Assessment and Mitigation of Mud Induced Formation Damage

Maximilian Franz Gotthardt

Research output: ThesisMaster's Thesis


The damage to reservoirs, caused by drilling fluids, is often underestimated and, despite remedial operations, well performance can be significantly impacted. This study aimed at 1) developing capabilities and comprehensive workflows to assess the potential damage caused by drilling fluids and 2) reviewing the practicalities of applying chemicals, known in the industry as ‘breakers’, to reduce this damage. To do so, an extensive literature survey on breaker systems was performed and three distinct experimental series were conducted and cross-analysed. The first series tested static and/or semi-dynamic filtration of mud through core, plugged from sandstone outcrop. The resulting damage was assessed using return permeability testing. Influence of i) temperature, ii) confining pressure, iii) filtration regime and iv) subsequent flushing quantified by displaced pore volumes (PV) on return permeability, were qualitatively and quantitatively reviewed. It was found that an increase in temperature and presence of confining pressure considerably reduce the obtained return permeability. Further, applying semi-dynamic filtration regime prior a static regime decreased the measured return permeability by almost 40%, at room temperature. The PV displacement to maximize return permeability varied, as damage taken varied between cores. The second testing series compared the influence of mud solids on filtration behaviour of glycol-based mud. Tests were performed with a HPHT filter press using cellulose fibres at low concentrations and drilled solids sourced and prepared from core offcuts. An in-depth evaluation showed that the filtration reducing effect of the drilled solids outweighed the one of cellulose fibres at low concentrations. For the third testing series, a HPHT filter press was used to examine the efficiency of two breaker systems on a reservoir drill-in fluid (RDF). The first breaker system contained an acid precursor and polymer specific enzymes (PSE) and the second contained a combination of a chelating agent and an enzyme. Evidence suggests that the first product exhibited a slightly better clean-up efficiency than the second one. Nevertheless, both products performed well with overall return flows of over 90% after 48 hours of soaking the filter cake with breaker fluids. This study established workflows to support qualitative and quantitative assessment of the damage caused by drilling fluids. It also describes a practical procedure of evaluating and comparing breaker efficiency. Future work in this area may benefit from and extend the synergies developed in this study.
Translated title of the contributionBewertung und Minderung der durch Bohrspülungen induzierten Formationsschädigung
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Hofstätter, Herbert, Supervisor (internal)
Award date25 Oct 2019
Publication statusPublished - 2019

Bibliographical note

embargoed until 07-10-2024


  • breaker
  • enzyme
  • formation damage
  • mud induced damage
  • return permeability
  • drilled solids
  • cellulose fibres
  • chelating agent
  • acid precursor

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