Factors to be considered
- Well pressure must be considered since a packers selection must be done with the proper pressure capabilities for the well. It is necessary to know if pressure differentials will be from the top or the bottom of the packer and if the differential will change from one side to the other during the life of the well. Some completion packers will only withstand very limited pressure from one side.
- The pressure change is also a factor in tubing movement (elongation or contraction). Temperature is a consideration since some packers will perform at higher temperatures than others. Retrievable packers should normally be limited to temperatures of 300oF maximum. Sealing compounds used on seal units for permanent packers or packer bore receptacles will be selected for best performance at a given temperature range.
- Corrosive agents in the well fluids must be considered. Usually, retrievable packers do not perform well in wells with high H2S concentration. Many times, the alloys used in the manufacture of a packer must be selected to withstand the corrosive agents they will encounter.
- Longevity of a producing interval is a prime consideration in the selection of packers. If a zone is anticipated to produce for many years with no need of remedial work, it may be desirable to use a permanent type packer or hydraulic set retrievable packer. However, if it is anticipated that remedial work to the well will be necessary within a short period of time, it may be more desirable to use a mechanical set packer.
- If the well is to be treated with acid or frac materials or pumped into at high rates and pressures for any reason, the proper packer must be selected Packer failures most often occur during treating operations. Tubing contractions may be very severe during treatment. Contraction can cause retrievable packers to release, or it can cause the seal elements to move out of the seal bore in a permanent packer or packer bore receptacle.
Compatibility with other downhole equipment.
- Often packers are selected because of their compatibility with other equipment. For example, where hanger systems are used with surface-controlled subsurface safety systems, it is desirable to use hydraulic set packers. Hydraulic set packers allow the operator to install and set the complete safety system and the tree before setting the packers. Well fluids may then be displaced with lighter fluids while the well is under complete control. The packers can be set after the displacement of fluids is completed.
- If wireline equipment is to be serviced in the tubing or through tubing perforating is to be accomplished, it is desirable to use packers that do not require tubing weight to keep them set. Wireline operations can be more successfully completed if the tubing is kept straight by landing it in neutral or tension. This is increasingly important in deeper wells.
- In many instances, packers selection are done for use with gas lift valves to keep lift pressure off of the producing formation and to prevent gas from blowing around the end of the tubing.
- If a packer is to be used with a rod pumping unit, it is usually desirable that the tubing be placed in tension. A packer selection must be done to allow this.
It must be recognized that oftentimes, several different types of packers may be successfully used in the same installation. Many times, a packer may be selected by the operator because he has experienced good success using it in the past.
Economics may become a factor in packers selection. In some instances, the operator must complete a well as cost-effective as possible and will select a packer because of its lower cost.
If a packer is set by an electric conductor line, it is possible to place the packer in the casing very accurately. Sometimes, producing intervals are very close together, making it necessary to place the packer accurately.
An important parameter for defining the characteristics of a packer is the degree of difficulty of the well to be completed. To this end four classes of well have been identified which are used to analyze the various problems involved in the selection of the packers:
1) High corrosive wells
- The fluids have high corrosive problems.
2) Highly critical wells:
- Deep depths > 4500m.
- High temperatures, SBHT > 130°C. High pressures, SBHP > 700 atm. Subsea well-head well.
- Platform well (drilling platform) having the risk of failure due to the potential collision from a vessel with the structure.
- Gas injection well with pressures, ITHP above 3,000psi.
3) Critical Well
- Temperatures between 100 and 130°C Depths between 3,000 and 4,500m.
4) Non-critical well
- Depth of less than 3,000m. Temperatures below 100 °C.
- The depths indicated are true vertical depths.
Packers Selection For Single String Completion
Type Of Packer Procedure
The choice is mainly linked to the type of well:
- In the case of a highly critical well, select a permanent packer.
- If the well has high corrosive, selection a permanent/retrievable or permanent packers is done, with priority be given to the former.
- If the well is critical or non-critical, (Refer to figure b).
Explanation of figure b:
- (A) High frequency of tubing pullout.
- (B) High frequency of tubing-packer pullout.
- (C) Use of TCP drilling techniques.
- (D) Measured well depth ≥ 3000 m.
- (E) The workover fluid damages the formation.
- (F) The packer fluid is a high-density mud (> 1.6 kg/l) with probable solid deposits
- on the packer.
- (G) Gas injection well with injection pressure > 3,000psi.
At points A and B, a high frequency of extraction corresponds to a completion life of less than five years.
The rectangle ‘Choose’ indicates the choice between the two alternatives, and the priority is indicated by a number (‘1’ corresponds to a higher priority than ‘2’). For example, in the choice is made on the basis of point (D) then there are no particular constraints (no workovers, or requests due to the completion fluid characteristics).
The safety factor of using a retrievable packer or not depends on the criticality of the well and, in particular, on its depth.
Packers Setting Method Selection
The selection of packers is dependent mainly on the well characteristics:
- If the well is corrosive or very critical, choose hydraulic setting.
- If the well is critical or not critical, (Refer to figure c).
- Reference (A) is only true if one of the following conditions are relevant:
- SBHT > 150 °C (= 270 °F).
- Is a deviated well, with a maximum deviation angle > 50°.
- The completion fluid = mud with density > 1.6 kg/l. Gas a production liner with inclination > 30°.
For a mechanical type permanent packer, the setting is defined by the conditions detailed in (A). The same procedure will also be used later for packers of the type used in a selective type completion.
Retrievable Packer Setting Method
The method of setting used for retrievable packers is made, following the diagram in figure d:
- Check (A) is only true if one of the following conditions are relevant:
- The well is deviated with a maximum deviation angle of > 20°.
- The bottom-hole temperature (SBHT) is > 60 °C.
- The vertical depth of the packer setting is > 2,000m (this is true to definitive and not test completions).
- Stimulations are planned.
- Check (B): Using TCP shooting techniques.
- Check (C): There is high frequency of tubing pullout (life of the completion < 5 years).
- Check (E): Completion fluid and damage to the formation
- Check (F): The packer fluid is a high density mud (> 1.6 kg/l) with the probability that it leaves solid deposits on the packer.
The decision of whether to use a hydraulic, or hydrostatic, set is left to the engineer. The main consideration is the required setting pressure (lower for hydrostatic packers) which influences the wellhead pressure rating.
The conditions at the moment of packer setting decides whether to use a retrievable packer. If these are outwith the capacity of the retrievable packer, a permanent/retrievable packer will be utilised and consequently, the corresponding setting procedure will have to be adopted (see permanent packers above).
Permanent And Permanent/Retrievable Packers Setting Method Selection
There are principally two aspects to analyse:
- The choice of the tubing-packer connection.
- To integrate this choice with the stress analysis procedures.
If during the application of the stress analyses of the string gives negative results, a configuration which fulfils the stress analysis requirements must be considered for the packer-tubing connection5.
The shear ring value is generally set by increasing the maximum force applied to the packer by 25%. The maximum force is determined using stress analysis (to take into account the tolerance of the nominal shear value 5 to 10%). The shear value is checked for the stress conditions at the wellhead section during the packer release stage.
Tubing-packer connections seal assembly elements will be of the moulded seal type when subjected to alternating pressure cycles, e.g. gas injection wells where the IBHP is greater than the packer fluid pressure and SBHP is lower than the packer fluid pressure.
Highly Critical Well: Anchored Completion
For a highly critical well, the approach is the same as that for an anchored tubing-packer. defines the type of anchoring on the basis of the conditions for (A), in particular the choice is made between a shear release or anchor seal assembly.
The type of anchor to be used can be defined during this first stage for an anchored completion (without shear release):
- If the packer is set mechanically, the anchor will be a ratchet type or, alternatively, fixed.
If the stress analysis results are negative:
- If a shear release is needed, an anchor seal assembly is used.
- If anchor is needed, a dynamic seal is used (Refer to figure d).
- if it is an injection well it cannot be critical.
For an anchor with shear release:
- If the stress analysis upon releasing is negative, an anchor will be used and the check will be carried out again.
Highly Critical Well: Dynamic Seal
This stage considers an anchored completion which fails the stress analysis calculation because of problems associated with the tubing-packer connection. In this case a dynamic seal is used (Refer to figure f).
- Check (A): The packer fluid is a high density mud (> 1.6 kg/l) which may leave solid deposits on the packer.
- Check (B): The packer is one trip installation, i.e. run on the tubing. This is only possible with hydraulically packers.
The procedure illustrated in figure f gives a general description of the criteria behind the choice of dynamic seal to be adopted. Reference will be made to this later and also for cases which are different to those described in highly critical wells above.
Here, following any failure of the stress analysis, no other rules are apply as, in general, when using dynamic seals, the stress analysis results are corrected using factors other than the seal element.
Critical, Non-Critical Well
The easiest solution in these cases is to choose a Standard Seal Locator. This is the case with the following conditions:
- No stimulations are planned.
- The well is not an injection well.
- The packer is not set hydraulically.
If these conditions do not apply, the procedure illustrated in figure g is followed.
- Check (A): the packer fluid is a high density mud (> 1.6 kg/l) which may leave solid deposits on the packer.
- (B): deviated well with max. deviation angle > 20.
- (C): expected life of the completion < 5 years.
- (D): the packer is set mechanically.
Again in figure g, the outlet conditions included in the rectangle indicate, besides the choice of tubing-packer connection, the need to use the packing setting procedure specified.
In the case of a deviated well, anchored completion is not recommended. It is better to use a completion with a shear element which is more easily releasable, or a dynamic seal whenever feasible.
No additional adaptation of the seal element is foreseen as a consequence of any stress analysis.
Retrievable Packer Tubing-Packer Connections
The choice of the tubing-packer connection for retrievable packers (hydraulic and set down weight) is made on the basis of that in figure h.
Particular conditions raise questions over which type of retrievable packer to use. In these cases, a permanent/retrievable packer is the priority or a permanent should be used and consequently the associated setting procedure and seal assembly selected.
Single Selective Completion Packers Selection
The criteria illustrated here are valid for selective completions with 2 or 3 producing zones. The solutions given are for a case with only 2 zones and if a third zone is to be taken into consideration it is assumed that the selection made for the upper zone of the two zone scenario applies.
Single Selective Packers Selection
The first case classifies the well on the basis of depth characteristics (4,000m) but more on the basis of its complexity.
if several different configurations are available, as for example in figure i, the engineer has a certain degree of freedom of choice but is, however, governed by the order of priority specified along with the choices.
If the conditions as of figure i, are not applicable, these cases are classified by well depth:
In the case of depths less than 1,500m in a well not considered complex, it is strongly recommend that a retrievable type packer be used.
Application of the criteria illustrated in figure i through figure L is common with the only exception, in the case of multiple choices, being that the order of priority for the lower zone can be changed by applying the following rules:
- If workovers are planned with removal of the tubing and packer, and a retrievable packer is one in the list of possible choices, then it should be selected.
- If the completion fluid is a mud with deposition problems, and a permanent or permanent/retrievable packer are in the list of possible choices, then the permanent/retrievable should be selected over of the retrievable
Selective Packer Setting Method
The type of setting method proposed depends on the following factors:
- Type of packer
- Setting distance between the packers.
The setting criteria of a mechanical permanent packer (on a workstring, or wireline) are those already defined for the single completion described in section (Packers selection for single string).
Permanent Stacked Packers:
Refer to figure i with all permanent packers, if the setting distance between the packers is > 500m (check with the packer manufacturer), choose hydraulic setting for all the packers or else mechanical setting.
Lower Permanent Packer With Upper Retrievable:
Refer to figure j, figure k and figure L, in these cases the reference packer is permanent and the other packers are the retrievable or permanent/retrievable type. With these type of packers, if the completion fluid is a brine, hydraulic type setting should be used or else the packers can be set mechanically.
Mechanical setting is preferred for the reference packer and the setting should be by electric line when the distance between the packers is < 500 m.
If the reference packer is set by a workstring, a depth control procedure is necessary to verify the depth of the packer setting to ensure positioning of the blast joint across the upper zone which is open to production.
All packers are Retrievable
Refer to figure k and figure l where all packers are retrievable, hydraulic setting should be used for this type of packer. It is essential to check with manufacturers that the distance between the packers is sufficient for the packers to be set.
Tubing-Packers Connection Selection
The criteria continues by classifying the packers by type and setting with the zones treated separately. In some cases, three zones are assumed (upper, intermediate, lower). In cases where there is no specific mention of an Intermediate zone, it is treated with the same criteria used for the upper zone.
Generally, the results of the stress analysis specifically identifies the packers with releasing problems. Due to this, the zones are be treated separately; i.e. modifications are be made only to those packers which have the problems. It is recommended in any case to re-check the completion after having made the modifications.
The rules described for the single completion are applied to the upper packer (Refer to above sections).
Lower or Intermediate Packer
There are three possible ways of treating the lower zones:
- All the packers are of the permanent or permanent/retrievable types with hydraulic setting. Initially an anchor with shear release should be selected. In the case of failure of the stress analysis on this packer, a dynamic seal will be used (anchor with polished bore receptacle or telescopic joint).
- The lower zone packer is a permanent with mechanical setting. A dynamic seal should be used; in particular, a standard length locator. In the case of failure of the stress analysis, a longer locator with seal bore extension should be used. For the intermediate zone in the three zone case, an anchor or retrievable type packer will be used, for the intermediate packer.
- The lower zone packer is a retrievable. In the case of failure in the stress analysis a dynamic seal with telescopic joint will be used.
For the intermediate zone in the case of three zones, a telescopic joint should be used when there is failure in the stress analysis.