TY - THES

T1 - Assessment and Mitigation of Mud Induced Formation Damage

AU - Gotthardt, Maximilian Franz

N1 - embargoed until 07-10-2024

PY - 2019

Y1 - 2019

N2 - 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.

AB - 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.

KW - Breaker

KW - Enzyme

KW - Formationsschädigung

KW - bohrspülungsinduzierter Schaden

KW - wiederhergestellte Permeabilität

KW - Bohrklein

KW - Zellulosefasern

KW - Chelator

KW - Säurepräkursor

KW - breaker

KW - enzyme

KW - formation damage

KW - mud induced damage

KW - return permeability

KW - drilled solids

KW - cellulose fibres

KW - chelating agent

KW - acid precursor

M3 - Master's Thesis

ER -