EP0550254A2
Expired / Lapsed
EP
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Method of determining drillstring bottom hole assembly vibrations
Assignee: Phillips Petroleum Co
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Filing: 1992-12-23
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Granted: —
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Expires: 2012-12-23
Abstract
Abstract Lateral vibrations of drillstring bottom hole assemblies are confirmed by sensing longitudinal and torsional accelerations or displacements of the drillstring at or near its top end during rotation and determining the lateral critical speed and displacement of the drillstring from the mode shape of the bottom hole assembly which occurs during forward synchronous whirl and longitudinal shortening of the bottom hole assembly resulting from such whirl. Lateral motion of the bottom hole assembly, while drilling, is estimated based on longitudinal and torsional measurements at the top of the drillstring. Radial displacement of the bottom hole assembly due to impacting of the borehole wall imparts a torsional impulse which, together with considerable radial motion, is repeated each revolution. The lateral or radial motion causes a small axial motion to develop in the bottom hole assembly which results in an axial force on and axial shortening of the drillstring which varies once per revolution. <IMAGE>
Inventors
- 👤 Paul R. Paslay
- 👤 Yih-Min Jan
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 20:19
CPC Classifications
E; E21; E21B; E21B47/00; E21B47/007; G; G01; G01H; G01H1/00
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
141 words
A method for determining the occurrence of at least one of lateral vibration or whirling of at least a portion of an elongated drillstring during rotation of said drillstring in a wellbore, said method comprising the steps of: placing sensor means on said drillstring during the rotation of said drillstring and at a predetermined point in relation to said portion of said drillstring; determining at least one lateral critical speed of said portion of said drillstring; determining the mode shape of the lateral displacement of said portion of said drillstring at said critical speed; determining the instantaneous change in length of said drillstring as a result of said lateral displacement of said portion of said drillstring; and comparing said change in length of said drillstring with displacement of said drillstring at said predetermined point derived from measurements with said sensor means.
Claim 2
Dependent Claim
42 words
The method set forth in Claim 1 wherein: the step of determining the critical speed includes characterizing the drillstring as a plurality of discrete masses concentrated at selected points along the drillstring and interconnected by weightless beam sections between the concentrated masses.
Claim 3
Dependent Claim
70 words
The method set forth in Claim 2 wherein: said portion of said drillstring includes a bottom hole assembly comprising a bit connected to one end of a first member and a second member connected to said first member at the opposite end of said first member and, the mass of said bit and half of the mass of said first member are lumped together as at least one discrete mass.
Claim 4
Dependent Claim
32 words
The method set forth in Claim 3 wherein: a second mass is determined by combining the mass of half of the first member with the mass of half of the second member.
Claim 5
Dependent Claim
60 words
The method set forth in Claim 2 including the step of: deriving an adjusted mass for each of said concentrated masses based on a coefficient which has a value related to the diameter of said portion of said drillstring, the diameter of the wellbore, the speed of rotation of the drillstring, and the kinematic viscosity of fluid in the wellbore.
Claim 6
Dependent Claim
54 words
The method set forth in Claim 1 wherein: the step of determining the mode shape includes the steps of characterizing the displacement of said portion of said drillstring as plural incremental displacements of at least one of a half sine wave and a combination of a half sine wave and a straight line segment.
Claim 7
Dependent Claim
37 words
The method set forth in Claim 6 including the step of: summing all of said incremental displacements between support points of said portion of said drillstring to determine a longitudinal shortening of said portion of said drillstring.
Claim 8
Dependent Claim
47 words
The method set forth in Claim 7 wherein: the longitudinal shortening of said portion of said drillstring is determined from the equation: SHORT = (πA/2) ²/L + B²L/2 wherein L = the length of said portion of said drillstring between nodes and A and B are constants.
Claim 9
Independent Claim
86 words
The method set forth in Claims 1 or 8 wherein: the step of determining the instantaneous change in length of said drillstring includes the step of determining the displacement of said drillstring resulting from a force F top acting on said portion of said drillstring wherein: F top = KT*SHT*SIN(ωt) where KT is the axial stiffness of a top part of said portion of said drillstring, SHT is the shortening of said top part, ω is the rotational speed of said drillstring and t is time.
Claim 10
Dependent Claim
84 words
The method set forth in Claim 9 wherein: the step of determining the instantaneous change in length of said drillstring includes the step of determining the displacement of said drillstring resulting from a force F bot acting on said portion of said drillstring wherein: F bot = KB*SHB*SIN(ωt) where KB is the axial stiffness of a bottom part of said portion of said drillstring, SHB is the shortening of said bottom part, ω is the rotational speed of said drillstring and t is time.
Claim 11
Dependent Claim
70 words
The method set forth in Claim 10 wherein: the step of determining the instantaneous change in length of said drillstring includes the step of determining the displacement of said drillstring resulting from a force F res acting on said portion of said drillstring wherein: F res = (KB*SHB-KT*SHT)SIN(ωt) and the displacements due to F top , F bot and F res are summed to determine said instantaneous change in length.
Claim 12
Dependent Claim
81 words
The method set forth in Claim 1 including the steps of: determining a torsional impulse imparted to said portion of said drillstring resulting from impacting of said portion of said drillstring with the wellbore wall; determining the torsional motion at said predetermined point on said drillstring resulting from said torsional impulse; and comparing said torsional motion of said drillstring resulting from said torsional impulse with torsional motion of said drillstring at said predetermined point derived from measurements with said sensor means.
Claim 13
Dependent Claim
28 words
The method set forth in Claim 12 wherein: said torsional impulse is determined by estimating the impact velocity of said portion of said drillstring against said wellbore wall.
Claim 14
Dependent Claim
63 words
The method set forth in Claim 13 wherein: said torsional impulse is determined from the equation: TIMPULSE (I) = (COEFFICIENT OF FRICTION) * (DRILL STRING DIAMETER) * RIMPULSE (I)/2 wherein RIMPULSE is the change in momentum of the portion of the drillstring which impacts said wellbore wall based on the coefficient of restitution of said portion of said drillstring and its radial momentum.
Claim 15
Dependent Claim
47 words
The method set forth in Claim 12 wherein: said torsional motion at said predetermined point on said drillstring is determined based on the weight of said drillstring, the shear modulus of the material of said drillstring, said torsional impulse, and the torsional spring constant of said drillstring.
Claim 16
Dependent Claim
68 words
The method set forth in Claim 15 including the step of: determining the angular acceleration of said drillstring at said predetermined point as a function of time using said sensor means; and transferring said angular acceleration to indicate the amplitude of said angular acceleration as a function of frequency to determine if a peak amplitude of angular acceleration is occurring at a lateral critical speed of said drillstring.
References Cited (Backward Citations)
No citation records indexed.
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