|Ultra-lightweight hollow glass sphere slurries exhibit densities less than water
Many deepwater operations, especially in the Gulf of Mexico (GOM), are characterized by unique conditions that require high-strength, lightweight cements capable of withstanding cycling stresses for extended periods of time. An industry survey conducted in 1997 revealed that the average failure rate of cementing jobs was 15 percent, that industry spends an estimated $470 million per year to repair cementing failures, and that one third to one half of these failures could be prevented with an effective lightweight cementing system. Data also indicates a continuing problem in maintaining a long-term seal with conventional cementing systems. The U.S. Minerals Management Services estimates that 11,000 out of 14,000 producing wells in the GOM have gas pressure on one of the annuli. The use of ultra-lightweight cementing systems could improve well performance by enhancing zone isolation and reducing cementing failures.
Conventional lightweight cements typically use water to decrease density, and include materials that absorb the water and keep the slurry and cement homogenous. These cements, though low in cost, exhibit very low compressive strengths and have difficulty providing long-term zone isolation under severe stress conditions. In addition, they have a minimum density limit of 11.5 lb/gal. Conventional hollow glass spheres have been used to achieve densities as low as 9.5 lb/gal, however, they are limited in application because of the low crush strength of the beads under pressure. Foamed cements (using nitrogen) are employed to prevent lost circulation in low-pressure reservoirs, but have high permeability and low strength, resulting in cementing failures. Additional limitations with foam cements include higher friction in the well (which can lead to lost circulation), difficulty in controlling the cementing job, and the inability to measure bond strengths with sonic and ultrasonic evaluation tools. Despite these problems, foam cement slurries are the industry preference for attaining acceptable densities during critical cementing operations. Although lightweight hollow spheres have been used in the industry for some time, recent technology advances have improved the hollow spheres to be ultra-lightweight, while exhibiting superior crush strengths of 3,000 to 10,000 psi. These ULHS can attain a specific gravity of as low as 0.32 to 0.46 while resisting wellbore pressures as high as 6,000 psi.
Cementing Solutions, Inc. (CSI) – Project management and all research products
ExxonMobil Corporation – well data and/or product specification requirements
Shell Oil Company – well data and/or product specification requirements
BJ Services – well data and/or product specification requirements
Halliburton Energy Services – well data and/or product specification requirements
Schlumberger Inc. – well data and/or product specification requirements
3M Corporation – ULHS supplier
TXI – cement supplier
Chandler Engineering Company, LLC – testing equipment
Houston, TX 77073
The results of this project have provided a significant impact on the oil and gas industry. The use of ultra-lightweight hollow spheres (ULHS) provides operators the ability to reduce the weight of the cement, increase its strength and make it easing to pump and set the cement in place, in turn providing a much better seal in the annulus. This helps to reduce the safety and environmental hazards associated with cementing failures, which has been identified as a major problem in the GOM. The development of this ultra-lightweight cement will also provide significant benefit to drillers in low-pressure or depleted gas and oil fields as the reduced weight will help to avoid fracturing of the formations during cement, which would lead to lost circulation and failure of the cementing job. The ULHS systems are also beneficial in the sealing off shallow water flows, which is a major challenge in deep water drilling.
- Demonstrated that ultra-lightweight cement slurries using ultra-lightweight hollow spheres (ULHS) provide higher compressive strengths at lower densities and outperform conventional lightweight cement slurries in long-term durability,
- Demonstrated that ULHS cement slurries can be blended and pumped in the field without problems,
- Transferred technology to industry through publications, meetings and workshops, and
- Developed an electronic decision support tool, SmartCement to help operators choose the most cost efficient low-density cement system.
The project team for this effort included operating companies, service companies, and materials and equipment suppliers. Tests were designed based on conditions drawn from more than 5,000 data points from field jobs in the U.S. supplied to CSI by service companies. CSI used these data to determine the conditions under which lightweight cements are most commonly used, as well as to define the type of operations currently being performed in deepwater wells.
In addition to standard testing of cementing slurries containing ULHS, CSI performed a unique combination of tests to measure a slurry’s ability to withstand formation stresses over long periods of time. Although the mechanical properties of formations are commonly tested, the same mechanical properties tests are not commonly used to test cement. Triaxial load was applied to the samples to simulate wellbore conditions, and the samples were also tested for Young’s modulus and tensile strength. Stress cycling tests were also performed to ensure that the ultra-lightweight cement slurry could withstand the changes in temperature that occur within deepwater wells. Stress cycling within a well can cause the cement-to-pipe bond and ultimately the cement seal to deteriorate.
Test results using the ULHS slurry indicated that the slurry could withstand cycling temperature changes of 135°F. Additionally, special test cells were designed to test the cement’s shear bonding capability in both the hard formations typically found on land, as well as in the soft formations common to deepwater wells in the Gulf of Mexico (GOM). In both cases, test results indicated that the ULHS slurry could withstand a differential pressure stress of 5,000 psi.
Two field tests were designed to test the slurry’s performance in actual formations. The first field test, performed on a South Texas well operated by Conoco, was designed to ensure that the slurry could be easily blended, mixed, and pumped on location with little trouble. The second field test, performed on a well operated by the Rocky Mountain Oilfield Testing Center (RMOTC) in Wyoming, was designed to test the slurry’s performance in a land-based well that closely resembled deepwater operations. The slurry was easily blended on location, one hundred barrels of the ultra-lightweight cement slurry (using 3M 6K ULHS beads) were pumped with no problems, and the ULHS beads showed no breakage after one hour of conditioning at the surface. Ultrasonic logs performed on the well after the cement operation showed excellent application of the slurry, good bond properties, and good perforating qualities.
Current Status and Remaining Tasks:
This project has been completed. ULHS beads are available for use by service companies. SmartCement is available at no charge, upon request. The final project report is available below under "Additional Information".
Project Start: September 14, 2000
Project End: July 31, 2004
DOE Contribution: $800,038
Performer Contribution: $994,150
NETL – Gary Covatch (firstname.lastname@example.org or 304-285-4589)
CSI – Fred L. Sabins (email@example.com or 713-957-4210)
Final Report - July 2005: Ultra-Lightweight Cement [PDF-25947KB]