One of the most demanding materials in the present times is Cenosphere. Cenospheres are lightweight, inert, hollow, waterproof, rigid, and hard materials that can be used to produce a new class of engineering composites. They are 60% - 70% lighter than other substances due to their free-flowing, hard-shelled, and hollow structure. They are filled with air or inert gases and produced as coal combustion residuals (CCRs) at thermal power stations. The density of the Cenosphere is around 0.4–0.8 g/cm3 (0.014–0.029 lb/cu in), which enables high strength and workability in it. The size of the Cenosphere varies from 5 - 500 microns, the bulk density has a range between 0.3 - 0.6 g/cc, and its moisture absorption capacity is less than 2.5%. Cenosphere is known for specific heat capacity which is 0.28 Cal/g and its hardness is measured around 5-6 Mohr scale. The melting point of the Cenopshere ranges between 1250 - 1450 degrees Celsius and the coefficient of thermal conductivity is 0.09W/mK.
The combustion of stone-cold provides 41% of electricity to the whole world. A forecast report mentioned that by 2030 there will be an increase of 44% use of stone coal all around the world. China leading all the countries have 68wt% re-use of the coal residue. Russia and Europe following the trend have 25wt% and 15wt% reutilization of solid waste in their respective countries. Stone coal generates a significant amount of solid waste when burnt in proper conditions. When the coal is burnt, there is a dispersion of alumina-silicates in a diversified spatial form which is also known as Cenospheres. The developed countries that are technically advanced have proper management of stone coal waste residue. Cenospheres are abundant in alumina, quartz, and hematite minerals. They have 90 percent of all these minerals which enables them to be replaced by the conventional substances used in various industries. The cenosphere has a very high temperature with very high electrical resistivity (R=2.26*108Ω). This enables the nature of the Cenosphere to be highly porous with a negligible mass loss.
The primary constituents of the Cenosphere are sillimanite, dipotassium oxide, magnesium oxide, and rutile which makes it commercially utilizable. Cenospheres can be used in lightweight aggregates, cement production, concrete production, reinforced plastics, and other miscellaneous purposes. Cenospheres are useful in various industries but they are of utmost use in Oil & Gas Industry. The specific density of the Cenosphere lies in the range between 0.4–0.8 g/cm³ which makes it extraordinary light. This characteristic of the Cenosphere is used to solve the problem of drilling fluid density adjustment.
The presence of aluminosilicate particles in the Cenosphere is used to enhance the efficiency of drilling equipment and extracting oils from wells. For the oil extraction and drilling process, higher size particle distribution is required. An ideal Cenosphere has a particle size distribution between 0.001mm - 0.010 mm. The good quality Cenosphere has a range between 0.065mm to 0.160mm which entangled air inside rigid spheres. Since Cenosphere has a good density regulator their main usage is operating solid slurry and drilling fluids for oil extraction. In 1996, Mobi Oil Company became the first company to drill two wells by using Cenosphere. They use 10∼20% of the cenosphere with 21 Mpa of compressive strength and 0.8 kg/m3 of density to drill the wells. Later countries like Russia and the United States also started to use Cenosphere as a low-density oil-base drilling fluid and by the year 1990s, it started to gain worldwide attention. In the year 1999, Petra Buildcare products, India established the first high-equipped production plants for generation of consistent quality of Cenosphere and it currently leads the market with 6 high-end plants all across India. Recently in 2010, Shenyang Number 289 Well used Cenosphere as a drilling fluid. Their daily yield increases from 40.7 t to 74.6 t yet their maintenance cost was low. Cenospheres have replaced the conventional coal seam as they have a low-pressure coefficient. Cenosphere on the other hand exhibits excellent results in problems related to water-based density adjustment. It is further used for good reservoir protection effect and bearing pressure in bubble type of drilling fluid. The cenosphere enhances the rheological properties of drilling fluids. It has low filter loss, good density adjustments, excellent performance to protect the reservoir, and a good recovery rate.