Highly reinforced elastomer for use in downhole stators

Abstract

A Moineau stator for a downhole drilling motor and a method for fabricating the stator are disclosed. The stator includes an internal helical cavity component fabricated from an improved elastomeric material formulated to provide both high resilience and good processability. For example, in one exemplary embodiment the elastomer material includes rheological parameters M L in a range from about 1.0 to about 4.0 lb·in and M H in a range from about 75 to about 110 lb·in according to ASTM D2084 at 380 degrees F. Stators in accordance with this invention may exhibit improved efficiency (and may thus provide improved torque output) as compared with conventional stators without substantially increasing manufacturing costs.

1 . A stator for use in a downhole drilling motor, the stator comprising:
 an outer tube;   a helical cavity component deployed substantially coaxially in the outer tube, the helical cavity component providing an internal helical cavity and including a plurality of internal lobes; and   the helical cavity component including an elastomeric material, the elastomeric material including:
 33-3 nitrile butadiene rubber having about 30 percent by weight acrylonitrile and a Mooney viscosity of about 30; 
 at least 60 parts by weight carbon black per 100 parts by weight of the nitrile rubber; and 
 at least 15 parts by weight phenolic resin plasticizer per 100 parts by weight of the nitrile rubber, said phenolic resin plasticizer further including a hexa cross linking agent. 
   
   
   
       2 . The stator of  claim 1 , wherein the phenolic resin plasticizer includes from about 6.5 to about 8.5 percent by weight of the hexa cross linking agent. 
   
   
       3 . The stator of  claim 1 , wherein the elastomeric material comprises about 25 parts by weight of the phenolic resin plasticizer per 100 parts by weight of the nitrile rubber. 
   
   
       4 . The stator of  claim 1 , wherein the elastomeric material comprises about 25 parts by weight of the phenolic resin plasticizer and about 80 parts by weight carbon black per 100 parts by weight of the nitrile rubber. 
   
   
       5 . The stator of  claim 1 , wherein the helical cavity component is fabricated substantially entirely from the elastomeric material. 
   
   
       6 . The stator of  claim 1 , wherein the elastomeric material includes the following tensile properties:
 a modulus at 25% elongation in a range from about 550 to about 750 psi; and   a modulus at 100% elongation in a range from about 900 to about 1200 psi.   
   
   
       7 . The stator of  claim 1 , wherein the elastomeric material includes the following compressive properties:
 a modulus at 5% compression in a range from about 110 to about 150 psi;   a modulus at 10% compression in a range from about 225 to about 325 psi; and   a modulus at 15% compression in a range from about 350 to about 475 psi.   
   
   
       8 . The stator of  claim 1 , wherein the elastomeric material comprises a Shore A hardness in the range from about 88 to about 94. 
   
   
       9 . The stator of  claim 1 , wherein the elastomer material comprises rheological parameters M L  in a range from about 1.0 to about 4.0 lb·in and M H  in a range from about 75 to about 110 lb·in, said M L  and said M H  representative of a minimum and maximum torque as determined according to ASTM D2084 at 380 degrees F. with no preheat. 
   
   
       10 . The stator of  claim 1 , wherein the elastomer material comprises an aftercure tan δ at 250 degrees F. of less than about 0.25. 
   
   
       11 . A stator for a downhole drilling motor comprising:
 an outer tube;   a helical cavity component deployed substantially coaxially in the outer tube, the helical cavity component providing an internal helical cavity and including a plurality of internal lobes; and   the helical cavity component being fabricated from an elastomeric material, the elastomeric material including a nitrile rubber having from about 30 to about 40 percent acrylonitrile, the elastomeric material further including rheological parameters M L  in a range from about 1.0 to about 4.0 lb·in and M H  in a range from about 75 to about 110 lb·in, said M L  and said M H  representative of a minimum and maximum torque as determined according to ASTM D2084 at 380 degrees F. with no preheat.   
   
   
       12 . The stator of  claim 11 , wherein the elastomeric material comprises at least 15 parts by weight phenolic resin plasticizer per 100 parts by weight of the nitrile rubber, the phenolic resin plasticizer including a hexa cross linking agent. 
   
   
       13 . The stator of  claim 11 , wherein the elastomeric material comprises about 80 parts by weight carbon black per 100 parts by weight of the nitrile rubber. 
   
   
       14 . The stator of  claim 11 , wherein the nitrile rubber comprises a 33-3 nitrile butadiene rubber having about 30 percent by weight acrylonitrile and a Mooney viscosity of about 30. 
   
   
       15 . The stator of  claim 11 , wherein the elastomeric material includes the following tensile properties:
 a modulus at 25% elongation in a range from about 550 to about 750 psi; and   a modulus at 100% elongation in a range from about 900 to about 1200 psi.   
   
   
       16 . The stator of  claim 11 , wherein the elastomeric material includes the following compressive properties:
 a modulus at 5% compression in a range from about 110 to about 150 psi;   a modulus at 10% compression in a range from about 225 to about 325 psi; and   a modulus at 15% compression in a range from about 350 to about 475 psi.   
   
   
       17 . The stator of  claim 11 , wherein the elastomeric material comprises a Shore A hardness in the range from about 88 to about 94. 
   
   
       18 . The stator of  claim 11 , wherein the elastomer material comprises an aftercure tan δ at 250 degrees F. of less than about 0.25. 
   
   
       19 . The stator of  claim 11 , wherein ML is in a range from about 1.0 to about 3.5 lb·in. 
   
   
       20 . The stator of  claim 11 , wherein ML is in a range from about 1.0 to about 3.0 lb·in 
   
   
       21 . A method of manufacturing a stator for a downhole drilling motor, the method comprising:
 (a) providing an elastomeric compound including a nitrile rubber having from about 30 to about 40 percent acrylonitrile, the elastomeric compound further including rheological parameters M L  in a range from about 1.0 to about 4.0 lb·in and M H  in a range from about 75 to about 110 lb·in, said M L  and said M H  representative of a minimum and maximum torque as determined according to ASTM D2084 at 380 degrees F. with no preheat; and   (b) injection molding the elastomeric compound into a tubular stator housing to form a helical cavity component, the helical cavity component providing an internal helical cavity and including a plurality of internal lobes.   
   
   
       22 . The method of  claim 21 , wherein the nitrile rubber comprises a Nysyn 333 nitrile butadiene rubber having about 33 percent acrylonitrile and a Mooney viscosity of about 30. 
   
   
       23 . The method of  claim 21 , wherein the elastomeric compound comprises about 25 parts by weight phenolic resin plasticizer per 100 parts by weight of the nitrile rubber, the phenolic resin plasticizer including a hexa cross linking agent. 
   
   
       24 . The method of  claim 21 , wherein the elastomeric compound comprises about 80 parts by weight carbon black per 100 parts by weight of the nitrile rubber. 
   
   
       25 . A subterranean drilling motor comprising:
 a rotor having a plurality of rotor lobes on a helical outer surface of the rotor;   a stator including a helical cavity component, the helical cavity component providing an internal helical cavity and including a plurality of internal stator lobes;   the rotor deployable in the helical cavity of the stator such that the rotor lobes are in a rotational interference fit with the stator lobes, rotation of the rotor in a predetermined direction causing the rotor lobes to (i) contact the stator lobes on a loaded side thereof as the interference fit is encountered, and (ii) pass by the stator lobes on a non-loaded side thereof as the interference fit is completed; and   the internal stator lobes fabricated from an elastomeric material including (i) a 33-3 nitrile butadiene rubber having about 30 percent by weight acrylonitrile and a Mooney viscosity of about 30, (ii) about 80 parts by weight carbon black per 100 parts by weight of the nitrile rubber, (iii) and about 25 parts by weight phenolic resin plasticizer per 100 parts by weight of the nitrile rubber, said phenolic resin plasticizer further including a hexa cross linking agent.   
   
   
       26 . A subterranean drilling motor comprising:
 a rotor having a plurality of rotor lobes on a helical outer surface of the rotor;   a stator including a helical cavity component, the helical cavity component providing an internal helical cavity and including a plurality of internal stator lobes;   the rotor deployable in the helical cavity of the stator such that the rotor lobes are in a rotational interference fit with the stator lobes, rotation of the rotor in a predetermined direction causing the rotor lobes to (i) contact the stator lobes on a loaded side thereof as the interference fit is encountered, and (ii) pass by the stator lobes on a non-loaded side thereof as the interference fit is completed; and   the internal stator lobes fabricated from an elastomeric material having the following properties:   rheological parameter M L  in a range from about 1.0 to about 4.0 lb·in;   rheological parameter M H  in a range from about 75 to about 110 lb·in;   a tensile modulus at 25% elongation from about 550 to about 750 psi;   a tensile modulus at 100% elongation from about 900 to about 1200 psi;   a Shore A hardness in the range from about 88 to about 94; and   wherein said M L  and said M H  are representative of minimum and maximum torque as determined according to ASTM D2084 at 380 degrees F. with no preheat.