Production Test Analysis of XYZ-Well at Dieng Geothermal Field. Using Horizontal Discharge Lip Pressure Method with

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1 Proceedings World Geothermal Congress 2015 Melbourne, Australia, April 2015 Production Test Analysis of XYZ-Well at Dieng Geothermal Field Using Horizontal Discharge Lip Pressure Method with Russel James Equation and Hiriart Equation Aris Tristianto Wibowo 1, Muhammad Thasril 2, and Puji Sirait 3 1 Petroleum Engineering, ITB, aris.wibowo@outlook.com 2 Halliburton, m.thasril@gmail.com 3 Halliburton, pujigwa@yahoo.com Keywords: production test, horizontal discharge lip pressure method, Russel James equation, Hiriart equation ABSTRACT Production test is one of very crucial activities in the geothermal field development process because the condition of the well, reservoir characteristics, and production capacity of the well can be determined by the test. Production test data should be processed carefully to get the best possible determination of production capacity approaching the actual condition of the well, so that future development plans of production wells may be optimized and monitored. Errors in production test data processing would decrease the production efficiency of the wells based on the production wells development design that have been made. In the other hand, the production can be analyzed each time based on available baseline condition prior to mitigate the problems. This paper describes the production analysis results based on case studies of XYZ-well production test at Dieng geothermal field that uses the Horizontal Lip Pressure Method with two silencers and two different types of weir boxes simultaneously at the same time of production test. Data processing is accompanied by data selection process, lip pressure correction, and correction of the gas presence. Total rate and total enthalpy of the fluid, which become the objectives of this production test, will be determined by Russel James equation and Hiriart equation. The results from both equations are also compared to know the sensitivity of each equation toward the available production test data. All results will be presented in graphs, so that reservoir characteristics and XYZwell condition can be specified based on those graphs. 1. INTRODUCTION Dieng is a water-dominated geothermal field located in Dieng Plateau, Central Java and developed at an altitude of about meters above sea level with temperatures between C. Dieng field is made up of a series of volcanoes with andesite composition (Layman, 2). Geothermal manifestations that appear on the surface are in the form of solfatar, hot sping, mudpool, fumarole, and moffet. (Calibugan, et al., 0). Dieng field reservoir temperatures reach over 225 C and it is categorized as a hightemperature reservoir system. Based on the study results conducted by Layman (2), in general, Dieng geothermal field can be divided into two sectors, Sileri and Sikidang. Reservoir fluid of Sileri sector has moderate salinity, ph neutral, and low gas content characteristics, while fluid of Sikidang sector has high gas content with moderate feed zone depth and high enthalpy. Currently, Dieng geothermal field is managed by PT Geo Dipa Energy Dieng Unit (Persero). The field was developed with seven production wells and four injection wells for Unit 1, resulting in a production of 60 MW 2. THEORY 2.1 Horizontal Lip Pressure Method In this method, reservoir fluid will be ejected horizontally from the well through a lip pipe with certain diameter to the silencer. Measured parameters as input data for this method are wellhead pressure, lip pressure, and lip pipe diameter. Lip pressure is measured at the end of the lip pipe and fluid flow rate from silencer is determined using a weir box. 2.2 Weir Box Equation Weir box is used to determine the water mass flow rate from the silencer. In this case, there are two types of weir box that will be explained, V-Notch Weir Box and Rectangular Weir Box V-Notch Sharp Crested Weir Box Here are the equations used to determine water mass flow rate through the V-Notch Sharp Crested Weir Box. ( ) ( ) (1) (2) (3) 1

2 where Q, C, θ, h, and k are water flow rate (m 3 /hour), discharge coefficient, V-Notch angle (degree), weir height (m), and weir height correction (m), respectively Rectangular Sharp Crested Weir Box Figure 1: V-Notch Sharp Crested Weir Box. Slightly different from the equations before, these following equations are used for Sharp Crested Rectangular Weir Box. (4) where Q, C e, b e, h e, K, and g are water flow rate (m 3 /hour), discharge coefficient, space between weir plate (m), weir height (m), correction factor (m), and gravity acceleration (m/s 2 ), respectively. (5) (6) Figure 2. Rectangular Sharp Crested Weir Box. Discharge coefficient (C e ) and correction factor can be determined by following graphs. Figure 3. Graph to determine the value of discharge coefficient (C e ). 2

3 2.3 Russel James Equation Figure 4. Graph to determine the correction factor (K b ). Russel James equation connecting mass flow rate, enthalpy, lip pipe cross-sectional area, and lip pressure as follows. ( ) (7) (8) where W atm, H, P, A, h f, h g, h fg, and M are water mass flow rate (ton/hour), fluid enthalpy (kj/kg), lip pressure (bara), enthalpy of liquid-phase (kj/kg), enthalpy of vapor-phase (kj/kg), latent heat (kj/kg), and total mass flow rate (ton/hour), respectively. 2.4 Hiriart Equation Gerardo Hiriart creates an equation to determine the steam flow rate from vapor-dominated geothermal wells as follows. ( ) (9) This equation is quite simple, because it only requires pressure and lip pipe diameter as the variables. Hiriart equation negates the fluid enthalpy parameter, so that the accuracy level is lower than Russel James equation. Assumption applied in the Hiriart equation is steam flow to the atmosphere at sonic velocity condition as in perfect gas. However, Equation 6 can only be applied for vapor-dominated wells, so that to determine steam flow rate of the two-phase wells, Equation 6 needs to be corrected into the following equation. ( ) (10) where Q s, P, D, Q w, and Q s are vapor mass flow rate (ton/hour), lip pressure (psia), lip pipe diameter (inch), water mass flow rate at atmospheric pressure (ton/jam), and corrected vapor mass flow rate (ton/hour). 2.5 Lip Pressure Correction Equation Lip pressure obtained from measurement activity with a measuring device still needs to be corrected with a calibration factor based on lip pipe equation made by California Energy Company (CEC). ( ) (11) where P lip, P atm, P lip correction, and Corr. P lip are measured lip pressure (psig), atmospheric pressure (psia), calibration correction factor (inch), and corrected lip pressure (psia) 2.6 Gas Correction Equation Malcolm A. Grant develops an equation, which is a modification of the previous equation, to correct the results of enthalpy values due to the presence of gas in the well. The presence of gas that carried with the production fluid will give an impact on the results of enthalpy values. The effect can be very significant on certain conditions, so that the previous results need to be corrected by the following equation. ( ) ( ) ( ) (12) where ΔH, H, f lip, and H are enthalpy correction (kj/kg), initial enthalpy (kj/kg), gas mass fraction at lip pressure, and corrected enthalpy value (kj/kg). (13) 3

4 WHP (psig) Aris and Thasril 2.7 Two-Phase Fluid Enthalpy Equation Production test by using horizontal lip pressure method can also be conducted with more than one silencer for one well. If that condition exists, the enthalpy of the fluid can t be directly summed from the calculation of each silencer. Values that can be directly combined are the total fluid flow rate and water flow rate. By knowing the combination of both parameters from available silencers, enthalpy of the fluid can be determined from production test by the following equation. where H, x, W atm, M, h f, and h fg are fluid enthalpy (kj/kg), mass fraction of vapor, combined water flow rate (ton/hour), combined total fluid flow rate (ton/hour), enthalpy of liquid phase (kj/kg), and latent heat (kj/kg), respectively. 3. CASE STUDY Production test with horizontal lip pressure method, which performed on XYZ-well at Dieng geothermal field, used two lips and two different weir boxes. Lips and weir boxes specifications used are summarized in Table 1. Table 1: Lips and weir boxes specification used in XYZ-well production test. (14) (15) Static Data: Atmospheric Pressure: 11.5 psia ID of James Tube: 6.00 inch 8.00 inch Height from gauge to James Tube: cm cm Plip Correction: inch inch Left Right Rectangular Weir Box Type: V-Notch B = 1.20 m θ = 90 b = 0.34 m p = 0.73 m The production test was performed from March 24 th to 31 st, Production test profile during the time interval is shown in Figure 5. Production test measurements graph obtained shows inconsistent results in some particular time. Theoretically, the larger the valve is opened the wellhead pressure will be smaller and will be stabilized at a certain pressure during valve is opened at the same conditions. Therefore, production test data obtained need to be selected and validated more in accordance with the theory. Open valve 3.5" (10.7%) Open valve 5.25" (29.1%) WHP coming up Water turn to black Choke throtle valve due to sinker bar can not flow pass the fow tee Open valve 6.25" (40%) Open valve 7" (47.5%) 0 Open back to original position Weir on separator two overflow Open valve 7.25" (50.1%) Date and Time Figure 5: Wellhead pressure profile of XYZ-well production test. With the valid production test data, subsequent data processing can be conducted that begins with the mass flow rate calculation process of each weir box. Mass flow rate of both weir boxes are next combined to obtain total mass flow rate, so that it can be used to calculate total enthalpy of the fluid produced from XYZ-well. Total mass flow rate and total enthalpy of the fluid are determined by two equations, Russel James equation and Hiriart equation, so the results of both equations can be compared. Production potential of XYZ-well and its reservoir conditions can be predicted based on the Wellhead Pressure vs. Total Rate and Wellhead Pressure vs. Enthalpy plot. Analysis of the two plots is explained in Grant, Malcolm A. and Bixley, Paul F.: Geothermal Reservoir Engineering Second Edition, Elsevier Inc., (2011), Oxford. Plots for XYZ-well are shown in Figure 6 and Figure 7. According to Wellhead Pressure vs. Total Rate plot, it can be analyzed that XYZ-well producing two-phase fluid and the result is appropriate with the actual condition. Then, according to Wellhead Pressure vs. Enthalpy plot, it can be analyzed that XYZ-well producing two-phase fluid from the reservoir which has a pretty good permeability. Total mass flow rate and total enthalpy of the fluid obtained from the Russel James equation and the Hiriart Equation have a little difference. It happens because the two equations have different calculation assumptions. Russel James equation has more complex variables, so that the Russel James equation has better accuracy rate, while Hirirat equation is simpler because it only includes lip pressure and lip pipe diameter as the variables. 4

5 Figure 6: XYZ-well flow test plot before data selection process. Figure 7: XYZ-well flow test plot after data selection process. The data processing results based on the Hiriart equation always deliver greater value compared with the calculation results based on the Russel James equation, both for total flow rate and total enthalpy of fluid. Statistically, the average percentage of difference value resulting from the Russel James equation and the Hiriart equation is 5.34% for the total flow rate value and 3.42% for the total enthalpy value of the fluid. Hiriart equation, which is simple, can be modified in order to generate value that approaching Russel James equation, so that the modified Hiriart equation further can be easily used and produce an accurate value. Modified Hiriart equation is formulated by adding a constant in the earlier Hiriart equation. The constant is determined by calculating the average value ratio of the results obtained from the equations of line representing Russel James equation and Hiriart equation. The equations are interpolation results of the equations of line corresponding to the graphs in Figure 7. The following equations are equations of line to determine the total flow rate of fluid. Russel James: Hiriart: (16) (17) The following equations are equations of line to determine the total enthalpy of fluid. Russel James: Hiriart: 5 (18) (19)

6 Table 2: Calculation results based on Russel James equation and Hiriart Equation (a) Total Rate; (b) Enthalpy Total Rate (ton/hr) Pwh Difference (psig) Russel Hiriart (%) James Average Conversion Factor (a) 6 Enthalpy (kj/kg) Pwh Difference (psig) Russel Hiriart (%) James Average Conversion Factor (b)

7 Table 3: Calculation results based on Russel James equation and Modified Hiriart Equation (a) Total Rate; (b) Enthalpy Total Rate (ton/hr) Pwh Difference (psig) Russel Hiriart (%) James Average (a) Enthalpy (kj/kg) Pwh Difference (psig) Russel Hiriart (%) James Average (b) 7

8 The results obtained by the four equations above for some P wh values are shown in Table 2 (a) and (b). From the tables, it is known that the average value ratio obtained for the total flow rate of fluid is with error percentage 5.34%, while for the total enthalpy of fluid is with error percentage 3.42%. Based on these results, the constants used to determine the total flow rate and the total enthalpy of fluid by modified Hiriart equation are and respectively, so that modified Hiriart equation will be obtained as follows. ( ) (20) ( ) (21) Table 3 (a) and (b) show the errors of difference results between Russel James equation and modified Hiriart equation. According to the tables, it is known that the average error percentage of fluid total flow rate and fluid total enthalpy are reduced to 0.278% and 0.281% respectively. The great reduction in the average error shows that the results obtained from the modified Hiriart equation are very close to the results based on Russel James equation, as shown in Figure 8 and Figure 9. (a) Figure 8: Comparison of the total flow rate based on Russel James equation with (a) Hiriart equation; (b) modified Hiriart equation (b) (a) Figure 9: Comparison of the total enthalpy based on Russel James equation with (a) Hiriart equation; (b) modified Hiriart equation (b) 4. CONCLUSION The XYZ-well produces two-phase fluid from a geothermal reservoir that has a pretty good permeability. Total mass flow rate and total enthalpy value of the fluid based on Hiriart equation gives value that is always greater than the calculation results based on the Russel James equation. It is resulting average error percentage 5.34% for the total flow rate value and 3.42% for the total enthalpy value of the fluid. Modified Hiriart equation gives very close results according to Russel James equation with errors 0.278% for the total flow rate and 0.281% for the total enthalpy of the fluid. 8

9 REFERENCES Borromeo, CMR., and Orizonte, RG.: Output Computation for SNGP Wells Discharging Dry Steam, (1997). Cahyono, Yanuaris Dwi: The Application of Modified Hiriart for Fluids Flow Measurement in Geothermal Wells Flow Test Using Horizontal Lip Pressure Methode, (2013), Jakarta. Grant, Malcolm A. and Bixley, Paul F.: Geothermal Reservoir Engineering Second Edition, Elsevier Inc., (2011), Oxford. Hiriart, Gerardo: Steam Flow Rate Calculation by a Very Simple Equation, GRC6, , (1982). Saptadji, Nenny Miryani: Teknik Panas Bumi, ITB. 9