Discrete Element Modelling of Wellbore Integrity in High Temperature Geothermal Reservoirs

TerHeege, J. H. (TNO Applied Geosciences) | Wollenweber, J. (TNO Applied Geosciences) | Orlic, B. (TNO Applied Geosciences)

OnePetro 

ABSTRACT: Geothermal drilling environments are often hostile to well materials, especially in magmatic settings where properties of well casing and cements may rapidly change as a result of high temperatures and chemically active formation fluids. Prolonging the lifetime of such geothermal wells is one of the key challenges to achieve a commercially successful geothermal projects. This study aids analysis of critical stress conditions for well integrity and initiation of damage in wellbore cement during operation of geothermal wells using a combination of analytical and discrete element models. The analytical models are used to determine wellbore stresses that are applied to 3D discrete element models of typical well sections. Wellbore models and boundary conditions are based on subsurface conditions encountered in well IDDP-1 of the Iceland Deep Drilling Project. Possibilities of using the discrete element models to test the behavior of well materials under realistic pressure and temperature conditions in this type of wells are explored. The workflow may be used to test novel well materials and designs at different depths.

1. INTRODUCTION

Maintaining long term wellbore integrity in high temperature environments is one of the key challenges for the commercial success of geothermal projects. Geothermal drilling environments are often hostile to well materials, especially in magmatic settings where properties of well casing and cements may rapidly change as a result of high temperatures and chemically active formation fluids. Prevention and mitigation of well integrity problems under these conditions is aided by detailed knowledge of critical conditions for wellbore failure and by analysis of special requirements for well materials. The integrity of wellbore cement is particularly important in high temperature geothermal wells as cement damage promotes migration of reactive fluids along and through the cement sheath, and reduces thermal isolation of the casing by the cement sheath. The resulting reduction in zonal isolation, enhanced casing corrosion, and elevated thermo-mechanical stresses may significantly reduce the lifetime of geothermal wells.