Flotation apparatus for providing buoyancy to tubular members

A downhole tubular component for use in a completion string, the tubular component comprising:

• a housing having a central axis and comprising a chamber disposed between first and second housing ends;
• and
• a plug assembly disposed in the chamber and dividing the chamber into an up-hole portion and a downhole portion;
• wherein the plug assembly comprises:
• a first glass member having a predetermined residual surface compression, a first face and a second face spaced apart from the first face, and a stress concentrator in the first face;
• a second glass member positioned uphole of the first glass member;
• wherein a first clearance gap is radially positioned between the first glass member and the housing, wherein a second clearance gap is radially positioned between the second glass member and the housing, wherein the first clearance gap has a first width measured radially from the first glass member to the housing and the second clearance gap has a second width measured radially from the second glass member to the housing, wherein the first width of the first clearance gap is greater than the second width of the second clearance gap;
• wherein the stress concentrator is configured to cause the first glass member to fail when the plug assembly is exposed to a burst pressure in the up-hole portion of the chamber having a magnitude that, in comparison to the predetermined residual surface compression, creates a net positive tensile stress on the first face having the stress concentrator;
• wherein the first clearance gap defines a space disposed about the first glass member configured to allow the first glass member to flex and expand radially outward when the plug assembly is exposed to the burst pressure;
• and
• wherein the plug assembly is disposed within the chamber such that the first face having the stress concentrator faces towards the downhole portion of the chamber.

A completion string comprising:

• a gas-filled lower tubular segment;
• an upper tubular segment configured to receive a liquid, wherein the upper tubular segment is positioned up-hole relative to the lower tubular segment;
• and
• a plug assembly disposed in a housing positioned between the lower and upper tubular segments and having a breakable barrier separating the lower tubular segment from the upper tubular segment before the breakable barrier fails, wherein the housing has a central axis;
• wherein the breakable barrier is configured to resist pressure in the liquid in the upper tubular segment and to fail when the pressure of the liquid is increased to exceed a predetermined burst pressure;
• and
• wherein the breakable barrier of the plug assembly comprises:
• a first tempered glass member having a predetermined residual surface compression, a first face, and at least one strength-reducing surface feature on the first face, the strength-reducing surface feature being configured to cause the first glass member to fail when the breakable barrier is exposed to the predetermined burst pressure;
• and
• a second tempered glass member positioned uphole of the first tempered glass member;
• wherein a first clearance gap is radially positioned between the first tempered glass member and the housing, wherein a second clearance gap is radially positioned between the second tempered glass member and the housing, wherein the first clearance gap has a first width measured radially from the first tempered glass member to the housing and the second clearance gap has a second width measured radially from the second tempered glass member to the housing, wherein the first width of the first clearance gap is greater than the second width of the second clearance gap;
• wherein the first clearance gap defines a space disposed about the first tempered glass member configured to allow the first tempered glass member to flex and expand radially outward when the breakable barrier is exposed to the predetermined burst pressure;
• wherein the first face and the at least one strength-reducing feature face toward the gas in the lower tubular segment.

A flotation device for a tubular member, the flotation device comprising:

• a tubular housing having a central axis and a chamber extending axially between first and second housing ends;
• and
• a plug assembly disposed in the chamber and dividing the chamber into an up-hole portion and a downhole portion, wherein the plug assembly comprises a breakable barrier including:
• a first disk of tempered glass and having a face with a strength-reducing surface feature, wherein the face and the strength-reducing surface feature face toward the downhole portion of the chamber;
• a second disc of tempered glass positioned uphole of the first disk of tempered glass;
• wherein a first clearance gap is radially positioned between the first disc of tempered glass and the housing, wherein a second clearance gap is radially positioned between the second disc of tempered glass and the housing, wherein the first clearance gap has a first width measured radially from the first disc of tempered glass to the housing and the second clearance gap has a second width measured radially from the second disc of tempered glass to the housing, wherein the first width of the first clearance gap is greater than the second width of the second clearance gap;
• and
• an annular seal sealingly coupled between the tubular housing and the plug assembly to prevent fluid flow through the chamber until the first disk breaks;
• wherein the first clearance gap defines a space disposed about the first disc configured to allow the first disc to flex and expand radially outward when the breakable barrier is exposed to a predetermined burst pressure.