| 摘要 |
The invention provides water base drilling fluids containing lime and potassium compounds which have the following advantages as compared to prior art lime muds and potassium muds: (a) provide better borehole stability than lime muds; (b) easier to control than lime muds and potassium muds; (c) drilled solids have much less effect on the rheological properties of these drilling fluids as compared to lime muds and potassium muds; (d) the thermal gelation of these drilling fluids after contamination with shale is much less severe than that of shale contaminated lime muds or potassium muds; and (e) bit balling and cuttings agglomeration when drilling mud making shales is much less than when using lime muds or potassium muds. These drilling fluids comprise a suspension of clay, lime and 10-30 ppb of a lignitic material in an aqueous phase, the drilling fluid having a Pm in the range from 1 to 40 and a pH in the range from 12.4 to 13.5, the aqueous phase being saturated with lime having a Pf in the range from 1 to 8 and a K<+> concentration of at least 8000 ppm, wherein Pm > Pf. The invention also provides a method of preparing muds containing lime and potassium whereby the increase in viscosity and gel strength which normally accompanies the addition of lime to aqueous clay-containing muds is minimized which consists of adding to a suspension of clay and a lignitic material: KOH, KCl, and lime, in that order.
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