Patent Application: US-201314394585-A

Abstract:
enhanced oil recovery becomes increasingly important in satisfying the growing demand for fossil fuel . the efficiency of secondary recovery processes like water flooding is however largely influenced by the rock characteristics , fluid characteristics , chemistry and physics . for development of the full potential of secondary oil recovery , it remains a challenge to obtain sufficient knowledge about the reservoir conditions . the present invention provides a novel water - dispersed , nano - sensor composition based on . inp / zns quantum dots and atomic silver clusters , which exhibit a bright visible fluorescence combined with dedicated sensor functionalities . the qd and silver nano - sensors were tested in simulated reservoir conditions to determine their selected functionality to these reservoir conditions . the developed nano - sensors showed improved sensor functionalities towards ph , temperature , and subterranean reservoir rock , such , as clay or limestone .

Description:
referring to fig9 , in embodiments of the present invention , qds and noble metal clusters are implemented as a nano - sensor with specific functionality customized for reservoir management in a water flooding process . embodiments of the present invention develop a nano - sensor composition based on inp / zns core shell qds and atomic silver clusters . as these materials lay within the size range of 1 - 20 nm , there is no size limitation with respect to the pore size of the reservoir formation . 12 due to the differences in surface chemistry of the nanomaterials , they experience different reactions depending on the specific local conditions . the nano - sensors may be injected into a formation at an injection well , including accompanying a water flooding process . after recovery of the nano - sensors from the production well , they are analyzed and the chemical and optical properties are compared to the initial situation before injection . the differences between both measurements provide a unique fingerprint of the reservoir and allow each of its signals to be attributed to specific chemical and physical parameters . benefits of these nanoparticles are their proven robustness and chemical stability , 18 combined with the ability for extended surface chemistry to develop a mixed multifunctional sensor composition . to this end , developed were different types of qd and silver cluster based nano - sensors . these nano - sensors have their own specific targeted sensor functionality with respect to the reservoir environment . the relative bright and narrow band photoluminescence typically found for these nanomaterials enables the optical discrimination of the different sensor functionalities . the qd and ag nano - sensors are completely water dispersible to avoid partition into the oil phase . partial affinity for oil would increase the retention time tremendously . water - dispersed luminescent nano - sensors also have a much lower detection limit compared to oil - dispersed qds because their photoluminescence is not camouflaged by the absorption and background luminescence of crude oil itself . reagents : zinc n - undecylenate , indium chloride , tris ( trimethylsilyl ) phosphine ( tms ) 3 p , hexadecylamine ( hda ), stearic acid , sublimed sulfur , n - dodecanethiol , 1 - octadecene ( ode ), o -[ 2 -( 3 - mercaptopropionylaminolethyl ]- o ′- methylpolyethylene glycol 5000 , silver nitrate ( agno 3 ), α - lipoic acid , sodium borohydride ( nabh4 ), and calcium carbonate were commercially obtained from sigma aldrich . pe 18 : 0 / 18 : 0 - peg 2000 was commercially obtained from lipoid . natural crude oil ( e . g ., north sea ) was commercially provided by shell directly after production without any additional processing . the exms75 clay was commercially obtained from stidchemie , and rhodamine 101 commercially obtained from radient dyes chemie . synthesis of qds : inp / zns quantum dots were synthesized under a nitrogen flow in accordance to a method published by xu et al . 19 with modifications as described herein . ( tms ) 3 p ( 60 mg ; 0 . 2 mmol ) was dissolved in ode ( 1 ml ) and swiftly injected into a reaction mixture of stearic acid ( 57 mg ; 0 . 2 mmol ), hda ( 65 mg ; 0 . 7 mmol ), ode ( 6 ml ), zinc undecylenate ( 172 mg ; 0 . 39 mmol ) and indium chloride ( 44 mg , 0 . 2 mmol ) at 280 ° c . after stirring for 20 minutes at 240 ° c ., the reaction was allowed to cool down to room temperature , followed by the addition of 100 mg zinc undecylenate ( 0 . 23 mmol ), 108 mg hda ( 0 . 45 mmol ), and 6 ml ode . elemental sulfur ( 15 mg ; 0 . 47 mmol ) dissolved in ode ( 2 ml ) was added drop - wise during 20 minutes at 230 ° c ., followed by an annealing step of 60 minutes at 200 ° c . the core shell inp / zns crystals were subsequently isolated by dissolving the reaction mixture in chloroform ( 10 ml ), followed by precipitation through addition of acetone ( 20 ml ). the qds were isolated by centrifugation and re - dispersed in chloroform . synthesis of ag nano - clusters : the ag atomic clusters were synthesized following a method published by adhikari et al . 20 with modifications described herein . α -□ lipoic acid ( 19 mg ) and 14 ml of demi water were placed into a 50 ml flask . subsequently , 7 mg of sodium borohydride was added , while stirring , a clear solution was obtained after 30 minutes . a solution of 2 . 94 mg of agno 3 in 700 μl water was added to the reduced dihydrolipoic acid ( dhla ) solution while stirring . this was followed by the addition of an excess of sodium borohydride ( 10 mg dissolved in 2 ml water ). stirring was continued for more than 5 hours . a clear color change was observed from dark brown to a bright orange color after 4 - 5 hours . surface modification : the silica coating was performed with a procedure similar to the one published by nann et al . 19 the capping exchange of surface bound ligands ( hda and stearic acid ) with , o -[ 2 -( 3 - mercaptopropionylaminolethyl ]- o ′- methylpolyethylene glycol 5000 ( peg - sh ) or dodecanethiol , was performed following the procedure published by querner et al . 21 a 2 - fold excess amount of thiol ligands was added to a 0 . 5 ml colloidal dispersion of hda capped inp / zns qds ( 10 mg / ml ) and stirred at room temperature for & gt ; 12 hours . subsequently , the dodecanethiol - capped qds where isolated by two cycles of precipitation through addition of methanol ( 0 . 5 ml ) and redispersion in chloroform . lipid coating of qds : a micellar polyethylene glycol (“ peg ”) coating was applied to make the qds water - soluble . 22 this micellar coating comprised a pegylated phospholipid , peg - dspe ( 1 , 2 - distearoyl - sn - glycero - 3 - phosphoethanolamine - n -[ methoxy -( poly ( ethylene glycol ))- 2000 ]). the 6 mg inp / zns dodecanethiol - capped single washed qds ( 3 . 2 mg inp / zns from tga ) were dissolved in 2 ml of chloroform and mixed with 18 ml peg - dspe ( 174 mg ) dissolved in chloroform . the chloroform solution was slowly added to 70 ml water ( 1 . 5 hours ) at 80 ° c . under vigorous stirring and nitrogen flow . thermogravimetric analysis (“ tga ”) showed that on average 52 % ( w / w ) of the single washed quantum dot content consists of inp / zns , whereas 48 % of the mass was attributed to organic surfactants . optical spectroscopy : uv - vis spectra were recorded ( e . g ., using a hitachi u - 2001 or perkin elmer lambda 3b spectrophotometer ). steady state fluorescence spectra were measured ( e . g ., with a perkin elmer ls55 spectrophotometer ). quantum yield : photoluminescence quantum yields ( η f ) were estimated usi rhodamine 101 as a reference ( in ethanol + 0 . 01 % hcl ; η f = 100 %). 23 all solutions had optical density & lt ; 0 . 1 at the excitation wavelength ( λ ex = 520 nm ) to minimize re - absorpti and avoid absorbance saturation . the quantum yield was derived from luminescence spec by correcting for the optical density and the refractive index of the solvents used for sam and reference . 24 transmission electron microscopy : tem images were recorded ( e . g ., using tecnai g2 20 ( fei company ) microscope operated at 200 kv ). tem samples w prepared by placing a drop of qds dispersed in chloroform on a carbon coated copper ( e . 400 - mesh ) tem grid . the excess liquid was removed with a filtration paper . simulated subterranean reservoir conditions : the influence of simulated reserv conditions on the dispersed nano - sensors was tested using different media and the presence solids . the influence of salt concentrations was tested by dispersing the nano - sensors in 2 ( w / w ) aqueous solution of caci 2 , or 8 % ( w / w ) aqueous solution of nacl . subsequently , the influence of ph was tested in multi - component api brine solutions , simulating an act reservoir environment to this end , the nano - sensors were dispersed in buffered api bri ( ph 6 . 5 and ph 9 ), containing 8 % nacl and 2 % cacl 2 . the effect of elevated subterrane temperatures was tested by heating the dispersed nano - sensors in buffered ph 6 . 5 api bri ( 8 % nacl and 2 % caci 2 ) for 10 minutes at 120 ° c . the acidic api brines were buffer using a 0 . 1 m acid , sodium acetate buffer ( ph 6 . 5 ), and the alkaline brines were buffer using 0 . 1 m glycine at ph 9 . 5 . the behavior of the nano - sensors in the presence of solids was studied using the a brine ph 6 . 5 dispersed nano - sensors . followed by the addition of solid ca 2 co 3 or exm7 clay , after vigorously mixing , the solid and the liquid phase were separated by centrifugi the liquid phase was subsequently characterized using uv - vis and fluorescen spectroscopy . testing of influence of crude oil : in a reservoir , crude oil is in close contact with water phase ( brine ). the influence of the presence of crude oil in the near vicinity of t water - dispersed nano - sensors was tested using a light north sea crude oil . as - received cru oil was added to the dispersions . samples were shaken vigorously and left standing for t hours to redistribute in well - separated phases . the pl spectra of the water phase w recorded , and the optical absorbance of the qds was compared to the initial situation before addition of the oil . challenging reservoir conditions can affect the stability of the nano - sensor materials . therefore , several different bulk materials , which are commonly used for qds , were tested under commonly encountered reservoir conditions ( see supplementary information disclosed hereinafter ). these experiments showed stability for both zns as well as sio 2 under the predominant reservoir conditions . therefore zns and / or sio 2 may be selected as a protective outer surface for the qds . the inp / zns qds were synthesized from indium chloride and tris ( trimethylsilyl ) phosphine in a mixture of octadecene , stearicacid , zindundecylenate , and hexadecylamine ( hda ) in a similar procedure as described by xu et al . 19 the inp / zn core had a diameter of respectively 3 . 1 nm ( orange ) and 2 . 4 nm ( green ), as determined using the exciton energy derived from the emission maximum reference with literature values ( see supplementary information hereinafter with respect to fig8 ). the inp / zn cores were passivated by growing a shell of 2 mono layers zns using zincundecylnate and sulfur dissolved in octadecene . 19 the final inp / zns quantum dots showed fluorescence maximum at 600 nm ( orange ) and 531 nm ( green ) and a quantum yield of η f ≈ 70 % ( orange ) and η f ≈ 78 % ( green ). fig1 a shows the tem images of the orange inp / zns core shell qds . the luminescent ag clusters with an expected size of 4 - 5 atoms 20 were synthesized by the reduction of silver nitrate in the presence of α - lipoic acid in a similar method as described by adhikari et al . 20 the ag clusters showed a clear deep red emission with a maximum at 654 nm , and a sharp first absorption peak at 495 nm with a typical fluorescence quantum yield of η f = 5 %. sensor functionality of the nanomaterials was studied under simulated reservoir conditions , using the optical properties of the inp / zns qds and ag clusters . dh la - coated ag clusters and inp / zns qds with peg - sh , silica , and peg lipid surface coatings were tested in commonly encountered reservoir conditions as is described hereinafter . the nano - sensors were subjected to the following variables : temperature , ph , and composition ( presence of crude oil or additional solids like clay or calcium carbonate , which are added to the api brine ). a “ high ” salinity brine was formulated in accordance with standards set by the american petroleum institute (“ api ”). as shown in fig2 a - 2b , the specific environmental influences on the sensors may cause changes in the photoluminescence ( pl ) intensity and the optical absorbance spectra . the changes in optical properties are a measure of the stability and the sensor functionality upon exposure to different conditions . in fig2 a - 2b , the pl intensity is plotted relative to the intensity in pure water as a function of the different particles under different reservoir conditions . the relative pl intensity shows a small decrease in the presence of high salinity ( 8 % nac ) and calcium ions ( 2 %) for most of the particles , except for the peg - lipid coated qds , which showed a small increase in pl intensity . these differences in pl intensity can be the result of the difference in polarity between pure water and water with ( high ) salt concentrations . a similar decrease in pl intensity is described for organic chromophores as a consequence of the interaction of their excited energy state and with the solvents polarity . 25 , 26 the influence of the different ph - levels of the brine dispersions showed significant changes between pl intensities of the diverse particles . the silver clusters with an alpha lipoic acid coating showed an overall decrease in pl intensity of ≈ 50 % for both a high ph 9 and a low ph 6 . 5 . however , an opposite behavior ph dependence was found between the silica - coated qds and the peg - sh coated qds , where an average difference in the relative pl intensity was found of ≈ 40 % at the different ph levels ( ph 6 . 5 and ph 9 ). here the silica - coated qds showed a high relative ( 94 %) pl intensity at ph 9 , and peg - sh coated qds showed low relative ( 63 %) pl intensity . this was opposite at ph 6 . 5 , where the silica - coated qds showed a low relative ( 59 %) pl intensity and peg - sh coated qds showed high relative ( 100 %) pl intensity . the opposite ph behavior found for these two qds shows a clear application for a reservoir ph sensor . an exposure of these nanoparticles to a high temperature results , for all particles , in a strong decrease in pl intensity & gt ; 60 %. at these elevated temperatures , several effects can take place which can cause a decrease in pl intensity . the complete disappearance of the silver cluster emission upon heating was subsequently evaluated by the absorbance spectra of the ag clusters ( see fig7 in the supplementary information hereinafter ). this shows that clusters degrade at 120 ° c . in api brine , as the optical absorbance shows a strong decrease upon heating . furthermore , the decrease in pl intensity of the qds ( see fig2 a ) can possibly be contributed to an increased mobility of surface - bound ligands and oxidation of the qd surface introducing surface trap states , which reduce the overall pl intensity upon heating . the difference in pl stability of the various nano - sensors enables an application for reservoir temperature monitoring . an example is shown in fig2 b where a mixture of ag clusters ( red emission ) and peg - sh coated qds ( green emission ) may be used for this purpose in api brines . the emission spectrum shows ( upper line ) the emission spectrum of the mixture of red thiolated ag ( λ max = 650 nm ) and peg - sh green emissive ( λ max = 531 nm ) coated qds at room temperature (“ rt ”), and the inset photo of fig2 b shows that this mixture has a clear and predominantly orange emission . upon heating up to 120 ° ° c ., the emission spectrum shows the disappearance of the red ag clusters emission ( λ max = 650 nm ) and leaves the green qd emission ( λ max = 520 nm ) as the dominant emission . the effect remains preserved after cooling the sample down to rt . this is shown in the inset photo of fig2 b revealing a clear green qd emission . the presence of mineral solids in the reservoir on which the nano - sensors can absorb is an important element for the sensor composition of embodiments of the present invention . two mineral solids often encountered in reservoirs are clay and limestone . stability with respect to immobilization of the nano - sensors onto the natural clay ( caused by ion exchange ) was evaluated using a natural na - montmorillonite ( e . g ., exm757 ). this clay exhibits a large cationic exchange capacity and therefore closely resembles some natural clays that are commonly encountered in reservoirs . limestone is a sedimentary rock , which is primarily composed of caco 3 crystals . caco 3 is the primarily naturally occurring source of divalent calcium ions source in reservoirs . this is of significant consequence as it forms a specific thread with respect to the precipitation of anionic nano - particles dispersions . the api brine dispersed silver cluster and the peg - lipid coated qds were mixed with either the clay or the limestone to study the potential selective binding of these nano - sensors . fig3 c confirms that red emitting silver clusters do not show precipitation nor selective binding in the presence of exm757 clay in api brine ( ph 6 . 5 ). however , in a presence of caco 3 , silver clusters show complete immobilization on the solid caco 3 as result of the negatively charged carboxylic acid groups on their surface . the orange emitting peg - micelle coated inp / zns qds , on the other hand , show the opposite behavior . the peg - micelle coated qds remain well dispersed in api brine in the presence of additional calcium carbonate , but they reveal selective binding towards the exm757 clay . this opposite behavior in selective binding of the negatively charged silver clusters and the peg - micelle coated qds confirms that combinations of such particles can be used as a sensor with respect to the solids in the reservoir environment . the large heterogeneity of the conditions within a reservoir makes the design of the sensor composition challenging . the sensors according to embodiments of the present invention are designed for integration with a water flooding process and should therefore stay confined within the water phase of the reservoir . fig4 a - 4b show that the nanoparticles retain their bright luminescence in the presence of crude oil and stay confined in the water phase ; they do not partition into the oil phase . the nanoparticles were dispersed in api brine in the presence of northern sea crude oil . crude oil is a mixture of a wide variety of hydrocarbons , some of which exhibit fluorescence by themselves . 27 the influence of the crude oil on the stability and luminescence of the nanoparticles is shown in fig4 a ( a ), ( b ), and ( c ). the pl spectra of three types of qd sensors ( inp / zns - lipid coated , inp / zns - silica coated , and ag - clusters ) dispersed in water are shown in fig4 b . the presence of crude oil in the vicinity of the qds did not influence their bright luminescence , which can be clearly discriminated from the crude oil luminescence . challenging reservoir conditions are likely to affect the stability of nano - sensor materials ; therefore , several different bulk materials , which are typically used for qds , were tested under commonly encountered reservoir conditions ( e . g ., acidic and alkaline brine conditions at elevated temperatures ). materials were tested in bulk form before testing with nanoparticles . an instability of the bulk material is more easily determined and can function as an indication on the expected behavior of the nano - sized form of the materials . the stability of nano - sized materials is in general lower than their macroscopic counterpart . bulk cdse , cdte , zno , zns , si , and sio 2 powders were exposed to hot acidic api brine as well as hot alkaline api brine ( see table 1 , which shows stability with respect to reservoir conditions of bulk materials that are conventionally used for qdots ). both the acidic and alkaline brine were buffered with acetic acid ( ph 5 ) and glycine ( ph 9 ), respectively . samples were heated for approximately 1 hour at 150 ° c . ( e . g ., autoclave conditions ) after which they were filtered . precipitation experiments with the filtrate were conducted to confirm stability of the material . only zns and sio 2 met the basic stability requirements . silicon passes halfway , as it is stable in hot acidic brine but not in the hot alkaline brine . subsequently , it was determined if zns and sio 2 remain stable when scaling down to the nano - regime . an amorphous 200 nm film of zns was synthesized using chemical vapor deposition techniques . this inorganic film however dissolves in hot brine . as shown in fig5 , dispersed rolls of foil of 200 nm thick amorphous zns are clearly visible using an optical microscopy ( 50 ×). however , after exposure to hot brine , they cannot be seen anymore due to degradation . referring to fig6 a - 6c , alternatively , a 500 nm layer of sio 2 was thermally grown on a common silicon wafer . the silica layer was stable and protected a silicon wafer against degradation under influence of hot alkaline brine . summarizing these experiments , apart from silica , all conventional qd materials that were tested failed . other materials are required for the sensors that have a much higher chemical stability . fig6 a shows a piece of silicon wafer with a 200 nm protective layer of sio 2 before exposure to hot alkaline brine . fig6 b shows a piece of silicon wafer with a 200 nm protective layer of sio 2 after exposure to hot alkaline brine , which looks the same as the piece in fig6 a . fig6 c shows an unprotected reference piece of silicon that is severely damaged by exposure to hot alkaline brine . since it is expected that the divalent nature of the semiconductors could be the main cause of the observed leaching , alternatively , indiumphosphide qd was considered . inp is a trivalent component and therefore more stable compared to cadmiumselenide and other conventionally used qd materials . in addition , the inp core was overcoated with a zns shell , which further increased its chemical stability . some sulphur components have extremely low dissociation constants , which also explains why zns is much more stable than zno . silversulphide is another high stability component . the silver nanoclusters revealed a complete disappearance of their luminescence upon heating in api brine . the absorbance spectrum shown in fig7 showed an almost absence of the characteristic absorbance peaks of these silver clusters , indicating that the silver clusters were almost fully degraded upon heating in api brine at 120 ° c . fig7 shows the absorbance spectra of api brine dispersed silver clusters prior to heating ( upper line ) and after heating to 120 ° c . 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