Project Deep Drilling KLX02 – Phase 2 Methods, Scope of Activities and Results Summary Report
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Technical Report TR-01-11 Project Deep Drilling KLX02 – Phase 2 Methods, scope of activities and results Summary report Compiled by Lennart Ekman GEOSIGMA AB/LE Geokonsult AB April 2001 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 5864 SE-102 40 Stockholm Sweden Tel 08-459 84 00 +46 8 459 84 00 Fax 08-661 57 19 +46 8 661 57 19 Project Deep Drilling KLX02 – Phase 2 Methods, scope of activities and results Summary report Compiled by Lennart Ekman GEOSIGMA AB/LE Geokonsult AB April 2001 Keywords: deep drilling, core borehole, borehole investigations, geoscientific parameters. This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author(s) and do not necessarily coincide with those of the client. Foreword During the autumn 1992 a 1700 m deep, ∅ 76 mm core borehole was drilled at Laxemar, Oskarshamn, south-eastern Sweden. At the time being, this was the deepest core borehole drilled in crystalline rock in Scandinavia. The aim of the borehole was to test drilling technique and to enable investigations of the bedrock beyond 1000 m, which was the approximate depth limit in SKB´s previous geoscientific investigations. Two extensive borehole investigation programs were applied. A preliminary survey during and immediately after the drilling operations was succeeded by a five year period of extended investigations. The two investigation programs, named Phase 1 respectively Phase 2 of Project Deep Drilling KLX02, resulted in a large number of reports. The purpose of the present report is to provide a summary of the investigations performed in borehole KLX02 during Phase 2. In order to make different geoscientific conditions within the Laxemar area more understandable, selected results from Phase 1 and from geoscientific investigations previously (before Phase 1) and later (after Phase 2) performed within the Laxemar area are also presented. Lennart Ekman, LE Geokonsult (previously GEOSIGMA), was main author and editor of the report, Jan-Erik Ludvigson, GEOSIGMA, wrote Chapter 6 and Marcus Laaksuharju, GeoPoint (previously INTERA), was co-writer of Chapter 7. Uppsala April 2001 Lennart Ekman 3 Abstract Geoscientific investigations performed by SKB, including those at the Äspö Hard Rock Laboratory, have so far comprised the bedrock horizon down to about 1000 m. The primary purposes with the c. 1700 m deep, ∅ 76 mm, subvertical core borehole KLX02, drilled during the autumn 1992 at Laxemar, Oskarshamn, south-eastern Sweden, was to test core drilling technique at large depths and with a relatively large diameter and to enable geoscientific investigations beyond 1000 m. Drilling of borehole KLX02 was fulfilled very successfully. Results of the drilling commission and the borehole investigations conducted in conjunction with drilling have been reported earlier. The present report provides a summary of the investigations made during a five year period after completion of drilling. Results as well as methods applied are described. A variety of geoscientific investigations to depths exceeding 1600 m were successfully performed. However, the investigations were not entirely problem-free. For example, borehole equipment got stuck in the borehole at a several occasions. Special investigations, among them a fracture study, were initiated in order to reveal the mechanisms behind this problem. Different explanations seem possible, e.g. breakouts from the borehole wall, which may be a specific problem related to the stress situation in deep boreholes. The investigation approach for borehole KLX02 followed, in general outline, the SKB model for site investigations, where a number of key issues for site characterization are studied. For each of those, a number of geoscientific parameters are investigated and determined. One important aim is to erect a lithological-structural model of the site, which constitutes the basic requirement for modelling mechanical stability, thermal properties, groundwater flow, groundwater chemistry and transport of solutes. The investigations in borehole KLX02 resulted in a thorough lithological-structural characterization of the rock volume near the borehole. In order to attain a structural model valid for larger volumes of rock, different authors also included some results covering investigations performed in other parts of the Laxemar area. Rock mechanical investigations were conducted to depths exceeding 1300 m and the normal, horizontal and vertical stress magnitudes and orientations were determined as functions with depth. In connnection with the stress measurements, a hydromechanical study was performed. By temperature logging of the water column in the borehole, also thermal properties of the bedrock were, to some extent, studied. A hydrogeological test programme was applied, including single-hole measurements in borehole KLX02 as well as an interference test between this borehole and another deep (1078 m) borehole, KLX01, in the Laxemar area. Finally, extensive hydrogeochemical investigations were performed in borehole KLX02. Ensuing from advanced sampling, analysis and evaluation technique, the groundwater prevailing at different depths in and near the borehole was characterized regarding composition and evolution. For a better understanding of prevailing hydrogeochemical conditions in KLX02, also the flow regime in the open borehole was studied. 5 Abstract (in Swedish) SKBs geovetenskapliga undersökningar, inklusive de vid Äspölaboratoriet, har i huvudsak avsett djup ner till en tänkt förvarsnivå vid ca 500 m. Ett fåtal undersöknings- borrhål har nått drygt 1000 m. De viktigaste syftena med det ca 1700 m djupa, nästan vertikala kärnborrhålet KLX02, som under hösten 1992 borrades vid Laxemar, Oskarshamns kommun, var att möjliggöra geovetenskapliga undersökningar och test av borrhålsinstrument till större djup än 1000 m. Ett annat syfte var att undersöka möjligheterna att med befintlig kärnborrningsteknik utföra kärnborrhål med relativt grov diameter, ∅ 76 mm, till större djup än 1000 m. Borrningsentreprenaden, som genomfördes mycket framgångsrikt, jämte borrhålsundersökningar utförda under borrningsfasen har tidigare avrapporterats. I föreliggande rapport sammanfattas det undersökningsprogram som genomfördes under en femårsperiod efter avslutad borrning. Såväl metoder som resultat redovisas. Ett stort antal geovetenskapliga undersökningar till mer än 1600 m djup genomfördes framgångsrikt. Vissa problem uppkom dock. Exempelvis fastnade borrhålsutrustning i borrhålet vid olika tillfällen. Speciella undersökningar utfördes för att utröna orsaken till detta. Flera förklaringar är möjliga, t.ex. utfall från borrhålsväggen, vilket kan vara ett speciellt problem relaterat till spänningssituationen i djupa borrhål. Undersökningsprogrammet följde i stora drag det koncept som SKB upprättat för plats- undersökningar, där fokus inriktas på ett antal nyckelfaktorer. Var och en av dessa innefattar flera geovetenskapliga parametrar. Parameterbestämningen leder fram till en geovetenskaplig karaktärisering av undersökningsplatsen. I ett tidigt skede upprättas en litologisk-strukturgeologisk modell, som utgör huvudverktyget vid senare modellering av mekanisk stabilitet, termiska egenskaper, grundvattenflöde, grundvattenkemi och transport av lösta ämnen. Undersökningarna i KLX02 resulterade i en noggrann litologisk och strukturgeologisk karaktärisering av bergvolymen närmast borrhålet. Genom att anknyta till undersök- ningar utförda i andra delar av Laxemarområdet har några författare gjort försök att upprätta preliminära strukturgeologiska modeller som innefattar en stor del av Laxemar- området. Dessa modeller skiljer sig i vissa avseenden från varandra, främst beroende på vilket bakgrundsmaterial som varit tillgängligt vid olika tidpunkter. Bergmekaniska mätningar utfördes i KLX02 till mer än 1300 m djup, varvid storleken liksom orienteringarna på normal-, horisontal- och vertikalspänningarna kunde bestäm- mas som funktioner mot djupet. I samband med spänningsmätningarna utfördes hydro- mekanisk sprickkaraktärisering. Genom temperaturloggning av vattenpelaren i borrhålet erhölls även viss kunskap om bergets termala förhållanden. Det hydrogeologiska testprogram som applicerades i borrhål KLX02 omfattade såväl enhålsmätningar som en interferenstest mellan KLX02 och ett annat djupt (1078 m) borrhål, KLX01, i Laxemarområdet. Slutligen utfördes omfattande hydrogeokemiska undersökningar, varvid grundvattnet på olika djup karaktäriserades med avseende på sammansättning och utvecklingshistoria. För att uppnå bättre förståelse av de hydrogeokemiska förhållandena i KLX02 under- söktes även flödesregimen i borrhålet. 6 Contents 1 Introduction 9 1.1 Background 9 1.2 The Laxemar area 11 1.3 Investigation programme and reporting 13 2 Sequence of activities and project organization 15 2.1 Sequence of activities 15 2.2 Project organization 15 3 Geology 19 3.1 Introduction 19 3.2 Regional and local geological setting 20 3.2.1 Lithological conditions 20 3.2.2 Deformation 22 3.3 Geological investigations in the Laxemar area during Phase 2 24 3.3.1 Borehole design 25 3.3.2 Petrological classification of drill cuttings 28 3.3.3 Examination of thin sections 29 3.3.4 Core logging 32 3.3.5 Fission track studies 35 3.3.6 Geophysical logging 38 3.3.7 TV-logging 39 3.3.8 Borehole radar measurements 40 3.3.9 Summary of the geological conditions in connection with borehole KLX02 45 3.4 The structural character of the Laxemar area – studies performed