HP/HT tools improve cementing under full range of conditions
By Hank Rogers, Eric Snell, Earl Webb
Halliburton
Recent case histories demonstrate effectiveness
Relatively new, tested float equipment has been designed to perform reliably in the harshest downhole environments for tough cementing jobs under a full range of conditions, including deep wells, extreme temperatures, and extreme pressures.
All of the equipment involved in the Halliburton Super Seal II high-pressure/high-temperature (HP/HT) system meets or exceeds the American Petroleum Institute RP-10F IIIC rating. To qualify for the industry's toughest standard, the equipment had to endure a 24-hour flow of 10 bbl/min with a 2% to 4% sand-laden 12-12.5 lb/gal mud and withstand a 5,000-psi backpressure or an 80% casing burst pressure, whichever is smaller, after an eight-hour, 400°F heat soak.
In addition to these performance capabilities, the equipment is PDC drillable. This is possible because all components in the poppet assembly are chosen to meet performance requirements while maintaining drillability. The equipment was designed for most casing sizes, grades, and threads.
Two recent case histories demonstrate how the float equipment can be custom-designed for cementing strings and produce economic benefits.
Case histories
A South Texas well experienced major problems when the floating equipment failed downhole, costing the drilling company $1.2 million in lost time and associated expenses. To keep from repeating this major failure, the company used Halliburton's Super Seal II on the next well.
Because cementing would take place under the same HP/HT conditions, this floating equipment was recommended. Equipment was circulated for 55 hours with a bottom hole circulating temperature above 450°F and a bottom hole static temperature over 500°F. Hole depth was 16,500 ft with a final circulation pressure of 6,800 psi.
Despite these extreme conditions, the equipment performed to specifications. The project also included a new, high-wiping efficiency (HWE) cementing plug to meet the requirements of deeper, more hostile reservoirs. This plug provides a greater wiper-contact area for improved wiping efficiency. Additionally, the HWE plug is designed to work in the most hostile service environments with extreme temperatures, pressures, and fluids requirements.
Another example
In another instance, a major oil company faced a serious dilemma when performance requirements for a well it planned to drill in the Gulf of Mexico exceeded the capacity of other casing equipment. Because these well requirements were at the high end of the equipment range, qualification of the floating equipment through rigorous pressure testing was performed at the Halliburton research facility in Duncan, Oklahoma. With representatives present, a 2 3/4-in. float assembly and a 7-in. float collar were subjected to 10,000 psi for 3 hours and 15 minutes at temperatures ranging from 390°F to 400°F with no pressure loss.
The bottom plug includes a rupture disk rated to 750 psi to ensure against premature rupture.
An examination of the parts after the test showed no evidence of fluid on top of the concrete, indicating zero leakage of the poppet valve and the lower sealing seat. The cement bore above the poppet was also intact, and the throat of the tested collar displayed no noticeable cracks or fractures.
These results demonstrated that the poppet valve with its sealing arrangement could provide a leak-free check valve assembly at pressures and temperatures up to 10,000 psi and 400°F.
Success in the field
Because casing was being cemented near the top of a high-pressure zone, the float equipment was placed at the end of the casing in the form of two, double-valve assemblies. After the casing was cemented in place, the shoe joint was drilled out down to the float equipment to make room for perforating guns. In this situation, the float equipment acted as the primary barrier between the newly opened casing inside diameter (ID) and the high-pressure zone below.
Equipment was circulated for 7 hours and 30 minutes with a final differential pressure applied to the floats near 9,000 psi with a bottom hole circulating temperature of 330° F and a bottom hole static temperature of 380° F. The large differential pressure was caused by a change in the drilling fluid from over 18-ppg to 9-ppg brine for completion operations. Hole size was 8 1/4-in. with 6 5/8-in. casing. Hole depth was near 18,000 ft.
The equipment performed to specifications, allowing the driller to proceed with a well that might not otherwise have been drilled.
HWE cementing plugs
This class of cementing plug was developed to provide an economical alternative that could be employ in a full range of HP/HT environments. For wiping efficiency, the HWE plug includes a deep-cup design to increase the wipe-contact area while enhancing wear resistance. Rubber and plastic content were reduced to help increase drillability, and the plug contains no metal components.
The bottom plug includes a rupture disk rated to 750 psi to ensure against premature rupture. After rupture, the flow area is full bore. The plugs are completely compatible with the floating equipment. They are available in a range of sizes from 4 1/2-in. to 13 3/8-in. and can be used with both water or oil-based drilling fluids.
Field results
The HWE plug was field tested on four 4 1/2-in. jobs in South Texas and on a job in Indonesia. Each of these wells was displaced at an average rate of 10 bbl/min. Typical fill on top of the wiper plug with previous cementing-plug designs ranged from 70 to 100 ft. On two of the South Texas test wells, the HWE cementing plug produced no fill at all. On the other two, levels of fill were 5-ft and 8-ft, respectively. The highest level recorded was 19-ft on an Indonesia job, an improvement over previously recorded fill levels.
Eliminate bit trips
An operator in northwest Louisiana ran into difficulties when significant amounts of fill accumulated on top of the plug. Because the problem was caused by debris not being properly scraped off the casing, the HWE cementing plug was used. With this change, the job proceeded successfully. The plug improved wiping efficiency by providing a greater contact area, dramatically reducing the amount of fill and eliminating the need for a bit trip. Savings are estimated at $8,000.
