Pulsed Neutron Monitoring of Hydraulic Fracturing and Acid Treatment

Abstract

Hydraulic fracturing, acidizing and polymer injection using coiled tubing are commonly used techniques in wellbore completion. A pulsed neutron tool may be conveyed at the bottom of the coiled tubing to monitor the effectiveness of these operations by measuring the flow velocity of the borehole fluid of the annulus between the pulsed neutron tool and the borehole wall. Gamma rays resulting from Oxygen activation and/or Σ measurements are used for measuring the flow velocity.

1 . A method of monitoring a formation modification operation in a borehole, the method comprising:
 modifying a formation using a fluid conveyed into the borehole;   making measurements indicative of a flow velocity of the fluid in an annulus between an instrument conveyed in the borehole and a wall of the borehole, the instrument including a radiation source; and   estimating at least one parameter of the formation modification operation using the measurements at a plurality of positions along the borehole.   
     
     
         2 . The method of  claim 1  wherein the formation modification operation is at least one of: (i) a hydraulic fracturing, (ii) an acid treatment, and (iii) a polymer injection. 
     
     
         3 . The method of  claim 1  wherein the radiation source further comprises a pulsed radiation source, and making measurements indicative of the flow velocity of the fluid further comprises:
 irradiating the formation with the pulsed radiation source; 
 obtaining a first temporal signal resulting from the irradiation at a first detector; 
 obtaining at least one second temporal signal resulting from the irradiation at at least one second detector spaced apart from the first detector; and 
 determining the flow velocity based on analysis of the first temporal signal, the at least one second temporal signal, and a distance between one of (A) the first detector and the at least one second detector, and (B) the source and the at least one second detector. 
 
     
     
         4 . The method of  claim 1  wherein the at least one parameter of interest includes at least one of: (i) an indicator of a degree of fracturing in the formation, (ii) a change in fluid flow in the annulus, and (iii) flow rate of fluid into the formation. 
     
     
         5 . The method of  claim 3  wherein the first temporal signal is selected from: (i) gamma rays resulting from nitrogen-16 and (ii) a cross section Σ of the fluid. 
     
     
         6 . The method of  claim 3  wherein the first detector is proximate to the radiation source and is responsive immediately to inelastic and capture events resulting from the pulsed radiation, and wherein the at least one second detector is responsive to the produced gamma rays. 
     
     
         7 . The method of  claim 3  wherein determining the flow velocity is based on a correlation between the first temporal signal and the at least one second temporal signal. 
     
     
         8 . The method of  claim 1  further comprising:
 positioning a processor at a downhole location, wherein the processor is configured to estimate the at least one parameter using the measurements at a plurality of positions along the borehole; and 
 performing a remedial action based on the at least one parameter. 
 
     
     
         9 . An apparatus configured to monitor a formation modification operation in a borehole, the apparatus comprising:
 a wellbore tubular configured to convey a fluid in the borehole and modify the formation;   an instrument including a radiation source configured to be conveyed in the borehole and to make measurements indicative of a flow velocity of the fluid in an annulus between the instrument and a wall of the borehole; and   a processor configured to:
 estimate at least one parameter of the formation modification operation using the measurements at a plurality of positions along the borehole. 
   
     
     
         10 . The apparatus of  claim 9  wherein the formation modification operation is one of:
 (i) a hydraulic fracturing, (ii) an acid treatment, and (iii) a polymer injection. 
 
     
     
         11 . The apparatus of  claim 9  wherein the at least one parameter of interest includes at least one of: (i) an indicator of a degree of fracturing in the formation, (ii) a change in fluid flow in the annulus, and (iii) flow rate of fluid into the formation. 
     
     
         12 . The apparatus of  claim 9  wherein the radiation source further comprises a pulsed radiation source further configured to irradiate the earth formation with the pulsed radiation source; and wherein the instrument further comprises:
 a first detector configured to obtain a first temporal signal resulting from the irradiation; 
 at least one detector spaced apart from the first detector configured to obtain at least one second temporal signal resulting from the irradiation; and 
 wherein the processor is further configured to estimate the flow velocity based on analysis of the first temporal signal, the at least one second temporal signal, and a distance between one of (A) the first detector and the at least one second detector, and, (B) the source and the at least one second detector. 
 
     
     
         13 . The apparatus of  claim 12  wherein the first temporal signal is selected from: (i) gamma rays resulting from nitrogen-16 and (ii) a cross section Σ of the fluid. 
     
     
         14 . The apparatus of  claim 12  wherein the first detector is proximate to the source and is responsive to inelastic and capture events resulting from the pulsed radiation, and wherein said at least one second detector is responsive to the produced gamma rays. 
     
     
         15 . The apparatus of  claim 9  wherein the processor is configured to estimate the flow velocity based on a correlation between the first and at least one second signal. 
     
     
         16 . The apparatus of  claim 9  wherein the processor is further configured to perform a remedial action based on the at least one parameter. 
     
     
         17 . A non-transitory computer-readable medium product having instructions thereon that when read by a processor cause the processor to execute a method, the method comprising:
 modifying a formation using a fluid conveyed into a borehole;   making measurements indicative of a flow velocity of the fluid in an annulus between an instrument conveyed in the borehole and a wall of the borehole, the instrument including a radiation source; and   estimating at least one parameter of the formation modification operation using the measurements at a plurality of positions along the borehole.   
     
     
         18 . The non-transitory computer-readable medium product of  claim 17  further comprising at least one of: (i) a ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical disk. 
     
     
         19 . A method for monitoring a formation modification operation, the method comprising:
 acquiring information relating to the formation modification using an instrument conveyed in the borehole penetrating the formation; and   estimating at least one parameter of interest related to the formation modification using the acquired information, wherein the information is acquired at a plurality of positions along the borehole.   
     
     
         20 . The method of  claim 19 , further comprising:
 performing an additional operation based on the at least one estimated parameter of interest.   
     
     
         21 . The method of  claim 20 , further comprising:
 estimating a change in the formation after the additional operation.