Abstract: A bottom hole shut-in tool incorporating a ball and seat shut-off valve and a ball and seat pressure equalizing valve. The ball elements of the valves are formed of elastomeric material, which allows the ball elements to engage their seats in continuous annular sealing contact even when debris from the well is trapped between a ball and its seat or when a ball is not exactly aligned with its seat. This arrangement effectively seals off the pressure gauge used in conducting a pressure survey from fluid in the well tubing located above the shut-off valve.

Abstract: An oil-external microemulsion drilling fluid having a wide range of tolerance for salinity, having good gel strength and low fluid loss characteristics, and also obtained by mixing about 1% to about 30% of a sodium petroleum sulfonate having an average equivalent weight within the range of about 350 to about 525, about 5% to about 84% of a hydrocarbon (e.g. diesel fuel), about 15% to about 90% of an aqueous medium (can contain water soluble salts), about 0.01 to about 20% of a cosurfactant (e.g. alcohols such as primary amyl alcohol) and about 0.1 to about 15% of bentonite clay. Weighting agents, e.g. barite, and other desired additives can be added to the microemulsion.