Control system for well stimulation apparatus with response time temperature rise used in determining heater control temperature setpoint

A control system for well stimulation equipment, the well stimulation equipment including a downhole heater in the well, a source of electrical power, conductors connecting said downhole heater to said source of electrical power, and a fluid injection system including a source of fluid and a pump for pumping the fluid,

• the control system comprising:
• one or more of temperature, pressure and flow sensors to sense the flow of fluid past said heater and into a formation surrounding said well,
• a central computational unit and
• means for communicating readings from said sensors to said central computational unit and from said central computational unit to said source of electrical power, said central computational unit including means for receiving and manipulating said sensor readings and generating a control signal for said source of electrical power to vary the power to achieve a set point temperature at said heater, said control system having a response time defined as the time between a no flow condition occurring and a control signal from said control system substantially shutting off said source of electrical power;
• wherein said set point temperature is set at about a maximum permissable temperature less the temperature rise over time for a no flow condition in said heater times said response time.

A well treating system for stimulating hydrocarbon recovery from an underground formation, the formation being connected to a well extending from the formation to the surface and having a well head located at or near the surface, the well treating system comprising:

• a downhole electrical resistance heater which may be inserted into the well and located adjacent to the hydrocarbon bearing underground formation, the downhole heater having a rate of increase of temperature in a no flow condition at full power defined as a ballistic heat rate;
• a source of electrical power located at or near the well head;
• a microprocessor controlled power regulator;
• electrical conductors connected between the source of electrical power and the downhole heater for conducting electrical power to the downhole heater;
• a source of fluid located at or near the well head;
• at least one pump located at or near the well head for pumping a fluid from said fluid source past said downhole heater and into the formation;
• at least one first sensor, associated with the downhole heater, for providing at least one first output signal corresponding to an outlet temperature of said fluid flowing past said heater;
• at least one second sensor, associated with said well, for providing a second output signal corresponding to the flow rate of fluid flowing past the downhole heater and into the formation;
• and
• a control system comprising one or more of temperature, pressure and flow sensors to sense the flow of fluid past said heater and into a formation surrounding said well,
• a central computational unit and
• means for communicating readings from said sensors to said central computational unit and from said central computational unit to said source of electrical power, said control system receiving and manipulating said sensor readings and generating a control signal for said source of electrical power to vary the power to generally maintain a set point temperature at said heater, said control system having a response time defined as the time between a no flow condition occurring at said heater and a control signal from said control system substantially shutting off said source of electrical power;
• wherein said set point temperature is set at or less than a maximum permissable temperature for said well less the product of the ballistic heating rate for said heater times said response time.