Caprock breach determination technique

Abstract

A technique for determination of out of zone injection. The technique may include taking temperature readings of the well at locations adjacent the cap rock during injection of injection fluid into the injection well at temperatures that are below that of the cap rock. Analysis of the rate of change in temperatures adjacent the cap rock may be used to monitoring effects of the injection application including deciphering cap rock breach of injection fluid when the rate of change substantial enough.

1 . A method of determining out of zone injection of a fluid from an injection well and into cap rock over a reservoir at an oilfield, the method comprising:
 positioning a sensor device in the injection well adjacent the cap rock;   recording an initial temperature of the sensor device corresponding to the cap rock;   injecting the fluid into the injection well at a temperature different from that of the cap rock;   monitoring the sensor device for a change in temperature at an anomalous rate corresponding to out of zone injection of the fluid into the cap rock.   
     
     
         2 . The method of  claim 1 , further comprising:
 taking corrective action when the out of zone injection of the fluid into the cap rock is detected during the monitoring of the sensor device.   
     
     
         3 . The method of  claim 2 , wherein the corrective action comprises one of reducing a rate of the injecting of the fluid into the injection well and shutting off the injection well. 
     
     
         4 . The method of  claim 2 , further comprising:
 shutting in the injection well; and   monitoring temperature of the sensor device during the shutting in of the injection well for a warmback period to confirm the reduction in temperature at a rate corresponding to the out of zone injection in advance of the taking of the corrective action.   
     
     
         5 . The method of  claim 1 , further comprising:
 shutting in the injection well; and   storing temperature of the sensor device during the shutting in of the injection well for a warmback period to establish reference temperature data.   
     
     
         6 . The method of  claim 1 , wherein the injecting of the fluid into the injection well raises a pressure in the reservoir, the method further comprising recovering production fluids from the reservoir through a production well at the oilfield. 
     
     
         7 . The method of  claim 1 , wherein a rate of reduction in temperature is greater at the lowermost location of the sensor device. 
     
     
         8 . The method of  claim 1 , wherein the rate of reduction in temperature is detected in less than about 10 days of the emergence of the out of zone injection into the cap rock. 
     
     
         9 . A system for detecting breach of cap rock with injection fluid at an injection well at an oilfield, the system comprising:
 a vertically disposed sensor device in the injection well adjacent the cap rock;   a control unit with a processor in communication with the sensor device to monitor temperature during injection of the injection fluid for an anomalous rate of change indicative of cap rock breach.   
     
     
         10 . The system of  claim 9 , wherein the sensor device is selected from a group consisting of an array of discrete sensors and a fiber optic distributed temperature change sensor. 
     
     
         11 . The system of  claim 9 , wherein at least one of the discrete sensors is selected from a group consisting of a resistance temperature thermometer, fiber Bragg temperature sensor, and a heat-flux sensor. 
     
     
         12 . The system of  claim 9 , wherein the sensor device is mounted to one of an interior of casing defining the well at the location of the cap rock and an exterior of the casing defining the well at the location of the cap rock.