Reservoir Drill-in Fluids, Completion and Workover Fluids
Author
Chiriac, Alexandru
Term
4. term
Education
Publication year
2014
Submitted on
2014-06-06
Pages
97
Abstract
Når olie- og gasbrønde bores og færdiggøres, pumpes særlige væsker ned i brønden for at køle, transportere borekaks og beskytte reservoiret. Konventionelle borevæsker kan i de sidste faser give problemer som nærbrønds "skin"-skade, indtrængning af væsker og faste partikler i porerne samt svulmning af ler/skifer, hvilket kan reducere produktionen. Dette projekt sammenligner en konventionel oliebase-borevæske med to specialiserede systemer, der skal beskytte reservoiret: reservoir drill-in fluids (RDF, reservoir-borevæsker) og færdiggørelses- og workover-væsker (completion-væsker). Det forklarer, hvilke opgaver disse væsker skal løse i reservoirsektionen og under færdiggørelsen, og hvordan deres egenskaber adskiller sig. Metode: Undersøgelsen bygger på borelaboratorietests af fire væsker: en konventionel oliebase-mudder (VersaClean), en oliebase-RDF (VersaPRO) og to natriumklorid (NaCl) briner anvendt som completion-væsker (densiteter 9,4 lb/gal og 10 lb/gal). For de to boresystemer (OBM og RDF) er resultaterne gennemsnit over ni dage; hver brine blev testet én gang. Væskerne blev løbende behandlet for at holde dem inden for boreprogrammets specifikationer, svarende til almindelig feltvedligehold. Vigtigste resultater (illustrative mål): - Indhold af faste partikler: OBM 25 %, RDF 14 %. - Plastisk viskositet (tykkelse ved høj forskydning): OBM 29 cP, RDF 19 cP, briner ca. 5 cP. - Flydegrænse/yield point (evne til at bære borekaks): OBM 22 lb/100 ft^2, RDF 14 lb/100 ft^2, briner 2 lb/100 ft^2. - Fluid loss/filtration (gennem en testfilter): OBM 2,1 mL/30 min, RDF 2,4 mL/30 min. Tolkning: Sammenlignet med en konventionel OBM havde RDF lavere indhold af faste stoffer og lavere viskositet, samtidig med at filtrationskontrollen var på tilsvarende niveau. Det hjælper med at begrænse indtrængning og formationsskader. De lav-solide, lavviskose briner er velegnede til færdiggørelse, fordi de minimerer tilstopning af reservoirporer. Samlet set er brug af RDF og passende completion-/workover-væsker i reservoirsektionen mere effektivt end at fortsætte med konventionelle borevæsker og kan reducere de samlede projektomkostninger.
When drilling and finishing oil and gas wells, special fluids are pumped downhole to cool, carry cuttings, and protect the reservoir. In the final stages, conventional drilling fluids can cause problems such as near-wellbore “skin” damage, invasion of liquids and solids into reservoir pores, and clay/shale swelling, all of which can reduce production. This thesis compares a conventional oil-based mud with two fluid systems designed to protect the reservoir: reservoir drill-in fluids (RDFs) and completion/workover brines. It explains what these fluids are intended to do in the reservoir section and during completion, and how their properties differ. Methods: Rig laboratory tests were run on four fluids: a conventional oil-based mud (VersaClean), an oil-based RDF (VersaPRO), and two sodium chloride (NaCl) brines used as completion fluids (densities 9.4 lb/gal and 10 lb/gal). For the two drilling systems (OBM and RDF), results are averaged over nine days; each brine was tested once. Fluids were periodically treated to keep them within drilling program specifications, similar to routine field maintenance. Key findings (illustrative metrics): - Solids content (amount of fine particles): OBM 25%, RDF 14%. - Plastic viscosity (thickness at high shear): OBM 29 cP, RDF 19 cP, brines ~5 cP. - Yield point (ability to carry cuttings): OBM 22 lb/100 ft^2, RDF 14 lb/100 ft^2, brines 2 lb/100 ft^2. - Fluid loss (filtration through a test filter): OBM 2.1 mL/30 min, RDF 2.4 mL/30 min. Interpretation: Compared with a conventional OBM, the RDF had lower solids and lower viscosity while maintaining similar fluid-loss control, which helps limit invasion and formation damage. The low-solids, low-viscosity brines suit completion because they minimize plugging of reservoir pores. Overall, using RDFs and appropriate completion/workover fluids in the reservoir section is more effective than continuing with conventional drilling fluids and can reduce total project costs.
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