in order to validate the model. Hydrostatic compression tests are performed using different kinds of saturating fluid. The chalk responses obtained can be classified into two groups corresponding to two groups of fluids : water and oil. The dependency of chalk behaviour with saturating fluid is explained through the capillary effect and "wettability" of the fluid. A new approach for numerical modeling is proposed it is assumed that there are two chalk materials, oil and water saturated, superposed on the same material point. Some validation examples are presented. P. 495