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Electrical Submersible Pump (ESP) is not a new invention to oil production line. In fact, the ESP systems powered by electrical downhole motor have been used for decades to lift fluids from oil fields. However, during the wide range of harsh downhole environments, the ESP systems have to face various challenges from production.
ESP has become a vital component of world's oil product lines recently. It has been designed more resistant to abrasion by sand, broad range of high operating temperature and more gas handling. These advances make ESP able to be applied in harsh environments all over the world wide. The following discussion of this paper is based on the specific model of ESP in using on Jacky well which developed by ITHACA ENERGY.
The model of ESP in using on Jacky well is 562 series, P110 SXD pump, 120 stages which is made by Baker-Hughes Centrilift. The ESP system includes all the required components to transfer electrical power from Jacky platform to downhole, convert the power into motion power to push the produced fluids to the surface. The ESP downhole system includes:
The components of ESP system can variously depends on the production requirements, the Figure 1.1 shows the basic components of Jacky ESP system.
The ESP system downhole components are designed and manufactured based on Jacky well data and production requirements. For the Jacky ESP system, the gas separator is not required during the low gas ratio and low bubble point of fluids.
Jacky is a small oil accumulation close to the Beatrice Field in the Inner Moray Firth area of the UKCS North Sea. The field is penetrated by two wells: the discovery well 12/21-2. Drilled in 1982 and a second oil-bearing well 12/21c-6 early on the year 2007. Well 12/21c-6 is a vertical exploration well, drilled by ADIT on behalf of ITHACA ENERGY (UK) Ltd. The field has been developed using a normally unmanned wellhead platform with well 12/21c-6 being completed with a dual ESP system which is made by Baker-Hughes Centrilift, just before first oil in April 2009. The ESP system was designed to operating under a range of harsh conditions. The ESP system has been successfully operated and monitored remotely from Beatrice Alpha platform.(ref)
Scale Formation in the Jack ESP
Scaling is the one of most main issues that can cause an ESP failure. Unmanaged scale may require an ESP change out and/or the need of scale removal (e.g. chemical removal). The cost an ESP change out can be as high as £6M (rig at £200k/day for 14days plus with new ESP/equipments). In order to optimise running life of ESP, the scaling prediction in the ESP is required. Unlike other components in the production system, due to the extreme operating conditions (high temperature, pressure swings and small gaps in the ESP, etc), carbonate scaling risk in the ESP increases with increased temperature and decreased pressure. Once scale is built up, it can significantly impact the pump performance and even cause a pump failure.
Since the profitability of the Jacky field is heavily depends on the development and operation cost. In order to achieve the biggest profit, one of the key factors to driving the project strategy of Jacky field is to control the operational cost of ESP as low as practicable. In the Jacky fields dealing with the production of crude oil and produced water, the run-life of ESP is a key fact for the Jacky project to make benefit.
Like any other oil field, the Jacky field also produces water in the fluids; the water cut of Jacky well is about 32% till now, this means the well has not face any scaling problem during the production. Because the water in oil emulsion is stabilised in the ESP at current water cut and the produced water has not been in touch with ESP wet surfaces. However, the stability of water in oil emulsion will decrease as water cut increase and eventually will flip into water emulsion. Since then, the ESP will suffer scaling problem.
The inside ESP operating temperature rising and pressure dropping are the key factors to impact the scales drop out from produced water. The scales could be deposit on the internal surface of ESP, and since the first layer of nucleation built up in the ESP, the scaling will format very fast. It is one of the key issues affecting the pump efficiency and performance. And the pump performance is an important factor for the production to be profitable. So, thus a need to optimize the performance of Jacky ESP, the scaling prediction inside the ESP under the operating conditions with produced water is required.
Aim and Objectives
This main aim of this project is to assess the scaling risk in the Jacky ESP.
The objectives below were identified to satisfy the aim of this project.
To review the existing cases and information to understand the Baker-Hughes ESP system, and find out the power flow of ESP system to estimate the heat transfer performance in the ESP system.
To study the scaling formation requirements, and find out when and where the scale forms inside the Jacky ESP.
To analyze the data obtained by the well developer, other co-operated and commissioned companies, in order to estimate the optimized and the worst situations of Jacky ESP.
Report the result of this project, and list the further research could be done in the future.
This project is commissioned to assess the scaling risk in the Jacky ESP, including estimation of heat transfer performance in the ESP, heat effects to scaling tendency and scaling prediction inside the ESP. This project estimates the ESP system power flow, scaling simulations, and how fast the ESP will be blocked by scales at critical points. The estimation is based on the obtained data which from reliable sources.
In order to complete the project's objectives, the following methodologies have been adopted.
The ESP Review
Review literature on Jacky ESP system and to understand the power flow between the different components in the system.
Estimate the factors which can rise up temperatures of insider ESP and fluids by heat transfer and system power loss.
Jacky Water Analysis
Review literature of scale formation to understand the process of scaling, especially under the ESP operating conditions.
Analyze the Jacky water samples and predict the scaling tendency by using the commercially available software, Solmineq.
Collect results from the software for analysis and prediction of the scales.
Predict the Scaling Tendency insider the ESP
Analyzes the data which obtained from the ESP study and Jacky water samples analysis to estimate the scaling tendency insider of Jacky ESP under possible operating conditions.
Chapter 2 - The ESP Review
The Electrical Submersible Pumping System
The pressure difference between reservoir and surface is caused by the natural energy of the compressed fluids stored in the reservoir. If the diving force of pressure difference is great enough, the fluids will flow to the surface naturally. However, during the production, when the downhole pressure dropped below the level sufficient to lift fluids to the surface, the downhole pressure must be reinforced by artificial lift.
The electrical submersible pump system is a multiple stages centrifugal pump. It has a minimum requirement of intake pressure to fill the fluids into the pump before it started. The ESP system cannot lift fluids from intake pressure to zero. The centrifugal pump has been designed, engineered and built to handle wide range of harsh production conditions for high durability and reliability. Since the ESP can operate down to considerably low pressure, it can be considered as an effective and economical way to pumping reservoir fluids.
Over the decades, the technologies of ESP have been improved by ESP companies; the ESP has been designed, engineered and manufactured to operate under the high temperature, high viscosity, gassy, abrasive and corrosive conditions, meanwhile it can lift more fluids.
The ESP components
As has been shown in Figure 1.1, the ESP downhole facilities include all the required components to diving fluids from downhole to surface. Each component will be discussed as follow.
The ESP Pump
Jacky ESP system pump is a multi-stage centrifugal pump which converts the rotation energy from shaft into velocity/pressure that drives fluids to surface. In order to achieve the production target rate (12,000bbl/d) of Jacky well, the category of Jacky ESP system pump is designed as mixed flow type to handle high flow rate. In this kind of pump, the fluids flow though the stages both parallel and vertical of the shaft direction.
The Pump Components
The ESP pump is built up as following essential components:
Figure 2.1 The ESP Cutaway
Impeller and Shaft - As shown in Figure 2.2, the impellers are fixed on the shaft, and the shaft is rotated by electrical motor. As the impellers rotating, Vanes are convert centrifugal force to velocity/pressure to impact production fluids.
Figure 2.2 The
Diffuser - The diffuser directs the compressed fluids into the suction eye of next impeller, and it does not spin.
Shaft - The pump shaft transfers rotation power from electrical motor to the pump though the seal section.
Pump Stage - A pump stage is assembled by uniting an impeller and a diffuser. Figure 2.3 shows a cutaway of an operating pump stage, an impeller assembled into a diffuser and fluids flowing pathway.
Figure 2.3 The cutaway of pump stage (impeller and diffuser)
Intake - The pump intake (Figure 2.4) is the connection between the end of pump housing and a flange to join the ESP seal section, while provides a pathway for productions to flow into the ESP.
Figure 2.4 The pump intake
Multi-stage Pump Operation
Figure 2.5 shows a multi-stage centrifugal pump. The red arrows are presented as fluids impacted by the rotating impeller. As the impeller rotates, it converts motion force into the velocity of fluids. The yellow arrows are presented as fluids directed by diffuser into the next impeller above it and transfer the velocity energy into pressure to lift fluids from downhole to surface.