ENHANCED OIL RECOVERY recent developments in slim tube testing

ENHANCED OIL RECOVERY T.E RANDALL Gulf Canada Resources Limited and D.B BENNION Hycal Energy Research Laboratories Ltd ABSTRACT Testingof solvent effectivenessrelatedto a given crude oil under simulated reservoir conditions beganin the early 1950s.The initial apparatus useda small-diameterstainlesssteel tube, capable of sustaining high internal pressures,to contain a porous medium similar to reservoirrock This "slim tube" wasmounted within an oven maintained at reservoir temperature The desiredtest result wasthe minimum pressurerequired to achieve solvent/oil miscibility, characterizedby high oil recovery from the slim tube As interest in enhancedoil recoveryby the hydrocarbon miscibleflood (HCMF) processhasincreased,slim tube test equipment and procedures have become more sophisticated The current state of the technology is discussed,including laboratory equipment, instrumentation, operating procedures and analysis of results Proceduresfor analysisand interpretation of slim tube test results are discussed,leading to improved solvent design concepts.Examplesare provided to demonstratethe impact of solvent design on the hydrocarbon miscibleflood process Introduction The object of solvent designis to find the combination of available NGL and mixing gas streamsto give a hydrocarbon mixture whidt demonstratesinteraction with the reservoir oil as good as or exceedingsomereferenceparameters Design engineersseekto find a solventwhich will havea reasonablechance of attaining the desiredincreasein oil recoveryin the reservoir Enrichment with intermediatesmust exceedan economically acceptable safety margin above the minimum miscibility concentration (MMC), which defines the boundary between multicontact miscible (MCM) and immiscible perfonnance This usually implies selectingthe solvent analysiscorresponding to one or more percentilesof slim tube oil recoveryabove the MMC recovery, or a critical temperatureone or more degreeshigher than for MMC This definition requires results from successful slim tube tests with solventscharacterizedas both immiscible and multi-contact miscible The plot of recovery against Keywords: Slimtube Solvent flood Hydrocaft)oQ Labocatory tcst Solvent design, Miscible flood Enhanced oil recovery solvent mole average critical temperaturetll can then be used as the basis for solvent selection Slim tube tests are performed to observeactual solvent-oil interaction in a physical simulation of reservoir pore space If the slim tube is packed with angular grains, the variability of pore and pore throat sizesand shapessimulatesreservoir rock but allows each test to be run at a fraction of coreflood cost The slim tube can then be consideredto representa single chain of connectedreservoir poresexhibiting realisticsolventdisplacement efficiency Diffusion and convectivedispersioneffectsconCurrent with the fluid flow direction are included in the result, but not the tri-dimensional sweepefficienciescharacteristic of a real reservoir element Data enhancement procedures, verified by improved agreement between measured and calculated initial oil density and effluent reservoir volumes, improve comparisonsbetweenslim tube runs Interpretion benchmarkscan be establishedto clarify the characterization of each run as MCM or immiscible A set of four key performance correlations for eachrun show how solvent performance comparesto benchmarks,and aid characterization of the dominant solvent process Historical Equipment Until recently, the slim tube equipmentin usevaried little from the original designsof the early 19505.The slim tube was usually 13 metresof nominal 6.2 mrn 0.0 stainlesssteeltubing packed with glass beadsor 100meshsand and coiled into a tight helix The pore volume was usually 90 to 140 Rml After pore volume determination, the procedure was to fill the tube with reservoir oil Solvent was then injected from a high pressurecontainer located outSidethe oven The effluent ejected from the tube flowed through a capillary sight glassand the back pressurevalve, then proceededoutside the oven to a continuously operating ambient separator.Periodic samplesof separator gas were analyzed to C6 Separator gas and oil volu~es were accumulatedand an over-all analysisof eachwas obtained at the end of the test The slim tube wasusually washed with solvent and the residual solvent and oil delermined from the extracted fluid volume and composition to check the mass balance for the run The data developed by this equipment comprised the "oil recovery" derived from the combined separatorliquid volume~ Paper reviewed and accepted for publication by the Editorial Board of the Journal of Canadian Petroleum Technology November-December1988.Volume 27 No.6 33 FIGURE Experimental slim tube apparatus and analysis; and the indication of solvent/oil mixing zone arrival associatedwith appearanceof two phasesin the capillary sight glass The information could not be checkedto iden-" tify errors in reponed volumes or analyses,and the indicated solvent performance could not be critically appraised mit photographs of the phasecondition for eachinjection step The equipment givesthe advantageof steadystateobservation and quantitative evaluationof phasevolumesaccumuJatedover a period of time, rather than observation of unstable bubbles passing through a capillary sight glass The equipment is enclosedin a 0.7 m by 0.7 m by 1.7 m oven, with 5.08 cm thick walls filled with high temperature insulaImproved Equipment tion The oven is split into a lower portion containing the high FIgUreI provides a schematicillustration of improved slim tube pressurefluid storagecylinders and an upper portion containequipment used to evaluate solvent-reservoir oil interactions The slim tube is 18.29mof9.53 mmO.D 316SStubing, packed ing the slim tube, effluent accumulatorsand density measurewith 200 meshangular crushedquartz by mechanical vibration ment cell The two compartmentsare separatedby a perforated and coiled into a 35.6 cm diameter tight helix Each end conbaffle (10 holes/cm2),and have separateaccesshatchesto permit work in the lower chamber during a slim tube run with tains mm of fiberglass packing and a micron in-line filter minimal impact on temperaturestability in the upper chamber The pore s~ce, approximately 225 Rml, assures sufficient volume errors associatedwith the systempiping This represents The front accesshatch is equippedwith two, cm thick pieces of explosion-proof tempered glassto permit observation and an important improvement over the historically used 6.2 mm O.D by 13 m slim tube, which was much harder to pack.and photography of the ~ cellsandtheircontentswithoutopening the oven door The improved oven design allows the contained only half the pore volume Injected fluids are stored in high pressurecylinders, located temperature-sensitiveeffluent densitometer to be used in the upper chamber with only minor fluctuations in-the oven with the slim tube to ensure thermal equilibrium Figure desaibes the ambient conditions separationsystem in the system and maintained at the upstream entry pressure fluids in the oven are handledby mercury displacementto avoid The heart of this apparatus, a gasometercapable of 0.1 ml accuracy, is initially evacuatedand purged with helium to elimisolubility effects related to CO2 and H~ The mercury injection rate is controlled by highly accurate positive displacement nate unwanted atmospheric residual gas contamination Slim pumps at 0.4 to 240 mVh up to 70 MPa with 0.01 ml accuracy tube effluent is choked to ambient pressurethrough a needle This fluid handling equipment givesmuch better experimental valve against a baffle plate Oil and water fall into a graduated stabilitY than previousequipment, which had the fluid cylinders centrifuge tube and the separatorgas entersthe gasometer for volume measurementand correctionto standardconditions The stored outside the oven Slim tube effluent first passesthrough a high pressuredens- centrifuge tube is capped; spun at 210 rad/sec for 15 miD; and ity cell, then is collected inside the oven by water displacement read to give the separator oil volume Portions of each separafrom two high pressurevisual cells Standard operation keeps tor product are transferred by gasand liquid syringesto a chroone cell on line to the slim tube, while the other is being emp- matograph for analysis tied through the separatorand refilled with distilled water The duration of this cycle defines eachsolvent "injection step" for Intrumentation the slim tube run The water displaced passesthrough a back- System pressureand pressuredifferential acrossthe slim tube pressureregulating systemrated to 70 MPa, accurate to 0.1'1 during a test are measuredusingtestgauges,accurateto SOkPa of the setpoint value and monitored by a high accuracy record- The gaugesare calibrated using a deadweighttester An injecing transducer The water volume is measuredin a graduated tion pressureprofde provides another generally useful indicacylinder and used to confirm the slim tube output related to tion of solvent performance, with a pressure drop usually each injection step The visual effluent accumulator cells per- observed at breakthrough 34 The Journal of CanadianPetroleumTechnology Procedure and Data Assembly The separatorsamplesare subjectedto compositionalanalysis using gaschromatographs, with helium carrier gas The analysis processingdeletesoxygen and nitrogen associatedas air for the gas samples, and reports components to C6 for the gas and alkanes to C.,- for the liquid Another significant improvement in the slim tube apparatus is a high pressureremote density meaurementsystem for continuous measurementof the effluent density at conditions up to 35 MPa and 175°C This aids in the accuratedetermination of the solvent/resen.oiroil mixing zoneconfiguration after 18 m of transit through the porous medium The densitometer consistsof a small stainlesssteelU tube mounted againsta counterweight vibration damper The U tube is ultrasonically excited on a continuous basis, and the resonant frequency of oscillation is measured.The frequency of oscillation ("T" factor) is directly related to the density of the material contained in the U tube With temperaturecontrol under normal operating conditions, accuracy is approximately 0.5 kg/m) The densitometermust be calibrated at the specific test temperature and pressurewith standards of known density that bracket the range of densities expected Ethane and propane are generally selectedas standards, due to the availability of density-data for thesematerials over a wide range of temperatures and pressures The slim tube is initially cleaned with toluene and trichloroethaneto removeany residualoil and asphalticheavyends from the previous run This is followed by methanol and then a vigorous nitrogen flush at reservoiuemperature and ambient pressure for 24 hours to vaporize residual methanol The slim tube is then evacuated for a 24-hour period Mercury manometers, attached to the injection and production ends of the slim tube, indicate when a satisfactory vacuum has been obtained The slim tube is saturated at reservoir temperature and pressure with toluene to determine the pore volume If the pore volume has decreasedcomparedto previous measurements,the tube is either recleaned or replaced Initial Conditions Fluid Tested Recombinedoil is then displacedthrough the toluene-saturated slim tube at reservoir conditions, with effluent being processed through the separator This is a first-contact miscible displacement of the toluene from the slim tube, leaving it saturated with reservoiroil The operation is completewhen the effluent gas/oil ratio is equal to the solution gas/oil ratio of the initial recombined oil and the liquid phaseanalysisis comparableto the stock tank oil analysis from the single-stageflash test The slim tube run commencesby the injection of an additional 0.20 pore volumes of pure live oil through the slim tube and densitometer Effluent is separatedand collected in 0.10 pore volume increments, with gas and liquid volumes and analysesreported This portion of the test provides an analytical benchmark for the initial oil composition Reservoiroil is obtainedby recombimngseparatorgasand liquid samplesat reservoirconditions to yield the desiredbubble point pressureand solution gas/oil ratio A pressure/volume test is conducted on the live oil to check the bubble point A singlestage flash test is conducted to determine the solution gas/oil ratio of the oil, and to provide the formation volume factor for use in later recovery calculations Figure provides an illustration of the equipment used to synthesIzehydrocarbon solventsfrom samplesof the NGL mix and mixing gas available at the reservoir under study Mixing gasesare transferredby cryogeniccondensationinto a high pressure storage cylinder and heated and pressuredto test conditions Heavier components (C5 to C.O>are added as liquids under pressure-The solvent analysisis then checkedand density measuredwith the effluent densitometer.A pressure/volume test is also conducted on the solvent to ensurethat it is single phase at test conditions Salven injection then begins, continuing until 1.2 PV has entered the tube Normal fluid injection rates are 0.1 to 0.15 PV/hr, with effluent accu~ulated in 0.1 PV increments for separation and analysis Effluent density is logged at least In times during eachincrement The effluent accumulator is photographed at the end of eachincrement.Upstreamand differential pressuresacrossthe slim tube are recordedthroughout each run The data available for each sample interval of a slim tube run includes separator gas/liquid pair volumes and analyses; the fraction of the upper phasein the effluent accumulator from photographs; and the effluent accumulator water withdrawals In addition, the raw data set includes the measuredslim tube pore volume; the solvent analysis and measureddensity; and the measureddensity, sOlution GOR and FVF for the reservoir November-December1988.Volume 27 No.6 Slim Tube Operation 35 TABLE SEP GAS COMP H,s co N, C c c IC, nC, 'c nc C c c c c Co SEP OIL SOLVENT MASS OUT MOLE FR MOLE FR MOLE FR GRAMS interval 0.3 to 0.4 PV nominal injection SOLVENT RET GRAMS 0.0000 0.0000 0.00 0.00 0.00 0.0131 0.0000 0.0185 0.07 0.17 0.18 0.0243 0.0000 0.0328 0.08 0.18 0.18 0.5427 0.0232 0.~05 1.01 1.50 ~.44 0.1832 0.0171 0.0844 0.84 0.48 0.48 0.1523 0.01&0 0.1483 0.88 1.14 1.11 0.0181 0.0051 0.0000 0.17 0.00 0.00 0.0578 0.0171 0.0866 0.51 0.88 0.88 0.0116 0.0158 0.0000 0.22 0.00 0.00 0.0116 0.0157 0.0485 0.22 0.58 0.58 0.0024 0.0701 0.0144 0.64 0.21 0.21 0.0013 0.1021 0.0172 1.05 0.30 0.30 0.0003 0.012 0.0000 1.07 0.00 0.00 0.0002 0.073& 0.0000 0.16 0.00 0.00 0.0000 0.0&05 0.0000 0.87 0.00 0.00 0.0000 0.4&87 0.0000 13.20 0.00 0.00 TOTAL 1.0000 1.0000 1.0000 21.67 6.43 5.33 VOl., ml 2511.3 22.5 22.49 MEAS DENSITY kg/Rm3 em WATER nil 712.1 112.5 110.80 31.30 COMP RES OIL 0-0.2 PV MOLEFR 888.1'377.3 INITIAL OIL TOTAL WITHD GRAMS TRUE OIL GRAMS GRAMS CUM CUM XS WITHD GRAMS SOLVENT RET % H,S 0.0000 0.00 0.00 0.00 0.00 100.0 CO, 0.0068 0.48 0.07 0.07 0.01 87.1 N, 0.0110 0.50 0.08 0.07 0.01 87.3 C 0.2888 7.58 1.08 1.05 0.06 88.0 C, 0.1008 4.84 0.84 0.88 0.00 100.0 C 0.0871 1.25 0.18 0.86 0.03 88.7 IC 0.0140 1.33 0.17 0.18 0.00 100.0 nC 0.0428 4.07 0.51 0.56 0.00 100.0 Ic, 0.0142 1.87 0.22 0.23 0.00 100.0 nc, 0.0145 1.70 0.22 0.23 0.00 100.0 C 0.0330 4.83 0.84 0.64 0.00 100.0 c, 0.0577 8.41 1.05 1.30 0.00 190.0 c, 0.0462 8.58 1.07 1.18 0.00 100.0 c, 0.0343 7.11 0.86 0.88 0.00 100.0 C 0.0277 8.43 0.87 0.88 0.00 100.0 C 0.2188 85.56 13.20 13.20 0.00 100.0 rOTAL 1.0000 0.3280 180.33 117.76 21.87 11.10 22.14 16.27 0.13 0.00 OCT + SOL GOR 108.0 IMea.uredl FVF DENSITY kg/Rm3 1.347 IMea.utedl 712.8 ICalcuiatedl 888.8/377.3 IMea.uredl True 011 Wlthdra.al 241.3 RECOMB SOlVENT IN GRAMS 0.0000 DENS 1.35 kg/m3 MOLE 21.13 MASS kg Examplemass balance - unadjusted TABLE Exampleslim tube raw data set interval 0.3 to 0.4 PV nominal injection Exce - 113.20/85.511IComponent - Total Wllhdra.al Initial 011 In Placel True 011 30.11 with respect to the reported injection The total pore volume can then be used to convert the octanes plus mass reduction to reservoir volume, which must compare favourably with the oil An exampleraw data setover the interval 0.3 to 0.4 PV total volume of effluent accumulator water ejected Application of injection (0.] to 0.2 PV solvent injection) is shown in Table I these calculations to the example data yielded 22.49 Rml for The toluene produced from the cleaning of the slim tube can 100/0PV, comparedto 30.99Rml for effluent accumulator water also be subjected to composition analysis to determine the coUectedand 31.07 Rml for resevoir oil withdrawals based on volume of remaining residual oil at the conclusion of a run octanesplus depletion This comparison suggeststhe actual inThis data can be used together with the recovery data from the jection interval to be great-erthan 1007.PV test to close the material balanceon the system.This data was As an additional check, the initial oil density can be calcunot available for the example slim tube run lated from the produced oil and gas volumes, their respective calculated molal averagedensities and the measured FVF If Data Interpretation this result is significantly higherthan the measuredeffluent denThe gas and liquid analyses can be used to define the cor- sity for the first 0.2 PV (oil displacing oil), the separator oil responding densities at standard conditions using the molal analysis is suggestedto be deficient in light components In advolume procedurefZ)and GPAO) pure component properties dition, the measureddensity for the 0.2 to 0.3 PV injection step The analysesmay also be converted to mass fraction, and the should not be significantly lower than measured for the first molecular massof eachmiXture calculated.Combination of the 0.2 PV, unlessbreakthrough of the solvent leading edgeat the densities,volumesand massfraction analysesthen yields a com- downstream end of the slim tube is clearly indicated from the pilation of the mass in, out and retained in the slim tube for accilmulator phasebehaviour or densitometer data Such defieachcomponent at the end of each0.] PV increment, as shown cienciesagain suggestloss of light components from the sepain Table Trial I calallation results for the example data are rator liquid during handling summarlzd in Table As previously described,the slim tube f1lling processinvolved The initial massin place for eachcomponent can be defmed displacement of dead oil with live reservoir oil This operation by averagingthe results for the flfSt 0.2 PV of the displacement, may not have beencomplete at 0.2 PV total injection To offwhen only pure reservoir oil was displacedfrom the slim tube set this problem, the fluid analysesfor the 0.2 to 0.3 PV interThe reduction in octanesplus content in the slim tube, or «oil val can be used as the original reservoir oil, providing there is recovery", can then be calculated for eachsample interval dur- no solvent breakthrough indication by the densitometer data ing the solventdisplacement.This calculationeliminatesthe need The massbalance calculations can then be rerun to repeat the to correct the oil recovery for "breakthrough solvent" because test described above This redefinition of the initial reservoir the solvent contains no significant octanesplus concentration oil analysis can be better than the initial trial, but may stil1 be deficient in the same ways For the example data in Table 3, Exposure of Inconsistencies the Trial redeftnition of original reservoir oil for the example The massbalance results permit critical review of the raw data run reduced the initial massin place by 2'1 but did not affect to ensurethe final interpretation of solvent performance is on the octanes plus "fraction The octanes plus depletion was still 14'1 for the first 10'" PV increment, indicating more oil a sound foundation For example, the initial massin place for the reservoir oil used in the calculations contains a fIXed frac- production than solvent injection tions of octanes plus The octanesplus massreduction during each ]0 PV increment should thus be 10'11.Any discrepancy Component Retention indicates inconsistenciesin the raw data provided, particularly The material balanceresultsalso make possible the assessment Em 36 ACCUMULATOR FRACTION UPPER PHASE TheJournal of CanadianPetroleum Technology - TABLE Examplemassbalance unadjusted TABLE Example adjustment factors interval0.3 to 0.4 PV nominal,trial RECOMB CUM XS GRAMS WITHD GRAMS TRUE OIL GRAMS 0.0000 0.0074 0.0124 0.3118 0.0887 0.1018 0.0128 0.0388 0.0128 0.0133 0.0321 0.0453 0.0382 0.00 0.55 0.58 8.30 4.82 7.45 1.23 3.12 1.64 1.68 4.&8 7.68 7.44 0.00 0.07 0.08 1.01 0.84 0.88 0.17 0.51 0.22 0.22 0.84 1.05 1.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Co 0.0320 8.81 0.88 0.00 100.0 Co c 0.0277 0.2130 8.64 84.30 0.17 13.20 0.00 0.08 0.08 1.18 0.88 1.04 0.17 0.53 0.22 0.22 0.84 1.05 1.04 0.85 0.82 13.20 0.00 0.00 100.0 100.0 TOTAL 1.0000 OCT+ 0.3118 157.18 115.08 21.87 18.10 21.88 18.11 0.00 0.00 SOL GOR FVF 108.0 (M Ul.dl 1.347 (M ur.dl DENSITY.kg/Rm3 e88.8 (Calculated} 88e.8/877.8 (Mea.ured) INmAl OIL COMP MOLE FR H,S CO, N C C, C, IC "C IC, "C, Co C, C Tru 011 Wltltdrawal (18.20/t4.S0ltComponent WrTHD GRAMS RESERVOIR OIL CUM TOTAL RES OIL 0-0.2 PV - trial SOLVENT UNITS SOLVENT Ref % NItrogen/Methene Retlo Carbon Dioxide/Ethane Ratio Hydrogen Sulfide/Propane Ratio 'aobutane/Nonnal Butane Ratio laopentene/Normel Pentane Ratio Separator Uquld 0.0702 0.1171 0.0000 0.3243 0.8870 22.7 18.28 Separatorae 2511.3 3.15 Maaa fraction Propane 0.0474 0.124' 0.3881 0.0000 0.0000 0.0000 gIg gIg gIg gig gIg ml g ml g a non-steady-state compressibledisplacement.Investigation subsequentlyrevealedthe poSSlolesource for this to be initial inequity betweenthe solvent container pressureand the slim tube entry pressure,which could causeinjection volumes different from those indicated by Ruska pump reading These could, in turn, causeincreasesin produced volume as the back pressure regulator openedto prevent pressureincreasein the slim tube Data Enhancement InIUel 011 In Place} Exceaa Total Wlthdrewala rru on of retention for eachsolvent component as the flood progresses.Expected"true oil" component effluent massproduced can be dermed from the initial oil analysis and the effluent mass of the heaviestcomponent Production in excessof this "amount can then be deducted from the injected mass, and the indicated net accumulation expressedas a percent of the massinjected The cumulative form of this calculation was found to be most useful in comparing slim tube runs The example calculations in Table indicate that solvent breakthrough has not yet occurred at 0.4 PV total injection This result is in direct disagreementwith effluent density, which abruptly declines from 686.9 kg/RM3 to 377.3 kg/RM3 when the interval is 70'1 complete.The comparisonof calculatedtrue oil to total withdrawals givesgeneralindication that the octanes plus mole fraction reported in the liquid is too high The most likely reason is loss of light ends while handling the separator liquid in equilibrium with air The purpose for the following activities is to -establishconfidence in each set of slim tube data by examining the internal consistencyof the various performance parameters recorded; and to ensurethat companion slim tube runs can be compared on a common basis Comparison of slim tube runs is complicated by the physical constraintswithin laboratory equipment, and unavoidable variances in operating procedure Review suggeststhe following sources for these problems: sample contamination by air and/or toluene in equipment; loss of carbon dioxide to distilled water used for fluid handling; loss of hydrogen sulphide to distilled water and/or by diffusion through steel tubing; non-standard identification of iso- and nonnal- butanes and pentanesduring GC analysis integration; unreported or lost light hydrocarbons resulting from separator liquid handling and/or air extraction while centrifuging or pipette sampling; and injected pore volume errors caused by pressure or phase in- equities at the start of injection The intendedbenefitsfrom elimination of the impact of these problemsis avoidanceof erroneousconclusionsabout the relative reservoir risk for the solvents being compared Volume Balance Lost Light Components A reservoir voidageversion of the massbalancecan also be calculated for each 10 PV increment Expected "true oil" production for each component can again be calculated from the effluent massfor the heaviestcomponent, the initial separator gas and liquid analysesand the solution GOR from the recombination Production by componentin excessof the "true oil" expectedcan be derived to make up an excessfluid analysis The excessfluid density at reservoir conditions can then be estimatedby calculations ~ CD :J ~ ~ Q, ~ FIGURE CorftlatiOD of equDlbrfum COOStaDtto critical temperatures at staDdard coDditioos ~ 100 c ~ ~ j ~ t:I: U L ~,.I 70 ~ >= Iii\~ z \AI ~ a a i&J z ~ i&J Q: ~ 60 Iz \AI 1000 so- 0.2 0.4 -+ 0.6 0.8 TOTAL HPV INJECTED, FIGURE 10 JMCM solvent performance cumulative 1.2 ~ ~ \AI FR etbane meatio fusing, becausethe recoveryis always negative for solvent comwhich contains no solvent components and can indicate oil recovery without the needfor breakthroughsolventcorrections ponents, becomes increasingly more negative until breakthrough, changesvariably during leading edgeproduction Ideal FCM Performance and increaseswith the arrival of the real mixing zone For componentswith low concentrations in the solvent, the correlations The characteristicsof the key correlations can be usedto idencan evenbe horizontal, indicating little or no component rCt;Ov- tify solvent-reservoir oil 5Y5tCln$ which perform as fir5t conery becauseproduction is being replacedby injection The most tact miscible (FCM) The effluent density plot should be meaningful correlation is the one for the octanes plus group, horizontal up to 0.8 PV solvent injection then decline as an 42 The Journal of CanadianPetroleumTechnology 100 DEfLECTION AT W U ~ ~ ~ ~ W ~ ,: .; i: W ., 'i" I -" , (' ',- W I:: " ' L-",':"'