Water-dispersible resin system helps stabilize offshore multi-well completions
Global economic conditions require innovative, state-of-the-art wellbore stabilization methods to help reduce the total costs associated with the construction and life cycle of a well. Wellbore stabilization is the prevention of unwanted flow of fluid or gas into or out of the well and mitigation of formation compressive or tensile failure.
Stabilization methods should be based on real-time drilling data obtained from measuring-while-drilling (MWD) and logging-while-drilling (LWD) systems, advanced fluid chemistries, computer-generated placement procedures, and job histories of wells with similar problems. A properly designed wellbore stability process can help decrease well construction costs by reducing non-drilling rig time, eliminating emergency or unplanned casing strings, and preventing environmental hazards caused by unwanted fluid or gas flow from the formation.
A water-dispersible resin (WDR) system has been developed to help plug fractures/vugs, help reduce formation permeability, and help artificially increase formation fracture gradients. The WDR system can allow operators to stabilize high-permeability or weak formations, thus helping to prevent shear failure. Additionally, the system can help change a formation's mechanical properties by increasing tensile strength, Young's modulus, compressive strength, and fracture gradients.
Option to mechanical solutions
Historically, drilling engineers have used steel casing or liners to solve formation-integrity problems associated with weak or damaged formations that have not been improved by changes in drilling-mud composition or cement repairs (squeezing, setting plugs). Unlike other systems, aromatic epoxy resins, such as those used to seal disposal wells, will penetrate the formation matrix. However, the resins are not sufficiently tolerant to aqueous contamination, and contamination by any fluid media can completely alter the properties of the fluid, and find-set resin. A water-dispersible resin (WDR) system provides a fast, cost-effective option for altering and strengthening weak or damaged formations during drilling.
The WDR system consists of an aliphatic epoxy resin, a hardener, an accelerator, and (for some applications) a bonding agent. The system can be applied at bottomhole circulating temperatures (BHCT) ranging from 40° F to 250°F. Unlike more commonly used aromatic epoxy resins, which exhibit no water tolerance and typically require hydrocarbon spacers, aliphatic epoxy resins impart water tolerance to the WDR system.
Aliphatic resins can be formulated as a dispersion in water-based drilling fluids. In addition, the WDR system can be pumped as a neat resin, a resin/solids slurry, or as a dispersion in oil-based drilling fluids. The filtrate from these mixtures can penetrate and consolidate the formation.
A neat resin system is most often used in matrix treatments for altering the formation's mechanical properties. Solids (sand, barite) can be added to the resin to help increase viscosity, help provide a bridging agent, or help increase the density of the mixture. Increasing a formation's mechanical properties can help:
- Prevent formation movement, which can lead to collapsed pipe and the loss of a well
- Protect formations that have been weakened by high production rates over long periods
- Prevent subsidence problems.
During drilling operations, the WDR system helps consolidate weak zones that can result in lost circulation, hole collapse, and other events. By mixing the resin with drilling fluid, an operator can strategically spot a pill without altering the density of the mud in the hole, and additional barite can be added to maintain or exceed the original mud density.
After the pill is spotted, pressure applied below the fracture gradient forces the resin filtrate through the mud filter cake into the formation. Drilling operations can continue after the resin hardens. By helping to modify or strengthen the formation, the WDR system can allow operators to continue drilling without setting casing or performing remedial cementing operations.
R&D testing
During laboratory testing, holes with diameters of 1.25-4.25 in. were drilled in a hydrostone block and filled with sand. Then, the sand was treated with the WDR system. After the resin set, a wellbore was drilled into the treated sand, and casing was inserted, leaving an open hole section. Pressure was applied to the open hole section through the casing until the set sand and resin failed, as shown for the various hole diameters (Figure 1). Test results demonstrate that an increase in fracture gradient can be achieved with a WDR system treatment of a formation at various depths. Assumptions of the test were:
- WDR system penetrated to a depth of 2 in.
- Formation fracturing pressure increased by 1,000 psi.
- Pore pressure was 8.5 lb/gal.
The WDR system can be used for the drilling applications, inlcuding sealing and strengthening depleted sands, strengthening fractured or faulted formations, and sealing and consolidating rubble zones associated with subsalt drilling.
In production operations, annular pressure buildup caused by gas leaks can pose a safety hazard, and pressure should be bled from the annulus periodically. Studies indicate that more than 10,000 annulus leaks exist in the Gulf of Mexico. Many of the affected wells may have to be abandoned if the leaks are not repaired.
A potential solution to this problem is a top-down squeeze performed with the WDR system through the annulus. If the top of cement (TOC) is near the wellhead, the resin can be pumped through a direct connection to the wellhead. If the TOC is far from the wellhead, expandable annular tubing can be used for placing the resin. After (or during) placement, a high-pressure squeeze is used to force the resin into the cracks/microannu* in the cement sheath, where the resin forms an impermeable barrier to gas flow. WDR system treatments, such as the following, can also be used for these applications:
- Strengthening multilateral junctions
- Sealing casing leaks
- Zone abandonment
- Dump-bailer operations
- Water conformance
- Through-tubing plug and abandonment.
As energy companies search for hydrocarbons in increasingly harsh environments, new problems with zonal isolation and production are encountered. These problems can cost operators millions of dollars in repairs, and can even force the abandonment of potentially productive wells. The WDR system can help prevent such incidents by stabilizing unconsolidated wellbores and formations, allowing operators to place conventional cement systems without creating formation fractures or experiencing lost-circulation problems.
Authors
Larry Eoff is a Principal Chemist II in the Conformance Group at the Halliburton Energy Services Technology Center (Duncan, Oklahoma). He has been with Halliburton for seven years in conformance and cement product development. He holds a BS in chemistry and a PhD in organic chemistry.
Anthony Badalamenti is the Zonal Isolation PSL Global Products Champion for Wellbore Stabilization. Since joining Halliburton in 1979, he has held various engineering, business-development, and supervisory positions. He holds a BS in civil engineering and a BA degree in liberal arts. He holds patents in cementing processes, tools associated with cementing, and sand-control services.
