Electrical Submersible Pump Workover by Using Intermediate Completion Design

Introduction

One hundred years ago, the oil and gas industry produced resources from wells using the reservoir’s natural energy [1]. But after some time, notice was done that the removal of fluids from the underground reservoir reduced the bottom hole flowing pressure ; hence the reservoir’s energy was not more sufficient to drive the hydrocarbons to the surface [2, 3, 4]. Therefore, the necessity to employe an activation method which will enable an increase in the production rate.

Several artificial lift methods have been adopted in literature to increase the flow rate such as progressing cavity pump, sucker rod pump, electrical submersible pumps and gas lift [5, 6, 7, 8]. However, ESP units have proved to be one of the most commonly used activation methods in lifting a much higher liquid rate than the other methods and found their best use in high on- and offshore applications. It is believed that today approximately 10% of the world’s oil supply is produced with ESP installations [9, 10, 11, 12].

ESP is an artificial lift method easy to install and operate, which uses a submerged electrical motor driving a multistage centrifugal pump through a shaft. This pump enables the recovery of high liquid volumes [13, 14, 15]. After some years of production, the depleted reservoir starts producing abrasive particles such as sand and scales, which will reduce productivity and later cause pump failure [16, 17, 18]. Hence the need to change this pump preventing hydrocarbons from reaching the surface, which is very dangerous for the environment and the personnel on-site. To replace this pump, well killing must be made, but it is generally challenging to restart production after this [19, 20]. Majority of wells making use of an ESP face this problem. A central question emerges from this observation: Is it possible to mechanically isolate fluids produced from the reservoir, while performing the ESP workover?

This paper aims to propose an appropriate completion design that enables the mechanical isolation of fluids produced from the reservoir while performing the ESP workover in a field X. To achieve this paper, the following tasks will be performed: to choose the appropriate materials which are elastomers and metallurgy, to determine the working pressures and temperatures ; to select the appropriate and economical completion design ; to draw the completion schematic, and to write the installation procedures. The above objectives are achieved by using the technical and economic approaches. The present paper has three sections : The introduction is given in this section. Section 2 presents the data, tools, the proposed completion design, the completion method used, the selected materials, the completion schematic and the running procedures. The last section presents the conclusion.

Data, Methods and Results

The data used to design the completion is presented in Table 1.

The field X consists of a vertical well as depicted in Figure 1.

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In Figure 1, the well profile starts with a 20” conductor pipe (CP) hammered till 30 mMD, followed by three casings (13-3/8” surface casing with casing shoe at 300 mMD of grade K55; 9-5/8” intermediate casing with casing shoe at 1200mMD of grade N80 and a last 7” production casing at 3000 mMD of grade L80 with a nominal weight of 23 pounds per foot). The upper completion is 2-7/8” with a Tubing Retrievable Safety Valve (TRSV) to control the well at 50 mMD, a Hydro II packer at 200 mMD, a sliding sleeve door (SSD) to allow for slickline operations at 1000mMD, an ESP to increase the production rate at 2500 mMD and a 7x4” production packer at 2600 mMD. Table 2 presents the primary data needed for the completion design.

As presented in Table 2, the primary data required for a completion design are reservoir data, which takes into account pressure, temperature, fluids specific gravity and its composition, well data such as the measured depth.

Conclusion

The objective of this paper was to propose a feasible completion design that enables the mechanical isolation of fluids produced from the reservoir while performing the electrical submersible pump workover. It was found that the best material to be used is carbon steel for the metallurgy and hydrogenated nitrile as elastomers. Carbon steel is preferred since it is found in an environment of high temperature (212°F), low CO2 content (0.5 mole %), and H2S content 10 ppm. For the sealing elements, nitrile could be used in the presence of the produced fluid, completion fluid, and well kill fluid. Still, the operating temperature is too close to its upper limit applications, and it considers less than 10 ppm hydrogen sulfide, but it is 10 ppm. Hence hydrogenated nitrile is the appropriate elastomer for these conditions. The appropriate completion method is the intermediate completion design. It comprises one packer that isolates the annulus between the casing and the tubing string. Two extensions that account for spacing out, one ball valve which enables without well-killing formation isolation, and workover operations safely and a shifting tool that allows the opening and closure of the ball valve. This case was a typical case where the intermediate completion was the best because of the unavailability of a kick-over tool to fit in the last 7 inch casing size since it has a minimum outside diameter of 8-1/2 inches hence can only be used in wells with last casing size 9-5/8 inches or more.