Drill Bit Assembly Having Electrically Isolated Gap Joint for Measurement of Reservoir Properties

Abstract

A drill bit assembly for measuring reservoir formation properties comprises a bit head and a pin body, and an electrically insulated gap joint between two conductive parts of the drill bit assembly. The electrically insulating gap joint can fill a gap between bit head and pin body engagement sections such that the bit head and pin body are mechanically connected together at connecting ends but electrically separated. Alternatively or additionally, the pin body can have two pieces which are separated by an electrically insulating gap joint. An electrical conductor is electrically connected at a first end to the bit head and is communicable at a second end with an alternating current signal to transmit an alternating current into the bit head, thereby inducing an electric current into a reservoir formation adjacent the bit head.

1 - 22 . (canceled) 
     
     
         23 . A drill bit assembly for measuring reservoir formation properties, comprising
 an electrically conductive bit head having a cutting end and a connecting end opposite the cutting end;   an electrically conductive pin body comprising a pin body connecting end;   an electrically insulating gap joint filling a gap between the bit head and the pin body when the connecting end and the pin body connecting end are mechanically connected to maintain the bit head and the pin body electrically separated;   an electrical conductor extending through at least a portion of the pin body and into the bit head, the electrical conductor being conductively coupled with the bit head proximate the cutting end while being insulated from the pin body, and   electronic equipment including measurement circuitry configured to determine an alternating current at the bit head when the alternating current is transmitted into the bit head via the electrical conductor, the alternating current being inversely proportional to a bit resistivity of the formation.   
     
     
         24 . The drill bit assembly as recited in  claim 23 , wherein the electrical conductor is electrically coupled to an electrically conductive lower drill collar of a MWD module. 
     
     
         25 . The drill bit assembly as recited in  claim 24 , wherein the MWD module has an electrically insulating gap and is configured to emit an alternating current signal in the form of an electromagnetic wave across the MWD module insulating gap, thereby inducing the alternating current in the drill collar. 
     
     
         26 . The drill bit assembly as recited in  claim 23 , wherein the electronic equipment comprises measurement circuitry having a transformer with a first coil and a second coil electrically coupling the conductor to the pin body, an amplifier electrically coupled to the first coil, and analog/digital (A/D) converter electrically coupled to the amplifier for receiving an amplified analog signal representing the alternating current and converting the signal to a digital signal, and a processor electrically coupled to the A/D converter to receive and process the digital signal. 
     
     
         27 . The drill bit assembly as recited in  claim 26 , wherein the electronic equipment further comprises electromagnetic (EM) telemetry circuitry in communication with the processor and configured to transmit data received from the processor as an EM telemetry signal into the formation. 
     
     
         28 . The drill bit assembly as recited in  claim 23 , wherein the electronic equipment comprises measurement circuitry having a high input impedance operational amplifier with inputs electrically coupled to the pin body and the bit head, and a resistor of known resistance electrically coupled to the amplifier and to the electrical conductor, and wherein an alternating current signal source is coupled to the amplifier such that the alternating current at the bit head is determined from a voltage drop measured across the resistor. 
     
     
         29 . The drill bit assembly as recited in  claim 28 , wherein the measurement circuitry further comprises a processor having a memory with instructions for execution by the processor to calculate a bit resistivity from the determined alternating current, and from a measured voltage drop across insulating gap joint. 
     
     
         30 . The drill bit assembly as recited in  claim 23 , further comprising azimuthal resistivity electrodes, wherein the electronics equipment comprises measurement circuitry in communication with the azimuthal resistivity electrodes and configured to determine azimuthal resistivity of the formation from an alternating current measured at the azimuthal resistivity electrodes. 
     
     
         31 . The drill bit assembly as recited in  claim 30 , wherein the azimuthal resistivity electrodes are button electrodes located in at least one of a sidewall of the pin body, and in a cutting face of the bit head. 
     
     
         32 . The drill bit assembly as recited in  claim 23 , further comprising a streaming potential electrode on the pin body, wherein the electronics equipment comprises measurement circuitry in electrical communication with the streaming potential electrode and the bit head, the measurement circuitry being configured to measure the voltage difference therebetween and including a processor with a memory having instructions for execution by the processor to determine the streaming potential of a fluid in contact with the drill bit assembly from the measured voltage difference. 
     
     
         33 . A method for measuring reservoir formation properties by a drill bit assembly comprising
 transmitting an alternating current from an alternating current signal along an electrical conductor extending through at least a portion of a pin body of the drill bit assembly and to a bit head of the drill bit assembly while the pin body and bit head are mechanically connected to each other and electrically insulated from each other by an electrically insulating gap joint;   inducing an electromagnetic wave into a reservoir formation adjacent the bit head via the alternating current transmitted to the bit head along the electrical conductor; and   determining the alternating current at the bit head, the alternating current being proportional to a bit resistivity of the formation.   
     
     
         34 . The method as recited in  claim 33 , wherein transmitting comprises transmitting the alternating current signal as an electromagnetic wave generated by a MWD module having an electrically insulating gap, and wherein the electromagnetic wave crosses the MWD module gap and propagates into an electrically conductive lower drill collar of the MWD module to induce the alternating current which conducts from the lower drill collar to the electrical conductor, across the electrically insulating gap joint, and to the bit head. 
     
     
         35 . The method as recited in  claim 34 , further comprising transmitting an electromagnetic telemetry signal including the determined alternating current from the drill bit assembly to the MWD module and determining at the MWD module the bit resistivity from the determined alternating current, and a voltage drop across the MWD module insulating gap. 
     
     
         36 . The method as recited in  claim 33 , wherein the electrical conductor is connected to the bit head between a plurality of blades of the bit head. 
     
     
         37 . The method as recited in  claim 33 , further comprising determining azimuthal resistivity of the formation by measuring an alternating current at an azimuthal resistivity electrode on the drill bit assembly. 
     
     
         38 . The method as claimed in  claim 33 , further comprising determining a streaming potential of the formation by measuring a voltage difference between a streaming potential electrode on the surface the pin body and the bit head. 
     
     
         39 . A drill bit assembly for measuring reservoir formation properties, comprising
 an electrically conductive bit head having a cutting end and an opposite connecting end with a threaded head engagement section;   an electrically conductive pin body comprising a connecting end with a threaded pin body engagement section, the threaded head engagement section and the threaded pin body engagement section being threadably engaged with an electrically non-conductive layer therebetween;   an electrical conductor extending through at least a portion of the pin body and being electrically isolated from the pin body, the electrical conductor having a first end electrically coupled to the bit head and a second end in electrical communication with an alternating current signal to enable transmission of an alternating current into the bit head, thereby inducing an electric current into a reservoir formation adjacent the bit head, and   electronic equipment including measurement circuitry configured to determine the alternating current at the bit head.   
     
     
         40 . The drill bit assembly as recited in  claim 39 , wherein the alternating current at the bit head is inversely proportional to a bit resistivity of the formation. 
     
     
         41 . The drill bit assembly as recited in  claim 39 , further comprising azimuthal resistivity electrodes, wherein the electronics equipment comprises measurement circuitry in communication with the azimuthal resistivity electrodes and configured to determine azimuthal resistivity of the formation from an alternating current measured at the azimuthal resistivity electrodes. 
     
     
         42 . The drill bit assembly as recited in  claim 39 , further comprising a streaming potential electrode on the pin body, wherein the electronics equipment comprises measurement circuitry in electrical communication with the streaming potential electrode and the bit head, the measurement circuitry being configured to measure the voltage difference therebetween and including a processor with a memory having instructions for execution by the processor to determine the streaming potential of a fluid in contact with the drill bit assembly from the measured voltage difference.