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Abstract A new mechanistic model to predict the natural separation efficiency in deviated pumped wells has been developed based upon the combined phase momentum equations and a general slip closure relationship. The model incorporates two important parameters that are both functions of flow pattern; the local void fraction in front of the pump intake ports and the drag coefficient. The void fraction is, in turn, a function of the bubble rise velocity. The model uses existing void fraction and bubble rise velocity correlations developed by Hasan and Kabir for both bubbly and slug flow. The transition between bubbly and slug flow is determined by using the Hasan and Hasan and Kabir criteria. The Barnea et al. critical angle criterion below which bubbly flow cannot exist is also used by the model. A general drag coefficient correlation for slug flow has been developed based on data gathered by Serrano on a water-air system for inclination angles of 30 and 60 degrees. Comparisons between the model's predictions and the experimental data of Serrano show excellent agreement. Sensitivity studies developed using the model indicates that the natural separation efficiency decreases as the liquid rate, inclination angle and gas-liquid ratio increase and as the annulus area decreases. For the wellbore configuration and operating conditions under investigation, the model predicts the existence of a minimum liquid rate below which the system reaches 100 percent gas separation efficiency. Introduction Natural separation in the tubing-casing annulus is an integral part of the overall bottomhole separation process in pumped wells. For ESP systems, when part of the gas phase enters the pump intake ports it affects the amount of free gas entering the pump thereby influencing the overall pump efficiency. Alhanati developed a simple theoretical model to predict the natural separation efficiency of ESP systems incorporating a rotary gas separator. The two main assumptions in the model are: a uniform void fraction from the motor section up to the gas separator's gas outlet ports, and a no-slip condition between the gas and liquid phases within the control volume immediately preceding the gas separator's intake ports. The model is strictly limited to the vertical configuration only. Serrano conducted an experimental study of natural separation in an ESP system (5 in. ID casing and 3.75 in. OD motor) as a function of operating conditions and inclination angle. Using a water and air fluid system, Serrano gathered 81 data points covering a maximum void fraction of 20 percent, liquid rate of about 2000 B/D, pressure of 150 psi, and inclination angles of 30 and 60 degree from horizontal. Serrano5 extended Alhanati's model by developing an empirical correlation to predict the local void fraction within the control volume in front of pump inlet ports for two different flow patterns, i.e., bubbly and slug flow. Harun et al. developed a simple model to predict the natural separation efficiency in vertical pumped wells. The model was developed based on the combined phase momentum equations and a general slip closure relationship applied to a single control volume in front of the pump intake ports. The model assumes no slip between the liquid and gas phases at the pump intake ports and a uniform void fraction across the annulus. Empirical correlations were developed to calculate the drag coefficient for all void fractions, however the model was limited to the vertical configuration only.
- North America > United States > Oklahoma (0.28)
- North America > United States > Texas (0.28)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (1.00)
- Production and Well Operations > Artificial Lift Systems > Electric submersible pumps (1.00)
- Facilities Design, Construction and Operation > Processing Systems and Design > Separation and treating (1.00)
Abstract To deal with gas and sand problems in their conversion and rod pump wells an operator company in south Texas started introducing a combined technology of two-stages filtration with a modified poor boy gas separator obtaining excellent results. This paper explains the technology used and shares the information used to design the tools and the results achieved in the first wells completed. The screening process to choose the best technology started trying different technologies for gas and sand control below the rod pump. Different technologies were revised sharing data like sand particle size, pump design, fluid production expected and wellbore configuration to get the best design from different companies. The technical and economic evaluation determined the combined system with two-stages filtration and gas separation was the best technology among all the installations. After the results, same technology was applied to other wells changing the configuration based on the well conditions but maintaining the same principle of operation. After the installation of this technology in each well, it was clear that there was a substantial increase in production among the wells that was caused for the improvement in the pump cards after the installation. The downhole equipment has been able to handle better gas production and no sand problems have been reported so far. The success of this technology has extended the operational capabilities of the pumps allowing the engineers to operate their wells better. Pump cards before and after the installations are summarized in the presentation to show evidence of the good results obtained. After the wells are converted from ESP to rod pump or when the gas represents an issue in the rod pumped wells, the production engineers are limited in the drawdown and the production they can get out of the wells. We are presenting an alternative for the operators to optimize the production's BHA and overcomsand and gas problems that limit the ability to increase the income of the oil fields.
ABSTRACT ABSTRACT Gas interference continues to be one of the major operating problems in pumping wells. In order to combat this problem effectively, a better understanding is needed of what the pump volumetric efficiency should be under various well subsurface conditions. Once it is known how the pump should perform, it will be possible to select the best setting depth and determine whether a gas anchor is needed. Care must be used in the selection and installation of gas anchors, otherwise the results will be disappointing. If free gas is present, not only must an effective gas anchor be used but the pump must develop a high compression ratio. Thus, the type and design pump used is critical. Pumping wells from under a packer and small-diameter casing completions are two practices that have increased the gas-interference problem. Pump efficiencies and production can often be improved in such wells. UNDERSTANDING PUMP VOLUMETRIC EFFICIENCY In order to better understand gas interference, the pumping conditions as they occur in an oil well need to be analyzed. In Fig. 1 the pump volumetric efficiency is plotted vs. the pump intake pressure. Pump intake pressure is defined as the pressure In the casing opposite the pump under producing conditions. Fig. 1 is for a typical reservoir and for conditions where there is , no slippage of fluid past the plunger; and , near-zero clearance between the standing and traveling valves at the bottom of the stroke. Such a graph can be drawn for any field or reservoir using the appropriate PVT conditions. Under bottom-hole conditions, a barrel of stock-tank oil will occupy a greater volume because of the gas in solution; thus, a larger volume must be pumped to obtain 1 bbl of stock-tank oil. If all the gas can be vented, the pump efficiency will increase as the pressure is reduced. This is shown by line BC In Fig. 1. At pressures greater than the bubble point (line AB) the pump efficiency remains almost constant. The lower curve (line BF) shows that the efficiency rapidly decreases for pressures less than the bubble point if all the free gas is pumped. If part of the gas can be vented, then the pump efficiencies will be higher. Usually very little gas is vented from the casing at pressures approaching the bubble point. This probably results since at the high pressures the gas bubbles are small, thus gravity has very little influence in separation. The small-size gas bubbles are easily entrained and are carried in the same direction as the oil. As the pressure is decreased, the gas bubbles grow in size and more separation occurs. As reported by Peebles and Garber,1 relatively large gas bubbles will rise at about 0.5-0.6 ft/sec. In general, the rising velocity depends upon the bubble size and shape and the physical characteristics of the liquid. When the pressure is decreased, bubble size increases and gas separation begins to improve.
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (1.00)
- (2 more...)
Pertinent experimental results and theoretical prediction techniques are summarized and evaluated in terms of the influence of viscous effects on cavitation inception and the extent to which the boundary-layer properties complicate the correlation of model and full-scale cavitation inception. Consideration is given both to bodies having natural transition and bodies having laminar flow separation. The present approach assumes that cavitation inception is controlled by the pressure fluctuations in the region of natural transition or laminar separation superimposed upon the static pressure. In general, these pressure fluctuations occur very close to the minimum potential-flow pressure for full-scale bodies but occur farther aft of the minimum pressure for corresponding models evaluated at a lower Reynolds number. Predictions are in good agreement with results from numerous experiments on cavitating bodies which have either natural transition or laminar separation. Numerical examples demonstrate the order of magnitude of viscous effects on model/full-scale cavitation-inception scaling for a typical propeller blade section. Areas for additional cavitation research to strengthen the present approach are recommended.
- Europe (0.46)
- North America > United States (0.28)
- Transportation > Marine (1.00)
- Shipbuilding (1.00)
Results of studies of submersible centrifugal gas separators operation during OOO RN-Purneftegaz wells' operation with high input gas content. Comparison of bench and field tests
Drozdov, A.N., Verbitckiy, V.S., Dengaev, A.V., Arseniev, A.A., Litvinenko, V.A., Habibbulin, R., Litvinenko, K.V., Elichev, V.A.
Abstract Monitoring and testing of subsurface equipment is crucial when stepping up artificial lift efficiency. Oil production using electrical submersible pumps (ESP) in RN-Purneftegas was initially complicated by a strong gas influence. The main method to increase ESP performance in wells with a high GOR is using rotary gas separators. Subsurface equipment adjustment for high GOR conditions, including gas separator calibration, is of primary importance, due to a strong influence of the ESP design on well performance. To perform the corresponding calculations, appropriate data is necessary. Currently, there are many tools and measurement devices for oil production monitoring and controlling, however, it is impossible to use its data without a good understanding of all the parts of the "reservoir-well-pump" production chain. The artificial lift team formed under Rosneft's New Technology System program conducted a wide range of field tests. The main goal of such tests was gathering information for parameter analysis and proper timing of ESPs with malfunctions in rotary gas separators. The collected information about real field performance was then used for validation of the accuracy of the lab data for gas separator performance, acquired by Russian State Oil&Gas University. It was concluded that the gas separator performance data obtained in laboratory if combined with correlation for natural separation prediction can be used for total separation efficiency estimation. The test results allowed us to estimate the potential for oil production increase at over 700 tons per day in Purneftegas. Importance of separation efficiency for well performance A number of geological and technical factors such as pump performance acquired in lab tests with a single phase fluid (typically water), or well operation history are used in ESP calibration. However, gas separator performance had not been adequately modeled during previous ESP sizing. The separator was treated as an intake module with constant separation efficiency in most cases.