Effect of Gases and Vapors

In selecting pumping equipment for oil wells remember that in a majority of cases some of the constituents of the fluid being pumped are above or near their boiling points at the pressure and temperature conditions existing within the pump. Technical Data used in the field explained in petroleum courses in Rawalpindi. These conditions may cause release of large volumes of dissolved gases and vapors with a slight drop in pressure of the well tluid, in addition to the free gas initially in the fluid.

 For this reason it is very difficult to pump some wells down. Many wells apparently will pump off with several hundred feet of fluid standing in the hole because the condensable vapors and gases occupy the entire displacement volume of the pump. Under these conditions. without a relatively high intake pressure, which decreases compression ratio, the pressure below the plunger cannot be raised to the tubing pressure. (This is necessary before the traveling valve can open and deliver oil to the tubing.) On the downstroke the vapors may condense and occupy a very small volume without an appreciable increase in  pressure, and only the permanent gases are effective in increasing the pressure in accordance with the gas laws. Some more details of petroleum courses in rawalpindi are as under.

There are two precautions to take to minimize the adverse effects of vapors and gases. The compression ratio should be made as high as possible. This is accomplished by using a closed-cagetype valve below the plunger with a stationary-barrel pump, or a valve above the plunger with a travelingbarrel- type pump. It is also important to space the pump so the traveling valve and standing valve come as near to each other as possible at the lowest position of the rods without making contact, and to use as long a stroke as possible with the equipment available. Flow velocities and turbulence at the pump inlet should be kept at a minimum. This is accomplished by using the largest standing valve possible and a suitable gas anchor with the largest possible flow passages. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Islamabad.

Special Pumps

There are many other special types of subsurface pumps for use in special problem situations. Technical Data used in the field explained in petroleum courses in Rawalpindi. Most of these are considered “non-API” pumps, although they may use some parts that meet API specifications in their construction. One special pump is the casing pump, which is designed to be inserted directly into the casing without a string of tubing. Such pumps are set in the casing on a packer or casing anchor that grips the casing and holds the pump in position.

Such pumps are limited in size only by the casing size and can be made to have a very large capacity in relatively shallow wells. However, with this arrangement, all the gas produced with the well fluid must pass through the pump, and this may seriously limit the effective capacity in wells producing large quantities of gas. Some more details of petroleum courses in rawalpindi are as under.

Another special type of pump that is used to some extent  is an arrangement where two displacing  plungers are designed to act in series. This increases the displacement of a pump that will run in a given size of tubing and at a given stroke length. Another variation of this concept uses two valves and seats in the lower plunger and none in the upper plunger. This allows a fluid load on the lower plunger at all times and assists the sucker rods in falling on the down stroke. which is desirable for the more viscous fluids.

Fluids with large amounts of gas can cause gas locking or at least reduced flow because of expansion of gas in the chamber between the plunger and the standing valve  on the upstroke. This situation can sometimes be relieved by a special pump having two so-called compression chambers that serve to increase the compression ratio in those chambers above that normally obtainable in a standard pump. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in islamabad.

Three-Tube Pump

This type of pump is illustrated in Fig. 8.8 and gets its name from the three tubes used in its construction. Technical Data used in the field explained in petroleum courses in Rawalpindi. The complete pump assembly is lowered into the well on the sucker-rod string and is positioned in the well by contacting either a cup-seating assembly or a mechanical lock hold down.

 The middle tube of the pump is stationary, attached to the hold down. The other two tubes attached to the sucker-rod string move over the middle stationary  tube, one on the outside and one on the inside. The tubes used in this pump are relatively long and have a relatively large operating clearance in comparison with the usual pump plunger. The resistance to flow between the tubes is adequate to create the seal necessary to displace the fluid past the standing valve and through the traveling valve against the tubing pressure. Some more details of petroleum courses in rawalpindi are as under.

This pump is designed primarily to clean out wells after work over operations or formation-fracturing operations, which may make the well produce large quantities of sand for a considerable time. It is also used in wells producing from loose-sand formations that consistently produce quantities of fine floating sand.

Where conditions are such that there is considerable free gas in the well fluid at the pump intake, it is desirable to prevent as much gas as possible from entering the pump and permit the gas to rise to the surface through the casing annulus rather than through the tubing. Numerous so-called gas anchors are in use that are designed to separate the free gas and deflect it up the casing annulus.

Fig. 8.9 illustrates a common type of gas-anchor arrangement in which the well fluid must enter the perforated nipple and circulate downward at a low velocity before entering the gas-anchor tube, which is attached to the pump intake. This gives the free gas an opportunity to separate and rise to the uppermost ports in the perforated nipple where it may return to the casing. A large portion of the gas will rise through the casing before passing through the perforated nipple. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in rawalpindi

Double Valves

Common arrangements of two valves in series used both as traveling valves and as standing valves. Technical Data used in the field explained in petroleum courses in Rawalpindi. Experience has shown that two valves in series will give much longer service than a single valve if the valve life is determined by wear or fluid cutting, rather than by corrosive action.

This result appears entirely logical where sand or other solid material is lifted with the oil. In such cases failure is likely to occur as a result of fluid cutting when a solid particle is caught between the ball and seat and prevents perfect seating. A pressure differential of 2,000 psi will produce a jet of fluid having a velocity of over 500 ft/sec, which can easily damage the lapped valve-seating surface on balls and seats in a short time. The rate of damage is accelerated if the fluid jet carries solid material in suspension. Some more details of petroleum courses in Rawalpindi are as under.

The life of a ball and seat will depend largely on the number of times it is subjected to damage by fluid jets. By use of double valves this can be greatly decreased, since a jet cannot occur until both balls are held off their  seats during the same stroke. For example, if conditions are such that a single ball and seat is prevented from seating properly once out of each 100 strokes, the chances of both valves in series failing to seat properly will be reduced to 1 in 10,000 strokes. Furthermore, if the two valves fail to seat, the pressure drop will be distributed between the two valves and the cutting action will be less severe than with a single valve. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.

Soft-Packed Plungers

the cup- and ring-type plungers. The left side shows composition-formed cups used to seal the plunger against the barrel. Technical Data used in the field explained in petroleum courses in Rawalpindi. The right side shows composition rings (generally square or rectangular in shape) used for sealing. Some operators prefer a combination of both cups and rings on a single plunger.

The applications of such soft-packing arrangements generally are limited to shallow wells and to those where abrasive conditions  are not excessively severe. Where this type of plunger is satisfactory, it has the advantage of being easily and less expensively reconditioned with new cups or rings, and the flexible packing will compensate for considerable wear of the barrel as long as the barrel surface remains smooth. Some more details of petroleum courses in rawalpindi are as under.

Thus it is seen that a plunger pump may operate with acceptable efficiency in a well producing a highly viscous oil, whereas the same pump operated at the same speed and stroke may fail to deliver any oil to the surface when installed at the same depth in a well producing oil of low viscosity.

the type of ball-and-seat combination commonly used for check valves in subsurface pumps. Balls and seats are made in a variety of materials to resist extremely abrasive and corrosive conditions. API Standard 11 AX ’ lists the important dimensions of standard sizes along with the pump sizes with which they are commonly used. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in islamabad.