Fundamentals of Petroleum in details processes
- 2. It means the processes by which we can recover oil or gas from the reservoir. They are of three categories: Recovery Processes Primary recovery Artificial Lift Methods Enhanced oil recovery Secondary recovery Tertiary Recovery
- 3. It means in this process the reservoir fluid is recovered by its natural energy.
- 4. For oil reservoirs the Primary recovery processes fall under following categories: Water Drive Gas Drive Combination Drive Gravity Drainage
- 5. Water Drive: Water drive occurs when there is enough energy available from free water in the reservoir to move hydrocarbons out of the reservoir, into the well bore and up to the surface. Water located beneath the oil in the reservoir is under pressure proportional to the depth beneath the surface, in other words, the deeper the water, the higher the pressure. Water drive mechanism can either have bottom water drive or edge water drive. It is the most efficient natural drive. Sometimes 50% or more of the oil in the reservoir will flow out due only to water drive.
- 7. Gas drive: This works on the principle that gas in the reservoir is under high pressure such that highly compressed so it tries to attain the pore spaces occupied by oil so it displaces the oil and takes its place, there are two possibilities of Gas drive mechanism: Gas Cap drive Dissolved Gas Drive
- 8. Gas cap drive: The gas cap above the oil pushes the oil as it tries to attain the pore spaces of the oil and in this way oil is achieved but as the gas expands to a considerable volume the energy is declined and flow rate will decrease and ultimately production will be stopped. About 20-40 % of oil can be achieved through this. Dissolved Gas Drive: If the gas is dissolved in the oil in the reservoir then as the hole is dilled, the production starts and reservoir pressure will decrease such that it deceases to bubble point pressure at which bubbles of gas will form, which carry the oil up to the surface along with them making it less viscous. Oil achieved is about 30-50%.
- 10. Combination Drive: In combination drive both gas and water drives are present. Water pushes the oil in upward direction, while gas pushes it in downward direction and hence the oil becomes more compressed in between the two and is produced with much more energy in this case as compared to water and gas drives.
- 11. Gravity Drainage: The least common type of reservoir drive is gravity drainage. In highly permeable, steeply dipping reservoirs, the oil flows down the hill into the well bore.
- 13. Under saturated Reservoir: In this reservoir pressure (PR) is greater than Bubble point pressure (PB) initially and a gas cap already exists there (primary gas cap). Saturated Reservoir: In this reservoir pressure PR is less than PB and gas is present in dissolved form and as the production is carried out the PR decreases and ultimately reaches below the PB and the secondary gas cap is formed.
- 14. In gas reservoir, the natural recovery may be due to following two reasons: o Gas is highly compressible state of matter and can flow readily as it is less viscous as compared to oil so whenever gas is present in the reservoir in highly compressed form then as soon as the hole is drilled, its production is started. o There is possibility of water drive beneath the gas, pushing it upward in the well bore and up to the surface.
- 16. Beam Pumping Jet Pump Hydraulic Pumps Electrical submersible pump Gas injection
- 22. A method of improved recovery in which water is injected into a reservoir to remove additional quantities of oil that have been left behind after primary recovery. Water flooding usually involves the injection of water through wells specially set up for water injection and the removal of water and oil from production wells drilled adjacent to the injection wells.
- 23. In this natural gas or nitrogen is injected, to maintain formation pressure and to enhance the natural energy of the reservoir.
- 25. A second type of gas injection uses a gas that is miscible (mixable) with oil to move the oil to the well. When a miscible gas in injected, some of its molecules mix with the oil molecules. It works similarly to the natural dissolved gas drive. As injection continues, the gas moves part of the oil to the producing well.
- 26. Chemical flooding is a general term for injection processes that use special chemicals in water to push oil out of the formation.
- 27. Oil in some reservoirs is so viscous that they need to be heated to make them flow so the recovery techniques that utilize heating are called as thermal recovery processes. A hot fluid is injected into the injection wells and moved towards the producing wells. It is categorized as: Steam Injection In-situ combustion
- 30. The phase of well servicing and work over operation comes when a well stops producing or do not produce at the desired rate after producing for a long time, the main difference is: The well servicing is mainly related to the maintenance of the equipments attached to the well. Work over operations are mainly related to the reservoir rock. The first step in work over is to kill the well by using high density drilling fluid.
- 31. Well Servicing Lubricating the valves of well head Maintenance of beam pumping unit Repairing production tubing and Packers Work over Well Stimulation Sand cleanout Replacing Screen liner Sand Control Squeeze cementing Schematic diagram of well servicing and work over
- 33. What is well stimulation How formation damage occurs During drilling During Completion Perforation During production How well stimulation is done Hydraulic fracturing Acidization
- 34. Sand cleanout, the sand particles, which are produced during production with oil and gets stuck to the tubing and other equipments of the well is cleaned. Sand control Replacing screen liner Squeeze cementing
- 36. Lubricating the valves of well head. The beam pumping unit needs some maintenance: Regular lubrication of the moving parts. The sucker rod may also be corroded and eroded and needs to replaced or repaired. Tubing and Packers may fail due to corrosion and erosion and needs to replaced. Paraffin deposits along the walls of tubing reduce its diameter and slows the production, so with the help of scraper they are removed or chemically dissolved in special chemicals or solvents which are kept in the well for 24-72 hours to dissolve all paraffin.
- 37. Kate Van Dyke www.oilgasglossary.com