16 Tex. Admin. Code § 3.19
In cable tool drilling, no operator shall drill into a known oil, gas, or geothermal resource producing formation with water from a higher formation in the hole, or with a sufficient head of water introduced into the hole to prevent gas blowing to the surface. The well shall either be allowed to blow until it has been drilled-in or it shall be drilled under a head of fluid whose weight shall average not less than 9 1/2 pounds per gallon; but in no case shall gas be allowed to blow for a longer period than three days after completion of the well. Mud-laden fluid used for protecting oil, gas, or geothermal resource bearing sands in upper formations while oil, gas, or geothermal resource is being produced from deeper formations shall have an average weight of not less than 91 pounds per gallon.
16 Tex. Admin. Code § 3.19