Chalk production at Tyra Field, In the colloidal perspective
Translated title
Kalkproduktion på Tyra Feltet, i det kolloide perspektiv
Author
Jepsen, Henrik
Term
4. term
Education
Publication year
2012
Submitted on
2012-06-06
Pages
122
Abstract
Dette speciale undersøger kalkpartikler i produktionsstrømme fra Tyra-feltet i Nordsøen. Reservoirbjergarten består af kalk, så fragmenter kan løsne sig og følge med produceret vand og gas. En litteraturgennemgang peger på trykvariationer ved skift fra gasinjicering til gasproduktion som en mulig årsag til pludselige, store kalkindstrømninger. Vi vurderer metoder til at fjerne meget små kalkpartikler fra produceret vand (det vand, der kommer op sammen med olie og gas). Vi foreslår at bruge centrifuger til vandbehandling, fordi de, afhængigt af mængden af faste stoffer, kan fjerne partikler ned til ca. 0,1 µm, mens typiske hydrocykloner har en grænse omkring 10 µm. Vi målte kalkpartiklernes zeta-potentiale (et mål for partiklernes overfladeladning i vand) og fandt, at opløste ioner påvirker det. Zeta-potentialet skifter tegn mellem lavt og højt pH. Forsøg og analyser tyder på, at dette hænger sammen med, hvilke ioner dominerer: hydrogencarbonat/bicarbonat (HCO3−) ved lavt pH og hydroksokomplekserne CaOH+ og MgOH+ ved højt pH. Disse arter foreslås som potentialebestemmende ioner for kalk. Vi undersøgte også, om små kalkpartikler kan stabilisere olie–vand-emulsioner. Resultaterne gav ikke klar evidens for, at kalk stabiliserer emulsioner. Vi observerede dog, at kalk kan trække olie over i vandfasen; mikroskopi viste kalkpartikler, der var omgivet af olie.
This thesis examines chalk particles in production streams from the Tyra Field in the North Sea. The reservoir rock is chalk, so fragments can break loose and travel with produced water and gas. A literature review points to pressure variations during operational switches from gas injection to gas production as a possible cause of sudden, large chalk influxes. We assessed methods to remove very small chalk particles from produced water (the water that comes up with oil and gas). We propose using centrifuges for water treatment because, depending on solids loading, they can remove particles down to about 0.1 µm, whereas typical hydrocyclones are limited to around 10 µm. We measured the zeta potential (an indicator of particle surface charge in water) of chalk and found that dissolved ions influence it. The zeta potential changes sign between low and high pH. Experiments and analyses suggest this relates to which ionic species dominate: bicarbonate (HCO3−) at low pH, and the hydroxo complexes CaOH+ and MgOH+ at high pH. These species are proposed as potential-determining ions for chalk. We also examined whether tiny chalk particles help stabilize oil–water emulsions. The results did not provide clear evidence of emulsion stabilization by chalk. However, we observed that chalk can transfer oil from the oil phase into the water phase; microscopy showed chalk particles encircled by oil.
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