Sand control in intelligent wells

The challenge of applying downhole flow control to poorly consolidated, high-permeability, high-productivity, clastic reservoirs is their propensity to produce significant amounts of formation solids. While sand can be a problem for most downhole equipment, it can compromise the ability of intelligent well equipment to do its job. Erosion of choke elements, seal surfaces, control lines, and interference with device movement can render the intelligent completion inoperable, thus losing its functionality and the ability of the operator to use the equipment to realize its long-term value.

Sand-control techniques have been applied in these environments with varying degrees of success, and it is safe to say that a properly conceived and executed sand-control strategy can be very effective in reducing or eliminating solid production without unduly restricting productivity. New techniques, such as expandable screens, have been added to tried-and-true techniques such as gravel packs. But combining sand-control technology with intelligent-well technology can be a significant challenge, particularly when producing fluid from multiple, unconsolidated, high-productivity zones. The intelligent-completion industry is attacking this challenge in concert with the sand-control industry to generate innovative integrated solutions that bring maximum value to the customer.

Issues specific to intelligent wells

The challenge to the completions industry is how to effectively integrate intelligent-well technologies with modern sand-control strategies. The following issues must be considered when using intelligent flow control and monitoring in a sand-producing environment.

Protection and isolation of zones or layers

Intelligent-well completions may be used to:

• Monitor and control flow from separate reservoirs
• Separate layers
• Separate regions of a heterogeneous formation

Some or all of these zones may require some form of sand control, but the hydraulic isolation of one zone from the other is critical to the effectiveness of the flow control. Isolation may be achieved by using cemented and perforated liners with blank sections between zones. Openhole completions with screens or gravel packs may require blank sections of liner with inflatable external casing packers and multistage gravel-packing equipment.

Equipment diameters and available space

Intelligent flow-control equipment, transducer mandrels, and flatpacks or control lines all take significantly more space than conventional completion equipment and may need to be deployed directly inside the sand-control equipment. This can create conflicts when attempting to keep casing and completion equipment sizes within conventional designs while maximizing flow areas to reduce flow velocity and maximize productivity.

Fluid velocity, pressure drop, and erosion

The bane of completion equipment in a solids-producing environment is erosion, and restricted flow areas and tortuous flow paths (typical around and through flow-control equipment) contribute to the effects of high velocity causing equipment erosion. When producing compressible fluids, such as gas, the flowing pressure drop associated with high velocity and restricted flow areas result not only in lower productivity but also in higher flow velocity. If the producing environment is corrosive, erosion/corrosion mechanisms must also be considered in the material selection for the completion.

Protection of sensors, cables, and control lines

Control lines, cables, and sensors represent the nervous and circulatory system of an intelligent-well completion, and damage to these elements may mean partial or total loss of the functionality of the intelligent completion. These elements must be adequately protected from erosion (or the potential thereof from sand-control failure), vibration, and thermal stresses by use of appropriately designed clamps and encapsulating blast joints. Some manufacturers provide systems using dual redundant control line and electronic systems capable of operating on one system in the event of failure of the other.

Mechanical interference of moving components

The solids produced with the fluids can interfere with movement and sealing of dynamic components, particularly sleeves on flow-control chokes and valves. The design of these components must be sand tolerant—either they must exclude solids from entering cavities that may cause interference with movement, or they must be able to easily wipe away the solids or function despite the presence of solids. Actuators and spring returns must generate sufficient force to move the dynamic components despite buildup of solids or scale. Frequent cycling of the valves may prevent accumulation of significant amounts of solid but may also cause more wear and tear on seals and bearing surfaces.

Injection wells

In multizone reservoirs where the production wells require sand control, sand control should also be considered for the injections wells. Dissolution of the natural cementing materials in water-injection wells can destabilize the formation. During shut-in of these wells, flowback and crossflow between layers at different reservoir pressures will result in significant production of solids into the wellbore, which can cause plugging and interference with flow-control devices. Closing the flow-control devices during shut-in to reduce crossflow will help alleviate the problem but may not prevent it.

Sand control in intelligent wells

Use of intelligent-completion elements can significantly contribute to the management and prevention of sand production while maximizing hydrocarbon productivity. By monitoring actual inflow conditions and controlling and restricting fluid flow into the wellbore, intelligent wells can maintain the flow below critical rates that would otherwise destabilize the formation matrix or gravel pack. Zones that develop a propensity for water production can be choked back or closed in, also reducing the tendency for sand production aggravated by multiphase flow and aqueous dissolution of natural cements.

Dip tube or siphon tube solution

One of the simplest solutions for controlling two zones with sand control is the dip tube or siphon tube solution. The well is completed with a conventional two-stage gravel pack (or screens), isolating the two zones from each other with a section of blank pipe and a packer. The completion is composed, top down, of the production tubing, feed-through production packer, gauge mandrel, Internal Control Valve (ICV), a shrouded ICV, and dip tube with seal assembly which stings into a sealbore in the packer isolating the two zones. Production from the lower zone flows through the dip tube and through the shroud on the lowermost ICV, entering the production tubing through the lowermost ICV. Production from the upper zone flows in the annular area between the upper gravel-pack screen, in the annular area between the lowermost ICV shroud and the production casing, and enters the production tubing through the uppermost ICV. The gauge mandrel enables pressure monitoring of both internal and annular areas.

Isolation packer, sleeve, and an internal control valve system (ICV)

A second solution for controlling multiple zones with sand control is done where each zone is completed with (from top down) a hydraulic set, hydraulic feed-through isolation packer, a gravel slurry placement sleeve, a shrouded ICV with the shroud attached to the gravel-pack screen base pipe and the ICV attached to an internal, concentric, through-wellbore, production conduit, which ties into the isolation packer of the next lower interval. The gravel-pack slurry is placed with coiled tubing or a small work string stung into the sand placement sleeve, which acts as a crossover device for flow from the coil to the casing annular area for gravel packing, with returns back up the coiled tubing/tubing annulus. This completion can also be run with screens only, without gravel packing.

A limitation of the second solution is the limited flow area imposed by the multiple concentric strings and flow-control equipment. This solution is only practical with a production casing (liner) size of 9 5/8 in. or greater. A variation on this theme has been designed and tested in a proof of concept well wherein the ICV has been integrated with the screen base pipe; the base pipe becomes the main flow conduit, and the screen has been designed with increased standoff from the base pipe. Flow from the formation travels through the gravel pack, enters the screen, and flows in the annular area between the screen and the base pipe to the ICV, through which it joins the flow in the main production conduit. This solution provides an increased production conduit flow area. In both design cases, the relative flow areas between the casing and the screen, the screen and the flow tube (or base pipe) and up the main production conduit must be thoroughly examined to balance fluid velocities.

Expandable screens

A third and most promising solution is the use of intelligent-well equipment with expandable screens. This solution maximizes flow areas in both the annulus and the production conduit.

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See also

Intelligent wells

PEH:Intelligent_Well_Completions