Plunger lifted, and free-flowing gas wells experience a wide range of issues and operational inefficiencies such as liquid-loading, downhole and surface restrictions, stuck or leaking motor control valves, and metering issues. These issues can lead to extended downtime, equipment failures, and other production inefficiencies. Using data science and machine-learning algorithms, a self-adjusting anomaly detection model considers all sensor data, including the associated statistical behavior and correlations, to parse any underlying issues and anomalies and classifies the potential cause(s). This paper presents the result of a Proof of Concept (PoC) study conducted for a South Texas operator encompassing 50 wells over a three-month period. The results indicate an improvement compared to the operators' visual inspection and surveillance anomaly detection system. The model allows operators to focus their time on solving problems instead of discovering them. This novel approach to anomaly detection improves workflow efficiencies, decreases lease operating expenses (LOE), and increases production by reducing downtime.
Coutinho, Renato P. (Louisiana State University) | Williams, Wesley C. (Louisiana State University) | Waltrich, Paulo J. (Louisiana State University) | Mehdizadeh, Parviz (Consultant, Production Technology Incorporated) | Scott, Stuart (Shell Exploration and Production Company) | Xu, Jun (Shell Exploration and Production Company) | Mabry, Wayne (Shell International Exploration and Production)
This work demonstrates that the injection of a gas/liquid mixture allows the transport of gas to a deep injection point with injection pressure considerably lower than single-phase gas injection. The LAGL is demonstrated in a 2,880-ft-deep test well, by use of natural gas and water. The test well is kicked off with an injection pressure that would normally be higher than the pressure for single-point single-phase gas injection at this depth. Introduction Gas lift is widely used as an artificial-lift technique. Gas lift operations can be broadly classified into two different types: (i) continuous injection and (ii) intermittent injection. Conventional operations for gas lift unloading are transient processes in which high-pressure gas is injected in the annulus space between the casing and production tubing. The diagram presented in Figure 1 is based on the industry standard practices for gas lift unloading (Takács 2005). Both annulus and tubing are filled with liquid (formation and/or completion fluids). The gas injected in the annulus pushes the liquid out of the tubing. The bottomhole pressure will be kept constant as long as the production tubing is filled with liquid. When the unloading process reaches steady production, the unloading ends, and regular production operation begins (Tang et al. 1999).
Onshore gas developments are often characterized by drilling, fracturing, and production of wells before low-pressure gas-gathering systems are in place. As well production declines, liquid-loading issues begin to appear. Gas-well deliquefication (GWD) can be accomplished with compression or in-well artificial-lift methods or both. Wellhead wet-gas compression is desirable in that it does not require well intervention to provide GWD, and it is especially useful in maintaining well production in the interim period before field-wide compression is available. Even when fieldwide compression is available, local wellhead compression is desirable at various locations in a field as high-rate wells are added or for wells located at peripheral locations. The use of a twin-screw pump to provide boost for high-gas-volume-fraction (GVF) multiphase flow was investigated experimentally. Tests were conducted with pressure rises ranging up to 250 psi for GVF’s greater than 90%. Water and air were used as the working fluids. The pumping system is a commercially available 230-gal/min twin-screw pump (60 hp) with a design speed of 3,600 rev/min used in conjunction with a knock-out tank that recirculates liquid from the pump exit to provide seal flush. The amount of electrical power required to operate the pump, the inlet liquid- and gas-flow rates, the pressure rise, and the inlet and exit temperatures were recorded. From these data, the volumetric efficiency (flow rate), pump effectiveness, and mechanical efficiency were calculated. Because there is a fixed clearance between the rotating screws and the pump housing, there is a leakage from the high- to low-pressure regions of the pump that will reduce the volumetric efficiency of the pump. It was found that the volumetric efficiency decreased significantly with decreasing pump speed and increasing GVF. At full speed, the volumetric efficiency was between 70 and 88% at ?P=50 psi. Increasing ?P to 250 psi decreased these values to 55 and 81%, respectively. The mechanical efficiency was relatively constant over the pressure-rise range, varying from a high of 48% at the lowest inlet pressure (10 psig) at 0% GVF to a low of 14% for both inlet pressures (10 and 50 psig) at 100% GVF. Overall, the testing demonstrated the ability of a surface twin-screw pump to provide wet-gas compression.
The ESP system is an important artificial lift method commonly used for medium- to high-flow-rate wells for subsea developments. Multiphase flow and viscous fluids can cause severe problems in pump applications. Free gas inside an ESP causes operational problems and lead to system failures. Under two-phase flow conditions, loss of pump performance or gas lock condition can be observed. Under viscous fluids, the pump performance degrades as well. This paper provides a model on the effects of viscosity and two phase (liquid & gas) fluids on electric submersible pumps (ESPs), which are multistage centrifugal pumps for deep boreholes. The theoretical study includes a mechanistic model based on Barrios (2011) for the prediction of the degradation due to bubble accumulation. The model comprises a one-dimensional force balance to predict occurrence of the stagnant bubbles at the channel intake as a main cause of deviation from homogeneus flow model.
The testing at Shell's Gasmer facility revealed that the ESP system performed as theoretical over the range of single flowrates and light viscosity oils up to Gas Volume Fractions (GVF) around 25%. ESP performance observed gas lock condition at gas fraction higher than 45%. Homogeneous Model has a fairly good agreement with pump performance up to 30% GVF. Pump flowrate can be obtained from electrical current and boost for all range of GVF and speed. Correlation depends strongly in fluid viscosity and pump configuration.
The main technical contributions of this study are the determination of flow patterns under two important variables, high viscosity and two-phase flow inside the ESP to predict operational conditions that cause pump head degradation and the beginning of bubble accumulation that lead to surging Barrios (2011). For similar applications, pump performance degradation can be predicted in viscous environment and two-phase flow conditions.
The concept of compact separation is attractive in a number of operating environments. These include offshore and arctic operations where both space and weight are at a premium and subsea and downhole processing where space is very limited. Compact separators often rely on centrifugal forces to enhance the separation process and are therefore highly dependent on inlet geometry. This paper investigates expanding the operational envelope of a compact Gas Liquid Cylindrical Cyclone separator through the use of a novel inlet, which can be easily altered to respond to changing well conditions. To demonstrate the importance of inlet geometry, historical production from the Gloyd-Mitchell zone of the Rodessa Field in Louisiana was examined over a 40-month period. As in most oil field production, there were significant changes in the water cut and GOR. This field data clearly shows that a compact separator equipped with single inlet geometry is not able to perform effectively over the wide range of conditions exhibited in a typical oil field. This paper models the hydrodynamics in the separator inlet. Three different inlet geometries were investigated through the use of a changeable inlet sleeve. New experimental data were acquired utilizing a 7.62-cm I.D compact separator, which was 3.0 m in height. The effect of inlet geometry on separator performance was investigated over a wide range of flow conditions. Fluid viscosities from 1-12 cp and the effect of fluid level within the separator were also examined. The results indicate that the operational envelope for liquid carry-over and gas carry-under can be expanded by more that 300% by altering the inlet to respond to changing field conditions.
Economic pressures continue to force the petroleum industry to seek less expensive and more efficient alternatives to conventional separators. Recently, the compact separator has been proposed as a key element in reducing cost of production operations. Compact separators, such as the Gas-Liquid Cylindrical Cyclone are becoming increasingly popular as attractive alternatives to conventional separators, as they are simple, compact, low weight, low-cost, require little maintenance, and are easy to install and operate. In addition, gas-liquid cylindrical cyclones are used to enhance the performance of multiphase meters, multiphase flow pumps, and de-sanders, through control of the gas- liquid ratio. Compact separators are also used as partial separators, portable well testing equipment, flare gas scrubbers, slug catchers, down-hole separators, pre-separators and primary separators.
Presently, more than a hundred and fifty gas-liquid cylindrical cyclone units have been installed and put into use in the field for various applications (Wang et al., 2000).1 The size of these compact separators varies from 7.62-cm. to 1.52-m in diameter and 2.13-m to 9.14-m in height. The gas liquid cylindrical cyclone separator is a simple device, which has neither moving parts nor internal devices. It is a vertically installed pipe/vessel mounted with a downward inclined tangential inlet, with outlets for gas and liquid provided at the top and bottom, respectively. The two-phases of the incoming mixture are separated due to the centrifugal/buoyancy forces caused by swirling motion and gravity forces. The heavier liquid is forced radially towards the wall of the cylinder and is collected from the bottom, while the lighter gas moves to the center of the cyclone and is taken out from the top.
Applications of gas-liquid cylindrical cyclone can be in a metering loop configuration, where the gas and liquid outlets are recombined, or in a separation configuration, where the gas and liquid outlets are separated. The metering loop configuration is capable of self-regulating the liquid level for small flow variations. However, compact separator used in separation configuration must have liquid level and/or pressure control so as to prevent, or delay, the onset of liquid carry-over (LCO) into the gas stream or gas carry-under (GCU) into the liquid stream.