These notes have been written to bring up to date information contained in the report "Evaluation and Application of Gypsum Q-Broxin Muds"published in December, 1958.

During the past year calcium Q-Broxin muds have been used in eight wells which had total depths varying from 13,200 feet to 15,500 feet. In seven of the eight wells no drilling trouble of any kind was experienced, and in the eighth where stuck pipe resulted, this has been ascribed to differential pressure effects due to the use of excessively heavy mud. In all wells maintenance of excellent rheological and filtration properties of the muds has been easily attained at relatively low cost.

Flattening of the profile of the self potential curve when using this type of mud led to difficulties in quantitative evaluation of the fluid content of formations and in subsurface correlation studies. Investigation revealed that this was due to the low resistivity of the muds and modifications in mud treatment have resolved this problem

Since this type of mud has been used in wells with very high bottom hole temperatures, an examination of the filtration characteristics at a series of temperatures and pressures has been commenced.

A very simple relationship has been established between the rheological properties of a mud at any two given temperatures. This has permitted the comparison of results obtained in the laboratory with those measured at flowline temperatures at the well site.

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