Understanding the effect of injected water salinity is becoming crucial, as it has been shown to have a strong impact on the efficiency of oil recovery process. Various experiments have concluded that carbonate wettability is altered when the water ionic-composition is changed. In this work, a numerical investigation of an oil blob mobilized by water is conducted inside a single pore. The presented model studies the synergy effect of multiphase flow and water salinity at the pore level.
To model the multiphase flow at the pore-scale, the full hydrodynamic Navier-Stokes equations are solved using direct numerical simulation (DNS). The effect of brine ionic-composition is examined through the electric double layer effect. Experimental zeta potential values, published in the literature, of crude oil/water and water/carbonate interfaces have been employed in the model, which capture the water salinity effect.
The simulation results show that the water wetting film surrounding the oil-droplet collapses to an adsorbed nanometer water layer when high salinity water is used. As a result, a large pressure gradient is required to mobilize the oil inside the pore and overcome the attractive surface forces between the oil/water and water/carbonate interfaces. For low-salinity injected water, the carbonate surface becomes more water-wet. The wetting film surrounding the oil blob becomes stable due to the repulsive electric double layer force. Therefore, less energy is required to mobilize the oil blob inside the pore compared to high water salinity. The effect of solid roughness and injected water flow rate are also studied, which show to have a strong impact on the oil displacement efficiency.
The novelty of the numerical method lies in efficiently capturing the nanoscale effect of the electric double layer in pore-scale multiphase flow at the microscale. The simulation results provide fundamental insights on the efficiency of low-salinity waterflooding at the pore level.
Motor bearings are a critical component in electric submersible pumping systems (ESP) motors. In many cases, dismantle analyses are unable to identify a definitive root cause for bearing failure. Several hypotheses have been studied to explain motor bearing failures. Some applications experience a higher bearing failure rate than other applications. In this paper, typical motor bearing failure modes will be reviewed, more specifically, the source of shaft voltage and the consequence of bearing electrical discharge failure will be discussed.
During bearing failure root-cause analysis, mechanical components have been the primary focus. Critical thermal expansion coefficients have been verified. The bearing running stress, temperature, eccentricity, film thickness, and lubrication flow have been simulated using cutting-edge finite element analysis (FEA) and computational fluid dynamics (CFD). Results show that in certain material combinations, the incompatibility of the thermal growth of bearing and sleeve material could reduce the running clearance, which would then increase the oil shear loss, and the bearing rubbing. However, tiny pitting has been found in the outside diameters (OD) of cracked bearings returned from the field, with more pitting found on the sleeve ODs. This evidence indicates another bearing failure mode: shaft-induced voltage and bearing electrical discharge.
The direct consequence of electrical discharge is generation of debris, vaporization of motor oil, quenching of bearing/sleeve surfaces, and increase in surface roughness. The debris size (0.001 in.) is larger than the hydrodynamic film thickness and can score the sleeve surfaces due to the loss of oil film protection. The chain of the motor bearing failure due to the electrical discharge is summarized, and this cannot be ruled out in other sizes, bearing systems, or material combinations in an ESP motor. By duplicating the poor power quality conditions, the pitting phenomenon on sleeve is confirmed. Future measurements have been planned to determine the correlation between the power quality and shaft voltage. This paper discusses the risk level for the bearing electrical discharge based the induced shaft voltage.
Electrical discharge bearing damage is a widespread problem that has been studied in other industries since 1992. Electrical discharge / shaft voltage problems can occur on any variable-speed drive motor. The source of electrical discharge through the bearing comes from the voltage potential building from the shaft to the ground (motor housing). However, ESP industries, which produce small motors with multiple rotor sections, have not conducted sufficient analysis to understand this problem. This paper fills the gap to discuss detailed indication evidence and analysis that can be used as a toolbox for motor bearing failure analysis for the ESP industry.
Double layer Expansion (DLE) is proposed as one of the mechanisms responsible for Improved Oil Recovery (IOR) during Low Salinity Water Flooding (LSWF). This expansion is triggered by the overlap between the diffuse double layers. We performed molecular simulation to study this phenomenon where both kaolinite and montmorillonite are used as substrates contacting water with varying concentration of monovalent and divalent ions. Our results, and several molecular simulations, have confirmed that the location of the adsorption planes is independent of the ionic strength. However, the potential developed on these surfaces and how it decays depends on both the ionic strength and ion nature. A shrinkage is observed in the double layer for the case of low salinity, supported by both film thickness estimations and interaction energy analysis. This shrinkage, which contradicts the prevailing assumption, is consistent with molecular simulation studies, and casts some doubts on the efficiency of DLE as a mechanism for explaining IOR observed during LSWF. This brings into question the role of double layer expansion in enhancing oil recovery, and raises the need to investigate other mechanisms that could be responsible for the experimental and field observations made in this area.
Wang, Zhibin (Southwest Petroleum University and Xi'an Jiaotong University) | Guo, Liejin (Xi'an Jiaotong University) | Zhu, Suyang (Southwest Petroleum University) | Nydal, Ole Jørgen (Norwegian University of Science and Technology)
Summary Analysis of the experimental data for liquid-entrainment rate, forces exerted on liquid droplet, and secondary flow occurring in the gas core show that the liquid is mainly carried in the form of film in the inclined annular flow. Therefore, it is more reasonable to establish a mathematical model from the bottom-film reversal than from the droplet reversal. In this study, a new analytical model is developed from force balance of the bottom film of the inclined tubing after studying the bottom-film thickness and gas/liquid interfacial friction factor to reveal the liquid-loading mechanism. The new analytical model, having an average error of 8.45%, agrees well with the published experimental data, and it also performs well in predicting the pressure gradient at liquid unloading condition. The new empirical model could be applied for the prediction of real field operations and has been validated with an accuracy rate of 95% against data newly collected from 60 horizontal wells. The new work can accurately and easily judge the liquid-loading status, and it also reveals how the fluid properties under downhole flowing condition affect the liquid loading. Introduction Horizontal wells have been widely used in low-permeability gas reservoirs because they have a larger drainage area and a higher production rate than vertical wells. An accurate prediction of the critical gas velocity of liquid loading is the basis to optimize the production rate of a gas well.
As a significant contributor to Well Integrity, the use of Premium Connections has increased in modern oilfield developments, where combined mechanical loading and a growing need for fluid tightness are becoming more common than before. This type of "specialty connectors" feature a metal-to-metal seal (MTM) which assures enhanced fluid tightness by means of distribution of contact stress generated during the make up process. In applications in which high amounts of torque or where rough field handling are the norm (e.g. Casing Drilling), the risk for damage at the MTM are big enough to put at risk the integrity of the well against leakage events. By means of understanding the mechanical and tribological aspects impacting the performance of such connectors a better understanding of their importance can be given, at the same time well defined areas of opportunity can be identified in the context of challenging drilling processes like drilling with casing.
After gas wells are drilled and start producing, early production rates are high enough to carry any liquid produced to the surface. However, as the reservoir pressure declines, the gas-production rate also declines. Eventually, the gas well starts experiencing liquid loading. Liquid loading starts when the current gas rate is incapable of lifting the liquid up to the surface. The liquid can be either water produced from the formation or the condensate. Several correlations in the literature predict the onset of liquid loading. The most famous equation, the Turner et al. (1969) equation, has many limitations, including the inability to account for effects such as diameter of the pipe and inclination angle of well, and incorrect physical assumptions regarding the onset of liquid loading. Belfroid et al. (2008) modified the Turner et al. (1969) equation for inclined wells; however, their expression is also dependent on incorrect physical assumptions and does not account for the diameter of the pipe. Another method, proposed by Shu et al. (2014), uses the correct physical assumption of liquid loading, but is overly conservative. This paper discusses a new modification to the original method proposed by Barnea (1986), which overcomes many limitations of the previous models. The new method is dependent on an assumption that liquid loading initiates when the liquid film starts falling backward. The proposed method accounts for the effect of diameter and inclination angle of the gas well. The method predicts the onset of liquid loading for a wide range of inclination angles, from vertical well to nearly horizontal well. The application of the method has been verified by comparing the results with both laboratory and field data. The method is observed to be better at predicting the onset of liquid loading compared with the other existing models in the literature.
ABSTRACTThe use of single component water based coatings for protection of military metal substrates continues to grow due to their low odor, health and safety advantages, easy cleanup and environmental friendliness. Nevertheless, the challenge continues to find alternatives to the traditional chromate, zinc or similar heavy metal type corrosion inhibitors which tend to rely on passivation or sacrificial cathodic protection4. Additionally, ongoing regulatory developments, which require lower VOCs and elimination of carcinogenic materials continue to tighten the usage of products containing these heavy metals thus forcing the need for alternative technologies. The use of nano vapor phase corrosion inhibitors(VCIs) provide an attractive alternative by adsorbing onto the metal substrate and filling the voids or micro-crevices of the substrate and preventing corrosion from starting or growing once the surface of the coating has been damaged. This technology has been proven effective in single component water based coatings at dry film thickness(DFTs) of 1 mil(25 microns)2,5.Four Learning Objectives1. How VCIs work in a coatingVCIs are formulated into a coating thru a complex development process which involves determining chemical compatibility of the VCIs with the other components of the coating such as the resin, solvents, pigments and other additives used for a variety of reasons. VCIs work by adsorbing onto the metal surface in a non-reactive attractive capacity, in other words, they are attracted to the metal thru the particle charge.2. How VCIs compare to traditional inhibitorsVCIs compare with traditional inhibitor systems by using smaller particles as well as relying not only on contact inhibition but also vapor phase inhibition, providing more complete coverage and protection of the surface. This can be illustrated as follows:The larger platelets are representative of traditional inhibitors which are unable to fill the micro-crevices, leaving gaps where corrosion can start and/or grow3.3. What type of coating systems can use VCIsVCIs can be used with most coating systems. There are many variations of VCIs and the key is to choose the correct VCI for the corresponding coating system by checking compatibility, effectiveness and processability.
Ferreira, F. C. (Schlumberger) | Booth, R. (Schlumberger) | Oliveira, R. (Schlumberger) | Bize-Forest, N. (Schlumberger) | Boyd, A. (Schlumberger) | Souza, A. (Schlumberger) | Carneiro, G. (Schlumberger) | Mesquita, P. (Schlumberger)
Irreducible water saturation is a key property for the estimation of original oil and gas-in-place. It is also key to end-point scaling of capillary pressure and relative permeability, with significant impact on simulation results of reservoirs under improved/enhanced oil recovery (IOR/EOR). Several definitions of irreducible water saturation exist, based on different experimental measurements and standard estimation methods. We propose a comprehensive model and a new method for improved estimation of irreducible water saturation.
The model considers rock wettability; the thin film of water that coats portions of the rock grains; the pore size distribution; the tortuosity; and the ratio between pore-throat and pore-body sizes (BTR). Different components of the irreducible water saturation are identified for multimodal, heterogeneous rocks: a nano-porosity system completely filled with water and other pore systems with their walls coated by water. The model also considers an additional residual water saturation resulting from laboratory experimental limits as the maximum applied pressure and duration. The method adjusts the model parameters by fitting to a set of irreducible saturation data, obtained from both mercury injection (MICP) and air-brine drainage capillary pressure experiments. The method estimates the irreducible water saturation for the asymptotic ideal condition - very high capillary pressure and reservoir geological times – as well as for other laboratory and reservoir conditions.
We applied the proposed method to experimental data from Corelab's worldwide rock catalog. The fraction of nano-porosity not revealed by MICP experiment was estimated by comparing MICP porosity with routine effective porosity. Hydraulic tortuosity and truncated multi-Gaussian decomposition of pore-throat-size distribution were also obtained from MICP data. BTR range was estimated from NMR data, thin sections, and hydraulic tortuosity data. Water thin film thickness range was estimated from the literature. Model parameters were then successfully estimated using data from 49 carbonate and 106 clastic samples from all over the world. The results showed that, in several cases, the asymptotic irreducible water saturation might be significantly smaller than the observed value from the air-brine experiment. Therefore, the corresponding reservoir irreducible water saturation could also be overestimated. The relative importance of the different components of the irreducible water saturation varied from one sample to the other, confirming the relevance and completeness of the proposed method.
When compared to traditional methods, the proposed method significantly improves irreducible water saturation estimates, resulting in better saturation-height and end-point scaling functions, and more accurate reserves. It is particularly important for simulation of IOR/EOR processes. The method may also be integrated with dielectric and NMR well log measurements, increasing the resolution of dynamic reservoir characterization, with particular importance to mixed-wet rock environments.
Every gas well will suffer from liquid loading problem as the rate from the well declines. Every gas well produces some produced water (if not also condensate) and that water cannot be carried to the surface at lower gas flow rates. Liquid loading results in premature abandonment of a gas well as the liquid accumulates at the bottom of the well. With the proliferation of horizontal wells producing from gas reservoirs, it is not only important to predict the liquid loading in these wells but also the vertical location where the liquid loading is initiated. The proposed methodology predicts the liquid loading in inclined wells and also the location where it is initiated. The method is superior to commonly used technique of Turner et al. equation which is valid for vertical wells. We have validated the method by applying it to the literature data as well as to large number of horizontal wells.
Liang, Xingxin (Wuhan University of Technology) | Liu, Zhenglin (Wuhan University of Technology) | Yuan, Chengqing (Wuhan University of Technology) | Ouyang, Wu (Wuhan University of Technology) | Yan, Xinping (Wuhan University of Technology)
In order to prevent the leakage of lubricant of oil lubricated thrust bearing to cause pollution of the marine environment, a rubber supported water lubricated tilting pad thrust bearing was designed. The influences of the thickness, thickness ratio, the width ratio of the elastic step rubber cushion and the elastic modulus of surface layer material on the lubrication performance of bearing were studied. The optimum size range of the step rubber cushion are recommended. The results also showed that the higher the elastic modulus of surface layer material, the better performance the bearing had.
At present, most of the thrust bearing of ship and underwater vehicle propulsion are oil lubricated, lubrication oil is flammable, easy to leak, not economical and environment friendly and other problems (Wu et al., 2011). If lubrication oil can be replaced with water, not only can overcome the shortcomings mentioned above, but also can save a lot of oil and precious nonferrous metals, which has important theoretical significance and engineering application value for saving energy and reducing water pollution (He et al., 2009).
Water lubricated thrust bearing was widely used in submersible pump (He et al., 2010), hydro generator (Godeke E. et al., 2010) and nuclear pump (Ou et al., 2014). The materials used for the friction pair of water lubricated thrust bearing are SiC (Wang et al., 2003), graphite (Leon et al., 1995), PEEK (Wang et al., 2002), Si3N4 and Si3N4/carbon fiber composites (Hideki et al., 2008), etc. The water lubricated thrust bearing (Godeke et al., 2010) developed by Alston Hydropower Company for the French Lotte Lu Eller project (Power plant 450MW, water head 450m), its total power consumption is only 20% of the oil lubricated bearings under the same conditions. The KANSAI and Hitachi Mitsubishi Hydro developed and studied the water-lubricated thrust bearing for vertical type hydraulic turbine generator (Inoue et al., 2012), and the research results showed that the application of water lubricated bearings in the actual hydropower plant is feasible.
Elastic rubber supported thrust bearing is one kind of tilting pad bearing. By using the elastic deformation of rubber pad, on the one hand, the tile automatically adjusts the inclination angle, facilitating the production of hydrodynamic lubrication film, on the other hand, can make the bearing load tends to be uniform. In addition, the elastic cushion can effectively absorb and digest the vertical and radial vibration, and can obviously improve the stability of the mechanical equipment. This supporting way has applied in oil lubricated (Wang et al., 2015), water lubricated (Van Beek A. et al., 1997) and gas lubricated (Zhou et al., 2009) thrust bearing.