Development of Intermittent Gas Lift Optimum Time Module Using Automatic Pneumatic System

Development of Intermittent Gas Lift Optimum Time Module Using Automatic Pneumatic System Rit Nanda, Shashank Gupta, Himanshu Shukla, Pulkita Rohilla, Kush Patel, Ajit Kumar N Shukla* School of Petroleum Technology, Pandit Deendayal Petroleum University, Gandhinagar, India ABSTRACT Artificial lift technique is used to bring hydrocarbons to the surface when they cannot come to the surface on their own. Gas lift is an artificial lift technique which is classified into continuous and intermittent gas lifts. Continuous gas lift is used when the hydrocarbon fills into the wellbore continuously but is not able to come to the surface while intermittent gas lift is used when the fluid flow into the wellbore is not continuous and the operating valve is not always submerged. At the heart of the latter system lies the time interval for the liquid to submerge the operating valve which in turn dictates the injection time module of the gas. This paper presents the studies done till date on gas lift techniques and specifically deals with the time control module of intermittent gas lift. The purpose of this paper is to present a robust system of time control that uses pneumatic test rig and develop automatic actuator using the pressure of the injected gas. The pressure, which is the only factor responsible for the opening and closing of the valve, controls the injection time interval and eliminates the monitoring of any other parameter. The expected pattern of produced fluid with frequency of injection matches with the experimental data which concludes the veracity of this system as an effective time module controller. Keywords: Intermittent, gas lift, production, time module, injection gas, valves *Author for correspondence E-mail: ajit.shukla@spt.pdpu.ac.in, Tel: + 91-7923275065, Fax: + 91-7923275030 1. INTRODUCTION Intermittent gas lift is a type of artificial lift technique being used worldwide nowadays. Artificial lift, as the term suggests, is the lifting of crude to the surface, once it has lost its natural energy, by imparting artificial energy to let it come to the surface. In gas lift, this energy is provided by gas. An equivalent example may be understood by taking the case of lifting of water where air that goes in lifts the water to the surface. However, for the purpose of lifting oil, air is not a suitable medium because oxygen in the air can not only corrode the metal installations but also form an explosive mixture with hydrocarbons. Hence, compressed natural gas or pressurized natural gas is used in gas lift, as has been detailed in the subsequent sections of this paper. This paper identifies a broad historical outline of intermittent gas lift and focuses primarily on time controller systems used in such lifts. The authors try to create a simplistic model as given in Figure 1 and present the broad findings from their studies and experiments. The paper eventually proposes the integration of a pneumatic test rig into the gas lift system as a robust and effective time controller. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 1

Fig. 1: Typical Gas Lift Valve Configuration. 2. LITERATURE SURVEY OF THE PAST RESEARCH PAPERS TO DEVELOP A NEW MODEL Tutschule [1] presents charts linking the analysis of gas lift through one-and-a-half inch (macaroni) tubing. Vincent [2] designed gas lift system with moving pistons instead of a fixed plunger. White et al. [3] presented a solution to find out the relation among pressure, velocity and production rate with the help of velocity and pressure ratios in different sections of the well so that measurement of these properties by a system of strings can be done. Neely et al. [4] showed that liquid fallback is not only a function of velocity but it is a function of half the product of density and square of velocity. Based on experiments, the equations for tubing pressure beneath slug, tubing pressure at injection valve and gas injection rate were developed. Cedeno et al. [5] developed a method of optimization using SOLAG (software) which takes into account five parameters which are GOR, time, availability of gas, gas injection pressure and daily well performance. Gasbarri et al. [6] simplified reservoir simulation models which could be developed to determine the inflow performance of reservoirs produced by intermittent lift methods. Hernandez et al. [7] gave a dynamic solution for a plunger lift method by dividing the fluid in the plunger into three sections, namely the gas expansion above liquid slug, plunger and liquid slug and gas expansion behind plunger. The solution of the momentum equations give us the pressure below plunger, pressure at the top of the liquid slug in tubing and pressure at the front of the liquid slug in flow line. Gasbarri et al. [8] presented economic factors that determine the success of an artificial lift in a mature field, especially the problems and economic considerations related to Intermittent Gas Lift. Prado Pablo et al. [9] designed a pilot valve with increased internal dimensions, combination of spring force and nitrogen pressure which in turn increase the efficiency. Hernandez et al. [10] presented Downhole Water Sink (DWS) technology which could be used to control water coning in dual completed wells by concurrently producing water and oil. Marcano et al. [11] showed the liquid column height in intermittent gas lift wells could be best determined based on the solutions of ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 2

Aziz s and Wallis correlations. Cheung et al. [12] showed the IGL well performance can be optimized towards the maximization of produced oil and the economic gain of production. Ayatollahi et al. [13] investigated the hydrodynamic of the intermittent gas lift in order to obtain the distribution of the pressure, oil; and gas production parameters at different locations of the artificially lifted oil reservoirs which are useful in calculation and formulation of mathematical model of transient pressure gradient. The outcome from this is used to decide the objective of further study. 3. OBJECTIVES OF THE STUDY The major objectives of the project identified after literature survey were to design and create a simplified model of a pneumatic time controller system for adjusting the cycle of injection; to demonstrate the different scheme of arrangement of gas lifting using pneumatic system rig through air realised by the timing device; obtain data to model and confirm the intermittent gas lift principles of jet pump. 4. SOLUTIONS SUGGESTED To fulfil the objectives of the project, the scheme of solution considered is model the intermittent gas lift system; validate the model experimentally; simulate the result; and obtain the set of data for the model. 5. INTERMITTENT GAS LIFT MODEL To model the intermittent gas lift system, the pneumatic test rig situated in Fabrication Technology Laboratory of Pandit Deendayal Petroleum University (PDPU) was used. It incorporates air compressor, pressure regulator, different drives, actuator and piston. Flexible line was used with this to simulate motion and displacement. Taking help of this, additional materials were used to make the setup comprising of pneumatic system, stock tank and reservoir tank. The experimental setup so assembled used the following major components. 5.1. The Pneumatic System The pneumatic system consisted of the components as shown in Figures 2 and 3. These components are air compressor unit, FRL unit, flow controller, single pilot valve, double acting cylinder, solenoid valve and gas injection valve. 5.2. Reservoir A plastic tank filled with water serves the purpose of reservoir. An inverted funnel is put in the tank to keep the tubing section steady as well as to work as the casing for the production tubing. The production tubing is energized with a connection from the pneumatic system fitted with a non-returning valve (NRV) which injects air at regular intervals. Apart from NRV which acts like injection valve, a suction pipe draws the fluid to bottom of the production tubing. The complete actual setup is shown in Figure 4. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 3

Fig. 2: Assembled Logic Diagram of Pneumatic Time Module. Fig. 3: Developed Model of Gas Lift Mechanism Fig. 4: The Actual Experimental Model. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 4

5.3. Stock Tank A measuring flask is used to serve the function of stock tank external to reservoir. This arrangement facilitates the collection of produced fluid by the injection process which is measured. The stock tank in setup is shown in Figure 5. Fig. 5: Actual Reservoir and Stock Tank Arrangement. 5.4. Experimental Validation The basic principle of working involved in actuation of the pneumatic system as a timer device is using the pilot valve as described in the following section. 5.5. Working of the Pilot Valve The logic used for construction of the timer of pneumatic test rig is as under: The actuator used is a 5/2 double pilot valve. At the start of the cycle, the input given to the pilot valve is high. This causes the port to open which is denoted by a high output. Over time as the pressure decreases and the fluid is lifted, the pressure drops and the corresponding output shows low value. After this, the pressure builds up again and the cycle is repeated. The process logic diagram is shown in Figure 6. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 5

Fig. 6: Process Flow Logic Diagram of Pneumatic Actuation 5.6. Lifting Technique The timer logic so developed is connected to well tubing as under: As the port opening and closing is controlled through the pilot valve, the output is fed into the production tubing. As the valve opens, the gas, in this case air, is sent to a NRV as shown in Figure 3. The NRV allows the gas to flow into the tubing and lift the fluid, water in this case. As the pressure drops, the NRV prevents backflow of the gas. During this time, the suction line acts as a capillary of reservoir and the fluid fills in the tubing. The process repeats thereafter. A flow control valve (FCV) is used to change the injection flow rate of the gas and therefore the strokes per minute (SPM) of the double acting cylinder. Each SPM involves the opening of the gas injection port once and its closing once. The SPM is calculated by taking the average of two observations for the same flow rate so that any variations in pressure do not affect the experimentation process and repeatability is checked. Thus the arrangement of such a material and method is able to lift the fluid at regular intervals which is needed to be experimented and results stimulated. 6. THEORY A gas lift system has been described in the previous sections. In this section, the production profile of a gas lift system has been discussed. The representative production profile is taken from a field study done by Oil and Natural Gas Corporation of India Ltd. at IOGPT [14]. The flow through the well is modeled as a second order differential equation using the analogy of U-Tube holding fluid. The flow through it is modeled against the periodic pressure input as: 2 d h L dh L 32 ( ) ( g) h p( t) 2 2 dt D dt Where L is length of the fluid in annulus and tubing, is the density of the fluid, h is the relative displacement of fluid in two columns, is the viscosity of the fluid, D is the diameter of the tubing and p is the injection pressure. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 6

rates as shown in Figure 7. This is due to the In this profile, it is observed that as the gas injection rate is low, liquid production rate is also low. As the gas injection rate is increased, the liquid production also increases. This is due to the fact that as more amount of gas is injected per unit time, the more it can lift the liquid. However, after a certain gas injection rate, the value of the liquid being lifted decreases despite increasing the gas injection fact that the gas breaks through the liquid and does not lift the liquid. Thus the production on the surface has more amount of gas and less amount of produced fluid. Thus, an optimum gas injection rate must be determined so that the maximum amount of fluid is produced. The purpose of this study is to create such a facility so that at a given setting experimental optimum gas injection rate could be found. 1700 1650 Production, m 3 1600 1550 1500 1450 1 2 3 4 5 6 7 8 9 10 Injection rate, m 3 /d Fig. 7: Actual Production Profile from Field Study in India. 7. EXPERIMENTATION 8. RESULTS AND DISCUSSION As per the methods described in the previous sections, the experiments were carried out and the readings with results are shown in Table 1. Water level in the tubing was 245 mm, while level up to which water lifted was 381 mm. 127 mm of water column lift head was measured at room temperature of 35 C. It is clear from the experimental data that at the lowest SPM of around 35, the volume filled is the least, i.e., 305 ml. It is also found that the maximum volume filled is 430 ml at an SPM of 61. As the SPM is further increased, the average volume filled is lesser. It is also noted that after a while, increasing the SPM has negligible effect on the volume ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 7

filled as is demonstrated when only 356 365 ml is filled as the SPM increases from 142 220 SPM. As the number of strokes is counted manually, the readings were taken twice and average was calculated. It has been found that there is variation in measurement of SPM which is in order of 3% to 11% when calculated with respect to average value. The effect of variation of temperature on the performance of intermittent gas lift is not evaluated. Table I: Working Performance IGL System Using Pneumatic Test Module. Sr. No. Number of Strokes in 2 min Average number of Strokes SPM Volume Filled (ml) Average Volume Filled (ml) 1 2 3 4 5 6 68 35 300 305 69 70 310 119 61 450 430 122 125 410 134 70 420 422.5 140 146 425 174 92 400 400 184 194 400 276 142 352 356 284 292 360 430 220 360 365 439 448 370 The production profile of the experimental data, as given in Figure 8, shows that the least volume is filled when the SPM is the lowest. The highest volume is lifted at 61 SPM and it decreases as SPM increases further. This denotes that this is the optimum SPM for production of this simulated well. Thus, our time module must cover the opening and closing of valve for 61 times a minute to achieve the highest production. The profile is in consistent with expected results and thus confirms it. At lower SPM, the gas is being injected at a lesser rate to lift the fluid resulting in lower production. As the SPM increases, so does the production, until an optimum value is reached. Thereafter, the SPM value is too high and gas is injected at a rate much faster than the accumulation of fluid in the tubing up to the point of submergence of the operating valve. Hence, gas breaks through and only gas is produced instead of the fluid. At even higher SPMs, the volume lifted decreases to a plateau when the rate is so high that it does not affect the amount of liquid being lifted ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 8

Fig. 8: Experimental Gas Lift Performance. 9. CONCLUSIONS Creation of intermittent gas lift using pneumatic test rig has been presented in this study. An initial attempt was made to study the previous research in this domain and bring in the cardinal point in the evolution of gas lift system. This involves the various types of systems, parameters involved in intermittent gas lift, economics and development of software to design an optimum time module. Following on that a demonstrative pneumatically actuated system was designed and built. This study also details the use of a pneumatic system that includes the pneumatic actuation as a simulated gas lift model. The current capacity created uses the pressure parameter to control the time module. It does not require the conversion of pressure to any digital form and subsequent analysis using software. The pressure is used to open the valve and is used as feedback through the pilot valve to control the pneumatic actuator as shown in Figure 9. Thus the salient features of this pneumatic system are no external or feedback conversions are required to control or optimize the time module; the production profile follows the expected pattern and thus this system may be considered as a prototype for upscaling to real field problems; it is a robust and cost-effective system that does not ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 9

require any external control system to optimize and regulate the time module. varied to judge the capability of this system and derive its performance characteristics. It is proposed that using this experimental capacity, various fluids of varying density may be lifted to check the range of this system s applicability; other gases apart from air may be used to lift the fluid and the applicability of system be checked; lifting heads may be While carrying out experiments, the following precautions must be taken the reservoir potential has to be so determined that the well does not self-flow, the diameter of the tubing should allow the liquid to build up to the operating valve. Fig. 9: Pneumatic Test Rig Setup Used for Automation of the Process. ACKNOWLEDGEMENT We take this opportunity to extend our obligation to School of Petroleum Technology, Pandit Deendayal Petroleum University, Gandhinagar for providing us with the facility of their Fabrication Technology Lab where this experiment was carried out. This work is the result of group effort and if the method of Percent Contribution Indicator (PCI) is employed to give credit, the corresponding author will take five points each from the last two members of the group and add to the first three. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 10

REFERENCES 1. Tutschulte A. C. Spring Meeting. Pacific Coast District, Division of Production, API Conference, Los Angeles. 1945. 9 16p. 2. Vincent R. P., Wilder L. B. Society of Petroleum Engineers. 000282G. 1953. 1 5p. 3. White W. Gerald, Bryan T. O Connell, Roy C. Davis, et al. Journal of Petroleum Technology. SPE 439-PA. 1963. 301 308p. 4. Neely A. B., Montgomery J. W., J. V. Vogel. Society of Petroleum Engineers.- AIME 48th annual meeting. 1973. 502 512p. 5. Cedeno M., Ortiz J. L., Lagoven. Society of Petroleum Engineers. 26972-MS. 2007. 1 8p. 6. Gasbarri S., Gupta A. J., Wiggins M. L. Inflow of Performance of Reservoir Produced by Intermittent Lift Methods. PSC 97 135, Canada. 1997. 1 6p. 7. Hernandez A., Perez C., Navarro U. et al. Society of Petroleum Engineers. 53968- MS. 1999.1 8p. 8. Gasbarri Sandro, SPE, Michael L. Wiggins, Society of Petroleum Engineers. 72057-PA, Oklahoma. 2001. 89 96p. 9. Prado Pablo, Mario Brarda. Society of Petroleum Engineers. 69154, 2001. 1 9p. 10. Hernandez, Cesar Perez, Balmiro Villalobos, et al. Society of Petroleum Engineers. 69402. 2001..1 4p. 11. Marcano L., Wojtanowicz A. Canadian International Petroleum Conference. 238. 2002. 1 12p. 12. Cheung S. C. Moy, Gasbarri S. Canadian International Petroleum Conference. 2002. 1 10p. 13. Ayatollahi Shahaboddin, Mostafa Narimani, Mahmood Moshfeghian. Journal of Petroleum Science and Engineering. 2004. 42..245 255p. 14. Mandal T. K. Training on Gas Lift Optimization. Institute of Oil, Gas and Production Technology, India. 2005. ISSN: 2231 1785 STM Journals 2012. All Rights Reserved Page 11