Available online at www.sciencedirect.com ScienceDirect nergy Procedia 61 (2014 ) 179 1798 The 6 th International Conerence on Applied nergy ICA2014 Pressure Analysis o ZK212 Well o Yangyi High Temperature Geothermal Field (Tibet, China) *Xiuhua Zheng, Haiyang Liu, Rongsheng Ji, Zhanxue Bai School o ngineering and Technology, China University o Geosciences, Beijing 10008, China Abstract Pressures are critical or sae drilling o high temperature geothermal reservoir. In this paper, racturing pressure, ormation pressure, leaking pressure and annular riction loss and equivalent circulating density o the irst mediumdeep geothermal well ZK212 is calculated and analyzed by conducting leako test and observing the wellbore water table, and contour map o zero pressure point is drawn by the integration o investigation data in 1990s, which could be used to aid designing drilling luid system avoiding blowout and racturing ormation. 2014 The The Authors. Authors. Published Published by lsevier by lsevier Ltd. This Ltd. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/.0/). Selection and/or peer-review under responsibility o ICA Peer-review under responsibility o the Organizing Committee o ICA2014 Keywords: equivalent density; ormation pressure; racturing pressure; leaking pressure; zero pressure point Nomenclature al annular equivalent riction loss density (g/cm ) cir equivalent circulating density (g/cm ) equivalent density o ormation pressure (g/cm ) rac equivalent density o racturing pressure (g/cm ) l equivalent density o leaking pressure (g/cm ) g accelerated gravity (g=9.8m/s 2 ) h elevation o well head (m) h0 elevation o zero pressure point (m) P ormation pressure (MPa) * Corresponding author. Tel.:+ 86 10 8221976; ax: +86 10 8222624 -mail address: xiuhuazh@cugb.edu.cn 1876-6102 2014 The Authors. Published by lsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/.0/). Peer-review under responsibility o the Organizing Committee o ICA2014 doi:10.1016/j.egypro.2014.12.215
1794 Xiuhua Zheng et al. / nergy Procedia 61 ( 2014 ) 179 1798 Pl P rac Pp T y z h leaking pressure (MPa) racturing pressure (MPa) pumping pressure (MPa) luid temperature () elevation o calculating depth (m) depth o calculating borehole point (m) over height o zero pressure point (m) luid density in wellbore (g/cm ) Subscripts a average value cold water c 1. Introduction [1], [2] Yangyi Geothermal Field, which located in the southern part o the Nagqu-Ngemo geothermal active belt and 45km southwest o Yangbajing and 75km west o Lhasa, is one o the high-temperature convective hydrothermal geothermal systems with lithologic character [], [4] o mainly granite and andesite in Tibet. Pressure analysis to determine racturing pressure and ormation pressure is critical and helpul to design drilling luid system and its rheological and hydraulic properties, with which sae drilling o high temperature wells could be achieved avoiding blow out or lost circulation. 2. Tests and Observations 2.1. Leako test to determine racturing pressure Leako test was conducted at the depth o 1154m [5] -[7]. The data o the pumping pressure was recorded every 1 minute at the same time (Figure 1), in which point A iners leako beginning and point B iners ormation ractured. Pumping pressure MPa 6 B: P pb =5MPa 5 4 A: P pa =4MPa 2 density o pumping cold water 1 c is 0.992 g/cm at temperature T c o 40 0 0 2 4 6 8 10 12 Time, min Fig.1.Pumping Pressure Changes with Time during Leako Test
Xiuhua Zheng et al. / nergy Procedia 61 ( 2014 ) 179 1798 1795 2.2. Leako observation Leako observation during circulating was taken at the depth o about 467m and 1154m. Parameters o leako rate, average temperature and density o drilling luid were recorded and analyzed, with which annular equivalent riction loss density and equivalent circulating density were calculated [8]-[11]. The results are shown in Table 1. Table 1. Leako Observation and Calculation o quivalent Density z, m Leako Rate, m /h Ta o drilling luid,, g/cm al, g/cm cir, g/cm 466-467 20.44 20 0.998 0.24 1.22 467-468 6.552 0.994 0.189 1.18 1154-1157 28.5 28 0.996 0.56 1.52 1161-1164 12 1 0.995 0.527 1.522 2.. Formation pressure test Ater drilling was completed 20 hours, elevation o water table o ZK212 in wellbore with the total well depth o 1510m was tested with metal wires and a multimeter (Fig.2). levation o Water Table o ZK212m. Results and Discussion 4692 4688.1. Leaking and racturing pressures o ZK212 According to Figure 1 and Bourgoyne [6], Pl PpA 10 cgz 15. 22MPa l Prac PpB 10 cgz 16. 22MPa 4684 well depth=1510m 4680 h=4700m T a =140 4676 h 0 =4688.1m 0.00 50.00 100.00 150.00 200.00 Timeh Fig.2.levation o Water Table o ZK212 10 P gz 10 Prac 1.44g / cm gz (2) l 1.46g / cm (1) rac
1796 Xiuhua Zheng et al. / nergy Procedia 61 ( 2014 ) 179 1798 From these results, it could be deduced that Pl and Prac o ZK212 are relatively low, indicating the probability o leako and ormation racturing during drilling procedure. This is proved by the leako during drilling operation. Table 1 shows leako rate is related to the properties o drilling luid which determines the equivalent circulating density..2. Formation pressure o ZK212 According to Figure 2 and Wang [12], P could be calculated by P 10 g( h ( h y)) () a a When P 0, then y h 0 h h, and the point o h0 is called zero pressure point. ah a (4) z 2 4 2 1.02 0.04 10 T 0.02 10 T 0.924 (5) a 10. 977 0.9248 (6) z Formula (6) indicates that o ZK212 decreases with the well depth and smaller than 0.9248, which means it could be drilled with cold water without kick and blowout... Contour map o zero pressure point o Yangyi High Temperature Geothermal Field Integrated o ZK212 and Liang [1], elevation distribution o zero pressure points is calculated in Table 2 and drawn as Figure, which illustrate that some wells might kick or blow out while some might leak o depending on the value o h, which urther suggests that some wells could be drilled with cold resh water, and some should be drilled with brine or weighting drilling luids to balance the ormation pressure. This matches the observations on ields. Over height o zero pressure point h o a well could be deduced by contour map o zero pressure point o Yangyi Geothermal Field when its well head elevation is located. Table 2. Pressure Characteristics o Wells on Yangyi High Temperature Geothermal Field Well No. h, m h 0, m h, m T, a, g/cm, g/cm ZK206 4619.04 4711.58 92.54 152.4 0.91 1.080 ZK200 468.21 4729.25 91.04 172.9 0.89 1.127 ZK208 4641.4 478.99 97.65 207.16 0.85 1.286 ZK20 4657.10 478.99 81.89 201.77 0.86 1.188 ZK207 4666.56 4719.6 5.07 16.51 0.90 1.05 ZK212 4700.00 4688.1-11.87 140.00 0.92 0.916 ZK205 4704.2 4704.2 0 74.00 0.98 0.980 ZK150 4710.57 4649.67-60.9 119.00 0.94 0.881 ZK250 4719.61 4719.61 0 189.9 0.87 0.980
Xiuhua Zheng et al. / nergy Procedia 61 ( 2014 ) 179 1798 1797 4. Conclusion Fig..Contour Map o Zero Pressure Points o Yangyi High Temperature Geothermal Field According to the results discussed above some conclusions are drawn as ollows: (1)ZK212 is o rather low rac and l and is prone to leak o or racture during drilling. (2) o a well o Yangyi Geothermal Field is related to its relative elevation o well head and zero pressure point, which means drilling luids with dierent density should be designed to balance its ormation pressure. ()Over height o zero pressure point h o a well could be deduced by contour map o zero pressure point o Yangyi Geothermal Field when its well head elevation is located. Acknowledgements This research is supported by National Geothermal Resource Investigation project o China Geological Survey Bureau. Code:1212011120064 Reerences
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