Echometer Gas Separator Simulator 1.2

The performance of down hole gas separators is simulated in software. Different production rates, different sizes of separators, different SPM and different gas bubble rise velocities are simulated to show the performance of different separators and different well conditions. This simulation software is a great aid in educating personnel in the operation, performance, selection and proper design of gas separators. Knowledge and use of this software will help operators increase pump fillage and total production and also reduce operating expenses.

A frequent reason for inefficient down-hole pump operation is incomplete liquid fillage caused by gas interference especially when the pump intake is set above the perforations that are producing gas and liquid. A common solution of this problem is to install, at the bottom of the tubing, a down hole gas separator just below the pump intake or to configure the completion so that the pump intake is located below the gas entry point into the wellbore. These designs take advantage of natural separation due to gravity segregation of the gas and liquid phases to maximize the volume of liquid delivered to the pump intake.

The above figure is a simplified schematic of what is defined as a “tubing conveyed down hole gas separator” installed above the producing formation and showing the fluids (liquid and gas) entering from the perforations and flowing upwards in the wellbore annulus to the separator openings. The gas is shown as red bubbles and the liquid movement is shows as small debris in the water. The majority of the produced gas flows past the separator inlet openings and continues up through the casing-tubing annulus to the surface¹ while the liquid and a smaller amount of gas enter the separator inner annulus. At the top of the separator outer barrel or mud anchor are several openings through which the produced liquid and some gas enter the separator and also through which the separated gas can return to the wellbore. The dip tube is a small diameter tube inside the separator outer barrel that directs the produced fluid to the pump intake and into the pump barrel. Inside the separator annulus there is a gas/liquid mixture with the liquid flowing down towards the dip tube suction during the pump upstroke. The less dense fluid in the mixture, i.e. the gas, has an upward velocity relative to the denser liquid. Depending on its size, each gas bubble in the separator annulus (annular area between the separator outer barrel and the dip tube) has an upward velocity relative to the liquid, known as the slip velocity. The motion and position of the gas bubbles depend on the difference between the downward liquid velocity and upwards bubble slip velocity. For a given liquid flow rate and separator design, small bubbles (less than 1/16 of an inch) may be dragged by the liquid into the dip tube while larger gas bubbles (greater than 1/4 inch) may flow upwards and out through the separator ports, ultimately venting out through the casing-tubing annulus. Therefore, the slower the liquid is moving down the smaller the volume of gas that is dragged by the liquid into the dip tube. Consequently the pump liquid fillage would be near 100%.

In this gravity separation system, the efficiency of separation of gas from liquid is controlled by the downward liquid velocity in the annulus between the separator outer barrel and the inner dip tube. The liquid velocity is controlled by two variables:

• The actual pump displacement rate. For a rod pump this rate is determined by the plunger area, the plunger velocity and the plunger leakage.

• The annular area between the internal diameter (ID) of the separator outer barrel and the outer diameter (OD) of the dip tube.