Completion method, stabilization system
Through-tubing sand control techniques present an economically attractive completion option. Recently, the industry has emphasized recovery of bypassed hydrocarbon reserves and extending field production. Since economics is a key decision criterion in these types of developments, the availability of reliable and cost-effective through-tubing sand control techniques can be a major deciding factor.
When a wellbore is drilled through a friable or weakly consolidated sand formation, a plastic zone develops and formation failure may follow. Production flow, cyclic loading caused by shut-ins, and water production can expand the plastic failure zone away from the wellbore into the formation. Production of formation sand can lead to plugging and damage to tubulars, surface equipment, and flowlines, which leads to loss in production.
Without a means to control the production of formation sand for these types of reservoirs, reserve recovery will fall short of that possible with sand control measures applied to the well. The pay zone may be a new completion or an existing zone that needs some method of sand control to allow economic reserves recovery. In either case, for existing wells, an effective sand control procedure that can be performed through the existing tubing without a rig has significant cost advantages. Halliburton says it has developed a new sand consolidation system to take advantage of the through tubing economies while offering improvements over previous systems.
Formation consolidation is not a new concept, and in many applications has proved to be a successful means of providing sand control. According to Halliburton, this newly developed consolidation system features resin consolidation for oil and gas sands requiring sand control. These features the company lists include:
- Operational simplicity with brine and solvent preflush stages, two-component consolidation fluid, and brine post-flush
- Internally catalyzed consolidation fluid for improved reliability
- Low-viscosity fluids for more effective placement into reservoirs with variable permeability
- Consolidation fluids system that is attracted to and uniformly coats formation grains
- Good consolidation performance in sands with clay mineral content
- Post-flush displaces the consolidation fluid to retain pay sand permeability.
Two preflush stages prepare the formation sand for high-strength consolidation and improved permeability retention, the company says. The brine preflush allows the mineral surfaces to attract the consolidation fluid so that a thin, uniform coating of consolidation fluid coats the formation matrix grains. Connate water is displaced from the pore spaces to improve penetration of the treatment into the pores, and subsequent displacement by the post-flush enhances consolidation strength and permeability retention. The result, Halliburton says, is that high consolidation strength for improved sand stability can be attained without significant loss of the reservoir permeability.
Near-wellbore stabilization
Injecting curable resin directly into the permeable formation to lock fines in place and prevent the production of sand stabilizes the unconsolidated or friable near-wellbore region, the company says. Frequently, this method is used where completions using gravel packing and sand control screens are economically unattractive or where wellbore restrictions are limiting.
This new system can be applied to new or existing sand completions. The treatment can be placed several ways:
- Down production tubing
- With jointed pipe and service packer
- With coiled tubing.
New perforations can be treated down production tubing for zone changes or recompletions to access additional reserves. Coiled tubing and the consolidation system can put existing zones back on production without the expense of a rig-based workover. For wells with failed gravel packs, a simple pumping procedure can be used to consolidate the existing gravel pack and reservoir sand in the problem area to put a shut-in well back online, the company says. Sand consolidation treatment fluids commingled with nitrogen have proved to be an effective solution for gravel pack repair.
According to Halliburton, contact of the treatment with the gravel pack and surrounding sand can be enhanced with coiled tubing deployed tools so that the treatment can more effectively penetrate the gravel pack and the adjacent formation. Some of the tools, which have been used to improve treatment penetration and uniformity, include jetting nozzles and the newer pressure pulse tools. A type of tool that combines pressure pulse generation and jetting action at the point of treatment injection can enhance effectiveness of the treatment both by helping to break through areas of restriction to injection and by improving contact with the pulsing fluid agitation.
Sand control with stabilization
Halliburton says experience with completions combining near-wellbore stabilization treatments with tip screen out fracture stimulation has shown that certain wells can be produced successfully when both are combined; especially when reservoir conditions that are not good candidates for either treatment alone.
Not every pay zone is a good candidate for sand control using near-wellbore stabilization. Some conditions, which are recognized as posing a higher risk of sand control failure, low post treatment production rates, or both after near-wellbore consolidation include:
- Low reservoir permeability
- Severely destabilized near-wellbore region often caused by pre-treatment sand production or drilling practices not appropriate for sand control completions
- Significant near-wellbore damage, which both limits placement of treatment fluids and causes poor post-treatment production rates
- Plugged perforations that accept limited consolidation treatment and cause weak stabilization of the adjacent formation
- Non-uniform permeability contrast over the pay interval.