Stator compound having an NBIR terpolymer elastomeric base and stators and downhole motors using the same

Abstract

A stator compound including an acrylonitrile butadiene isoprene rubber (NBIR) terpolymer elastomeric base.

Claims

1. A stator compound including an acrylonitrile butadiene isoprene rubber (NBIR) polymer elastomeric base, wherein the acrylonitrile butadiene isoprene polymer elastomeric base is 100% non-hydrogenated.

2. The stator compound of claim 1, wherein the NBIR polymer elastomeric base comprises a carboxylated acrylonitrile butadiene isoprene rubber (XNBIR) polymer elastomeric base.

3. The stator compound of claim 1, further comprising at least one of a high reinforcing carbon black and a semi-reinforcing carbon black selected such that the stator compound has a tensile strength from about 800 to about 2000 psi.sup.2, an elongation from about 125 to about 300%, and a 25% modulus from about 250 to about 600 psi, when measured at 121 C.

4. The stator compound of claim 3, wherein the high reinforcing carbon black has a surface area of about 80 to about 250 (Iodine # mg/g) and a structure of about 70 to about 178 (DBP Absorption-cc/100 g).

5. The stator compound of claim 3, wherein the semi-reinforcing carbon black has a surface area of about 20 to about 50 (Iodine # mg/g) and a structure of about 60 to about 125 (DBP Absorption-cc/100 g).

6. The stator compound of claim 3, wherein the stator compound comprises high reinforcing carbon black of about 5 to about 40 parts per hundred parts of the NBIR polymer elastomeric base and semi-reinforcing carbon black of about 40 to about 120 parts per hundred parts of the NBIR polymer elastomeric base.

7. The stator compound of claim 6, wherein: the high reinforcing carbon black has a surface area of about 80 to about 250 (Iodine # mg/g) and a structure of about 70 to about 178 (DBP Absorption-cc/100 g); and the semi-reinforcing carbon black has a surface area of about 20 to about 50 (Iodine # mg/g) and a structure of about 60 to about 125 (DBP Absorption-cc/100 g).

8. The stator compound of claim 3, wherein the at least one of a high reinforcing carbon black and a semi-reinforcing carbon black is further selected to provide tear characteristics at 121 C. including Die C of about 50 ppi to about 200 ppi and trouser of about 5 ppi.sup.3 to about 100 ppi.sup.3.

9. The stator compound of claim 1, wherein the NBIR polymer elastomeric base has a Mooney viscosity range of about 30 to about 85 and an acrylonitrile content range of about 28 to about 50.

10. The stator compound of claim 1, further comprising at least one plasticizer selected from the group consisting of polymeric and ester plasticizers.

11. The stator compound of claim 1, wherein the stator compound comprises high reinforcing carbon black of about 5 to about 40 parts per hundred parts of the NBIR polymer elastomeric base and semi-reinforcing carbon black of about 40 to about 120 parts per hundred parts of the NBIR polymer elastomeric base.

12. The stator compound of claim 11, wherein: the high reinforcing carbon black has a surface area of about 80 to about 250 (Iodine # mg/g) and a structure of about 70 to about 178 (DBP Absorption-cc/100 g); and the semi-reinforcing carbon black has a surface area of about 20 to about 50 (Iodine # mg/g) and a structure of about 60 to about 125 (DBP Absorption-cc/100 g).

13. The stator compound of claim 11, wherein the at least one of a high reinforcing carbon black and a semi-reinforcing carbon black is further selected to provide tear characteristics at 121 C. including Die C of about 50 ppi to about 200 ppi and trouser of about 5 ppi.sup.3 to about 100 ppi.sup.3.

14. A stator compound comprising: an acrylonitrile butadiene isoprene rubber (NBIR) polymer elastomeric base that has an isoprene content nominally in the range of 5-50%, wherein the acrylonitrile butadiene isoprene polymer elastomeric base is 100% non-hydrogenated; and at least one of a high reinforcing carbon black and a semi-reinforcing carbon black selected such that the stator compound has a tensile strength from about 800 to about 2000 psi.sup.2, an elongation from about 125 to about 300%, and a 25% modulus from about 250 to about 600 psi, when measured at 121 C.

15. The stator compound of claim 14, wherein the at least one of the high reinforcing carbon black and the semi-reinforcing carbon black comprises a high reinforcing carbon black of about 5 to about 40 parts per hundred parts of the NBIR polymer elastomeric base and a semi-reinforcing carbon black of about 40 to about 120 parts per hundred parts of the NBIR polymer elastomeric base.

16. The stator compound of claim 15, wherein the high reinforcing carbon black has a surface area of about 80 to about 250 (Iodine # mg/g) and a structure of about 70 to about 178 (DBP Absorption-cc/100 g).

17. The stator compound of claim 15, wherein the semi-reinforcing carbon black has a surface area of about 20 to about 50 (Iodine # mg/g) and a structure of about 60 to about 125 (DBP Absorption-cc/100 g).

18. The stator compound of claim 14, wherein the at least one of a high reinforcing black and a semi-reinforcing black is further selected to provide tear characteristics at 121 C. including Die C of about 50 ppi to about 200 ppi and trouser of about 5 ppi.sup.3 to about 100 ppi.sup.3.

19. A stator compound comprised of an acrylonitrile butadiene isoprene rubber (NBIR) polymer elastomeric base, wherein the acrylonitrile butadiene isoprene polymer elastomeric base is 100% non-hydrogenated; the NBIR polymer elastomeric base comprises a carboxylated acrylonitrile butadiene isoprene rubber (XNBIR) polymer elastomeric base; and the stator compound further comprises at least one of a high reinforcing carbon black and a semi-reinforcing carbon black selected such that the stator compound has a tensile strength from about 800 to about 2000 psi.sup.2, an elongation from about 125 to about 300%, and a 25% modulus from about 250 to about 600 psi, when measured at 121 C.

20. The stator compound of claim 19, wherein the high reinforcing carbon black has a surface area of about 80 to about 250 (Iodine # mg/g) and a structure of about 70 to about 178 (DBP Absorption-cc/100 g).

21. The stator compound of claim 19, wherein the semi-reinforcing carbon black has a surface area of about 20 to about 50 (Iodine # mg/g) and a structure of about 60 to about 125 (DBP Absorption-cc/100 g).

22. The stator compound of claim 19, wherein the NBIR polymer elastomeric base has a Mooney viscosity range of about 30 to about 85 and an acrylonitrile content range of about 28 to about 50.

23. The stator compound of claim 19, further comprising at least one plasticizer selected from the group consisting of polymeric and ester plasticizers.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1A is a perspective view of a downhole motor assembly suitable for describing a typical application of the principles of the present invention;

(3) FIG. 1B is a top cross-sectional view of the rotor and stator assembly of FIG. 1A; and

(4) FIG. 2 is cutaway view showing a portion of the stator of FIGS. 1A and 1B including a molded stator elastomeric liner fabricated using an NBIR terpolymer according to the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in FIGS. 1-2 of the drawings, in which like numbers designate like parts.

(6) FIG. 1A is a diagram of an exemplary downhole motor assembly 100, which attaches to the end of a drilling string during oil and gas drilling operations. Exemplary downhole motor assembly 100 includes a top sub 101, stator and rotor assembly 102, transmission 103, offset or adjustable housing 104, bearing assembly 105, and drill bit 106. FIG. 1B is an end cut-away view of stator and rotor assembly 102 and shows the helical rotor 109 offset within the helical liner 108 of stator tube 107.

(7) FIG. 2 is a side cutaway view of stator and rotor assembly 102 of FIG. 1, which shows stator tube 107 and associated molded stator elastomer lining 106 in further detail. The fabrication of molded stator elastomer lining 108 is one exemplary use of a NBIR terpolymer embodying the principles of the present invention.

(8) Moreover, stator compounds of according to the principles of the present invention are also suitable for the fabrication of NBIR terpolymer stator liners used in downhole pumps. (Generally, downhole motors and pumps are structurally similar, and both implement power conversion, with downhole motors typically used to provide torque and rotation to the drill bit and downhole pumps typically used to provide pressure and flow rate for moving fluids. The typical downhole pump stator will have as few as two lobes and the typical downhole motor stator will have between three and ten lobes.)

(9) Several elastomers types and cure systems were investigated by the inventors. The focus was to fabricate a stator lining with good dynamic mechanical properties, low swell in diesel-based muds and good hot mechanical properties at 200-350 F. It was found that the use of NBIR terpolymer in stator compounds improved dynamic mechanical properties such as sealing, hysteresis (Tan Delta) modulus, tensile strength, tear and flex-fatigue resistance. An isoprene unit was selected to be the same as in natural rubber, which is known to have these good dynamic properties. The isoprene content is nominally in the range of 5-50%, and preferably in the range of 10-30%. The acrylonitrile group (ACN) provides the resistance to drilling fluids such as oil and diesel-based muds.

(10) According to one preferred process, the selected NBIR Terpolymer is mixed in a production rubber mixer using a two step mixing procedure to ensure dispersion of high reinforcing carbon black and other additives. In addition, this procedure also produces optimum flow (viscosity) properties and mechanical strength. A sulfur, sulfur phenolic or peroxide/co-agent cure system is preferably used to cure the compound. This cure system was developed to produce optimum scorch and curing properties. A blend of plasticizers is used to achieve good flow and diesel extraction properties.

(11) Table 1 illustrates the preferred ingredients for the first step in producing NBIR stator compounds according to the principles of the present invention. Ranges for the preferred ingredients are listed in parts per one hundred parts of rubber (PHR). In particular, the high reinforcing carbon black has a surface area of 80-250 (Iodine # mg/g) and structure of 70-178 (DBP Absorption-cc/100 g) and the semi-reinforcing carbon black has a surface area of 20-50 (Iodine # mg/g) and structure of 60-125 (DBP Absorption-cc/100 g).

(12) During the first step, the ingredients in Table 1 are mixed in a commercial rubber mixer for approximately 4-10 minutes and a temperature below 300 F. The mixture (i.e., the first pass masterbatch) is then allowed to cool to ambient temperature prior to the second mixing step.

(13) TABLE-US-00001 TABLE 1 INGREDIENTS (1.sup.ST MIX CYCLE) PHR NBIR TERPOLYMER 100.0 ANTIOXIDANT 0.2-2.0 ANTIOZONANT 0.5-3.0 SEMI-REINFORCING CARBON 40-120 BLACK HIGH REINFORCING CARBON 5.0-40 BLACK POLYMERIC PLASTICIZER 5.0-40.0 ESTER PLASTICIZER 5.0-20.0 PHENOLIC RESIN 10.0-50.0 ZINC OXIDE 3.0-5.0 STEARIC ACID 1.0-5.0 HEXAMETHYLENE 1.0-8.0 TETRAAMINE RETARDERS 0.2-4.0

(14) The preferred ingredients for the second mixing step are shown in Table 2. During the second mixing step, the ingredients of Table 2 are mixed for approximately 2-5 minutes at less than 225 F., after which mixture is dumped from the mixer and onto a two-roll mill.

(15) TABLE-US-00002 TABLE 2 INGREDIENTS (2.sup.ND MIX CYCLE) 1.sup.ST PASS MASTERBATCH PHR SULFUR 0.50-5.0 RUBBER ACCELERATORS 0.5-5.0

(16) The resulting NBIR terpolymer compound has been shown to have good resistance in water and diesel-based drilling fluids. This compound also shows good dynamic mechanical properties, flex fatigue life and tear resistance at high temperatures (200-350 F.). The high value at low strain modulus (i.e., less than 25%) reduces flexing of the stator lobe, which results in improved performance.

(17) The characteristics of the preferred embodiment of the present NBIR terpolymer stator compound are provided in Table 3:

(18) TABLE-US-00003 TABLE 3 RHEOLOGICAL, CURE AND MECHANICAL PROPERTIES FOR NBIR STATOR COMPOUND VISCOSITY MOONEY VISC. 20-100 (ASTM D1646) (ML1 + 4) @ 100 C. MU MOONEY SCORCH >60 T5@100 C. minutes RHEOLOGY MDR (Rheometer) 60 @ 160 C. (ASTM 2084) ML (dNm).sup.1 0.5-3.0 MH (dNm) 20-80 TS (2) minutes 1.5 5.0 TC (90) minutes 5.0-25.0 Tan Delta 0.10-0.30 MICRODUMBELL HOT PROPERTIES (ASTM D1708) TENSILE 800-2000 Tested @ STRENGTH (psi).sup.2 121 C. ELONGATION % 125-300 25% MODULUS (psi) 250-600 TEAR DIE C @ 121 C. 50-200 (ASTM D624) (ppi) TROUSER @ 121 C. 5-100 (ppi).sup.3 DIN ABRASION 100-250 (ASTM D5963) cured 30@ 177 C. (mm.sup.3) DeMattia Flex Final Crack Width 18.5 (ASTM D813) (mm) --- Initial piercing Cycles to Final 5,000-20,000 is 2 mm wide per Width ASTM D813. Width of specimen is 25.4 mm. Capillary Rheometer Load: 35 kg Shear 5-20 (ASTM D5099) Rate (s.sup.1) Die: 1.0 mm Kgkilograms 2.0 mm/Temp: 100 C. Viscosity (Pa .Math. s).sup.4 100-400 DIESEL-BASED MUD 72 H @ 250 F. RESISTANCE % VOLUME CHANGE - +5.0/2.0 SHORE A HARDNESS +5/5 CHANGE 25% MODULUS +25/10 (% CHANGE) TENSILE STRENGTH +25/10 (% CHANGE) ELONGATION +10/25 (% CHANGE) .sup.1dNm = decinewtons meter .sup.2Psi = pounds per square inch .sup.3Ppi = pounds per inch .sup.4Pa .Math. s = Pascal .Math. second

(19) Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

(20) It is therefore contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.