Sand Control Completion Methods
Gravel packing is the most widely used method of sand control in the oil industry, accounting for nearly 75% of all sand face treatments. During gravel pack operations, a slurry of accurately sized gravel is pumped into the annular space between the screen and perforated casing or open hole. When executing a circulating pack, the carrier fluid leaks off into the formation or through the screen and back to surface. The gravel pack creates a permeable filter that prevents formation sand from migrating into the wellbore. For a gravel pack to maintain long-term productivity, the carrying fluid and gravel must be clean and free of contamination, the gravel should be void free and tightly packed, and placed with minimum damage to the producing formation. To achieve optimum sand control, these requirements depend on the correct selection of proppant, well cleanliness, well screen design, and the proper completion method.
Prepacking the Perforated Interval
Prepacking is the method of pumping gravel into the perforation tunnels. Gravel placement into the perforations is achieved either with a dedicated prepack operation before the gravel pack, or is accomplished simultaneously with the gravel pack. Unless dictated by well parameters, M.I. recommends prepacking prior to screen installation.
Benefits of Prepacking
Prepacking a cased-hole perforated interval is critical to productivity and completion longevity. Benefits of prepacking include:
- Stabilized perforation tunnels
- Improved pressure drop of reservoir fluids entering the welbore
- Increased wellbore pressure (helps lift reservoir fluid to surface)
- Extends gravel/formation interface further away from the wellbore
Since traditional prepacking operations are performed below fracture pressure, it is important to examine several factors that can impact the overall success of the prepack. If pump pressure will not exceed the frac gradient, it is critical that the perforation tunnels are clean and clear of debris. Hydraulic fracturing operations are able to overcome or bypass near wellbore damage with pump pressure, whereas traditional prepacking is achieved by filling void space in and around the perforation tunnel at lower pressure. When attempting a traditional prepack, it is critical to have fluid loss through the perforations. Historical data shows that prepacking with brine has a higher success rate than with viscous fluids. The reason being is that viscous fluids suspend the proppant within the slurry and rarely fill the perforation tunnel fully. Furthermore, post-gravel-pack acid treatments may be required to remove the gel slurry from the perforations prior to bringing the well online. Prepack considerations include:
- shot density and size (large diameter/deep penetrating shots are recommended)
- perforation cleanup (debris removal for improved communication)
- choice of transport fluid
- reservoir injection rate (fluid loss through perforations is critical)
- Cased hole perforated intervals
- Vertical and deviated wellbores
- Newly drilled and mature wells
- Unconsolidated sandstone reservoirs
Gravel Pack Crossover Tool
Over the Top Gravel Pack Tool
The Mitchell Crossover Tool is a field proven service tool used in gravel pack operations to mitigate sand production in unconsolidated reservoirs. This single zone gravel packing system uses a simple and robust tool design to achieve a circulating gravel pack.
The standard running configuration consists of the crossover tool, releasing tool, hook-up-nipple (or landing nipple), blank tubing, tell tale screen, and sand control screen. The assembly is run to depth and the sand control screen is set across the perforated interval, or in the open hole.
During gravel pack operations, the gravel slurry is pumped down the workstring and exits the crossover port below the downward facing packer cups. The dual packer cups seal against the casing wall, directing flow down towards the lower screen. The carrying fluid deposits the gravel into the annular space between the screen and perforated casing, or open hole. Returns are taken through the screen, into the blank pipe, then exit the through the bypass ports above the cups, and return up the annulus to surface.
Once the gravel pack is complete, the releasing tools is rotated to the right and is disengaged from the hook-up-nipple. The well is reverse circulated to remove any excess gravel or debris.
Features and Applications
- Field proven, robust tool design
- Significantly reduces risk of mechanical failure during setting operation
- Reliable solution for cased hole gravel packs and open hole gravel packs
- Supports ‘gravel pack cycling’ function (direct fluid path through screen and into producing zone)
Gravel Pack Packer Method
Retrievable Packer System
The Mitchell GP Packer gravel pack system uses a Model R-3 double-grip retrievable packer in lieu of the M.I. Crossover Tool. The Model R packer features a proven three element packing system and a large bypass flow area. The double-grip version of this packer has hydraulic hold-down buttons located below the pressure equalization valve, allowing the packer to be used when pressure is applied from below. The packer is fitted with an integral crossover kit that allows the gravel pack to be achieved in both squeeze and/or circulating mode. The system is also equipped with a clutch joint that provides +/- 30 inches of stroke when setting or unsetting the packer.
The standard running configuration consists of the GP Packer, crossover kit with releasing mechanism, hook-up-nipple (or landing nipple), blank tubing, tell tale screen, and sand control screen. The assembly is run to PBTD and the sand control screen is set across the perforated interval, or in the open hole. The packer is set and pressure is applied to the annulus above the packer to ensure that the packer is set and holding.
During gravel pack operations, the gravel slurry is pumped down the workstring and out the crossover ports below the three sealing elements. The carrying fluid deposits the gravel into the annular space between the screen and the perforated casing, or the open hole. When in circulating mode, returns are taken through the screen and into the blank pipe, then through the packer bypass, and up the annulus to surface. When in squeeze mode, the carrying fluid is pumped away and leaks off to the formation.
Once screen out is achieved, the workstring is raised to open the bypass. Fluid is pumped down the annulus, through the bypass, and is reverse circulated up the workstring to surface. After the well is circulated clean, the workstring is raised to release the packer and engage the clutch joint. Right-hand rotation is applied to the workstring to disengage the releasing mechanism from the hook-up-nipple, and the packer assembly is pulled from the well.
Features and Applications
- Sufficient bypass flow area
- Allows for gravel pack to be executed in squeeze and circulating mode
- Pressure capabilities up to 5,000 psi
- Suitable for cased hole gravel packs, open hole gravel packs, and HRWP
Multi Zone Isolation
Multiple Zone Stack Pack System
The Mitchell multiple zone stack pack system is commonly used when two or more intervals are completed in the same well, in one operation. The initial step is to set a sump packer, on wireline or tubing, below the lowermost zone. The lower zone is then perforated and prepped for the prepacking process. After the zone is prepacked and circulated clean, the lower gravel pack assembly is run into the well and located in the sump packer with a snap-latch seal assembly. The seal assembly provides positive indication that the screen assembly is anchored and sealed in the sump packer. The gravel pack service tool is then set and the gravel pack is executed. Once screen out is achieved, the service tool is released from the hook-up-nipple and retrieved from the well.
The next step is to run an upper sump packer on top of the lower gravel pack completion. The upper sump packer configuration consists of the sump packer, an isolation valve, and an overshot seal extension. The seal extension is landed over the hook-up-nipple in the lower completion, and the upper sump packer is set. The upper zone is then perforated and prepped for the prepacking process. The isolation valve below the upper sump packer prevents any perforating debris or gravel from falling into the lower completion. The isolation valve also protects the lower zone from treating pressures and potential fluid loss. After the zone is prepacked and circulated clean, the upper gravel pack assembly is run into the well and located in the upper sump packer with a snap-latch seal assembly. The service tool is set and the upper gravel pack is executed. Once the upper gravel pack is completed, the service tool is released from the landing nipple and retrieved from the well.
After the lower and upper gravel packs are in place, the production assembly can be run in the well. The production assembly typically consists of a production packer, profile nipple, and an overshot seal extension. The seal extension is landed over the upper hook-up-nipple and the production packer is set. After the production assembly is installed, the isolation valve can be opened via wireline or slickline at any time in the wells life cycle.
Stand-Alone Screen Installations
In certain applications, a conventional gravel pack completion may not be required in order to achieve sand control. Stand-alone screen (SAS) completions can be deployed as a simple and effective means of sand control in producing formations with uniform particle-size distribution and less than 5% fines content. The use of a SAS system, in the proper environment, can provide reliable sand control at a reduced cost and with less complexity than other open hole sand control completions.
Proper screen selection and well preparation are critical to the longevity and overall success of the SAS completion. The screen must be capable of filtering larger formation sand particles, and must be designed correctly to promote the establishment of a natural gravel pack. M.I.’s typical stand-alone screen options include our PerfGuard™ Premium Mesh screen and our M.I. Accu-Weld™ Prepacked screen. Prior to screen installation, the well should be displaced with filtered clear fluid or highly conditioned mud to minimize the risk of screen plugging. When considering a SAS system for a cased hole completion, M.I. highly recommends prepacking the perforations to improve the inflow area and reduce the pressure drop across the completion.
Typically the stand-alone screen assembly is deployed under a production packer, providing a single-trip completion. In addition, internal wash pipe, an o-ring seal sub, and dual valve set shoe can be incorporated into the assembly to provide circulation out the end of the screen. This tool setup is used to assist in screen deployment and to circulate filter cake breaker fluids in the open hole. M.I. can also provide swivel joints for rotational purposes and shear safety subs for detachment, when required.
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