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Tech Trends

Crystal ball for under-balanced drilling3M’s Hollow Glass Spheres were adopted by PetroChina foruse in an under-balanced drilling project in the Sichuan Basinin April 2007. The lightweight glass spheres were blended intoa water-based mixture to produce drilling fluids with densitiesof 0.9 g/cc, targeted at under-pressured or depleted reser-voirs. High formation temperatures and pressures, a tendencyfor borehole collapse, borehole deviation, poor drillabilityand low drilling speed have long hampered gas prospectingand production in this region.

To raise productivity, the operator undertook a major proj-ect to evaluate the use of hollow glass spheres (HGS) indrilling fluids for the first time in China, at the Guang An gasfield in the Sichuan Basin. The target well, Guang An 002-H1is the longest horizontal well in the basin, with a horizontal sec-tion stretching approximately 6,562 ft (2,000 m).

The exercise optimized well parameters by designingdrilling fluids to manage the pressure differentials in theformation, thereby reducing formation damage. As aresult, the well recorded a threefold increase in productiv-ity over that of the vertical wells in the region. This is duein part to the non-invasive nature of the drilling fluid whendrilled under-balanced.

Hollow glass sphere-based drilling fluids are non-compress-ible fluids with stable densities across the well bore that allowfor managed-pressure drilling in low-pressure formationswithout the use of air or other gases. This allows for reduceddrilling-related problems and increased rates of penetration.The glass spheres create a low head differential or near-bal-anced drilling condition where the hydrostatic head of thewellbore fluid column is reduced to slightly greater than theformation pressure, thereby containing the flow of formationfluids during drilling.

Hollow glass spheres can be added to virtually any type ofexisting fluid system in order to reduce density. The glassspheres extend the density window of a single phase liquidinto a density range that is normally only achievable byinjecting a gas into the liquid.

The drilling fluids used in the wells at Guang An werewater based and designed to a density of approximately 0.9g/cc. www.3m.com/oil&gas

The concept of low density drilling fluids designed around hollowglass spheres is gaining momentum in China with more fieldapplications recorded in the Sichuan and Ordos Basins.(Photocourtesy of 3M)

A Hart Energy PublicationApril 2008www.eandp.info

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