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22 JournalofCanadianPtrolumTchnology

Liquid Addition to Steam for EnhancingRecovery (LASER) of Bitumen with CSS:

Results from the First Pilot CycleR.P.LAUT,B.S.CAReY

ImprialOilRsourcs

Peer reviewed PaPer (review and Publication Process can be found on our web site)

Introduction

The LASER process has been described in patents issued re-cently in both the US and Canada(1). It essentially consists of com-bining thermal and solvent effects in a cyclic mode of operationsto improve CSS performance. The preferred solvent for LASER isdiluent that is already used to pipeline produced bitumen to mar-kets. In cyclic-type operations, the mixing and contacting of sol-vent with targeted bitumen is expected to be more effective than in

continuous thermal operations conducted at constant pressures.Background information on LASER technology has been de-

scribed previously(2). This background includes: a description of both CSS and LASER processes for Cold

Lake; the laboratory physical proof of the principle for the LASER

process; the validation of that potential using single-well numerical

simulations; and, a brief outline of the LASER demonstration pilot scope and

design facilities.The primary objective of the field pilot was to collect sufficient

high quality data to allow an accurate assessment of key perfor-mance indicators such as: 1) bitumen production increase; and, 2)

diluent recovery. Based on the initial simulation work conducted

Astract

Research aspects for the Liquid Addition to Steam for En-hancing Recovery (LASER) process were described in a pre-vious paper(1). The research concept has since been field-tested

for a single cycle at a pad at Imperial Oils CSS (Cyclic SteamStimulation) operation at Cold Lake. The pilot entailed the addi-tion of a small 6% volume fraction of C5+ condensate (diluent)into eight wells during CSS Cycle 7. The key pilot objectiveswere to assess: 1) the increase in oil-steam ratio (OSR) over CSS;and, 2) the level of diluent recovery.

The overall performance of the pilot to date has been encour-aging. The diluent recovered is estimated to exceed original ex-pectations and is similar in composition to the injected diluent.The increase in OSR was consistent with original expectations.

Suites of monitoring instrumentation and analytical methodswere developed to allow quantification of the recovery of in-jected diluent. In addition, multivariate analysis (MVA) sta-tistical methods were used to develop a model of CSS process

performance. This model reduced the statistical background per-formance noise associated with normal base CSS operationsand allowed an improved analysis of the OSR increase in thepilot to be made.

with 6% volume ratio of diluent in steam, performance expecta-tions were for an OSR increase of 33% over CSS and a recovery of66% of the injected diluent.

Currently, Imperial Oil produces approximately 22,260 m3/d (140,000 bpd) of bitumen using the Cyclic Steam Stimulation(CSS) process from its Cold Lake field in east central Alberta. Theprocess is expected to recover approximately 25% of the originalbitumen in place (OBIP). Previous work has indicated that, if suc-cessful, the LASER process could increase this recovery factor by3 6% OBIP.

LASER Pilot Design

PilotLocationSlctionandWllLayoutThe H22 (LASER Pilot) and H21 (CSS Control) pads are located

in the northwestern area of Imperials operations at Cold Lake. Thepads provided the most opportune location to conduct the LASERdemonstration field test in 2002. Many factors, such as geology

or reservoir quality, perforation practices and excellent well integ-rity, were first considered in this choice. The key deciding factorwas the consistency of their past CSS historical production perfor-mance prior to pilot initiation, as shown in Figure 1.

Both pads can be considered to have performed identicallyunder CSS prior to the LASER pilot. It is worthwhile to examinethe CSS performance variations between individual well perfor-mance experienced at both the H21 and H22 pads. Figure 2 dis-plays the oil-steam ratio (OSR) performance of each well for eachof the six CSS cycles. There are 20 blue wells from the H21 padand 20 red wells from the neighboring H22 pad. The standard

Pad Bitumen Rates Prior to LASER Pilot

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FIGURE 1: CSS pad performance by week since beginning of 1997.

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Sptmbr2007,Volum46,No.9 23

deviation of the OSR values for the wells is higher in early cycles,

but decreases to about a value of 0.1 after Cycle 3. In general, therelative OSR performance of a well within the data set remains es-sentially the same from cycle-to-cycle. Thus far, it has not beenpossible to relate differences in well performance to any obviousvariations in local geology.

Figure 3 provides the basic layout of the pilot test. The red dotscorrespond to the eight LASER injection wells. These 8 wells, theremaining 12 wells on the H22 pad and the three wells that offsetthe LASER injectors on adjacent pads were equipped with well-head fluid samplers to measure diluent concentrations in the pro-duced liquids. The wells at H21 were not equipped with manualsamplers.

FacilitistoMonitorDiluntProduction

Figure 4 shows the H22 pad schematic and sampling surveil-lance locations used in this pilot to monitor diluent with the pilotfluids. During production, a majority of liquids are producedthrough the tubing string (wellhead liquids) while most of the va-pour phase is produced through the casing annulus (vent fluids).Individual water and bitumen production phase volumes (wellheadliquids) were measured at each well using existing test separatorequipment. Each well was tested about three times a week duringpilot cycle operations from 2002 to 2004. To determine the diluentcontent in the bitumen phase, wellhead samples were also takeneach week from wells equipped with manual samplers as shown inFigure 4. A group line sampler, PS0, was installed to take a weeklycomposite sample from the pad bitumen production stream to help

validate results obtained from individual wells.It was anticipated that a substantial fraction of diluent mightbe produced from the pad venting facilities. New mass/density

coriolis flow meters were installed on the discharge outlet of boththe V1 vent gas condensate liquids and the V2 condensate sepa-rator liquid pumps prior to the return of these liquids to the produc-

tion group line. A proportional sampler was installed in-line witheach coriolis meter to provide a sample of hydrocarbon condensateand determine the composition of hydrocarbons produced from thecasing annulus on a weekly basis. Appendix A describes how thedata were processed.

As discussed later, a large fraction of the diluent produced wasrecovered from the well casings with steam condensate and othernon-condensable gases, such as methane and carbon dioxide. Theuse of accurate, sensitive and reliable coriolis meters proved to beessential for interpreting the performance of the LASER pilot.

AnalyticalMthodstoMasurDiluntSuccessful interpretation of the LASER pilot required accu-

rate methods to measure diluent concentrations in the producedbitumen emulsions. Extensive laboratory and statistical analyseswere conducted to ensure that solid particles, emulsified water anddiluent fractionation could be accounted for within our measure-ment methods and protocols.

The primary method for determining concentrations of diluentin the produced bitumen was gas chromatography. The gas chro-matography method used is analogous to method ASTM D5307 orGCD that is normally used to determine equivalent boiling pointdistribution of hydrocarbon fractions in crude oils. The methodwas essential in determining weekly compositional variations insamples supplied from the various sources during the pilot.

Figure 5 displays a typical chromatogram of the injected diluentat the LASER pilot. The entire diluent profile has been divided into

three fractions, referred to as Light (L), Medium (M) and Heavy(H). These correspond to equivalent hydrocarbon boiling pointfractions that are C10, respectively. As shown in

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FIGURE 2: OSR variations of individual CSS wells.

LASER Well

H22 CSS Well with Manual Sampler

H21 CSS control well

Adjacent CSS Well with Manual Sampler

H21 PAD

H22 PAD

FIGURE 3: Field layout of LASER and CSS wells.

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FIGURE 4: Surface facilities to monitor diluent production.

L M H

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Mass Split of Injected Diluent

FIGURE 5: GC characteristics of injected diluent.

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the Figure 5 insert, the mass fraction of these three fractions in theinjected diluent amounted to 49.8 wt%, 28.6 wt% and 21.6 wt%,respectively. One limitation of the GC method is that for diluent-in-bitumen mixtures, the lighter bitumen fractions overlap with theheavy C10+ diluent fractions. A minimum conservative estimate ofthe diluent produced from the pilot can be made by ignoring anyoverlap of heavy diluent fractions with light bitumen fractions.

Methods based on density and viscosity measurements werealso developed to determine diluent concentrations in the producedbitumen from wellhead samples. However, because only about15% of the produced diluent was measured in the produced liq-uids, these methods did not prove sufficiently accurate during the

pilot. These methods were, however, useful in qualitatively corrob-orating results obtained by gas chromatography for the producedwellhead samples.

PilotInjctionPhasThe injection of steam and diluent proceeded smoothly between

March and July 2002 at the H22 pad. Due to the early arrival ofthe steam bank in the area, there was a minor steam-schedulingmisalignment between H22 and the adjacent H21 pad. As a result,Cycle 7 steam injection proceeded earlier (between December andApril 2002) at H21 than at the adjacent rows at H22. This misalign-ment displaced some bitumen from the H21 wells that border H22to the bordering H22 wells (as in a steam drive operation). As dis-

cussed later, these border wells from both pads were subsequentlyfactored out of the analysis.Targeted steam volumes of 20,000 m3/well were achieved at

each pad, with variations of less than 1,000 m3. Reservoir pres-sures of 4 MPa were measured at both pads at the start of the Cycle7 production phase.

The targeted 6% volume ratio of diluent injection in steam wasclosely achieved, varying from 1,202 to 1,217 m3 between theeight LASER wells. Each diluent well treatment was conductedduring the middle third of its steam injection cycle by injecting18% volume ratio of diluent in steam. The injection strategy waschosen to ensure that all CSS wells surrounding each LASER wellwere being steamed during diluent injection. The objective wasto maximize confinement of injected diluent to its targeted well,rather than allowing diluent to communicate more freely betweenadjacent rows of wells across the H22 pad. Prior singe-well sim-ulations had indicated that the injection of 18% volume ratio ofdiluent during the middle third of the injection phase yielded es-sentially the same results as continuous injection of a 6% volumeratio of diluent.

The composition of injected diluent into the LASER wells re-mained consistent at the four rows with a typical diluent profiledistribution as shown by GC in Figure 5. The diluent density alsoremained consistent, with an overall average of 726.5 kg/m3 for the

pilot. The total volume of injected diluent in this pilot amounted to9,660 m3 or 7,018 metric tonnes.

Diluent Production Results From Pilot

DiluntFromProductionWllhadsFigure 6 plots the weekly profiles for diluent concentrations in

the bitumen produced from all H22 wellheads, as measured by GC.The profiles shown correspond to three groups of wells:

the red line corresponds to the concentrations in the eightLASER wells;

the orange line corresponds to the concentrations in four CSSwells adjacent to the LASER wells that produced significantconcentrations of diluent; and,

the blue line shows the concentrations from the remainingseven CSS wells (1 CSS well was dropped from the analysisdue to production problems).

The locations of these wells on the H22 pad are shown on theinset schematic that has been colour-coded to correspond to its pro-file. The three wells adjacent to LASER wells outside of the H22pad did not show any detectable amount of diluent in their pro-duced bitumen.

The profiles in Figure 6 correspond to the average diluent con-tent measured each week in each of these three groups of wells.

The profiles that are shown start at the time the H22 pad began toramp-up production in November. Before that time, most of thewells had not yet been vented and were produced directly throughthe group line without testing. The dots in Figure 6 correspond tothe samples taken from the pad group line sampler shown in Figure4. It appears to provide an excellent consistency check with thetrends of the three groups of H22 wells.

It is interesting to note that the end of peak bitumen production(July 2003) corresponded to the time when diluent was no longerproduced from the group of four diluent-communicating wells.Prior to that, using the relative gap with other CSS wells in black,these four wells showed nearly 40% as much diluent as the corre-sponding average of the eight LASER wells shown in red. Later,during the production decline of the pilot cycle from July 2003 to

October 2004, only the LASER wells continued to show the pres-ence of diluent in their produced bitumen.Figure 7 covers the same time frame as Figure 6. It shows the

trends in composition of the average produced diluent within bi-tumen from the eight LASER wells. The key diluent character-istic shown on the vertical axis is the ratio of L to (L+M) diluentfractions remaining in their wellhead samples. This ratio has beencalculated by GC analysis for all weekly samples. The green hori-zontal line on the plot corresponds to the reference value of 63.5%for the injected diluent. Initially, during ramp-up and early peakin bitumen production, the GC ratio remained only slightly lowerthan that for the injected diluent before declining steadily until thebeginning of 2004 when it remained relatively stable at a lower

-1%

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)

L AS ER-8 w el ls C SS -7 w el ls D IL CS S-4 w el ls G RO UP

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FIGURE 6: Concentration of diluent produced from H22wellheads.

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FIGURE 7: Diluent composition profile from H22 wellheads.

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level near 30%. Allowing for variations between wells, a similartrend was observed for each of the eight LASER wells. Thus, thediluent remaining in the produced bitumen phase became increas-ingly stripped from its lighter fractions, until reaching a plateau

level later into the production cycle. However, the loss of lighterfractions from the residual diluent left in the produced wellhead bi-tumen has remained much lower than would normally be expectedfrom the much larger amount (almost four times) of diluent thatwas vented during the production cycle.

Results from a relatively recent published study(3) have shownthat the relative volatility of light hydrocarbons is not strongly af-fected by the presence of bitumen and water. Therefore, we con-ducted separate evaporation studies with our diluent to correlatechanges in remaining diluent composition to the amount of diluentloss by evaporation. The results from these evaporation studiessuggest that, based on the L and M weight fractions found in theproduced bitumen from the pilot wellheads, only 40% of the di-luent measured in bitumen should have been evaporated or vented.However, as will be shown in subsequent sections, a much largerfraction of injected diluent was actually recovered from ventingfacilities at the H22 pad. This led to the hypothesis of solvent re-fluxing discussed at the end of the paper.

The sample results for wellhead bitumen samples shown inFigure 7 were integrated with the bitumen production databasefrom the H22 wells to determine the overall amount and compo-sition of this source of produced diluent. The total amount of di-luent produced in bitumen was estimated to have been 930 tonnesor 13.2 wt% of the total mass of injected diluent. Both the quan-tity and composition of this stream of diluent has been tabulatedin Table 1.

DiluntinVntdFluids

A. Vented Gases

The composition of non-condensable vent gas samples collectedat the H22 pad from V3 overheads (GS in Figure 4) was analyzedby conventional gas chromatography used for natural gas conden-sate hydrocarbon gases. The results were compared with severalsamples taken in parallel at the H21 control CSS pad to differen-tiate between the compositions of their produced gases. The resultswere similar, however, concentrations of C4, C5 and C6 were higherat the H22 pad.

Produced gas from CSS wells generally consists of 90 mol% ofmethane and carbon dioxide. The gas rates are measured continu-ously at each pad with an orifice plate meter. For this pilot, thesevolumes were combined with weekly GC composition analyses to

determine the respective volumes of C4-C6 gases vented prior torecompression into the group line. The total amount of these light(L) diluent fractions attributed to the H22 pad amounted to 791

metric tonnes during this pilot. This corresponds to another 11.2wt% of the injected diluent. The distribution consists of 26% bu-tanes, 59.5% pentanes and 14.5% hexanes and a negligible amountof heavier components. Based on analyses of vented gas from the

adjacent CSS control H21 pad showing only 0.2, 0.2 and 0.4 mol%of C4, C5 and C6, we estimate that as much as 25% of the butanesand hexanes and 5% of the pentanes, or about 99 tonnes (approxi-mately 1.4 wt% of injected diluent) could have originated fromCSS gases at the H22 pad.

B. Vent Gas Separator Vessel V1

Liquids discharged from the V1 vessel prior to the cooling heatexchanger consisted mostly of entrained water and bitumen fromthe vented well casings. The primary purpose of this vessel is tocapture and prevent bitumen from fouling heat exchanger coolingsurfaces. The installed coriolis meter for the pilot indicated typ-ical daily discharge rates of 1 2 m3/day during the pad peak pro-duction period of the cycle in early 2003. However, GC analysisof the proportional samples taken from PS1 consistently showeddiluent contents in the entrained bitumen of about 1 wt%, sim-ilar to the amount measured via the group line sampler. Therefore,the amount of diluent produced from this outlet was deemed to benegligible.

C. Condensate Separator Vessel V2

Liquid discharged from vessel V2 was the largest source ofdiluent produced from the pilot. The V2 vessel collects the liq-uids that condense together in the heat exchanger. These liquidsconsisted of a mixture of steam and hydrocarbon condensates. A

TAbLE 1: Overall accounting of pilot diluent and light itumen production sources and composition.

Mass of Component L M H Diluent Light bitumen

(t) (< = C7) (C

7 C

10) (>C

10) Total Produced (~C

10 C

14)

Pilotdiluntinjction 3495 2007 1516 7018 3-5wt%of140Mt49.8%(L)-28.6%(M)-21.6%(H)

Wllhadsliquids 297 366 267 930 31.9%(L)-39.4%(M)-28.7%(H)

Vntdgas 791 - - 791 Commnt+/-100Mt26%C4,60%C5,15%C6

V3-vsslliquids 737 404 48 1,189 62%(L)-34%(M)-4%(H)

V2-vsslliquids 923 1,159 678 2,760 2,71133.4%(L)-42%(M)-24.6%(H)

Pilotdiluntproduction 2,748 1,929 993 5,670 2,71148.5%(L)-34%(M)-17.5%(H)

Diluntrcovry(%) 78.6% 96.1% 65.5% 80.8% about50%

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FIGURE 8: Production profile of vented liquid condensates.

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procedure was developed to estimate the relative amounts of steamand hydrocarbon condensate discharge from V2. Further details onthe methodology are included in Appendix A.

Figure 8 displays the estimated profiles of steam and hydro-carbon liquid condensates during the course of this pilot. Theamount of vented steam condensate is significant, reaching 1,562m3/well, equivalent to 31,240 metric tonnes of steam at the H22pad. This represents approximately 7% of the steam injected ateach well during the injection cycle. However, it is clear from thesemeasurements that, since the beginning of 2004, both vented steamand hydrocarbon condensates rates have reduced considerably.

As shown in Figure 8, the rate of vented hydrocarbon conden-sate peaked sharply ahead of the steam condensate peak in early2003. Hydrocarbon peak liquid rates reached almost half of themass flow rate of the steam condensate before decreasing sharplyin February 2003. At the same time, more steam was being vented.During this early period in early 2003, the condensate separatordischarge pump was operating at its maximum capacity until theend of February 2003.

Thereafter, from the second quarter of 2003 until the end of2003, the liquid mass ratio of steam to hydrocarbons remained es-sentially constant at a value of about 5. The downward trend con-tinued for the remainder of the cycle, except for a period of about1.5 months early in the summer of 2003. This secondary peak hasremained difficult to explain, but was observed to coincide withthe end of the extended bitumen peak production at the pad.

The GC chromatograms of vessel V2s weekly composite hy-drocarbon samples clearly indicated that a significant amountof light bitumen fractions were distilled in the reservoir and dis-charged from the V2 vessel. This is supported by two literaturestudies(3, 4). In these studies, there were findings of similar kero-sene-like or C10-C15 distillate fractions associated with steam dis-tillation processes in California steam drive operations, and in theprocess, breaking tight water-in-oil emulsions using distillationwith heteroazeotropy. This was not anticipated prior to this pilotand a method had to be developed to decouple GC areas belongingto the light bitumen distillates from the diluent fractions. The ap-proach and uncertainty are described in more detail in Appendix A.The results are also provided in Table 1.

D. Discharge Scrubber Vessel V3

As shown in Figure 4, the liquids discharged from this vesselare mixed with the V2 liquids prior to flowing through the coriolismeter. This complicated the analysis of the pilot, since the weeklyproportional samples taken from PS2 may not contain an accu-rate (representative) fraction of V3 discharge fluids. The PS2 sam-pler is programmed to extract small sample volumes only when theV2 discharge pump is activated in order to be filled over a periodof one week. This sampling is not related to the actual dischargecycle times of the V3-vessel over the course of operations. Thedischarges of V3 condensate are much more isolated over time as

detected by density and mass flow rate spikes recorded throughthe coriolis meter. This spiking is described and illustrated in Ap-pendix A for a typical 2-hour period.

All mass and density spike traces that originated from vesselV3 were filtered, processed and integrated to determine the totalvolume or mass of discharged hydrocarbons from the V3 vessel.In addition, this was complemented by a series of several manualliquid samples taken from V3 liquids over the course of the pilot.GC analyses were used to determine variations in density and com-position of condensed hydrocarbons from V3. All of these samplesshowed consistent condensate densities between 705-720 kg/m3and a small content of less than approximately 4 wt% heavier H-type fractions. The remaining distribution of lighter condensatefractions is also consistent with an average of 62% and 34% ofL- and M-type fractions, respectively, based on their analyses byGC.

Overall Diluent Production

The main plot in Figure 9 displays the cumulative diluent re-covery from each surveillance location at the H22 pad during theproduction cycle duration. Each coloured slice on the plot corre-sponds to a different source location, as labeled on the graph.

The first slice in black clearly shows the small fraction (13.2wt%) of injected diluent remaining within the bitumen and liftedfrom the tubing string of a well prior to testing. The average con-

tent of diluent is less than 2% of the prorated volume of bitumenfor the 12 wells that have shown the presence of significant diluent.The next three slices comprise over 57% (by weight) of injected di-luent that was collected from various sections of the pad ventingfacilities. This is a crucial finding; a field test conducted withoutthe installation of casing gas collection facilities would have sig-nificantly underestimated the level of solvent recovery.

The upper red slice represents a range of uncertainty in the de-gree of overlap between light bitumen fractions and heavy diluentfractions for the V2 hydrocarbon condensate phase. An interme-diate scenario that results in 80% diluent recovery is deemed themost plausible from all data collected during this pilot. Since themass of injected diluent amounted to 7,018 metric tonnes, the 80%recovery translates to 5,614 metric tonnes. This is further discussed

in Appendix A.Figure 9 also shows a very steep rise in diluent production duringthe early ramp-up and peak production phase in late 2002 and early2003. By mid-2003, the diluent production declined sharply afteralmost 2/3 of the diluent recovery had been achieved, less than oneyear into the cycle production phase. Apart from the relativelyearly, short-lived diluent peak, the diluent and bitumen productionprofile patterns remained in close harmony for the rest of the cycle.This trend strongly suggests that once the initial anomalous spikein diluent production had passed, excellent contact between mobilebitumen and the remaining diluent kept operating in situ. Further-more, the weekly and cumulative composition of the produced di-luent remained similar to that of the injected solvent (see Table 1).Sustained dynamic in situ steam flashing and refluxing of diluent

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FIGURE 9: Distribution of diluent reproduced.

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FIGURE 10: Comparison of LASER and CSS pilot performance.

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vapours is hypothesized to be a crucial mechanism in the LASERprocess. This is discussed in a later section.

bitumen Production Results From Pilot

Figure 10 provides the most direct illustration of the significantbitumen production increase achieved from the LASER pilot usingthe official Cold Lake bitumen production database. The bitumenproduction rates and the cumulative OSR profiles for the last twocycles are shown for H21 and H22, including the most recent Cycle7 with the LASER intervention at the H22 pad. The wells used toconstruct the orange and blue curves on the plot are shown on theinsert map in Figure 10:

The blue dots correspond to the 19 base CSS wells excludingthe seven black wells that have been influenced by other op-erational events;

The red dots correspond to the LASER injection wells; and, The orange dots correspond to the CSS wells that produced

substantial diluent.The results in this chart show that LASER has clearly surpassed

that of the reference CSS wells in this cycle. In Cycle 6, the 12 di-luent-influenced wells performed essentially the same as the 19wells as shown at the front end of the plot. Between Cycles 6 and7, the OSR of the CSS wells declined from 0.32 to 0.27. This 0.05OSR decline value is typical for CSS wells at this stage of deple-

tion at Cold Lake. In contrast, the OSR of the 12 wells associatedwith the LASER process increased from 0.29 to 0.39 between Cy-cles 6 and 7. On this basis, the OSR increase attributable to theLASER process would be 0.12 (= 0.39 0.27). Note that factoringout the diluent content measured in those wells reduces the netOSR by about 0.005. This translates into 26 27 e3m3 of incre-mental bitumen achieved from the 12 wells in this LASER cyclebased on the steam injection volumes. This exceeds, by a factor of2, the expected production increase based on generic simulationsconducted in 2002 prior to the pilot(2).

As shown in Figure 10, the LASER bitumen production in-crease developed across the peak production period of the wellsin Cycle 7. Later in the cycle, the two well groups show an iden-tical production decline as they had in previous cycles. This sug-

gests that the increase in production with LASER was more than asimple acceleration of bitumen production and may correspond toa net increase in bitumen recovery.

OSRIncrasbyMultivariatAnalysis(MVA)To further evaluate the accuracy of the above apparent large bi-

tumen production increase value, a multivariate analysis (MVA)model was developed to predict the performance expected fromeach individual well in Cycle 7 with ongoing CSS. The details ofthis model will be the subject of another paper.

The model incorporated factors to characterize the influence ofthe following parameters on the cycle OSR:

Pad maturity based on steam injected;

Cycle production time; Produced water volumes; and, Well location relative to other wells.The model provided a significant reduction in OSR variations

expectations between individual wells. This was then used to eval-uate the magnitude of the bitumen production increase achievedwith LASER in Cycle 7.

The curves shown in Figure 11 are for the same groups of wellsas in Figure 10, with the average OSR production increase of eachgroup plotted at four times during the production cycle. The OSRprofiles shown with dashed lines in Figure 11 correspond to the

CSS predictions from the MVA model for the same two groups ofwells. Until mid-2004, the MVA model predictions remained in linewith the field performance of the 19 CSS wells. Only in the secondhalf of 2004, when the production cycle had been substantially ex-tended to low bitumen production levels, did the model start todrift above the actual field performance of the base CSS wells.However, even at the end of the cycle, the deviations between themodel and field OSR values remained within 0.04, which is stillwithin the 95% confidence interval for the MVA model.

The bitumen OSR increase value of 0.09 from the MVA anal-ysis (referenced at 2003) is consistent and only slightly smallerthan the value of 0.12 discussed earlier. It also translates into asmaller overall bitumen production increase value of 20 21 e3m3for the pilot.

The overall LASER performance from this pilot is very encour-

aging. This can be best summarized by the value obtained in In-cremental-Oil to Lost-Solvent-Ratio or IOLSR. Combining theincremental volume of 20 e3m3 bitumen with the storage (loss toreservoir) of 1.95 e3m3 (20% of the total diluent) of unrecovereddiluent, the OSSR achieved for this pilot reaches a value close to10 m3 of incremental bitumen produced for every 1 m3 of diluentlost to the reservoir.

ProducdFluidProfils

Figure 12 displays rate profiles of all key fluid streams and com-ponents measured during this pilot cycle. The rates have been nor-malized on a per well basis for the 20 wells at the H22 pad. Thediluent has been assigned only to the 12 wells that indicated a sig-

nificant presence of diluent in their produced bitumen.The thick and thin black profiles correspond to bitumen pro-

duction from CSS and from LASER analogous to those shownin Figure 10. The blue dashed profile is also similar to the onein Figure 8 for vented steam normalized on a per well basis. Thegreen profile now includes all diluent streams and fractions fromthe LASER pilot, but excludes the light bitumen fractions col-lected from the V2 vessel which likely also originated from theCSS wells.

Comparing the black, blue and green profiles in Figure 12, it isclear that bitumen, venting of live steam and diluent all started toramp-up at the same time. Interestingly, the timing of their peakscame out as bitumen first, diluent second and live steam third. Thiswould suggest that the earliest part of the bitumen peak may have

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1-Jul-03 30-Sep-03 30-Dec-03 30-Mar-04 29-Jun-04 28-Sep-04

OSR

12 LASER wells

CSS MVA (12 wells)

19 CSS wells

CSS MVA (19 wells)

FIGURE 11: Mean OSR uplift for 12 wells from field and MVAanalysis.

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Diluentand

Steam

(m3/day/well)

CSSOIL(19 well)

LASEROIL(12 wells)

DILUENT

Vented STEAM

Low Vented

Liquids

LASER Uplift Peak Extended

FIGURE 12: Fluid production profile patterns observed at pilot.

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resulted from a very efficient solvent flushing of residual bitumenthat was left across previously steamed areas with CSS. This ad-ditional flushing of residual oil would help to explain the muchlower and slower rising peak of the average CSS well compared tothe average LASER well at the pad. The duration of the LASERbitumen production increase was also significantly extended untilmid-2003. As discussed in the next section, it is plausible that dy-namic refluxing of steam and solvent vapours across establishedsteamed areas help extend the contacting of more bitumen with di-luent condensate in the case of the LASER wells. This mechanismwould support the extension of the LASER peak until sufficientwind-down of internal steam flashing processes.

A second LASER cycle was being implemented in the field in2005 2007 at the same location using similar equipment. Theprimary objective will be to confirm the sustainability of the OSRproduction increase and diluent recovery across several cycles.

Hypothesis on Refluxing

A key learning from the pilot is derived from the observationthat there was only a small amount of produced diluent left in thebitumen phase of the LASER wells. Furthermore, this stream ofproduced diluent had a much lower level of stripping of its lighterfractions than expected based on the large amount of vented pro-duced diluent fractions. This provides a strong indication that the

injected diluent was likely continuously refluxed and recycled withsteam in situ while being also partly vented and commingled withlive steam through the well casings. At high reservoir-to-produc-tion refluxing or recycle ratios, the stripping of lighter fractions ofdiluent from the draining and produced bitumen can be reducedconsiderably. This is because of the continuous internal renewalof these lighter fractions as they are being progressively recycledwithin the reservoir system.

The combined overall composition of the diluent produced fromall sources also remained remarkably steady during the pilot cycle.This suggests that the natural preferential vapour flashing of lighterdiluent fractions did not result in a significantly earlier preferentialproduction of these fractions as might have been expected. Thisfurther supports the view that refluxing of diluent is induced con-currently with the steam distillation processes taking effect duringCSS operations. These diluent refluxing effects help renew contactand mixing with additional bitumen across the reservoir. Specifi-cally, at any given time, only a minor fraction of circulating va-pours are produced and withdrawn from the system. The majorityof the vapours continue to re-condense and are retained and recir-culated along the colder boundaries of the reservoir system.

This vision or representation is somewhat analogous to that of aclosed boiling kettle with a loose lid, where most of the generatedvapours return as condensate along the colder surrounding walls,leaving only a small fraction of vapours to escape into the atmo-sphere (or surface facilities in the case of the LASER pilot). Theupper red slice in Figure 9s insert corresponds to the uncertaintyin measuring produced H-diluent fractions. As discussed in Ap-pendix A, the most likely production scenario entails most of this

red slice resulting in an overall composition very close to that ofthe injected diluent shown earlier in the insert in Figure 5, and asindicated in Table 1.

Summary and Conclusions

1. 80% of the injected diluent was recovered from the firstLASER cycle of operations.

2. The composition of the produced diluent remained steadyand close to the composition of the injected diluent.

3. A large fraction of the produced diluent was recovered fromthe venting facilities.

4. An incremental-oil to lost-solvent-ratio of 10 (m3 bi-

tumen produced per m3

solvent retained in the reservoir)was achieved from the 12 wells influenced by the LASERintervention.

5. Dynamic refluxing of solvent fractions is hypothesized asa plausible positive attribute of cyclically-operated thermalsolvent recovery processes such as LASER-CSS. This is sup-ported by the large amount of vented diluent observed in thispilot as well as the relatively low degree of stripping for thediluent remaining in the produced bitumen phase.

Acknowledgements

The authors would like to thank Imperial Oil for permission topublish this paper. In addition, the authors express their gratitude to

the many colleagues from supporting departmental groups whoseinput and assistance allowed the flawless execution and demon-stration of LASER technology as a promising future enhancementprocess in CSS operations.

ReFeReNCeS1. LAUT, R.P., CORRY, K.E. and PUSTANYK, K., Liquid Addi-

tion to Steam for Enhancing Recovery of Cyclic Steam Stimulationor LASER-CSS; Canadian Patent. No. 2,342,955, Issued 14 June2005.

2. LAUT, R.P., Liquid Addition to Steam for Enhancing Recovery(LASER) of Bitumen with CSS: Evolution of Technology fromResearch Concept to a Field Pilot at Cold Lake; paper SPE 79011

presented at the SPE International Thermal Operations and Heavy

Oil Symposium and International Horizontal Well Technology Con-ference, Calgary, AB, 4-7 November 2002.

3. LUCENA, E., VERDUN, P., AURELLE, Y. and SECQ, A., Nou-veau Procd de Valorisation des Slops de Raffineries et DchetsHuileux par Distillation Htroazotropique; Oil & Gas Science andTechnologyRevue de lIFP, Vol. 58, No. 3, pp. 353-360, 2003.

4. RICHARDSON, W.C., BELADI, M.K. and WU, C.H., Steam Distil-lation Studies for the Kern River Field; SPE Reservoir Evaluation &

Engineering, Vol. 3, No. 1, February 2000.

Appendix A: Summary of Methods to

Evaluate Production of Vented Diluent

Condensate Fractions

Continuous online measurements of mass flow rates, fluid den-sities and fluid temperatures through the calibrated coriolis meterproved essential to the successful interpretation of this pilot. Thesedata could be consolidated and processed on a daily and weeklybasis and combined with the measured density of the hydrocarbonphase collected each week via the in-line proportional sampler lo-cated just upstream of the meter.

A1.DcouplingofWatrandHydrocarbonCondnsatPhass

A synopsis of typical events taken from the pilot during a 2-hourpilot period on February 19, 2003 is displayed in Figure A1. The

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February 19, 2002 from 0:00 to 2:00 A.M

MassFlowrate

(100xt/d)

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1,000 Density-Temperature

(kg/m3|10XDeg

C)

Flowr at e Densit y Temperature

V3 Spike

V2 PumpONV2OFF

HC@ 65C

H2O @ 65C

FIGURE A1: Coriolis meter output traces to determine pilot ventedliquids.

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traces that are shown are from the coriolis meters installed for thepilot downstream of the liquid condensate discharges of both theV2 and V3 vessels. The three traces correspond to mass flow rate,fluid density and temperature of these discharged fluids, which arerecorded as sample averages from the field every 30 seconds.

For most of the period, apart from the pronounced spike offluids after less than an hour had elapsed, the instrument traces re-mained relatively steady. The spike corresponded to an occasional,but regular, discharge event from V3 liquids into the nearly con-tinuous discharge of V2 liquids. As shown on the graph in green,aside from the V3 spike, the mass flow rate levels remained near

500 Mt/d, which is the maximum capacity of the discharge pump.Only during brief periods when the pump paused did the ratesspike down before returning to their base discharge level. The reddensity trace was also essentially flat but showed a more distinctundulating character. This is because the V2 fluids comprised aheterogeneous mixture of both water and hydrocarbon condensatesthat were dispersed and entrained together. If the fraction of lighterhydrocarbon condensates increased, the density trace moved lowerand vice versa. These internal variations in the fluid phases createdthe periodic undulations that are recorded continuously during thepilot. The temperature trace of flowing fluids remained steady atapproximately 65C as should be expected.

However, as indicated on the graph with the blue annotations,the flowing fluid temperature was used to calculate the density

of both water and hydrocarbon phases at any given time. Whilethe base density of water and its temperature dependency is wellknown, the base density of the hydrocarbon phase needed to bemeasured and referenced weekly using the proportional samplestaken from PS2 in the field. The temperature dependency of thesample density was then taken from standard values used for pe-troleum fractions of similar gravity. The blue arrow in FigureA1 depicts the typical spread in the two immiscible phase densi-ties flowing through the coriolis meter. The position of the fieldtrace recording relative to the two base densities was used in dailyspreadsheets for each minute of operation to calculate the split inmass flow rates between the two flowing phases. When the V2pump is off, the density readings were filtered out and not includedin the integrated daily reports.

A2.DcouplingofDischargsFromV2andV3Vssls

Each V3 spike of fluids needed to be filtered out daily fromthe instrument output traces. During these periodic spike events,the flow of V2 fluids was assumed to proceed at the average massflow rate and density that were independently computed on adaily basis. This provided a basis to evaluate, by difference, theoverall mass of each spike originating from V3 discharge. To fur-ther analyze the V3 spike, separate manual samples were taken to

determine the base density of hydrocarbons discharged from thatvessel, as well as their distribution in the three L-, M- and H-GCfractions. The GC characteristics of these samples have been dis-cussed in the main text and are listed in Table 1.

Since it not possible to know how much of the V3 spikes werecaptured within the weekly PS2 samples of discharge vented liq-uids, a conservative approach was adopted by assuming that noneof these spikes was introduced in the samples in our analysis of thecoriolis density traces. Because V3 hydrocarbons (705 720 kg/m3) are always lighter than V2 hydrocarbons (770 820 kg/m3)that condense before the compression step, our method of evalua-

tion remains conservative. We did conduct separate computationsassuming that our field samples represent a true mixture of thefluids discharged from both vessels. These calculations led to anoverall increase in diluent production by close to 5 wt% of totalinjected diluent. This is because, with that scenario assumption, alower apparent combined density by 10 20 kg/m3 for the sampledhydrocarbons is used when incorporating the lighter hydrocarbonV3 spikes. It then requires more V2 hydrocarbons to compensatefor this larger difference in density. Therefore, we have chosento remain conservative in reporting the diluent recovery from theLASER pilot by not considering the latter option.

A3.DcouplingBtwnLightBitumnandHavyH-DiluntFractionsFromV2Vssl

Figure A2 plots the weekly weight fraction split between diluentand bitumen measured from V2 hydrocarbon samples. The upperprofile with the solid red markers is the most conservative scenario.It is constructed by attributing all the GC fractions with equiva-lent boiling points higher than C10 exclusively to light bitumen in-stead of diluent. This conservative scenario of analysis results in anoverall tally of 3,388 metric tonnes of vented light bitumen frac-tions. The lower profile shown with the solid yellow markers usesa methodology based on diluent aging evaporation studies to attri-bute some of the heavier GC fractions to the presence of diluent. Itreduces the overall mass of vented light bitumen by 24.8% to 2,548metric tonnes. This also results in a corresponding differential in-crease of 840 metric tonnes of heavy diluent fractions produced

from the pilot, close to 12 wt% of the diluent mass injected. It wasestablished previously in the main text that 268 metric tonnes ofH-diluent fractions have been produced in the wellhead bitumenemulsions.

It is worthwhile to recall that approximately 1,515 tonnes ofheavy H-diluent fractions had been injected in this cycle. At thesame time, the bitumen produced from H22 in this cycle amountedto close to 140,000 m3. Cold Lake bitumen fractions that overlapwith the GC spectrum observed with condensate samples are alsoknown to constitute between 3 5 wt% of the whole bitumen bulkmass. This corresponds to a range between 5,000 to 7,000 tonnesof light bitumen materials. This is also 3 to 5 times the amountof H-diluent fractions injected at the pad into the eight LASERwells. Accordingly, based on the overall material supply ratio, it

appears judicious that nearly four times as much of these ventedheavy fractions might have originated from the native bitumen in-stead of the diluent.

The most likely basis to interpret the pilot results consists ofan intermediate scenario. It assumes that 20% of the C10+ ventedhydrocarbon fractions, or 678 tonnes, have originated from the in-jected diluent source. The overall recovery of H-diluent fractionsfrom the pilot reaches 62.4% after accounting for the heavy frac-tions that were left in bitumen. This results in leaving 2,711 tonnesof vented light bitumen fractions during the pilot cycle. Indepen-dent density measurements taken at the H21 pad indicate that thisvented light bitumen remains close to a 40API cut. Thereforeabout 3,200 m3 of light bitumen 40API fractions are estimated tobe vented during CSS Cycle 7 at the H22 pad.

The overall accounting summary of diluent fractions dischargedfrom the V2 condensate separator has also been listed in Table 1.

0%

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Oct-02 Dec-02 Apr-03 Jul-03 Oct-03 Jan-04 Apr-04 Jul-04

MassRatio

Conservative More likely

Light bitumen fraction (C10 to ~C15)

Diluent heavy fraction ( >C10 )

Ramp-up Bitumen Peak ...Production Decline....

FIGURE A2: Diluent/bitumen split in condensate separatorsamples.

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Authors biographies

Dr. Roland Laut is currently SeniorResearch Specialist for Imperial Oil Re-sources in Calgary where he leads the on-going LASER Research and Pilot project.He has over 25 years of experience in heavyoil production and upgrading processes. Heobtained his chemical engineering diplomain France before moving to Canada. Heobtained a Ph.D. degree in chemical en-

gineering from the University of Albertabefore joining Esso Resources ResearchDepartment in 1979. Since then, he has worked on key researchand development technical assignments associated with in situcombustion processes, evaluation of thermal horizontal well fieldpilots, heavy oil upgrading pilots and cyclic steam stimulation en-hancement recovery processes such as LASER, He is the primaryauthor of four patents.

Dr. Bruce Carey is currently the SouthernReservoir Engineering Manager for Impe-rial Oil Resources in Calgary. He has over25 years of experience in both conventionaland heavy oil production. He has a B.S. de-gree in chemical engineering from Stanfordand a Ph.D. degree in chemical engineeringfrom the University of Minnesota. Fol-lowing research and management assign-ments at Exxon Production Research Co.in Houston, he moved to Calgary in 1988

to lead Imperials research efforts in enhanced oil recovery andthermal recovery. Prior to his current position, he has also held po-sitions as Drilling/Completions Technical Manager and Cold LakeReservoir Engineering Manager, and has served as Imperials rep-resentative on several research consortia.

ProvenanceOriginal Petroleum Society manuscript, Liquid Addition toSteam for Enhancing Recovery (LASER) of Bitumen With CSS: Re-sults From the First Pilot Cycle (2005-161), first presented at the 6thCanadian International Petroleum Conference the 56th Annual TechnicalMeeting of the Petroleum Society), June 7-9, 2005, in Calgary, Alberta.Abstract submitted for review December 13, 2004; editorial comments sentto the author(s) September 21, 2006; revised manuscript received October24, 2006; paper approved for pre-press October 24, 2006; final approvalAugust 8, 2007.M

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