Gulf of Mexico operators have used Halliburton’s SeaQuest stimulation service in fracturing treatments for over a year.
The trend for high-permeability offshore fracturing systems has reduced treatment fluid damage while maintaining the viscosity and thermal stability needed to perform the job, the company says. As the industry moves farther offshore into deeper water, operators place higher demands for a successful job on fracturing fluids.
In the production enhancement area of oilfield completions, there is a balancing act between gel performance and gel damage. Typically, a gel performs better when it has a high viscosity, yet the oil and gas industry associates a higher viscosity with more gelling agents and more gel damage. An all-too-familiar approach in stimulation and sand-control treatments is the compromise of completion efficiency from the less than adequate frac geometry with lower gel loading or reduced treatment sizes to avoid damage from fluids. Fracturing fluids can reduce completion efficiency by lowering the conductivity of the proppant pack when unbroken gel or insoluble polymer residue from broken gel remains in the formation. Reducing the gel loading can cause less damage, the company explains, but a loss in fracture inflow capacity due to the reduced geometry resulting from a loss in viscosity of the fracturing gel negates that gain. Lowered fluid viscosity and smaller treatments can lead to the potential loss of completion efficiency from a stimulation standpoint, which can result in lower producing rates.
SeaQuest stimulation service contains an advanced breaking system that Halliburton can tailor for temperatures in offshore environments. The proprietary breaker system can break the crosslinked gel back to the viscosity of water and can do so in a controlled manner, which assists in a fast cleanup following a stimulation treatment. Higher temperatures require additional gel loading to increase thermal stability. Heavily loaded gels can be difficult to break back to the viscosity of water, causing damage to the proppant pack. Halliburton says its SeaQuest fluid uses various proprietary low-temperature and high-temperature oxidizing breakers to cover the temperature ranges seen offshore around the world.
SeaQuest stimulation service requires 20% lower gel loading than standard crosslinked fluid systems for the same temperature range while maintaining viscosity and thermal stability, the company says. Optimizing the system chemistry as well as the selection of gelling agents attains sustainable reduction in gel loading. Halliburton is pleased with the fresh approach to focusing on the entire fluid system instead of just the viscosifier.
The industry long has associated gel loading with thermal stability of a fracture fluid. With conventional fluids, the higher the bottomhole reservoir temperature, the heavier the gel loading needs to be to yield adequate thermal stability. SeaQuest fluid can maintain thermal stability despite the lowered gel loading and has shown some improvement above its counterpart systems in the field, the company says. SeaQuest fluid can be used in temperatures up to 300° F.
One aspect of measuring the performance of a fluid in fracturing stimulation treatments is the measure of net pressure increase. Net pressure is the pressure developed in the treatment that exceeds the formation stress pressure. The industry considers it a representative of the fracture width achieved. SeaQuest fluid has improved net pressure gains even though the fluid has reduced the gel loading.
Through its chemical optimization, SeaQuest fluid also is tolerant of variances that occur in the field, such as water quality, hydration times, and pH levels. Halliburton’s stimulation vessels use filtered seawater and the InstaVis system for on-the-fly fluid mixing and rheology control without waiting. The standard formulation includes the addition of NaCl to the seawater giving adequate clay control for the majority of formations. Halliburton formulated SeaQuest fluid specifically for seawater mixing to give enhanced frac fluid properties, controllable break characteristics, and improved cleanup without damaging precipitation of minerals.
SeaQuest fluid offers a high tolerance to changes in pH that would normally have a substantial influence on the viscosity of conventional fluid systems, the company says. Variations in pH can cause many other fracture fluid systems to exhibit either under- or over-crosslinking under downhole conditions. The problems associated with negative effects of pH variation can all translate into the reduced capability to create the propped frac geometry needed for the most effective stimulation of reservoir production.
Operators have selected SeaQuest service for more than 100 well treatments offshore in both the shelf and deepwater GoM and in deepwater West Africa.
DOT 2004 sets new record
PennWell’s 16th Annual Deep Offshore Technology International Conference and Exhibition in New Orleans in November brought in its largest ever attendance, reflecting growing participation from India, the Middle East, Mexico, and China as the need for deepwater knowledge expands around the globe.
Pennwell recognized the following people with 2004 DOT awards:
• Cindy Bowline of FMC Sofec Floating System Inc. won the Best Technical Presentation award for her paper “Understanding Fatigue for Deepwater Mooring Systems - The Footprint of Fatigue”
• Doug Korth of J. Ray McDermott won the Best Presenter award for his paper “Learning from EPCI Spar Projects”
• Julian Soles of GlobalSantaFe won the George Murray Memorial Young Engineer award for his paper “On-board Generation of Alert Offsets for Dynamically Positioned Vessels.”
This year’s host, BHP Billiton, passed conference sponsorship to Petrobras, which will host next year’s DOT in Vitõria, Brazil, Nov. 8-10.