Method for determining drill collar whirl in a bottom hole assembly and method for determining borehole size

A method for determining the existence of a whirling condition during the drilling of a borehole, comprising:

• determining the rotational rate of a tool in operation in a borehole;
• assuming the tool is in forward whirl, identifying in graphic representations locations where possible tool failure is likely, said locations being locations of transition from forward to backward and backward to forward whirl, modifying at least one parameter of drilling to prevent said failure, and comparing measurement values and determinations for the radius of the borehole, the point in space, and the tool rotational rate in an equation to verify the forward whirl assumption;
• assuming the tool is in backward whirl, identifying in graphic representations locations where possible tool failure is likely, said locations being locations of transition from forward to backward and backward to forward whirl, modifying at least one parameter of drilling to prevent said failure, and comparing the whirl rate, the tool rotational rate, the point in space, measurement values and determinations for the radius of the borehole, and time in an equation to verify the backward whirl assumption;
• and
• superimposing graphic representations of radii plotted over time to provide a continuous whirl curve whereby the existence of a forward or backward whirling condition of the tool in the borehole is determined.

A method for determining the existence of a whirling condition during the drilling of a borehole comprising:

• measuring acceleration of a bottom hole assembly to determine at least one acceleration value;
• measuring rotational speed of said bottom hole assembly to determine at least one rotational speed value;
• and
• calculating, based upon said at least one acceleration value and said at least one rotational speed value, a radius of rotation in the time domain to determine the existence and identification of a whirl condition within said bottom hole assembly, said calculating comprising,
• continuously determining one of computed borehole diameter and radius dimensions with equations for each of an assumed forward whirl condition and an assumed backward whirl condition over time,
• plotting said dimensions over time, and
• determining areas of forward synchronous whirl, with and without slip, and backward whirl, with and without slip, over time from said plot.