Khusainova, Alsu

Enzymer er for nylig blevet rapporteret, som effektive stoffer for forbedret olieindvinding(EOR). Både laboratorie undersøgelser og felttest viste en markant stigning af olieproduktion. Op til ekstra 16 % af olien blev produceret i laboratorie eksperimenter og op til ekstra 269 tønder olie per dag blev fremstillet under feltforsøg. Det var foreslået, at følgende mekanismer har medvirket tiløget olieproduktionen på grund af enzymer: forbedringer af bjergartsoverfladens befugtningsevne;dannelse af emulsioner; reduktion af olieviskositet; og fjernelse (kemisk nedbrydning) af højmolekylære paraffiner. Umiddelbart kan gevinsten ved at bruge enzymer til olieindvinding væresvær at få øje på. I de fleste af de undersøgelser, har man anvendt kommercielle enzymprodukterbestående af enzymer, overfladeaktive stoffer og stabilisatorer. Anvendelse af sådanne produkter gør det besværligt at tildele én positiv EOR effekt til én bestemt komponent, da en eller flere komponenter kan have overfladeaktive egenskaber. Hovedformålet for denne undersøgelse varderfor at fastslå, om enzymer alene kan forbedre olieproduktionen og identificere de mekanismer,der kan ligge til grund for enzymatiske EOR (EEOR), især under de forhold der findes i reservoirer i Nordsøen.I den første del af projektet, blev enzymer, der kunne have et potentiale for forbedretolieindvinding, valgt. Befugtningsevnen var bestemt via screening af kontaktvinkler og adhæsion.Lipaser/esteraser viste en stærk evne til at frigøre olie fra calcit overflader og blev identificeret som mest interessante gruppe for yderligere undersøgelser. Forbedringer af befugtningsevne, som følgeaf protein adsorption på mineralet, blev foreslået som den vigtigste mekanisme i EEOR. Det blevogså fundet, at selve enzymmolekylet forårsagede ændringer af befugtningstilstanden af calcit,mens stabiliserende ingredienser ikke havde indflydelse på resultaterne.Det er muligt, at tilstedeværelse af sådan mekanisme i oliereservoir kan være begrænset pga.retentionen af proteiner i porøst medium. For at verificere denne hypotese blev adsorption afenzymer/proteiner på reservoirsten undersøgt ved hjælp af de statiske adhæsion test og adsorptionpå pulvere, samt dynamiske gennemstrømningseksperimenter. Det blev konstateret, at en signifikant del af enzymer tabes under transporten gennem det porøse medium på grund af den irreversible adsorption. Det blev fundet at adsorptionsevnen på karbonat materialer er meget højere i forhold til sandsten. Forskellige metoder (fx ændring af ionstyrke og pH af enzymopløsningen og forskydningsfluid) blev anvendt i forsøget på at desorbere proteinmolekylerne, men desorptionen lykkedes ikke.En anden muligt mekanisme som kan forklare EEOR er dannelse af enzymstabiliseredeemulsioner. I overensstemmelse med screeningen af befugtningsevnen, udviste lipaser/esteraser de bedste overfladeaktive egenskaber: De dannede de mest stabile emulsioner med meget små dråber.De lette fraktioner af råolien dannede primært protein-stabiliserede emulsioner. Inkubering af olie-[enzym + havvand] systemet viste sig at være vigtig for at opnå høj stabilitet af emulsioner.Anvendelse af en kombination af enzymer og faste partikler var en alternativ måde at øge emulsionsstabiliteten på.Dansk ResuméxFlere studier af råolie-saltvand interaktioner afslørede yderligere problemer, som kunne opstå ved anvendelse af enzymatisk EOR. Interaktion af enzymopløsningen med råolien kan medføre geldannelse/emulgering af propylenglycol (den vigtigste komponent af stabilisatorerne ienzymproduktet). Derudover, førte anvendelse af det oprensede enzym med et minimalt indhold afstabilisatorer til dannelse af høj-viskøse olie-i-vand emulsioner.Endelig blev enzymer testet under betingelser svarende til olie reservoirer, ved hjælp af kerne fortrængningsforsøg (core flooding experiments). To typer af enzymer (lipase og amylase)blev udvalgt på baggrund af resultater fra studierne af befugtningsevnen og emulsioner. De blev kun testet i tertiær ”mode”, og der blev brugt forskellige injektionsplaner. Anvendelse af enzymer isandsten kerneprøver resulterede i en forøgelse af olieproduktionen med 0,23-1,69% i forhold tilden oprindelige oliemængde i kernen (original oil in place - OOIP), mens ingen ekstra olie blev produceret i kridtprøverne. Det blev bekræftet at ændringen af befugtningsevnen var den primæreE OR mekanisme, mens emulgering spillede en mindre rolle.Samlet set konkluderes, at enzymer har et lavt potentiale for forbedret olieindvinding, når der er tale om sandstens- og kridtreservoirer, som indeholder lette råolier. En alternativ teknik, der vil ændre adsorptionsbalancen mod reversibel adsorption, vil skulle udvikles førend enzymatisk EOR kan anses at være en effektiv og økonomisk rentabel olieudvinding metode.Enzymes have recently been reported as effective enhanced oil recovery (EOR) agents. Both laboratory and field tests demonstrated significant increase in the ultimate oil production. Up to16% of additional oil was produced in the laboratory conditions and up to 269 barrels of additional oil per day were recovered in the field applications. The following mechanisms were claimed to be responsible for the enhancement of the oil production due to enzymes: wettability improvement of the rock surface; formation of the emulsions; reduction of oil viscosity; and removal of high molecular weight paraffins. However, the positive effect of enzymes on oil recovery is not that obvious. In most of the studies commercial enzyme products composed of enzymes, surfactants and stabilisers were used. Application of such samples makes it difficult to assign a positive EOR effect to a certain compound, as several components of commercial mixture might possess surface-active properties. Hence, the main goals of the present study were to establish whether enzymes alone can improve oil production and to identify mechanisms that might underlie enzymatic EOR (EEOR), especially, under conditions of the North See petroleum reservoirs. At the first stage of the work enzyme samples that might have potential for EOR applications were selected. Wettability tests such as measurements of contact angles and determination of adhesion behaviour were applied as screening tools. The group of lipases/esterases demonstrated strong ability to detach oil from the calcite surface and was identified as the most promising group for further investigations. Wettability improvement due to protein adsorption on to the mineral was proposed as the main mechanism for EEOR. It was also proved that the enzyme molecules themselves caused change of the wetting state of calcite, while presence of stabilising ingredients did not interfere the results. Implementation of such a mechanism of enzymatic action under reservoir conditions might be limited by retention of the protein molecules in the porous medium. In order to verify this hypothesis, adsorption behaviour of enzymes/proteins on the reservoir rocks was studied by application of the static adhesion tests and adsorption experiments on powders, as well as of dynamic flow-through experiments. It was established that enzymes are indeed significantly lost during the transport in the porous media due to the irreversible adsorption. The adsorption capacity of carbonate material was found to be much higher compared to sandstone. Various methods (forexample, change of ionic strength and pH of the enzyme solution and displacing fluid) were applied in order to desorb attached protein molecules, but no desorption was observed. Another possible mechanism that might underlie EEOR is formation of enzyme-stabilised emulsions. Similar to the wettability screening, lipases/esterases demonstrated the best surface active properties: they formed the most stable emulsions with rather small drops. Light fractions of the crude oil participated mostly in formation of the protein-stabilised emulsions. Incubation of the oil-[enzyme + sea water] systems was found to be important in order to obtain high stability of emulsions. Combined application of enzymes and solid particles was an alternative way to increase emulsion stability. Other crude oil-brine interaction tests revealed additional problems that can rise during theapplication of enzymatic EOR. Interaction of the enzyme solution with the crude oil can induce gelation/emulsification of the propylene glycol (the main component of the enzyme productstabilisers). Moreover, when purified enzyme containing almost no stabilisers was used, a highly viscous oil-in-water emulsion was formed. Finally, assessment of enzymes as EOR agents under conditions similar to the conditions of the petroleum reservoirs was carried out in core flooding experiments. Two types of enzymes(lipase and amylase) were selected based on the results from the wettability and emulsion studies.They were only tested in tertiary mode, employing various injection schemes. Application of enzymes in sandstone core samples resulted in increase of the ultimate oil production by 0.23-1.69% relative to original oil in place, while no additional oil due to enzymes was produced from chalk. Wettability change was confirmed to be the main EOR mechanism, while emulsification plays less significant role. Overall, enzymes have possessed low potential for EOR applications at least in sandstone and chalk reservoirs containing light crude oils. An alternative technique that will shift adsorption balance towards reversible adsorption should be established in order to make enzymatic EOR aneffective and economically feasible oil recovery method

Online Research Database In Technology

Enhanced Oil Recovery with Application of Enzymes

http://orbit.dtu.dk/ws/files/128129452/AlsuKhusainova_phd_thesis_Enhanced_Oil_Recovery_with_application_of_Enzymes_Final.pdf

Enhanced Oil Recovery with Application of Enzymes

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Online Research Database In Technology