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Accelerators may be used in oil well cementing to reduce the required waiting time for cement to set and develop sufficient strength, especially at low temperature conditions (such as cold weather or subsea). Traditional cement accelerators mainly include inorganic salt such as CaCl2 and NaCl. In recent years, nanomaterials, especially nano C-S-H and nano silica, have also been shown to be capable of accelerating cement hydration. These nanomaterials also tend to have the additional benefit of reducing the permeability and increasing the mechanical strength of cement-based materials. This study investigates the feasibility of using nano silicas as cement accelerators in low temperature conditions and their effect on the mechanical properties of oil well cement during early ages.
Isothermal calorimetry, which measures the heat evolved from chemical reactions, is among the most effective methods to evaluate the effect of different additives on the hydration kinetics of cement. In this study, the heat evolution of the Class H cement with and without nanomaterials was measured by isothermal calorimetry at 59 °F. The nanomaterials used here mainly include different types of nano silica. Other materials such as lithium silicate and nano C-S-H were also studied for comparison purposes. The main variables studied were the dosage, size, and shape of the nano-silica. The effectiveness of the nanomaterials as accelerators was evaluated by comparing test results with those obtained with the traditional accelerators.
Test results show that the low-temperature hydration of oil well cement is accelerated with the addition of nano silica. Smaller silica particles tend to enhance the acceleration effect. In terms of increasing the rate of cement hydration reaction, the effectiveness of nano silica is relatively modest when compared to the traditional accelerators. However, in terms of enhancing mechanical strength, certain types of nano silica are capable of providing comparable results with the traditional accelerators.
A dependable method for converting fluid into a cementitiuos slurry has been sought for many years. Recent advancements in copolymer technology have made it possible to introduce Portland cement directly into drilling fluid while maintaining control over the rheology of the resultant slurry. For purposes of brevity, converted drilling fluid as described herein will be referred to as mud-to-cement, or MTC.
Conversion of drilling mud into a cement slurry has several unique advantages. As examples, conversion of spent drilling mud reduces disposal costs. Secondly, the superior compatibility into MTC significantly improves annular displacement efficiency by controlling the flocculation that normally results when drilling mud and cement contact. Thirdly, MTC makes the most benefit of manpower, equipment, time and materials by consolidating services at the rig site.
Consolidation of drilling mud and cementing technologies to cut costs while improving the quality of completions is the underlying topic of discourse in this paper. In addition to presentation of the slurry design paper. In addition to presentation of the slurry design process, laboratory data, mixing and handling concepts process, laboratory data, mixing and handling concepts and case histories are discussed. Also, several important avenues of potential savings are suggested. Applications in a variety of locations using different types of completions have all been successful both operationally and from the standpoint of results.
The basic purpose of cementing a wellbore is to return the annulus to as near the original state as possible. In general, this means removal of all drilling mud from the annulus and replacement with a contiguous cement sheath. Cement should provide at least four basic functions: (1) zone isolation, (2) casing support, (3) formation support, and (4) casing corrosion protection. The more complete the removal and replacement process, the more complete will be the provision of process, the more complete will be the provision of these four required functions. It is in this critical removal replacement process, however, that convention all cementing practice has often failed. The reason for that failure can be best explained as follows. Drilling mud and cement slurry are incompatible and formed a gelled mass when intermixed. Therefore, conventional cementing practice usually calls for a preflush or spacer fluid to separate mud and cement. preflush or spacer fluid to separate mud and cement. However, some spacer fluids available on today's market are incompatible with either mud or cement. Many spacer fluids are overwhelmed when all three slurries are commingled. A good spacer should have the dispersion power necessary to reduce the viscosity of such mixtures back to a level near that of the original fluids involved. Otherwise, large quantities of clabbered or severely gelled mixture will remain in the annulus. As a result, expensive remedial cementing is often required to correct inferior primary cementing applications.
To reduce the problems associated with mud and cement incompatibility into a cementitiuus slurry has been developed. Converting drilling fluid into a cement slurry has been a topic of research for many years. IN 1970, a Portland cement based formulation was introduced by Wyant et al., but it had a complex formulation, was very sensitive to temperature, and did not incorporate an adequate dispersant. Even so some field applications were done. Another formulation employing a magnesium based drilling fluid was introduced by Miller et al. in 1975.
Summary Accelerators are important cementing additives in deepwater wells where low temperatures can lengthen the wait-on-cement (WOC) time, potentially increasing the cost of operations. The cement-set accelerators traditionally used for shortening WOC times are inorganic salts, such as calcium chloride (CaCl2). These accelerators are known to have the potentially negative side effect of increasing the set-cement permeability. Nanosilicas, on the other hand, can be advantageous compared with conventional cement-set accelerators because they reduce the permeability and increase the mechanical strength of cement-based materials. For this reason, nanosilicas are known to be particularly good candidates as replacement materials for traditional salt accelerators. This study investigates the feasibility of the use of different sizes and aspect ratios of nanosilicas as cement hydration accelerators under low-temperature conditions of 59°F (15°C). The nanosilica activities are herein defined through their comparative advantages with respect to traditional accelerators, as well as through the advantages and disadvantages of the different nanosilicas resulting from their various sizes and shapes. Although hydration of oilwell cement is known to be accelerated by the addition of nanosilica, the effects of nanosilica particle shape on cement hydration kinetics has not been previously investigated. The isothermal calorimetry experiments conducted in this study reveal that just as smaller nanosilica particle sizes increase the cement-set acceleration, so do higher nanosilica aspect ratios. The effects of slurry density on the relative merits of CaCl2 and nanosilicas are also investigated. In regular-weight slurries, the effectiveness of nanosilica acceleration appears to be weaker than that of CaCl2, especially during early ages (≤ 3 days). In lightweight slurries, the effectiveness of nanosilica acceleration can be much stronger than that of CaCl2, especially when mid- to long-term properties (≥ 2 days) are considered. Smaller particle sizes and higher aspect ratios enhance the acceleration effect of nanosilicas. The compressive-strength development of lightweight oilwell cements with and without accelerators was also investigated. Lightweight cements accelerated with nanosilica displayed 7-day compressive strengths up to 136% higher than those accelerated with CaCl2.
To increase the safety and productivity of underground coal mines, the U.S. Bureau of Mines, through an in house research project beginning in lg75, demonstrated the feasibility of using fast setting hydraulic cements for grouting coal mine roof bolts. The Colorado School of Mines was funded through the Spokane Mining Research Center to select, test, and demonstrate inorganic cements for this application. A grout composed of gypsum cement and potassium sulfate accelerator was selected as having the best properties for roof bolting. This grout is rapid setting, and reaches the yield strength of roof bolts in about three minutes from the time of mixing the cement. This cement system was found through testing of a variety of cements in combinations with several types of accelerators through a series of laboratory tests. The laboratory tests consisted of penetration, shrinkage, cube strength and pull strength tests. Field tests were conducted in Sommerset Mine of the U.S. Steel Corporation. Two intersections were used to test and demonstrate the cement-grouted bolt system. One intersection was supported with only cement-grouted bolts and an adjacent intersection with resin roof bolts in the same bolting pattern. These two intersections were instrumented to measure roof parting. It was found that the roof sag was essentially the same with a magnitude of less than .6 inches for the two intersections. Field visual inspection of these intersections was also conducted and no apparent differences were found. On the basis of this successful field demonstration further testing and development of production installation methods is recommended. Also additional testing will be required before government approval can be expected.
This paper will establish the role of cement roof bolt grouting in coal mines by a brief discussion of rock bolting in general. Then the procedure and results of the cement grout project will be described. A more detailed compilation and analysis of the laboratory and field testing can be found in the final report to the U.S. Bureau of Mines, available soon from the National Technical Information Service.
The object of rock bolting is to bind together a discontinuous rock mass to increase the stability around an underground opening. Two types of action have been attributed to rock bolts: