Abstract: A method of controlling a continuous multi-component slurrying process at an oil or gas well comprises continuously flowing substances for creating a slurry in response to a slurry flow rate factor and continuously flowing another substance for the slurry in response to a flow rate of at least a predetermined one of the other substances or the slurry itself. The method can include density control, slurry (tub) level control, and a combination of such controls. The method can operate in either closed loop or open loop manner, and control can be effected with either of two types of control signals depending on whether the controlled device is an integrating or non-integrating type. The method can also provide for bumpless transition between manual and automatic control.

Abstract: A method of controlling an apparatus with a control signal responsive to a feedback signal comprises: detecting when a feedback signal is not being received; determining whether a control signal is being provided; and adjusting the control to the apparatus depending on whether the control signal is being provided. An apparatus for performing this method comprises a programmed computer and a control signal feedback circuit for providing to the programmed computer a signal indicating whether a valid control signal is being provided.

Abstract: A method and system provide automated, preferably electronic, monitoring and control of equipment used to pump and vaporize liquid nitrogen at an oil or gas well. The method comprises: pumping liquid nitrogen at the well; vaporizing pumped liquid nitrogen at the well; flowing vaporized nitrogen at the well; sensing temperature of the flowing vaporized nitrogen; sensing pressure of the flowing vaporized nitrogen; and automatically stopping the pumping of liquid nitrogen at the well when the sensed temperature is outside a predetermined temperature range or when the sensed pressure is outside a predetermined pressure range. A pre-stoppage warning can also be provided, and data about the vaporized nitrogen can be generated, displayed locally and transmitted remotely. A related system is also disclosed.