Increased drill bit or lower BHA inertia for reducing HFTO
A method for estimating and reducing high-frequency torsional oscillations (HFTO) during a downhole drilling operation includes estimating an HFTO propensity of an initial BHA configuration using a model that relates the HFTO propensity to at least a rock strength of a subterranean formation, a radius or diameter of the borehole, a drill bit body density, and a drill bit body radius or diameter. The estimated HFTO propensity is compared with an HFTO propensity threshold. The model is used to select a modified drill bit or bottom hole assembly (BHA) configuration that reduces the estimated HFTO propensity to a value below the HFTO propensity threshold. The modified drill bit or BHA configuration has an increased polar moment of inertia as compared to the initial drill bit or BHA configuration.
1 . A method for estimating and reducing high-frequency torsional oscillations (HFTO) during a downhole drilling operation, the method comprising:
providing an initial BHA configuration including an initial drill bit configuration;
estimating an HFTO propensity of the initial BHA configuration using a model, wherein the model defines the HFTO propensity as a function of parameters of a polar moment of inertia, a cutter depth of cut of a drill bit, a rotary speed of the drill bit, a rock strength of a subterranean formation, a radius of a subterranean borehole, and one or more constants, wherein the polar moment of inertia is a function of parameters including a radius of the drill bit, a body density of the drill bit, and a length of the drill bit and collar that is energized by the HFTO;
comparing the estimated HFTO propensity with an HFTO propensity threshold; and
in response to the estimated HFTO propensity exceeding the HFTO propensity threshold, using the model to select a modified drill bit or bottom hole assembly (BHA) configuration that reduces the estimated HFTO propensity to a value below the HFTO propensity threshold, wherein the selected modified drill bit or BHA configuration has an increased polar moment of inertia as compared to the initial drill bit or BHA configuration, wherein the selected modified drill bit has a gauge diameter between 6.75 inches and 12 inches and the increased polar moment of inertia is greater than 102 lb*in 2 .
2 . The method of claim 1 , further comprising drilling the subterranean borehole with the selected modified drill bit or BHA.
3 . The method of claim 1 , wherein the selected modified drill bit configuration has an increased body density of the drill bit or an increased radius of the drill bit as compared to the initial drill bit configuration.
4 . The method of claim 1 , wherein the increased polar moment of inertia of the selected modified drill bit or BHA configuration is at least 25% greater than a polar moment of inertia of the initial drill bit configuration.
5 . The method of claim 1 , wherein the selected modified drill bit configuration has an outer sleeve deployed about a lower shaft portion of the initial drill bit configuration, the outer sleeve providing the increased polar moment of inertia.
6 . The method of claim 1 , wherein the selected modified drill bit configuration has a plurality of blade extenders that extend a length of corresponding drill bit blades, the plurality of blade extenders providing the increased polar moment of inertia.
7 . The method of claim 1 , wherein the BHA comprises a rotary steerable system (RSS) and the selected modified BHA configuration comprises a sleeve deployed about a lower body portion of the RSS, the sleeve providing the increased polar moment of inertia.
8 . The method of claim 1 , wherein the polar moment of inertia is calculated by:
I
=
ρπ
r
bit
4
t
2
where r bit is the radius of the drill bit, ρ is the body density of the drill bit, and t is the length of the PDC drill bit and collar that is energized by the HFTO.
9 . The method of claim 1 , wherein the model is expressed mathematically as follows:
Δω
(
ω
-
Δω
/
2
)
=
-
2
k
σ
(
ch
r
h
o
l
e
)
1
.
5
ρπ
r
bit
4
t
wherein ω represents the rotary speed of the drill bit, Δω represents a change in the rotary speed and the HFTO propensity, σ represents the rock strength of the subterranean formation, h represents the cutter depth of cut of the drill bit, r hole represents the radius of the subterranean borehole, p represents the drill bit body density of the drill bit, r bit represents the radius of the drill bit, t represents the length of the drill bit and collar that is energized by the HFTO, and c and k are the one or more constants.
10 . A bottom hole assembly (BHA) configured for drilling a subterranean wellbore, the BHA comprising:
a drill bit coupled to at least one BHA tool, the drill bit including a fixed blade polycrystalline diamond compact (PDC) drill bit, the PDC drill bit including an upper pin end configured for coupling with the BHA tool and a drill bit body having a plurality of cuttings blades extending radially outward from the drill bit body, each of the cutting blades including a plurality of cutting elements deployed thereon,
wherein the PDC drill bit has a gauge diameter between 6.75 inches and 12 inches, a polar moment of inertia of greater than 102 lb*in 2 , and a high frequency torsional oscillation (HFTO) propensity of the BHA below a corresponding HFTO threshold,
wherein the polar moment of inertia is a function of parameters including a radius of the PDC drill bit, a body density of the PDC drill bit, and a length of the PDC drill bit and collar that is energized by the HFTO, and
wherein the HFTO propensity is a function of the parameters of the polar moment of inertia, a cutter depth of cut of the PDC drill bit, a rotary speed of the PDC drill bit, a rock strength of a subterranean formation, a radius of the subterranean wellbore, and one or more constants.
11 . The BHA of claim 10 , wherein:
the drill bit body comprises a high strength steel drill bit body.
12 . The BHA of claim 10 , wherein the PDC drill bit comprises an outer sleeve deployed about a lower shaft portion of the PDC drill bit, the outer sleeve increasing the polar moment of inertia of the PDC drill bit.
13 . The BHA of claim 10 , wherein the PDC drill bit comprises a plurality of blade extenders that extend a length of the corresponding cutting blades, the plurality of blade extenders increasing the polar moment of inertia of the PDC drill bit.
14 . The BHA of claim 13 , wherein the plurality of blade extenders are the same width as the corresponding drill bit blade.
15 . The BHA of claim 10 , wherein the polar moment of inertia is modeled with the equation:
Δ
ω
(
ω
-
Δω
/
2
)
=
-
2
k
σ
(
ch
r
h
o
l
e
)
1.5
ρπ
r
bit
4
t
wherein ω represents the rotary speed of the PDC drill bit, Δω represents the change in the rotary speed and the HFTO propensity, σ represents the rock strength of the subterranean formation, h represents the cutter depth of cut of the PDC drill bit, r hole represents the radius of the subterranean wellbore, ρ represents the body density of the PDC drill bit, r bit represents the radius of the PDC drill bit, t represents the length of the PDC drill bit and collar that is energized by the HFTO, and the one or more constants comprise c and k.
16 . The BHA of claim 10 , wherein the polar moment of inertia is calculated by:
I
=
ρπ
r
b
i
t
4
t
2
where r bit is the radius of the PDC drill bit, p is the body density of the PDC drill bit, and t is the length of the PDC drill bit and collar that is energized by the HFTO.
17 . A modified bottom hole assembly (BHA) configured for drilling a subterranean borehole and for reducing a susceptibility to high-frequency torsional oscillations (HFTO) while drilling, wherein the modified BHA comprises at least a drill bit with a gauge diameter between 6.75 inches and 12 inches and an additional annular mass coupled with a lower BHA tool, wherein the modified BHA has a polar moment of inertia that is greater than 102 lb*in 2 , wherein the polar moment of inertia is a function of parameters including a radius of the drill bit, a body density of the drill bit, and a length of the drill bit and collar that is energized by the HFTO, and wherein the HFTO propensity is a function of the parameters of the polar moment of inertia, a cutter depth of cut of the drill bit, a rotary speed of the drill bit, a rock strength of a subterranean formation, a radius of the subterranean borehole, and one or more constants.
18 . The modified BHA of claim 17 , wherein the additional annular mass in the modified BHA comprises an outer sleeve deployed about a lower shaft portion of the drill bit, the outer sleeve increasing the polar moment of inertia at least 25%.
19 . The modified BHA of claim 17 , wherein the lower BHA tool comprises a rotary steerable system (RSS) and the additional annular mass in the modified BHA comprises an outer sleeve deployed about a lower body portion of the RSS, the outer sleeve increasing the polar moment of inertia at least 25%.
20 . The modified BHA of claim 17 , wherein the drill bit in the modified BHA comprises a plurality of blade extenders that extend a length of corresponding drill bit blades, wherein the plurality of blade extenders are the same width as the corresponding drill bit blade.