Geothermal, ResoUl'ces Council, TRANSACTIONS Vol,. 4, September 1980

PROGRESS REPORT ON HGP-A WELLHEAD GEN~RATOR FEASIBILITY PROJECT

Bill H. Chen and louis P. Lopez

The Research Corporation of theUniversity of Hawaii

ABSTRACT

The HGP~A Well underwent a substantial work­over last fall. A new tie-back 7" casing was in­stalled from surface to 3000 ft. A two-weektest was conducted in January, 1980. with fullhydrogen sulfide and noise abatement. Pre­liminary test results showed a slight increasein total mass flow. Both noise and odor abate­ment were shown to be very effective. As a re­sult of 'the two week test, some changes havebeen made to the final design, and the projectedplant on-line date has been extended to 3/31/80.

WELL WORKOVER

The HGP-A Well on the Big Island of Hawaiiwas drilled by the University of Hawaii's HawaiiGeothermal Project in 1976 (Ref. 1). - After set­ting the 20" conductor and 17-3/8" surface ca~­ing; the 9-5/8" production cas-ing was set fromthesurrace to ~ 2200 ft. below surface. and aslotted liner was set off bottom from totaldepth at 6400 ft. to - 2100 ft, below surface.Prior to the well workover the wellhead pressureduring shut-in periods was approximately 140 psig,and the temperature profile inside the casing(See Fig. 1) was low until it reaches the 9-5/8"casing shoe.

However, after the well flow test inNovember. 1978. the static wellhead pressure be­gan to increase gradually to over 500 psig byJanuary. 1979. and the temperature profile in thecasing showed a dramatic rise. especially in thesection from ~ 1400 ft. to the bottom of the9-5/8" casing shoe. Furthermore. a gas capformed in the wellbore during static condition.which was not observed prior to November. 1978.These phenomena led us to speCUlate that therewas either a break in the ,casing which permittedhot fluids to circulate inside of the wellbore.or that the cement anchoring of the casing to theformation had deteriorated, allo~ing well fluidsto migrate upward on the outside of the casing.

A casing caliper log and a cement bond logwere run in May. 1979 to detennine whether therewas a break in the casing and/or that the cementhad deteriorated. No apparent break in thecasing was detected. However, substantialdeterioration of the cement bond was confirmed

James T. Kuwada and Ray J. Farrington

Rogers Engineering Co •• Inc.San Francisco. California

and the fact that high temperature cement had notbeen used in the original cementing programprompted the project to contact a drilling con­tractor to perform a casing perforation andcement squeeze job as part of the well workover.

Water Resources International. a localdrilling contractor. was selected to perfonn theday work. Mr. Sheldon Hopkins of Global Geother­mal served as the drilling supervisor and Mr.James Kuwada of Rogers Engineering was the drill­ing consultant. The workover started on Septem­ber 15. 1979 and was completed on October 18,1979 with a short four-hour flow test to confirmthe success of the well workover. During theworkover. the 9-5/8" casing was perforated atseveral intervals and high temperature cement wassqueezed particularly around the 9-5/8" production_casing shoe and around the 13-3/8" anchor casin~

shoe. A portion of the 7" slotted liner from·approx-imately 2100 to 3000 ft. was cut and re-­moved.- This zone which was a production zone oflower temperature water was cemented off after anew 7" tie-back casing string was run in andattached to the slotted liner and run back tosurface. A cement bond log was taken after thecementing of the 7" casing and over 80% bond wasshown on the entire string.

WELL TEST

After the well workover, a wellhead steamseparator and flow test system was installed so atwo week test could be performed to verify thefollowing: quantity of steam flow. the quantityof non-condensible gases and percentage of HZSpresent, to check out the steam collection systemwhich will be used in the final power plant opera­ting system, to prove out the effectiveness of thecaustic/peroxide H2S abatement system, and thenoise abatement system specifically designed forthe test.

The steam collecting system and its associatedtest eqUipment included the wel1head,christmastree. steam-water separator. control valves andflow venturis. H2S abatement system, and noiseabatement system.

After the steam is separated from the hotwater in the separator. the steam flow is meteredprior to discharge through the pressure control

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Chen et al.

valve. Ten percent caustic solution and fiftypercent hydrogen peroxide solution are sequen­tially sprayed into the steam line which contains~ections of static mixer following each spray.he static mixer consists of a series of doughnut

shaped rings placed inside the pipe to force thesprayed liquid to thoroughly mix with the steamand react with the H2S to fonn hydro-sulfide. Thetreated steam is allowed to flow to a rock· pitwhere the steam flows through a perforateddiffuser pipe and then through a five-foot layerof 1" to 1-1/2" crushed rock.

The results of the flow test are summarizedin Table I. Table II is an abbreviated versionof the well flow data performed in 1977, dupli­cated here for comparison purpose (Ref. 2). Thenoncondensible gases and the water chemistry willbe reported separately by Dr. Donald Thomas ofthe Hawaii Institute of Geophysics.

The rock muffler ~as very effective. In gen­eral a 30 dbA noise reduction was experienced atalmost all stations around the wellhead as com­pared to the old twin stack cyclone separatorarrangement.

The stoichoimetric mole ratio of sodiumhydroxide to hydrogen sulfide is two and that ofhydrogen peroxide is four. The caustic actuallydetermines the HZS abatement because it reactswith H2S and removes it from the steam as ahydro sulfide in liquid phase. The hydrogen per­oxide merely serves to oxidize the hydrosulfideto a sulfate so it cannot revert back to H2S asit would i.f the hydrosulfide steam became.acidi-fied~ . .

This caustic/peroxide abatement system wasfirst tried successfully at the Geysers duringair drilling operation and FMC furnished us withdata developed at Geyser (Ref. 4). This datashowed that in order to achieve approximately 92%abatement, the system had to deliver 7 moles ofcaustic per mole of H2S and 4.5 moles of hydrogenperoXide per mole of H2S. Our system was designedto provide that capacity.

During the two week test, analysis showed

approximately 16 ppm of H25 in the untreated brinefrom the bottom of the separator and approximately774 ppm of H2S present in the steam phase. TableIII summarizes our preliminary results withcaustic injection only. The analysis of the HZSin the steam discharged from the rock muffler wasdetermined with Draeger tube.

The extreme effectiveness of the caustictreatment was attributed to the static inlinemixers that were installed. The rock muffler alsocontributed to the effectiveness because the rocksurfaces provided an extremely large amount ofwetted interfacial area of contact for the H2Sand caustic.

When hydrogen peroxide was injected at theequivalent rate of 4.1 moles/mole H2S, we observeda remarkable change of color of liquor from therock muffler·drain. The color changed from theblack sulfide to water white soluble sulfate.However, since the liquor from the rock mufflerdrain immediately percolates into the groundthrough lava tubes and there is little oppor­tunity for the liquor to become acidified and torelease H2S, the peroxide system is probably notnecessary in the treatment.

The effectiveness of this caustic treatmentsystem will be verified and retested in February,19B1 prior to the starting-up of the power plant.More precise instrumentation and measurementswill be employed to determine the effects of theinline static mixers, residence time and the rockmuffler.

POWER PLANT

Due to the extreme effective perfonTIance ofthe H2S abatement system ~u~ing the two week test.the caustic/peroxide abatement system and therock muffler will be retained for the final powerplant design as the emergency abatement systemwhen the turbine trips out. Table IV summarizesthe major equipment procurement and theirsuppliers (See Ref. 3 for design considerations).The projected plant-on-line date is March 31, 1981.

TABLE ITHROTTLED FLOW DATA 1/3/80 - 1/18/80

Separator Total Mass Steam Flow Water Flow SteamPressure Flow Rate Rate Rate Qua 1ity

(PSIG) (Klb/hr) (Klb/hr) (Klb/hr) (%)

56 111.5 70.9 40.6 63.6110 110.3 64.7 45.6 58.7132 108.0 61.0 47.0 56.5161 105.9 56.6 49.3 53.4

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Chen et a1.

TABLE IITHROTTLED FLOW DATA 1/26/77 - 2/10/77

WellheadPressure(PSIG)

54100165

Total MassFlow Rate(Klb/hr)

999389

Steam FlowRate

(Klb/br)

655754

Water Flow. Rate

(Klb/hr)

343635

SteamQual i ty

(%)

666460

Caus ti c/H2SMole Ratio

1.523.28

TABLE IIIH2S ABATEMENT DATA 1/3/80 - 1/18/80

(CAUSTIC ONLY)

H2S in Discharged %Abatement in %Abatement in pHSteam . Steam Phase Total Flow

91 8B 86 720 97 95 116 99 97 > 111 99 98' > 11

TABLE IVMAJOR EQUIPMENT FOR HGP-A WELLHEAD GENERATOR

FEASIBILITY PROJECT

Equipment

1urbine/Generator

Condensors

Cooling Tower

H2S Abatement

Separator

Supplier

Ell iott·

Graham

Marley

John Zink

Peerless

Major Feature

-'6 stageturbine •. inletpr~ssure = 160 psig ..•exhaust pressure -= 4~ Hg .• output = 3"'"

Surface type units. inter and after condensersare integrally stacked.

All redwood construction, twin towers. commonbasin.

Incinerator and scrubber

Capable of producing 99.95% dry saturatedsteam at 160 psig.

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,Chen et al.

Temperature In °C

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2000

350

600

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2000

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Figure 1 Temperature Profiles of HGP-A Well.

ACKNOWLEDGMENTS REFERENCES

This work is performed under the DepartmentOf Energy Con,tract DE-AC03-78ET28420, and fundingsfrom the State and County of Hawaii and HawaiiElectric Light Company.

The authors would also like to thank theUniversity of Hawaii's Hawaii Geothenmal Projectfor their assistance in conducting the two-weekwell test. In particular, Drs. Paul Yuen, DeaneKihara, Mr. Art Seki and Ms. Ellen Kitamura.

1. Kingston, Reynolds, Thorn &A11ardice Limited,Hawaii Geothermal Project Well CompletionReport, HGP-A.

2. Chen, S.H., Kihara, D.H., Yuen, P.C. andTakahashi, P.K., 1978, Well Test Results fromHGP-A, Transactions of the GeothermalResources Council, Vol. 2, p. 99-102.

3. Chen, S.H., Lopez, L.P .• Farrington, R.J .•Kuwada, J.T. and Uemura. R.T., 1979, HGP-AWellhead Generator Project, Transactions ofthe Geothermal Resources Council, Vol. 3,p. 103-106.

4. Castrantas, Harry, FMC, private communication.

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