Downhole Environmental Risks Associated with Drilling and Well Completion Practices in the Cooper/Eromanga Basins Damien Mavroudis March 2001 Report Book 2001/00009 © Department of Primary Industries and Resources South Australia This report is subject to copyright. Apart from fair dealing for the purposes of study, research, criticism or review as permitted under the Copyright Act, no part may be reproduced without written permission of the Chief Executive of Primary Industries and Resources South Australia. 2 CONTENTS Acknowledgments.............................................................................................................................................6 Abstract .............................................................................................................................................................7 Executive summary..........................................................................................................................................7 Drilling fluid impacts ....................................................................................................................................7 Effectiveness of cementing for zonal isolation.............................................................................................7 Section One: Drilling fluids.............................................................................................................................8 Introduction ...................................................................................................................................................8 Mechanisms of drilling fluid filtration.....................................................................................................8 Filtration control materials and techniques..............................................................................................9 Bacterial contamination ..............................................................................................................................10 Drilling fluid contaminants .........................................................................................................................12 Mud recap reports ..................................................................................................................................12 Clay swelling..........................................................................................................................................15 Conclusion...................................................................................................................................................15 Recommendations .......................................................................................................................................16 Section Two: Cements....................................................................................................................................17 Introduction .................................................................................................................................................17 Annular gas migration............................................................................................................................17 Purpose of cementing..................................................................................................................................18 Primary cementing .................................................................................................................................18 Problems arising from poor primary cementing ....................................................................................18 Applications of API Cementing.............................................................................................................20 Current cementing practices...................................................................................................................21 Cement failure mechanisms ........................................................................................................................21 Carbon dioxide effects on cement in well..............................................................................................21 Migration of gas through cement pore structure....................................................................................22 Casing problem as part of the downhole risk study...............................................................................23 High temperature chemistry of Portland cement ...................................................................................25 Case history............................................................................................................................................27 Microannular formation in cements.......................................................................................................27 Mechanism of shrinkage and expansion ................................................................................................27 Long-term leaking oil wells ...................................................................................................................28 Mud cake removal for cementing job ....................................................................................................28 Remedial cementing....................................................................................................................................29 Applications of the squeeze cement job.................................................................................................30 Cement plugs..........................................................................................................................................32 Reasons for cement plug failure.............................................................................................................32 Testing the quality of cement jobs ..............................................................................................................34 Hydraulic testing....................................................................................................................................34 Temperature logging ..............................................................................................................................35 Communication tester ............................................................................................................................35 Noise logging .........................................................................................................................................35 Acoustic logging ....................................................................................................................................35 Cement bond log ....................................................................................................................................35 Limitations of cement bond log .............................................................................................................39 Cement evaluation tool ..........................................................................................................................39 Acoustic properties of cement ...............................................................................................................39 Channels.................................................................................................................................................41 Fast formations.......................................................................................................................................41 3 Preventative techniques...............................................................................................................................41 Prevention of gas migration ...................................................................................................................41 Use of foamed cement............................................................................................................................41 Foamed cement limitations ....................................................................................................................43 Displacement properties of foamed cement...........................................................................................43 Use of flexible cements..........................................................................................................................43 Comparison of foam and flexible cements ............................................................................................43 Durable zonal isolation (new cements)..................................................................................................44 Downhole corrosion prevention.............................................................................................................45 Corrosive agents.....................................................................................................................................45 Prevention methods................................................................................................................................46 Corrosion testing....................................................................................................................................46 Conclusion...................................................................................................................................................47