PRODUCTION METHODS

• There are three natural drive mechanisms can cause oil or gas flow up to well bore.

1. Water drive 2. Gas drive 3. Gas solution (Dissolved gas)

WATER DRIVE

• In water drive production, oil or gas trapped in a reservoir can be view as being sealed in a water filled U.tube.

• When tap is opened the oil or gas from the reservoir will flow upward due to the hydrostatic head of water.

• As the field is produced, water invades the lower part of trap to displace the oil.

• Only in case of uniform reservoir the oil, water contact rise evenly , Because the adjacent beds have same permeability , water enrichment at different rates giving rise to fingering.

• A further complication may be caused by coning of water adjacent to the boreholes.

• The extent of coning depends on the rate of production and ratio between vertical and horizontal permeability .

• With an effective water drive the flow rate remains constant during the life of fluid flow but oil production declines inversely with an increase in water production.

• The water drive mechanism is generally most effective , with a recovery factor of 60%.

GAS CAP DRIVE

• In gas cap drive mechanism field contains both oil and gas zones. • as production begins the drop in pressure cause gas dissolved in oil to come

out of the solution.• This gas move up to the gas cap and expands to occupy the pores vacated by

oil. A transitional zone of degassing thus forms at gas, oil contact.• Drawdown zones may b developed adjacent to bore holes in a manners

analogues to but reverse to the coning of oil, water contact.• The production history of gas cap drive fields is different from the water drive

mechanism.

• Pressure and oil production drop steadily , while the ratio of gas to oil increase naturally.

• Less effective than water drive mechanism ,with a recovery factor of 20-50%.

DISSOLVED GAS DRIVE

• This type of drive occurs in the fields that initially don’t have any gas cap, also known as solution gas drive mechanism.

• As production begins , pressure drops , gas bubbles form in the oil , expands forcing the oil out of pore system and towards the borehole.

• Initially gas bubbles separated as time passes, they come together and form a continuous free gas phase, which may accumulates as gas cap.

• This point is termed as critical gas saturation, and care should be taken to prevent from this point.

• It may be avoided by slow rate of production or by reinjecting the produced gas to maintain the original reservoir pressure.

• This drive mechanism is less effective than the other two types , with a recovery factor of 7-15% .

ENHANCED OIL RECOVERY

• One of the main objective of enhanced recovery oil is to maintain or reestablished the original reservoir pressure.

• This objective can be accomplished by several ways : By injecting gas ( Inert gases e.g. Carbon dioxide , Nitrogen). By injecting liquids ( Sea water , connate water ).