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№ 1 (January 2010)

Ultra-Lightweight Hollow Glass Spheres Improve Performance in Underbalanced Drilling

   Today many oil and gas fields around the world enter the early stages of depletion after years of continuous production. This, in turn, potentially prevents the maximum recovery from such fields.

By Pavel Lazarev, senior technical service engineer, 3M

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   Economic factors and the need to sustain current production levels force oil and gas producers to search constantly for new technologies which would ensure more efficient and more rational production of hydrocarbons.

   Drilling at negative differential pressure, or underbalanced drilling (UBD) is one such technology, accepted and widely used in many regions worldwide. The UBD technology allows producers to drill new wells in older, low-pressure beds, being in essence an intentional drilling of a well with a dynamic hydrostatic head lower than the formation pressure. The negative differential pressure occurs when the pressure in the drilled well is sustained at a level lower than the surrounding formation pressure or static formation pressure. That is why underbalanced drilling increasingly becomes an efficient option for many fields where depletion reaches a point when the pressure in the pay bed formation falls dramatically. Below this level a producer must switch to some kind of lightened drilling mud with the density lower (mainly below 1 g/cu. cm) than the pay bed pressure. The methods to produce lightened drilling muds in order to achieve negative differential pressure include addition of gas, air or foam, as well as creation of hydrocarbon emulsions, etc. Such muds allow maximum recovery while minimizing the mud loss and the pay bed damage, but they also have a few significant shortfalls.

   The limitations that characterize the aerated drilling muds technology can be overcome by the addition of hollow glass microspheres 3М Glass Bubbles to the base drilling fluid. This alternative approach improves the low-density drilling mud, making it incompressible and light. The 3М Glass Bubbles are single-cavity, sodium-borosilicate glass, chemically inactive hollow spheres with high water, temperature and pressure resistance (Fig. 1). The ideal spherical shape of 3M Glass Bubbles provides a number of useful properties, including better fluidity and lower viscosity of the solution, whereas good durability/density ratio ensures high resistance to harsh conditions inside the well. Hence, unlike the aerated drilling muds, which are multiphase fluids (liquid and gas), usage of 3M Glass Bubbles eliminates the need for the gas phase by providing a hydraulically simple, incompressible, single-phase liquid.

   Technological simplicity is the key advantage of the 3M Glass Bubbles microspheres. 3M Glass Bubbles-based drilling muds can be used in beds with low formation pressure, and have a range of other attractive properties:
Incompressible fluid;
Stable density characteristics;
Excellent borehole cleanout;
Borehole stability;
Achievement of drilling conditions at negative differential pressure;
Reduction of a pressure differential;
Improved rate of drilling (ROP);
Reduction or elimination of drilling mud loss;
Lower formation damage.

   It should also be mentioned that 3M Glass Bubbles microspheres can be added to reduce density in virtually any type of existing drilling muds. In other words, the low-density mud is more or less independent from the liquid phase and technically can be made on fresh water, marine water, diesel fuel or any other mud base. Essentially 3M Glass Bubbles microspheres expand the single-phase liquid density window to the levels usually achieved by means of aeration technology.

   The use of hollow glass microspheres in drilling muds creates unique opportunities. The field tests, held in recent years in the United States, India, China and other countries, have proven that microspheres reduce drilling muds density in difficult operating conditions. In Russia this method was first tested in 2008–2009 where a horizontal section of a well was drilled in a field in West Siberia. The test confirmed that 3M Glass Bubbles microspheres can successfully keep mud density levels within the allowed range (below 0.95 g/cu. cm) at affordable cost, proving its efficiency, convenience and reliability while performing the task.

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