Science & Technology: PETROLEUM ARTIFICIAL LIFT OVERVIEW

PETROLEUM ARTIFICIAL LIFT OVERVIEW

INTRODUCTION

With the time frame for the field appraisal and field development are completed, and then we are now ready to produce the well. Here it is important to remember that the steps we take the procedures we use throughout these process called recovery are vital in determining the present and a future economic value of our preproduction well.

Reservoir Production Cycle

As we know from reservoir performance, recovery is the controlled process of bringing tracked hydrocarbon to the surface. since it is impossible to commercially produced 100% (one hundred percent) of these trap hydrocarbons, with present technology good engineering practices dictate that we utilized different recovery methods both natural and man-made (Artificial) over different time periods throughout a reservoir production cycle.

Reservoir production cycle

In other words the term recovery is used to describe any and all methods using either natural or man-made (Artificial) energy sources that force the oil and gas to the surface in a controlled flow that can be captured.

Natural and man-made (Artificial) energy

Natural Lift & Artificial Lift

We begin with a discussion of the two sources of energy used in the initial and subsequent stages of recovery. The first source most commonly used in recovery is natural, and is called natural lift. The second source is man-made and is called artificial lift.

Natural lift

Artificial lift

The Type of Artificial Lift

Defining natural lift and then describing when and why this natural lift might decrease and be supplemented with artificial lift, this book outlines and highlights three different type artificial lift and mentions several others that are used less frequently. It concludes, with label diagrams of three of the most popular systems with detail explanations to show how each functions and why it is selected for its location and production requirements.

The type artificial lift

Three most popular artificial lift

Reservoir Underbalanced Conditions

So let's gets started recovery involved in the initial production stages of many newly producing wells realized for the most part on the natural energy present inside the reservoir that was trapped there along with the hydrocarbon molecules as the reservoirs was being created. In this newly trap reservoir the pressure inside them is usually greater that at the surface in what is known as underbalanced conditions. When the reservoir is un kept, in underbalanced condition a pressure differential from that inside the reservoir to that at the surface causes the trapped energy along with the hydrocarbons to be push to the surface in what is known as natural lift.

Reservoir underbalanced conditions

Let’s we look at an example that we are all familiar with that will help illustrate what we are talking about, take a moment to visualized a column of a carbonated leverage as it explodes upwards and out wards. As we know in general science the pressure inside the bottle is greater than on the outside in under balance conditions, this pressure differential remains an equilibrium only until the cap is removed, and removing the cap the pressure differential releases energy from inside the bottle, it carries with it the carbonated liquid that fuse up. The same thing happens inside the reservoir and this release is known as natural lift.

Underbalanced conditions carbonated bottle

In this illustration we see a hydrostatic head of a fluid column that stretches from the surface through the reservoir, as the column deepens PSI is increases about ½ psi/ft (one half psi per foot) of reservoir depth, so if this well were five 5,000 ft (five thousand feet) deep for example, the PSI at the bottom of the well would be about 2,500 psi (twenty five hundred psi), if the natural energy of the formation is more than 2,500 psi (two and a five hundred psi) then the well will flow naturally in natural lift.

Reservoir hydrostatic fluid column

Natural lift

Natural Lift Condition

Know that the wells own its natural energy must be sufficient to not only pushed liquid (oil and gas) to the surface it must also be enough so that the wells own natural lift can overcome the hydrostatic bore hole pressure and the friction created by the hydrocarbons moving up the tubing to the surface. In addition there must be sufficient energy to push these liquid or hydrocarbons through the surface facilities.

Natural energy overcome pressure, friction, pushes the liquids to surface

Natural energy pushes the liquids to surface facilities

As we know initial recovery usually relies on natural lift, but like with the carbonate soda bottle after the initial push the energy inside the reservoir made dissipate and not be strong enough to continue natural lift.

The Main Lift Obstacles

What can cause naturally lift to slow down and fail? There are four main obstacles, the first is encountered within the reservoir itself, as we might guess the thicker more viscous the fluid the more energy is needed to overcome the friction to push the fluid through the rock matrix to the wellbore. Over time this friction coupled with constriction that reduces the fluid volume can cause the pressure and for near the wellbore to drop in what is known as drawdown. Drawdowns are accelerated when production rate rise and when the fluids become more viscous.

Overcome the friction

Constriction and pressure can fall

The second obstacle comes about in fields with denser oils and deeper depth. The sheer volume of those heavier oils inside deep wells means that to push these to the surface more energy is needed from the reservoir to lift that added way to the surface.

More energy is needed to lift

The third obstacle is specific to very deep wells with high flow rate, in these wells just the movement of the fluid traveling up the long length of the tubing and rubbing up against the inside tubing wall create significant friction, as the frictional force slows the oils upward movement more energy is needed to ensure the flow of these fluids.

Friction the fluid traveling up of long length

The frictional force slows the oils upward

Finally the fourth obstacle is encountered at the surface having already been pushed up through the tubing to the surface, the hydrocarbons must now be pushed into and through the surface facilities that separate and clean them in preparation for transport. This can require several hundred addition psi.

Pushed fluids through the surface facilities

Artificial Lift Function

When natural lift starts to falter or give out it can no longer be relied on to get the trapped hydrocarbons to the surface and through the surface facilities. When this happens the wells production begins to fall and then stops. When production stops the well is said to have died. Rise to should however that when a well dies with commercial quantities of valuable resource is still traps within the reservoir, alternative method will be used to bring the well back into production. This is where artificial lift can supplement natural lift. its here that artificial lift can bring the well back into production.

When production stops the well is said to have died

The hydrocarbons still traps within the reservoir

Artificial lift bring the well back into production

Artificial lift is not limited to just supplementing natural lift used in primary lift it can also be used to supplement EOR (enhanced oil recovery) when the pressure in the reservoir falls to less than that at the surface.

Artificial lift supplement EOR

Regardless of the reasons for using artificial lift the main determine nerve for the popularity and extensive use strapped the industry is this relatively low cost.

Artificial lift relay on three main systems, the first three will be examined in some details the other two less lift systems will only be briefly described. the main systems are (1) sucker-rod pumping, (2) gas lift, (3) ESP (electric submersible pumping) and the other less used systems are (4) power oil, (5) PCP (progressing cavities pumps), (6) Plunger lift, (7) Hydraulic or Jet Pump.