High Total Inorganic Carbon Concentration, Dependent Carbonate Scaling and Mitigation System, in Moderate to High Enthalpy Geothermal Fields in Turkey

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1 Prceedings Wrld Gethermal Cngress 2015 Malburne Australia, April 2015 High Ttal Inrganic Carbn Cncentratin, Dependent Carbnate Scaling and Mitigatin System, in Mderate t High Enthalpy Gethermal Fields in Turkey Nazim Yildirim, Ali Yildirim nazimy@gmail.cm Keywrds: Gethermal, Inhibitr, Carbn, Scaling, Graben, Turkey ABSTRACT Mst f Turkey s gethermal fields cntain high ttal inrganic carbn cncentratins f wt. % CO 2 in the 150 ºC-240 ºC single-phase reservir liquid. This results in high flwing wellhead pressure and gas/steam rati in the well bre, and CO 2 cncentratins in high pressure steam f wt. %. At pwer plant gathering system design pressures, scale depsitin is relatively minr in the well bre, but severe in surface piping, with general calcium carbnate depsitin rates exceeding 1.5 meter/year, if apprpriate mitigatin techniques are nt implemented. Applicatin f rganic phsphates and plymeric inhibitr reduced calcium carbnate depsitin by mre than 98 % ver all well bres and plant surface equipment. Scale inhibitr must be injected belw the depth f gas breakut t fully mitigate scale frmatin in the well bre, but feeding additinal inhibitr at the surface is nt necessary t prevent scale frmatin frm the wellhead t the pwer plant. Gethermal develpment in Turkey has been hampered, in part, by high CO 2 cncentratins and the resulting severe calcium carbnate scale precipitatin. In this paper, the determinatin f true gas breakut depth and apprpriate scaling mitigatin techniques fr high carbn dixide gethermal fields in Turkey will be discussed. 1. INTRODUCTION One f chief prblems assciated with expliting water dminated fields like in Turkey, undubtedly caused by scale frmatin during utilizatin f the gethermal fluid. Many significant expenses encuntered by the gethermal energy industry are related t chemical effects f fluids. When the cmpsitin, temperature r pressure f the fluids in the gelgical frmatin are changed, during reservir evlutin, well prductin, energy extractin r injectin prcesses the fluids that were riginally at equilibrium with the frmatin minerals cme t a new equilibrium cmpsitin, temperature and pressure after gases separatin. As a result, slid material can be precipitated, disslved gases released and/r heat lst. Mst gethermal energy peratins experience these phenmena. Fr sme resurces, they create nly minr prblems fr thers, they can have serius results, such as majr scaling r crrsin f the wells and plant equipment, reservir permeability lsses and txic gas emissin that can significantly increase the csts f energy prductin and smetimes lead t site abandnment. The gethermal water has crrsive and scaling characteristics. Depsitin f calcite has been trublesme in a number f discharging wells at Turkey, and particularly at Kizildere, Germencik. T minimize scaling prblems, CaCO 3 scale inhibitr may be injected t the wells. This enables peratr t clean heat exchanger nce in a year r in several years. Due t the chemical prperties prper mitigatin system shuld be applied. In lw temperature wells the depsite are smetimes fund t be mixture f amrphus silica and calcium carbnate. S, the mitigatin shuld be selected t mitigate bth kinds f depsit. 2. TURKEYS GEOTHERMAL RESOURCES AND POSSESED PHYISICAL AND CHEMICAL There are apprximately a ttal f 1000 thermal and mineral water spring grups thrughut the cuntry (Simsek 2000). Gethermal resurces in Turkey vary in temperature frm C, and are either in the frm f a mixture f steam and water r just liquid water. The high (<242 C) and mderate-lw gethermal fields are fund in the western part f the cuntry in tw wrld wide famus Grabens cntain several carbnated reservir gethermal fields (Figure 1). BULGARIA BLACK SEA GEORGIA K GREECE İSTANBUL ARMENIA ÇANAKKALE KÜTAHYA ANKARA IRAN EAGEAN SEA İZMİR MANİSA (2) (2) AYDIN (3) (2) MEDITERRIANEAN SYRIA km SCALE DENİZLİ-KIZILDERE ( C) DENİZLİ-TEKKEHAMAM (162 ) AYDIN-GERMENCİK ( C) AYDIN-SALAVATLI (172 C) AYDIN-YILMAZKÖY (140 C) İZMİR-BALÇOVA (140 C) İZMİR-SEFERİHİSAR (137 C) MANİSA-GÖBEKLİ (182 C) MANİSA-CAFERBEYLİ (150 C) KÜTAHYA-SİMAV (162 C) ÇANAKKALE-TUZLA (174 C) IRAQ ANKARA C Figure 1. Distributin f high and mderate gethemal fields in Turkey 1

2 Yildrim et al. The high temperature gethermal areas f western Anatlia lie mainly alng the fllwing Grabens (Simsek et al 2003): Buyuk Menderes, Gediz and Edremit Grabens. Especially, ptentially prmising nes lie alng Buyuk Menderes Graben. The highest reservir temperatures measured in these Grabens are Denizli-Kizildere (243 C), Tekkehamam (168 C), Aydın-Germencik (231 C), Salavatli (172 C), Yilmazky (140 C), Seferihisar (137 C) and Izmir-Balcva (140 C). Canakkale-Tuzla (174 C) is lcated in Edremit Graben; Kutahya-Simav (162 C), Manisa-Caferbeyli (257 C) and Manisa-Alasehir ( C) fields lie alng Gediz Graben. Figure 2 illustrates mderate and high enthalpy gethermal fields in Turkey which are suitable fr electricity generatin. 2.1 High rganic carbn gethermal fields and experienced prblems due t high gas Turkey gethermal fields are characterized by a high CO2 pressure in carbnate reservirs and therefre by cnsiderable cncentratin f calcium a carbnate in the brine. The chemical cmpsitin f gethermal fluids can vary depending n the surce f water that feeds the reservirs. The big prtin f discharge waters in Turkey s gethermal fields which are currently being used in electricity generatin have mderate ttal disslved slids ( 5000 mg/l) and are rich in bicarbnate chlride and sulfate (Table1). The mst gaseus Kizildere gethermal fluids have been classified as Na-HCO3-SO4 type and cntain high ttal disslved slids ranging between 4500 and 5500 mg/l. Bth high and lw enthalpy water-dminated gethermal fields in Turkey prduce a fluid cntaining a large amunt f CO2 (Yildirim et al. 2002). The nn-cndensable gases (NCG) in steam, separated at apprximately 4.5 t 11 bar-a, range frm <10 t 37 % in weight. When cnverted t reservir cnditins, all the wells in the intermediate reservir cntains 1.6 t 2.5 weight % NCG. The deep reservirs f Kizildere, Germencik and Alaşehir shw a value f 3.0 weight % NCG at the beginning f explitatin. Recent measurements suggest that the NCG cntents f the reservir have decreased slightly due t reinjected brine withut gases. This decline can be attributed t several prcesses: influx f lw gas fluid such as injectate r cld water, r pssibly degassing by biling. Gas analyses shw that carbn dixide (CO2) is predminant 98 t 99% f the ttal. Minr amunts f nitrgen (N2) and methane (CH4) are fund, as well as traces f ammnia (NH3), hydrgen sulphide (H2S) and hydrgen (H2). Presently, the amunt f NCG delivered reaches 23 tns per hur fr the existing pwer plant in Kizildere and 54 tn/h in Germencik. Fr the new pwer plant f Kizildere the NCG will be arund 84 tns/h. Several prjects entailing gechemical studies f the gethermal fields in high t mderate reservir f B Menderes Graben and Gediz Garben (Figure 2) have been carried ut since abut In the fllwing sectin f the paper the chemistry f the gethermal fluids is discussed, fcusing n thse chemical characteristics which help characterize reservir prcesses and prperties such as biling, mixing and temperature changes and thse which affect the use f the fluids fr pwer generatin such as scaling and nncndensable gas (NCG). The gechemical data used in this evaluatin are presented in Table 1. In the areas expsed t this study, the deep carbnate aquifer cincides with the gethermal reservir. The istpe analyses shw that the reservir recharge ccurs thrugh infiltratin and circulatin f meteric water in the Meszic carbnate rcks utcrpping nrth and suthwest f the discussed Grabens. Figure 2. The tw Grabens create high rganic carbn fluids: Buyuk Menderes and Gediz Water Chemistry and Gas analysis The gethermal fields in Turkey which prduce fluids with high inrganic carbn cntent are mainly the Kizildere, Germencik, Pamukören, Salavatli-Sultanhisar and Ortaklar gethermal fields in Menderes Graben and Alasehir, Gbekli Salihli gethermal fields which lie in Gediz Graben. Detailed results f water chemistry and gas analysis f the wells represent fields characteristic in the tw mentined Graben gethermal systems are illustrated in Table 1. The chemical data shw that sdium, bicarbnate and carbn dixide are in high cncentratins in that gethermal water frm Turkey. The high carbnate cntent may affect scale frmatin. Germencik prductin liquid, sampled at the surface, is Na-(K)-Cl-HCO 3 in character, and cntains ppm TDS and 5-10 ppm Ca ++, with ph ranging frm , depending n separatin pressure (Osbrn et al. 2007). Steam sampled at the surface is 2

3 Yildrim et. al. very gas-rich, with gas/steam ratis exceeding 20 wt. % at 7 bar-g line pressure. Kizildere, abut 100 km east f Germencik, prduces Na-(K)-HCO 3 -(SO 4 ) liquid with ttal disslved slids f abut 4500 ppm, and nn-cndensable gas cntent with a reservir cncentratin f wt.% frm a ºC reservir in limestne and underlying schist and gneiss (Şimsek, 1986; Serpen and Ugur, 1998). The Pamukören gethermal field is abut 35 km west f Kizildere. The Pamukren GPP, a 45 MWe Atlas-Cpc facility, was cmmissined in The plant uses 7 artesian prductin wells and 7 injectin wells, prducing a Na- (K)-HCO 3 -Cl liquid with ttal disslved slids f abut 4000 ppm frm fractured marble in a 175 ºC reservir at m depth. Ortaklar gethermal field is nw under develpment with three dilled wells up t 3200 meters prducing a Na-(K)-Cl-HCO 3 liquid with ttal slid f 5350 ppm frm a reservir f 180 C at 3000 m depth. The Gediz Graben is a cmplex dynamic basin which hsts numerus gethermal systems. There are several licensed gethermal areas wned by private cmpanies between Salihli and Alaşehir. Like Alaşehir, the ther fields are lcated n the suth side f the graben. The chemistry f the Alkan and Piyadeler reservir fluids are cnsistent with a mderate t high temperature liquid dminated artesian gethermal reservir within carbnate-bearing reservir hst rcks. The sampled liquid frm Alasehir, Piyadeler, Alkan and Gbekli at the surface, is Na-(K)- HCO 3 - Cl in character, and cntains ppm TDS and 5-10 ppm Ca ++, with ph ranging frm , depending n separatin pressure. The mst distinctive chemical feature f the resurce is the high cncentratin f carbn dixide (CO 2 ). The rati f nn-cndensable gas relative t water by weight in the reservir average in Alkan and Piyadeler. This amunt f the nn cndensable gas is within the range f the nn-cndensable gas cncentratins bserved in the Menderes graben f 0.03 t kg NCG/kg brine. The Kizildere resurce cnsists f fluid znes at multiple depths and in separate lithlgies, which may represent multiple reservirs but which are likely t be cnnected. They appear t have different characteristics, mst specifically enthalpy and nncndensable gas cntent. Fluids in the intermediate reservir have an average enthalpy f apprximately 870 kj/kg and an average nn-cndensable gas cncentratin (NCG) cntent f 1.5% by weight (wt%). The deep fluids flwing int deep wells have an enthalpy f apprximately 1020 kj/kg and a ttal NCG cntent f 3 wt%. Germencik resurce cnsists f tw fluids zne at tw different depths intercnnected with fractures. The deeper zne has higher enthalpy with higher NCG cncentratin up t 2.5 wt %. Pamukren and Salavatli gethermal fields in the same Graben have mderate enthalpy which is nly suitable fr Binary cycle type pwer plant with relatively lwers gas cntent up t 1.5 wt %. The reservir chemistry f Buyuk Menderes Graben reservirs is sdium-bicarbnate brine with changeable sulfate and chlride cncentratins. The upper part f Buyuk Menderes and Gediz grabens gerthermal system acts as a reservir fr CO 2, while in it s the deepest parts sme CO 2 can be prduced by thermal metamrphic reactins. The main gas in the bulk nn-cndensable gas is CO 2 with mre than 98 % (vl) fr all representative wells. The field determinatin gave values clsed 99 % CO 2. Hydrgen sulfide (H 2 S) is very lw in Buyuk Menderes Graben Kizildere, Germencik Pamukren wells but is higher in the Alasehir Piyadeler wells f Gediz Graben. The amunt f gas in the steam has als been calculated. A direct field determinatin allws cnsidering a range wt % f CO 2 in the ttal fluid f representative wells (Table 1). The gas cncentratin f re-injected waste water in all mentined gethermal field is less than ml/l as CO 2. After emissin t atmsphere H 2 S in re-injected waste water is nt high enugh t be determined. S, gas amunt in all re injected water is depleted in gases. This means the gas cncentratin in the reservir will be lessened in lasting time f the peratins. Table 1. Fluids chemistry frm bth selected Menderes and Gediz Graben gethermal fields wells Lcatin Buyuk Menderes Graben Gediz Graben Field name and Well Cde Kizidere Pamukören Germencik Ortaklar Alaşehir Göbekli R1A AP7 OB-9 M44S2 BY1 GB1 Temp C ph/ C Cnd. µs/cm (25 C Na mg/l K mg/l Ca mg/l Mg mg/l <0.1 SiO 2 mg/l HCO 3 mg/l CO 3 mg/l SO 4 mg/l Cl mg/l B mg/l Fe mg/l <0.05 <0.05 <0.05 < <0.05 δ 2 H δ 2 O TDS mg/l NCG % in wt CO 2 % H 2 S % Others % (CH 4, N 2, H 2, Ar...)

4 Yildrim et al. 3. CACO 3 SCALING CONSTRAINED PRODUCTION WELL OUTPUT A small change in the cncentratin f calcium can cause a sizeable depsitin rate in a gethermal well f high utput (Figure 3). Fr example a lss f 10 ppm f calcite r silica frm a brine in a 9 5/8 inch diameter well prducing 300 tns/h, wuld give a depsit f 2 mm thick/day ver 30 m length f pipe. Practically depsitin rate may be much greater than this. A well in Buyuk Menderes Garaben r Gediz Graben f Turkey may develp CaCO 3 scale at the rate f 3-7 mm/day ver 50 m length f pipe. In thse Grabens fields cmplete plugging f wells may ccur in a matter f days in severe scaling cnditin if inhibitr is nt injected t prper depth in the mentined fields wells. Therefre, in case f develpments f such gethermal fields scale frmatin and depsit have t be paid attentin. The prper mitigatin systems have t be cnsidered t reduce frmatin rate and adequate inhibitr fr stpping scale frmatin have t be adpted. Frmatin f carbnate scale can be mitigated by: (1) acting n carbnate bicarbnate equilibrium (ph and CO 2 partial pressure cntrl) (2) using scale inhibiting prduct, r injecting CO 2 int the well (3) peridic cleaning r additin f acid t the brine. Acid additin did nt prve satisfactry due t prblems f crrsin by acidified brine and because f buffer capacities f the gethermal brines. Big amunts f acid are required t lwer the ph in rder nt prmte the scaling ccurrences. S, the methd is nt ecnmically feasible. Since peridically cleaning means cutting ut the wells prductin peridically and ecnmic feasibility has nt yet demnstrated with high CO 2 pressures, the use f scale inhibitrs ecnmically and ecnmically thus seems t be the mst successful technique t slve carbnate scaling in high carbn gethermal fields. The chice f the mst suitable inhibitr and injectin apparatus is the main prblems f the methd. A severe scale frmatin was remved frm the pipe inside well OB-9 during peratin withut inhibitr, when the prductin was stpped. The results f the chemical analysis f the slid scale cnsist f: 81.6 % Ca, 3.7% Mg, 0.5 %, Fe 8.9 % Sr and 1.4 Si, shwing that calcium is the main element f the slid depsitin frm Germanic well 9. Figure 3. Pipe spls after 2 hurs f n inhibitr injectin in Germencik well OB-9; upstream f cntrl valve and dwnstream thrugh cntrl valve (Frm W Osbrn et al. 2007) 3.1 Saturatin Index f the tw Grabens brine The calcite and aragnite carbnate minerals, CaCO 3, dlmite (CaMg(CO 3 ) 2 ) are saturated thrughut the gethermal reservirs in the Buyuk Menderes and Gediz Grabens, including Germencik, Kizildere, Pamukren, Alasehir-Piyadeler and Gbekli. Thse carbnate minerals shw a relatively high degree f supersaturatin upn biling. Cnsidering the chemical analyses f the high carbn cntent fluids fr several gethermal fields suitable fr electricity generatin using either flash r binary cycle methds, the result belw has been btained fr scaling and crrsin tendencies f water accrding t Langelier Saturatin Index (Yildirim et al. 2002) SI = ph (measured))-phs (calculated) (1) phs = p(ca) + p(alk) +C (2) Fields Name ph phs SI Characteristics Denizli- Kizildere Incrustative Aydin-Germencik Incrustative Aydin-Salavatli Incrustative Aydin- Pamukören Weak incrustative Aydın -Söke Incrustative Manisa -Alaşehir Incrustative Manisa-Caferbeyli Weak incrustative As can be seen abve, all f the fluids that subjected t this study are incrustative. It means they are liable t cause CaCO 3 depsitin during up-flw in the well-bres, in the separatrs and in the heat exchangers f the binary cycle plants. There are several methds in use t cntrl CaCO 3 scale in gethermal applicatins. 4

5 Yildrim et. al. 3.2 Aquifer gas pressure in high carbn gethermal fields Gas disslved in a reservir fluid cntributes t the ttal fluid pressure within the system. As mentined befre, fields like Kizildere, Germencik, Alaşehir and thers in the Grabens which cntain high gas, temperature and pressures are dminated by a cmplex biling pint depth relatinship different t that fr pure water. The high gas cntents significantly affect pressuretemperature pattern in the wells. Fr pure water, the ttal pressure, P TOT, at depth is given by ρgh where ρ is density f water at the biling pint (steam saturated) at all depths frm the water table t the depth h and the crrespnding temperature is btainable frm steam tables fr saturated cnditins (Henley et al. 1983). In a system with significant gas cncentratins, the ttal pressure is given by PTOT = ρgh= Pw +Pgas (1) Where Pw is the pressure f steam-saturated liquid water and P gas is the cntributed gas pressure calculated thrugh Henry s law (P=K H X). The gas breakut and biling depth change due t high gas cncentratin is shwn in Figure 4. As it can be seen in the figure, the biling depth in tested wells shifts frm 150 t 760 meter in BY-6 while shifts frm 90 meter t 500 m in M44S well due t gas cncentratin. Figure 4. Biling depth determinatin in three wells lcated in high carbn gethermal fields Graben: Biling depths shift due t CO 2 cntent 3.3 Carbnate scaling mitigatin The use f rganic phsphnate inhibitrs fr lw t mderate enthalpy and ply acrylic type fr high enthalpy gethermal fluids prved t be a feasible methd, bth technically and ecnmically, fr the preventin f carbnate scales in gethermal wells and surface equipment. The system designed fr injecting them int wells shwed itself functinal when a base type inhibitr injected t certain depth with adequate sinker bar weight. The schematic diagram f the inhibitr test facility system is given in Figure 5. The key cmpnents f the test system are: Prductin Well Inhibitr Strage and Pumping System and Prductin Well Inhibitr Dwnhle Feed System. Prductin Well Inhibitr Strage and Pumping System are mainly cmpsed f inhibitr strage tank, tw dsage pumps (ne f them as reserve), calibratin pt, and pressure gauges. Prductin Well Inhibitr Dwnhle Feed System, n the ther hand, includes stuffing bx, lubricatr, hay pulley, weight (sinker) bar, chamber, capillary tubing and drum. In rder t run the inhibitr injectin system prperly and effectively, the fllwing pints must be given special attentin (Tevfik et al. 2007): 1. The selected inhibitr must preserve its resistance when subjected t high temperature. 2. Flashing pint must be clearly identified fr each well s that tubing can be retrenched t at least 50 meters belw this pint. 3. The pump capacity must be selected in a flexible manner t be able t adpt changing well prductin rates. 4. Weight (sinker bar) calculatins must be made fr 5

6 Yildrim et al. Figure 5: The inhibitr injectin system. Several inhibitr tests have been cnducted recently and all shwed success in mitigating carbnate scaling.. It is nt pssible t give infrmatin abut all f them hear. The last was cnducted in May 2014 in Pamukren AP-5 gethermal well. Dwnhle additin f rganic phsphnete as an inhibitr f carbnate scale determines increase the cncentratin f calcium in the prduced fluid and hence a cnsiderable decrease in the frmatin f CaCO 3 scale in the wells and surface equipment (Yildirim 2009). The increase f calcium catin in the fluid is evident in all inhibitr applied wells but mre in AP-5. A severe scale frmed during clean ut test withut inhibitr was remved frm the pipe inside well AP-5 when the prductin was stpped. The results f the chemical analysis f the slid scale cnsist f: 93 % CaO, 3.8 % MgO, 1.1% Fe2O3 and 2.1 % thers. Significant variatins were nt bserved in the cncentratin f calcium in at well AP-5 fllwing the injectin f inhibitr at varis depth in the m range. S injecting the inhibitr dwnhle t 500 m depth in Pamukren lcated wells were fund t be adaquate fr preventing carbnate scale. These depths depend n CO 2 cncentratin f the field fluids. Fr exempla required depths fr wt % CO 2 cntents Kizildere and Germencik gethermal fields is in the m range. As far as calcium is cncerned a substantial increase was nt determined fllwing dwnhle treatment with inhibitr ranging between 12 and 6 ppm at AP-5 (Yildirim 2014). As a result 6 ppm inhibtr fund t be enugh fr preventing CaCO 3 scaling in this well (Figure 6). Figure 6. Organic phsphnate inhibitr perfrmans in Pamukren well AP-5 3. CONCLUSION The waters f the selected gethermal field wells fr the present study are displaying a cmplex chemical cmpsitin depending n the aquifers and gelgical cnditins in each f the gethermal systems. All f them may have a ptential fr scale frmatin due t either high inrganic carbn cntents r high salinity. The use f rganic phsphnate type fr lw t mderate enthalpy and plyacrylates type fr high enthalpy gethermal fluids prved t be a feasible methd, bth technically and ecnmically, fr the 6

7 Yildrim et. al. preventin f carbnate scales in gethermal wells and surface equipment. The flw line, weir bx and weir bx discharge were carefully mnitred visually and n silica depsitin was detected. This result suggesting that amrphus silica depsitin and ptential well perfrmance decline will nt be a significant factr in high inrganic carbn characteristic fluid prducer fields brine injectin. Mixing the separated water with cndensed steam is an imprtant step in treatment f the separated water t reduce the risk f silica scaling befre re-injectin. REFERENCES Henley R.W., Truesdel A.H., Bartn P.B. (1983) Fluid-Mineral Equilibria in Hydrtermal System JICA Internatinal Cperatin Agency (1986) the Dikili-Bergama Gethemal Develpment Prject Prgress 1 and Final Reprts. Osbrn W., Gulgr A., Erkan B., Demirci N., Yildirim N. (2007) Carbnate Scale Inhibitin in a High-Gas Gethermal Well, Germencik, Turkey Simsek S Gethermal Activity in Turkey. United Natins Wrkshp n Develpment and Explitatin f Gethermal Energy in Develping Cuntries Reykjavik, Iceland. Simsek, S., Dğdu, M.S., Akan, B., Yildirim, N. (2000) Chemical and Istpic Surveys f Gethermal Reservirs in Western Anatlia Turkey. Prceeding Wrld Gethermal Cngress, Japan. pp Simsek, S. (2003) Hydrgelgical and Istpic Survey f Gethermal Fields in Buyuk Menderes Graben, 118-Gethermics BMG simsek science. Pdf Yildirim N. ve Simsek S. Determinatin f Apprpriate Injectin Cnditins fr Kizildere Gethermal Waste Fluid t Avid Scale Frmatin and Cling. (2003) Eurpean Gethermal Cnference, Szeged, Hungary. Yıldırım N.: Inhibitr Trials fr Calcite Inhibitin Well KD- 14 Kızıldere Gethermal Field, (2009), Unpublished Reprt. 64 p., Ankara Yildirim N. Inhibitr selectin test in well AP-5 at Pamukören gethermal Field, (2014) Unpublished reprt. 20 p., Aydın, Turkey 7