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Abstract Hollow-glass microspheres (beads) are widely used during oilwell cementing operations to produce lightweight cement slurries; this paper discusses a new method of blending hollow-glass beads into cement slurries by creating a storable liquid suspension of hollow-glass microspheres (liquid beads). This new method enables efficient delivery of lightweight cement slurries in offshore and remote locations by eliminating bulk-blending logistics. The concept of liquid beads is not new; however, earlier attempts to develop liquid beads or similar products generally failed to address the storability problem. The buoyancy force tends to lift the beads to the surface of the suspension, forming a gel or crust and causing the mixture to lose flowability within a relatively short period of time. A special chemical-additive package developed in this study significantly extends the storability of liquid beads. This paper compares the gelation time of different liquid-bead formulas and evaluates the performance of cement slurries prepared with liquid beads. Laboratory test data show that the chemical-additive package developed in this study can extend the storage time (shelf life) of liquid beads from a few hours to at least one month without reagitation at room temperature; the shelf life can be further extended to at least one year with regular reagitation of the mixture. Cement slurries prepared with dry-blended beads and those prepared with liquid beads exhibit similar performance in terms of laboratory test results, such as free fluid, fluid loss, thickening time, and hydration kinetics. The liquid-bead system developed can be produced with cement batch mixers for field use and remain stable in tote tanks for at least several months with regular recirculation. Liquid beads can be added to cement slurries through liquid-additive pumps during a cementing operation. A novel liquid-bead product that can be stored for extended periods of time without separation is presented here along with necessary laboratory testing, actual field applications, and field-application case histories using liquid beads to produce low-density cement slurries.
Remedial cementing requires as much technical, engineering, and operational experience, as primary cementing but is often done when wellbore conditions are unknown or out of control, and when wasted rig time and escalating costs force poor decisions and high risk. Squeeze cementing is a "correction" process that is usually only necessary to correct a problem in the wellbore. Before using a squeeze application, a series of decisions must be made to determine (1) if a problem exists, (2) the magnitude of the problem, (3) if squeeze cementing will correct it, (4) the risk factors present, and (5) if economics will support it. Most squeeze applications are unnecessary because they result from poor primary-cement-job evaluations or job diagnostics. Squeeze cementing is a dehydration process.
A newly built mobile cement-testing laboratory assists in monitoring blended cement quality and design. The unit contains the equipment required to perform tests for oilwell cements described in API's Spec 10. Case histories are presented describing how use of the mobile cement laboratory improved cementing success on critical cement jobs.
Cementing practices, equipment, and materials have changed as wells have become deeper and technology has advanced. Many cementing systems have been devised. The number of different systems that can be designed by varying the components is almost endless. The pumping time of a cementing system is controlled by the class of cement, the well temperature and pressure, and the type and amounts of additives. In 1939, the first pressure/temperature thickening-time tester was developed, enabling, the industry to forecast slurry performance accurately. Proper "aboveground" density is essential to the successful accomplishment of any well-cementing operation. Only a small amount of water (about 25%) is necessary for cement to set satisfactorily. More water must be added, however, for the cement system to be pumpable. Mixing and pumping equipment has evolved continuously over the past few years. Unfortunately, maintaining slurry density during, cement jobs is still a problem. Cement is usually handled in bulk form, In most cases, additives can be blended with bulk cement to suit any well condition. To achieve success. critical cement-jobs require accurate testing in the laboratory, proper blending of the cement and additives, and correct mixing of the slurry to designed density. A gamut of pilot tests must be run to ensure a good slurry design. After the system has been blended, samples also must be tested. Many oil companies depend solely on the cement service companies to meet these criteria. Chevron, however, has developed a cooperative testing program that works closely with the service company field and laboratory personnel. This program relies heavily on monitoring the quality and performance of cement and additives. Using this program, Chevron and the service company can verify the slurry performance. Over the past few years, a number of major oil companies have experienced situations in which pilot test and blend sample test results did not correlate. Some companies are willing, to accept a 40% variation in thickening time between the pilot and blend tests. In 1982, we implemented a field study to evaluate service companies' blending equipment and procedures. The following recommendations resulted from this study: (1) layer the cement and additives, (2) weigh additives on a close tolerance scale, (3) move the cement a minimum of six times before samples are taken, and (4) obtain accurate (representative) samples while the blend is going to the tank in which it will be transported to the rig. Very close correlation between pilot and blend sample tests was achieved with the implementation of these recommended procedures. While developing these recommendations. we observed a long period between blending, of the cement with additives and testing of the samples. Although the samples were "hot shotted" to both the Chevron and service company laboratories, in most cases, the cement was on location before testing of the blend samples began. In the past, other methods of analyzing cement blend samples. such as a chemical analysis, have been attempted, but none provided the accuracy of a thickening-time test on a high-pressure, high-temperature consistometer. Because of the time required to ship samples and inadequate alternative testing methods, a full-scale testing laboratory with the ability to operate at remote wellsites or service company blending facilities was needed.
We designed the mobile cement-testing laboratory with the following objectives: (1) equip a self-contained vehicle with equipment that would reliably perform thickening-time. fluid-loss, free-water, and rheology tests on cement slurries for critical casing strings on any well: (2) to provide living accommodations for two people on location: (3) to provide reserve capabilities; (4) to be within the weight limitation of the vehicle: (5) to meet safety requirements; (6) to provide access to laboratory equipment for maintenance and service: (7) to provide for the calibration of the testing equipment; and (8) to be cost-effective.
Abstract Lightweight cements offer significant performance benefits over conventional higher density cement blends, including; improved mechanical properties and stress resilience, lower thermal conductivity, lower ECDs and improved returns to surface and potentially lower risk of casing collapse due to trapped annular pressure. However, a number of challenges exist in developing lightweight blends for thermal applications specifically concerning achieving short wait on cement at low bottom hole static temperature while also ensuring long-term chemical and mechanical stability at high temperatures. Here we report the development of a new lightweight thermal cement by utilizing hollow glass microspheres. Further fine-tuning of the desired slurry properties including controllable thickening times, zero free water, low fluid loss and short WOC was achieved through cost-effective additive adjustment, and the mechanical properties of the cement we validated by long term curing at both ambient and high temperaures (340 °C). To ensure that the high performance achieved in the controlled lab environment was maintained once deployed at full-scale field level an extensive QA/QC program was undertaken. This process involved collecting dry bulk field samples and confirming performance (thickening time, free water, rheology and fluid loss) prior to every job. After initial optimization of the blending process, a 100% success rate was achieved over the course of a more than a twenty jobs. Overall, a high quality lightweight thermal cement with excellent long-term mechanical properties was successfully developed and deployed.