Downhole Oil Water Separation Research Articles

Design of downhole oil-water separation device and study on separation mechanism based on rod pump heavy oil system

Abstract Downhole oil-water separation technology (DOWS) is a new type of separation technology, which can improve efficiency, reduce energy consumption, and can solve the problem of high water cut oilfield development. At present, there are only two separation methods in the same well injection-production separator, one is the swirl separation technology and the other is the gravity separation technology. Cyclone separation technology mainly relies on cyclone separators to separate oil and water, but it is affected by oil viscosity, water content, and temperature. The gravity separation technology mainly relies on the similar separation principle of a multi-cup equal-flow gas anchor to design a multi-cup equal-flow oil-water separator, but it requires the oil-water mixed production liquid to stay in the settling bowl for a long time. The centrifugal separator has the characteristics of a good separation effect, high efficiency, and low demand for oil. At present, the downhole centrifugal separator is not used in the same well injection-production technology, which mainly needs to solve the driving force problem of the centrifugal separator. The new injection-production device designed in this paper can better solve the driving problem of the centrifugal separator and meet the working requirements of the process.

Structure Optimization and Performance Evaluation of Downhole Oil–Water Separation Tools: A Novel Hydrocyclone

Abstract Based on the principle of cyclone separation and 3D printing technology, a novel variable pitch hydrocyclone structure was proposed for the axial flow hydrocyclone separators of oil wells. The structural parameters of this variable pitch hydrocyclone were optimized via a combined approach of the Plackett–Burman design, response surface design, and computational fluid dynamics. A quadratic polynomial mathematical relationship between significant structural parameters and separation efficiency was established. The effects of the inlet flowrate, split ratio, and oil phase volume fraction on oil–water separation performance were systematically analyzed. A laboratory test system for oil–water swirl separation was constructed to verify the accuracy of numerical simulation results and the efficiency of the optimized structure. The optimal overflow split ratio, inlet flowrate, and oil concentration for the hydrocyclone are 30%, 96 m3/day, and 2%, respectively. The combination of these optimal parameters results in an experimental separation efficiency of 99.38%, which is higher than that of the conventional structure (98.8%). The experimental results are in good agreement with the simulation results.

Research on working condition diagnosis method of downhole oil-water separation system with sucker-rod pump

Compared with the rod-pumping oil production system of the conventional pumping unit, the structure of the down-hole oil-water separation system from the rod pump is more complicated, and the down-hole working conditions are worse. Existing technology no longer meets the needs of its downhole condition diagnosis. It seriously affected the production output and economic benefits of the oil field. Because of this, a fault pre-diagnosis method for the downhole oil-water separation system from the rod pump was proposed. Through the theoretical calculation of oil well production and pump efficiency. After field investigation and collection of many suspension point indicators diagrammed for comparison and analysis, the injection pump’s failure probability was 90% above. At this time, the extraction pumps work normally. Therefore, a reverse calculation method is proposed: establish and solve the static/dynamic load model of the production pump, and obtain the load-displacement function of the production pump. The load-displacement function of the suspension point derived from the suspension point indicator diagram is subtracted from the calculated load-displacement function of the production pump to obtain the load-displacement function of the injection pump so that the working condition diagnosis can be performed according to the injection pump work diagram. In the application of 18 wells within the field, the judgment result of injection pump failure and the result of pump inspection coincided with 91.3%, which verified the correctness of the calculation model. This method provides necessary theoretical guidance for the field application and working condition diagnosis of rod pump downhole oil-water separation system and is of great significance for improving the comprehensive benefit of oilfield production.

Numerical Study of Oil-water Separation in Inline Axial Hydrocyclone

The fluid mixture hydrocyclone is an excellent tool for downhole oil/water separation (DOWS) for high water cut. In the present work the flow through inline axial inlet hydrocyclone is investigated computationally using ANSYS-FLUENT-19 software. The three dimensional continuity and momentum equations with SST k-omega turbulence model are used to simulate the strongly swirling, turbulent flow. Oil/water two phase mixture treated as the working fluid, water is considered as the primary phase and oil is the secondary phase. The considered oil volume fraction this work is 0.25 and flow split is 0.3 for three different flow rates of (14, 28, 56) m3/hr corresponding to Reynold's number range of (1.6 to 6.6)*104. The pressure and velocity fields were analyzed in the whole hydrocyclone with core recirculation. The results are helpful to predict the flow motion inside the cyclone to estimate the oil/water separation process. The present work indicates that the water purity at cyclone exit was 90%, while the obtained oil purity was 38%.

Numerical Investigation on Oil/Water Separation by Compact Nozzle- Axial Hydrocyclone

The separation of fluid-fluid mixtures is a major issue in various sectors. The liquid-liquid hydro-cyclone has a wide range of applications in various sectors due to its great efficiency in separating fluid mixtures, ease of installation, and low cost. In crude oil production, high water is consumed following the degrading of production quality, high processing costs, costs, and environmental impacts. Axial hydro cyclone is a tool for Downhole Oil/Water Separation (DOWS) in the petroleum production industry, but it has limitations. The main purpose of this work is to simulate the effect of compacting the conventional inline hydro cyclone with a converging-diverging nozzle on the oil/water dynamic flow and the separation process to resolve the high water cut problem. This study presents a three-dimensional simulation to compute fluid dynamics using the mixture multiphase and SST k-omega turbulence models for Reynolds numbers less than 66000. The operational flow variables are a mixture: flow rate (14, 28, and 56 m3/h) and oil/water ratio (15/85, 25/75, 30/70, and 35/65). Results indicate an enhancement in the axial and tangential velocity components by 15% and 50%, respectively, for the proposed design compared with the conventional cyclone. The oil separation efficiency for the new design is 89%, while for the conventional cyclone is 60%.

Numerical investigation on the swirler parameters for an axial liquid-liquid hydrocyclone

The exploitation of most oil fields has entered the middle and late stages and the proportion of water in the mixture extracted from the oil fields at this stage is very high, even reaching 80%-90%. In order to lower the cost of exploitation and make the oil field more sustainable, oil and water separation needs to be carried out downhole. The downhole space is small, and the separation device should be small and efficient. Therefore, this paper studies the axial flow oil-water separator that can be used for downhole oil-water separation. Study the influence of swirler structural parameters on the velocity field in the separator, and find structural parameters that are more beneficial to oil-water separation. The results show that increasing the outlet angle of the guide vane, the twisted diameter of the blade and the number of blades can all increase the tangential velocity of the flow field in the separation section, and generate centrifugal force to promote the aggregation of light fluid towards the center.

Experimental Study on a Novel Axial Separator for Oil–Water Separation

In order to ease the pressure on oil price, the downhole oil–water separation system has been adopted to preseparate the output production. However, both the gravity separator and the conventional ...

Study on the oil/water separation performance of a super-hydrophobic copper mesh under downhole conditions

The existing downhole oil–water separation (DOWS) technology has disadvantages in terms of separation efficiency, cost, complexity, etc. The novel filtration separation technology using metal meshes has been investigated and it displays the potential to increase DOWS efficiency. In current study, a super-hydrophobic copper mesh was fabricated by a simple dip-coating method and then characterized. Focusing on the application in DOWS technology, the separation of the mesh materials in the lifting process of produced liquid from the wellbore was simulated and investigated by a designed indoor device for the first time. The results show that the highly hydrophobic copper mesh with water contact angle of 153° can be obtained by oxidizing 40min, followed by immersing in a 50gL−1 stearic acid solution for 25min. The mesh can keep super-hydrophobicity and high separation stability after treatment at 100°C or in the pH range of 5–7, while the separation efficiency is susceptible to the oil viscosity and the clay contents of the produced fluids. The super-hydrophobic copper mesh can be a promising candidate for DOWS in moderate condition. The inherent separation mechanism was further discussed by the variation of wettability and surface structure in microscopic scale.

Acoustic Downhole Oil/Water/Fines Separation (ADOWFS)

Summary The oil and gas industry's global need for downhole-oil/water-separation (DOWS) systems is increasing with reservoir maturation and rising water cuts in producing wells in an effort to reduce the costs and environmental impacts associated with managing large volumes of produced water. Currently, between 3 and 10 barrels of formation water are produced to the surface for every produced barrel of oil. In general, existing and emerging DOWS technologies use hydrocyclones, gravitational-separation, or membrane-separation techniques to separate oil from water downhole. These methods suffer from high cost and limited capacity, in addition to numerous systemic problems and mechanical-parts failure. They are hardly tunable to changes in flow rate or water cut, unless special valves and pumping systems are used, and they are not capable of separating fine solids from the fluid-stream downhole. Acoustic-separation techniques can provide a viable solution to these limitations and can add numerous advantageous functions. In this paper, we introduce the concept of the Acoustic Downhole Oil-Water-Fines Separation (ADOWFS) and its field implementation. ADOWFS is a three-phase separation technique that uses a sequence of acoustic standing-wave patterns along a production tube with a decreasing number of loops in the direction of flow. It is capable of simultaneously separating oil droplets and solid fines from the water stream in the production tube. Oil droplets are directed and concentrated in the center of the production tube so it can be lifted to the surface while solid fines are directed and concentrated near the tube's walls. Water can then be injected downhole into a nonproducing formation after removing the acoustically separated hydrocarbon residues and fines. ADOWFS, thus, not only increases the oil-to-water ratios in producing wells, but also reduces the risk of pore clogging and formation contamination if water is reinjected back in the formation. Moreover, ADOWFS allows instantaneous tuning by means of surface controls to meet changes in flow rates and water cuts and can be integrated into existing downhole-separation infrastructures (e.g., to replace the hydrocyclones). A set of proof-of-concept experiments that used direct microscopic visualization in a microfluidic channel demonstrated the instantaneous separation of micron-sized oil droplets and solid fines from water by exciting the proper acoustic standing-wave fields in the flow channel. The oil droplets and solid fines were separated by a distance of λ/4 (λ is the wavelength of the acoustic wave), which is the expected separation between the pressure nodal and antinodal planes of the standing wave.

Structural optimization of downhole oil-water separator

Downhole oil-water separator is the most important component of downhole oil-water separation system. Its structure has great effects on oil concentration of underflow (OCU) thus requiring further optimization. This work aims to propose an optimization method for the structural optimization of downhole oil-water separator that consists of two series de-oiling hydrocyclones. Firstly, the significant factors influencing OCU are identified by two-level Plackett-Burman Design (PBD) with twelve factors. Then the central levels of the five significant factors identified from PBD are determined by steepest ascent design. Secondly, response surface methodology (RSM) is used to establish the second order model between the OCU and five significant factors for the implementation of particle swarm optimization (PSO). Finally, the optimal structural parameters are obtained by PSO algorithm. Computational fluid dynamics (CFD) is employed to calculate the OCU for each particular case and analyze the separation performance variations before and after optimization. The simulation results show that compared with the original geometry and the best geometry in CCF design, the OCU of the optimized decreases. And the separation performance of the optimized geometry is remarkably improved for the oil droplets whose particle sizes are smaller than 35.78µm. Furthermore, laboratory experiments have been conducted to validate the proposed optimization method. The experimental results confirm that the OCU also reduces following the proposed optimization method. It can be summarized that PSO algorithm combined with PBD, steepest ascent design and RSM can be an effective method for the structural optimization of the downhole oil-water separator.

A novel oil–water separator design and its performance prediction

Numerous oil wells, especially in their middle-late periods, are becoming less economic due to the high lifting costs and reduced recoveries. The downhole oil–water separation (DOWS) system is aimed to reduce the production cost, mitigate the environment impact, and enhance the oil recovery. However, current separators are of either poor separation effects or poor separation efficiencies.In this paper, a novel oil–water separator design is proposed based on the combination of two different flow resistance mechanisms and pipe serial-parallel theory, with the restrictive path restricting the heavier water, while the frictional path impeding the more viscous oil. Based on the combination of the flow pattern transformation criterion, homogenous model, two-fluid model, and pipe serial-parallel theory, a unified model of oil–water two-phase flow is developed to predict both the flow rate and water content distributions in different paths, which is then compared with the computational fluid dynamics (CFD) results. Unlike the CFD results, each path has a specific flow rate and water content, and as a consequence, specific flow regime and flow pattern.Both the CFD and model results show that the flow rate distributions in different paths of the separator will be adjusted automatically according to the fluid's property, while the model can also predict the water content distributions at the same time. And the average relative deviation between the CFD and model results for flow rate distribution is 14.24%, while that for water content distribution is 42.03%. Specifically, oil, being more viscous, mainly takes the restrictive path; while water, being heavier, tends to take the frictional path instead. To sum up, this autonomous function directs oil and water to different paths, hence oil and water is well separated.

Experimental Study on Downhole Oil-water Separation Hydrocyclone

In the process of downhole oil-water separation, the traditional liquid-liquid separation hydrocyclone (LLSH) is used in conjunction with screw pumps, which makes the hydrocyclone rotating around its own axis. The rotation of wall of hydrocyclone affects its internal flow characteristics and separation properties directly. The orthogonal experiment of the downhole oil-water separation hydrocyclone (DOWSH) is designed to analyze the effect of flowrate, rotating speed and split ratio on separation efficiency and pressure drop, The primary and secondary factors of operation parameters have been studied, and the optimum condition and reasonable working range of DOWSH have been obtained. It provides reliable basis for process of practical application of DOWSH􀀁so as to guide the production.

The Modal and Harmonic Response Analysis of the Oil and Water Separation Process under the Shaft

Compared with the traditional drilling string, the components of the new string downhole oil-water separation process is increased. To prevent the vibration fault and structure damage of the new downhole oil-water separation process string, the analysis of the finite element, modal and harmonic response on the structure system made. By solving the dynamics equation, the finite element model is determined, the inherent frequency and vibration model are calculated, and the vibration characteristics of system structure are analyzed. By analyzing the harmonic response and determining the reasonable speed of the string, the dynamic characteristics of the structure is optimized.

Numerical Study of Water Control with Downhole Oil-Water Separation Technology

The maturing oil fields with increasing water production can pose a challenging produced water handling and disposal issues. This paper presents a numerical study of a motorless hydrocyclone to enhance understanding of the downhole oil-water separation. The turbulence of fluid flow is obtained using K- Realizable Turbulence model for complex swirl dominated flow, while the interface between hydrocarbon and water is described using the Discrete Phase model. In this approach, factors which contribute to the hydrocyclone separation instability were discussed. Discussion is then extended to the relationship of residence time with pressure difference between overflow and underflow. These pressure differences are able to relate to pressure condition for high water cut well which require downhole separation.

Theoretical background and the flow fields in downhole liquid-liquid hydrocyclone (LLHC)

Hydrocyclone system for downhole oil-water separation provides an effective technique of enhancing the economic viability of higher water-cut wells while at the same time reducing the risk of environmental pollution. This paper describes the hydrodynamics of the liquid-liquid hydrocyclones and the flow fields within it are paramount for achieving successful separation process. Some of the important hydrodynamic flow phenomenon within the liquid-liquid hydrocyclone and how they influence the separation efficiency of water/oil was analyzed through analytical solution. The properties of the liquids were based on Bayan offshore field measured properties. The results indicated that there are two swirling zones separated by stagnant flow field. The inner is the light liquid zone, while the outer is the heavy liquid zone.

Research on Operating Characteristic of Downhole Dual-stage Tandem Oil-water Separator

The operating characteristic of down dual-stage tandem oil-water separator is essential for the condition diagnosis and adjustment of downhole oil-water separation system.Based on algebraic slip mixture model(ASMM) and large eddy simulation(LES),related parameters and boundary conditions are set according to T228 well status to research the split and separation characteristics of down dual-stage tandem oil-water separator.And the numerical simulation results compared with the ground text results.The results show that:When the inlet flow rate is between 80 m3·d–1 and 200 m3·d–1,the range of total split ratio become larger and larger,and the variation relationship between the ratio of the first and second hydrocyclones' overflow and the total split ratio is deterministic function,and the oil mass fraction of underflow decreases firstly and then increases with the increasing total split ratio;under the rated condition,the first hydrocyclone separates most of the oil and the second one plays a key role in further reducing the oil mass fraction of underflow;when the combinations of inlet flow rate and total split ratio are(120-140 m3·d–1/0.36-0.74),(140-160 m3·d–1/0.31-0.77) or(160-180 m3·d–1/0.33-0.76),the oil mass fraction of underflow is not more than 0.02%;the split characteristic predicted by numerical simulation is consistent with ground text result,while the relationship between the total split ratio and the oil mass fraction of underflow predicted by it is qualitatively consistent with ground text result.The reasonable ranges of inlet flow rate and total split ratio for the adjustment of downhole operating conditions are given through the comprehensive analysis of split and separation characteristics.It will provide guidance for field text.

Experimental and theoretical study of counter-current oil–water separation in wells with in-situ water injection

Abstract The study investigates a counter-current gravity separation in a downwards-flowing mixture of (up to 3%) oil in water. At much higher oil fraction, the separation is a basis for the conventional downhole oil–water separation (DOWS) where the whole oil and water separate in the well. In contrast, the counter-current separation of a very small oil content is needed in the new “downhole water loop” technique (DWL) prior to injecting the oil-free water in-situ. In the DWL triple-completed wells, the top completion produces oil and only trace of the oil contaminates the water drained by the lower “water sink” completion and is re-injected in-situ using the (third) bottom completion. A drift-flux concept was used to develop an empirical model for predicting the oil droplets raise velocity at different water flow velocities. The model was derived from experiments using seven different oils with a wide range of density, viscosity and interfacial tension values. The experiments monitored oil droplets ejected from a single perforation into the stream of water flowing downwards at various velocities. The results show that the oil–water interfacial tension is the most important factor in the separation process, as it controls the oil droplet size. This observation significantly simplifies the model by replacing the droplet size (most difficult to measure) with a correlation based on interfacial tension developed using the experimental results. The new model also considers the effect of oil viscosity that has been ignored in the co-current separation studies. (Our results reveal over 10% contribution of the viscosity effect to the counter-current separation process.) A practical finding in this study is the 0.33 ft/s (0.1 m/s) value of critical maximum water velocity for counter-current oil separation. In a real DWL well, this value corresponds to a point in the perforated well section above which separation takes place. It is also shown how oil separation could be predicted from a given water sink completion length and drainage–injection rate.

OPORTUNIDADES DE PRODUÇÃO MAIS LIMPA NO CONSUMO DE RECURSOS HÍDRICOS NA EXPLORAÇÃO & PRODUÇÃO DE PETRÓLEO ON SHORE NO ESTADO DO RN

This work presents a survey of opportunities for cleaner production applied to water used in the processes of exploration and production of oil on shore. The study consisted of literature review and investigative forays in the region of the state of Rio Grande do Norte. Opportunities arose in the following order of priority: eliminating at source, minimizing the consumption, recycling or reuse internal or external, treatment and final disposal. The results point to projects associated with the reduction of leaks in water pumping systems for the formulation of captured fluids, reduction of leakage of steam, use of brackish / saline uptake from deeper wells to replace the fresh water wells to capture ; use / reuse (external) water drains, replacing the freshwater abstracted and used for injection, use of ocean water (captured from the sea) in replacement of freshwater abstracted for the purpose of secondary recovery; adoption of equipment / system increase in oil resources DOWS Downhole Oil Water Separation and greater automation system with the use of smart wells and fields.

Mathematical modelling of a hydrocyclone for the down-hole oil–water separation (DOWS)

In this study, a mathematical model is developed to predict the efficiency of a down-hole oil–water separation hydrocyclone. In the proposed model, the separation efficiency is determined based on droplet trajectory of a single oil droplet through the continuous-phase. The droplet trajectory model is developed using a Lagrangian approach in which single droplets are traced in the continuous-phase. The droplet trajectory model uses the swirling flow of the continuous-phase to trace the oil droplets. By applying the droplet trajectory, a trial and error approach is used to determine the size of the oil droplet that reaches the reverse flow region, where they can be separated. The required input for the proposed model is hydrocyclone geometry, fluid properties, inlet droplet size distribution and operational conditions at the down hole. The model is capable of predicting the hydrocyclone hydrodynamic flow field, namely, the axial, tangential and radial velocity distributions of the continuous-phase. The model was then applied for some case studies from the field tested DOWS systems which exist in the literature. The results show that the proposed model can predict well the split ratio and separation efficiency of the hydrocyclone. Moreover, the results of the proposed model can be used as a preliminary evaluation for installing a down-hole oil–water separation hydrocyclone system in a producing well.

Experimental study of a vane-type pipe separator for oil–water separation

An experimental study of a new vane-type pipe separator (VTPS) was conducted for the possible application in the well-bore for oil–water separation and reinjection. Results by using particle image velocimetry (PIV) reveal a better flow field distribution for oil–water separation, which is formed in VTPS than that in hydrocyclone. The effects of split ratio, the oil content, guide vanes’ installation and number of guide vanes on oil–water separation performance have been investigated experimentally. Compared to a traditional single hydrocyclone, VTPS shows a good separation performance as the water content at the inlet of VTPS reaches 79.9%, the oil content at the water-rich outlet is about 400ppm while the split is near 0.70. These results are helpful to provide a possibly new design for downhole oil–water separation.