Packer Elements Information
Packer elements are sealing components used between sections of oil and gas production tubing to prevent fluids and pressure from leaking through the joints. This protects the casing, production tubing, liner and wellbore wall above and below the producing zone. Packer elements are designed for operating in corrosive or harsh conditions and manufactured from elastomers compatible with the media that needs to be sealed.
All packer mandrels (bodies) have three key attributes:
- The slip is wedge shaped and covered with teeth (wickers) that grip the casing when the item is set.
- The beveled surface matching the back of the slip is called the cone. This is designed to push the slip into the casing when the proper setting force is applied.
- The packing element is the elastomer sealing element that creates the seal between its exterior and the inner wall of the casing.
Packer elements serve a number of purposes:
- Partially supporting weight for the down-hole tubing
- Improving well flow and production rate
- Separating different producing zones
- Enhancing safety by limiting well control to tubing at the surface
- Holding fluid for well servicing in the casing annulus
- Preventing the downhole movement of the tubing string
- Guarding the annular casing from corrosion caused by the fluids and high pressures
Production packers are classified into two groups:
Structures classified as permanent are removed from wellbores by milling. These are of simple construction and provide high temperature and pressure performance ratings. The smaller outside diameter of permanent units enables superior running clearance on the inside of the casing string. The compact construction allows them to negotiate through narrow portions and deviations found in the wellbore. Their sizable inside diameter makes them suitable for use with tubing strings of increased diameters and in monobore completions.
They are run and set using electric wirelines, drill pipes, or tubing. Once set, the items are resistant to motion coming from either direction. Wireline settings transmit an electric current to set the packer via the detonation of an explosive charge. Then a release stud separates the assembly from the packer. Permanent elements are ideal for wells with high pressure or tubing load differentials.
Retrievable packers include both conventional low pressure/low temperature (LP/LT) models and more complex high pressure/high temperature (HP/HT) models. These products are more expensive than permanent structures offering comparable performance due to their design complexity when engaged with advanced tools. However, factors such as ease of packer wellbore removal and reusability serve for offsetting the cost indicator.
The products further divide into an assortment of types, including:
Mechanically set: Setting is accomplished via tubing movement of some form. This either includes a rotation or upwards/downwards motion. Furthermore, a load is involved in setting the units as the tubing weight either compresses or expands the sealing element. Pulling up on the string releases the items. These are most common in shallow, straight wells with low pressure.
Tension-set: Packer elements of this class are set via pulling a tension positioned on the tubing. Slack serves to release the item. They function best in shallow wells featuring moderate pressure differentials.
Rotation-set: These use the rotation of tubing to mechanically set and lock in a component.
Hydraulic-set: This category operates via fluid pressure driving the cone in place behind the slips. After setting, either a mechanical lock or trapped pressure keeps them stationary. Picking up the tubing drives the release function.
Inflatable: Also known as swellable elements, these components rely on fluid pressure to inflate cylindrical tubes for setting them. They are found in open-hole testing when drilling exploratory wells and for cement assurance in producing wells. They are also suitable for wells where packers need to pass through a restriction before setting at a more sizable diameter in casings or open holes.
A more detailed look at certain popular options follows below:
Retrievable tension packer elements support medium to shallow depth production or injection operations. These have a set of unidirectional slips gripping just the casing in situations with tension load on the tubing. Level tubing tension energizes the objects. This category is set mechanically and released with tube rotation. The majority of the models come with emergency shear-release in the event the primary release method fails.
Tension packers are applicable in situations where the pressure underneath is at all times higher than annulus pressure located at the tool. This upward pressure forces the items into the slip assembly for maintaining the tension.
Retrievable compression packer elements with fluid bypass are ideal for low and medium pressure oil and gas drilling environments at medium temperatures. A mechanical interlock keeps the component from setting. While it runs in the hole, tubing rotation activates the element. Drag blocks located on the object hold it in position and provide resistance necessary to set it. When the interlock is released, lowering of the tubing string permits the closure of the bypass seal and setting of slips. Applying continuous slack-off force creates the seal by energizing the products. The release is accomplished simply by pulling up on the tubing string.
This option possesses exceptional ability to withstand amplified pressures and temperatures than the tension alternatives. The bypass valve improves the packer's capacity to equalize pressures found in the tubing and the annulus and makes it easier to release the implement. Continuous compression or tubing weight is necessary to ensure the bypass valve stays closed. These are not suited for injection wells or minimum volume pressure treating operations.
Retrievable tension/compression set promote landing of tubing in tension, compression, or neutral. These are most common mechanically set retrieval units today. They have a broad range of configurations for tension, compression, or a combination of the two to set and pack off an item. The selection of systems and differential ratings make them useful in a vast spectrum of conditions. With these sets, the energizing force is locked in with an internal locking mechanism until the unit is released with a bypass valve. This valve assists in equalization as well.
These devices are more versatile than other solutions and exist in both production and injection situations.
Permanent and retrievable sealbore structures are positioned with electric wirelines or hydraulics on the tubing string. Setting with wireline offers increased speed and accuracy while one-trip hydraulic-setting options benefit in single pass installation. They facilitate the setting process with wellheads flanged up. This classification features polished internal sealbores. A tubing seal assembly featuring elastomeric packing forms the seal connecting the production tubing and packer bore. The positioning of the elastomeric seals in the bore creates the well isolation.
Locator assembly type permits seal movement during production and treating operations. Anchor assembly type secures seals within the packer bore to restrict tubing movement.
Permanent sealbore solutions provide improved performance than retrievable components. They possess greater complexity in design making them more expensive.
Packer elements cover a vast spectrum of applications and industries, including:
- Eliminating surging and heading
- Separating multiple zones
- Casing protection
- Isolation packers
- Sub-surface safety control
- Artificial/gas lift
- Oil and gas
- Geothermal mining
- Ground water development
- Contamination studies
- Coal bed methane
- Geothermal mining
- Geotechnical studies
Selecting packer elements involves considering factors such as:
- Differential pressure
- Borehole size
- Deployment and setting technique
- Ultimate tube landing
- Operational mode