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Title:
Damage to sandstone cores by particles from drilling fluids
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API drilling and production practices. : 158-176 ; 1954
Abstract:
A large number of 1-in. diameter by 12-in. long, water-insensitive Berca sandstone cores have been exposed to the effects of several typical field drilling fluids under dynamic high-pressure high-temperature conditions simulating those existing in the drilling of deep wells. Data from these tests showed that particles from all of these drilling fluids penetrated into the interstices of the sandstone and produced a permanent impairment of permeability which increased in magnitude directly woth the exposure time. Average reductions in permeability to oil of 30 percent to 60 percent were found after 5 days of such treatment with the different drilling fluids. The relative degree of impairment of permeability with time was found to depend upon the type of drilling fluid and test conditions. However, a correlation of impairment with cumulative filtrate loss has indicated that within the experimental accuracy all the drilling fluids investigated produced an equivalent amount of damage in a core for a given fluid loss. Particle damage from 2 in. to 12 in. or more deep was indicated qualitatively, depending upon the type of drilling fluid used. The latter portion of the paper is devoted to an attempt to interpret the laboratory results for field application. Calculations indicate that in the radial formation, the reduction in productivity by particle damage alone is approximately the same for each of the drilling fluids tested. After five days exposure to drilling conditions, it appears that the productivity of a formation would be reduced about 10 percent, and after 30 days about 30 percent. Whereas this impairment is shown to be less severe than that often found from fresh-water filtrate in a water-sensitive formation, the damage for long exposure time of 20 to 30 days is believed to be significant. It is suggested that for long exposure times completionof a well with oil-base drilling fluid, even in a non-water-sensitive formation, could result in a productivity approximately 20 percent greater than that for a completion with clay-water base mud or emulsion mud, provided the hole is rapidly under-reamed.
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30000001281090 MAK 208 Open Access Book Article
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