Dissolvable aluminum downhole plug

Abstract

A downhole plug for use in oil and gas well completions made of aluminum, dissolves in natural wellbore fluids, has a dissolvable seal made of aluminum split rings or a degradable elastomer, has a backup pump out ring, and may be provided to the well site as an interchangeable parts kit for adaption to the well's requirements, provides an interventionless plug in a well.

1 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, comprising:
 a mandrel;   a first non-elastomeric ring comprised of metal in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   a second non-elastomeric ring comprised of metal in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   the outer perimeter of the preset first ring has a greater axial width than the inner perimeter of the preset first ring and the outer perimeter of the preset second ring has a greater axial width than the inner perimeter of the preset second ring;   the preset first and second rings' outer perimeters do not obstruct movement of the tool in the well;   a non-gap portion of the preset first ring is adjacent the preset second ring's gap;   a non-gap portion of the preset second ring is adjacent the preset first ring's gap;   a first expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the first expander toward the first ring and expand the first ring radially outward to press the first ring's outer perimeter against the casing, the first ring's expanded configuration being the first ring's post-set configuration, and expanding the first ring radially outward will circumferentially expand the first ring's preset gap to a wider first ring post-set gap;   a second expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the second expander toward the second ring and expand the second ring radially outward to press the second ring's outer perimeter against the casing, the second ring's expanded configuration being the second ring's post-set configuration, and expanding the second ring radially outward will circumferentially expand the second ring's preset gap to a wider second ring post-set gap; and   the tool is configured and comprised so in the tool's post-set configuration:   the first ring's post-set gap is adjacent the casing;   the second ring's post-set gap is adjacent the casing;   a non-gap portion of the post-set first ring is adjacent the post-set second ring's gap;   a non-gap portion of the post-set second ring is adjacent the post-set first ring's gap;   the upper side of the post-set first ring is adjacent the lower side of the post-set second ring;   the post-set first ring and the post-set second ring are configured to cooperatively seal against axial fluid flow through any of the first ring gap, the second ring gap, and between the first and second rings and the casing, so the tool isolates a zone above the tool from a zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool;   the tool and the rings are configured and comprised to be interventionless, namely, the tool and the rings will degrade enough within less than five days after the tool is immersed in a natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than  7  and hydrocarbons can be produced from a zone below where the tool was set in the well, without milling out the tool, retrieval of the tool from the well, or other intervention on the tool from the surface; and the tool does not have an elastomeric sealing element for sealing the tool to the casing when the tool is set against the casing.   
     
     
         2 . The tool of  claim 1 , comprising: the tool and the rings are configured and comprised to be interventionless, namely, the tool and the rings degrade enough within less than two days after the tool is immersed in the natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than 7 so hydrocarbons can be produced from a zone below where the tool was set in the well without milling out the tool, retrieval of the tool from the well or other intervention on the tool from the surface. 
     
     
         3 . The tool of  claim 1 , comprising: the first ring's preset gap fully separates the first ring, the first ring being a fully split ring, and the second ring's preset gap fully separates the second ring, the second ring being a fully split ring. 
     
     
         4 . The tool of  claim 1 , comprising:
 a portion of the first ring's inner perimeter is canted relative to the mandrel's axis;   the first expander has an outer face facing the first ring which outer face is canted relative to the mandrel's axis;   the first ring's canted inner perimeter portion and the first expander's canted outer face are canted in the same direction relative to the mandrel's axis;   the first ring and the first expander are configured and located so moving the first expander toward the first ring when setting the tool moves the first expander's canted outer face toward the first ring's canted inner perimeter portion and radially expands the first ring outward against the casing; and   a portion of the second ring's inner perimeter is canted relative to the mandrel's axis;   the second expander has an outer face facing the first ring which outer face is canted relative to the mandrel's axis   the second ring's canted inner perimeter portion and the second expander's canted portion are canted in the same direction relative to the mandrel's axis; and   the second ring and the second expander are configured and located so moving the first expander toward the first ring when setting the tool moves the second expander's canted outer face against the second ring's canted inner perimeter portion and radially expands the second ring outward against the casing.   
     
     
         5 . The tool of  claim 1 , comprising: one of the preset rings has a circumferential groove on a side and the other of the preset rings has a circumferential tongue on a side, the groove and tongue being adjacent and engaging each other. 
     
     
         6 . The tool of  claim 1 , comprising: the first and second rings are comprised essentially of metal, the metal comprising aluminum or magnesium. 
     
     
         7 . The tool of  claim 1 , comprising:
 the preset first ring has a first end at a first side of the first ring's preset gap and has a second end at a second side of the first ring's preset gap, the first ring's first end has an extended circumferential portion and a retracted circumferential portion, and the first ring's second end has a reciprocal retracted circumferential portion opposite the first end's extended portion and a reciprocal extended circumferential portion opposite the first end's retracted portion;   the post-set first ring's first end extended portion and the post-set first ring's second end extended portion circumferentially overlap, and the post-set first ring's first end retracted portion and the post-set first ring's second end retracted portion do not circumferentially overlap;   the preset second ring has a first end at a first side of the second ring's preset gap and has a second end at a second side of the second ring's preset gap, the second ring's first end has an extended circumferential portion and a retracted circumferential portion, and the second ring's second end has a reciprocal retracted circumferential portion opposite the first end's extended portion and a reciprocal extended circumferential portion opposite the first end's retracted portion;   the post-set second ring's first end extended portion and the post-set ring's second end extended portion circumferentially overlap, and the post-set second ring's first end retracted portion and second end retracted portion do not circumferentially overlap; and   the post-set first ring and the post-set second ring are configured to cooperatively seal against axial fluid flow through any of the first ring gap, the second ring gap, and between the first and second rings and the casing, so the tool isolates the zone above the tool from the zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool.   
     
     
         8 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, comprising:
 a mandrel;   a first non-elastomeric ring comprised of metal in a retracted preset configuration located about the mandrel, the first ring having an outer perimeter, an inner perimeter, an upper side, and a lower side, the first ring being configured and comprised to be radially expandable during setting of the tool to a post-set configuration in which the first ring's outer perimeter is pressed against the casing;   the first ring has a predetermined separable portion, namely: a full separation in the first ring from the first ring's outer perimeter to the first ring's inner perimeter, a separation only part way through the first ring between the first ring's outer perimeter and the first ring's inner perimeter, or a weakening groove or frangible portion extending at least part way between the first ring's outer perimeter and the first ring's inner perimeter;   a second non-elastomeric ring comprised of metal in a preset configuration located about the mandrel, the second ring having an outer perimeter, an inner perimeter, an upper side, and a lower side, the first ring configured and comprised to be radially expandable during setting of the tool to a post-set configuration in which the second ring's outer perimeter is pressed against the casing;   the second ring has a predetermined separable portion, namely: a full separation in the second ring from the second ring's outer perimeter to the second ring's inner perimeter, a separation only part way through the second ring between the second ring's outer perimeter and the second ring's inner perimeter, or a weakening groove or frangible portion extending at least part way between the second ring's outer perimeter and second ring's inner perimeter;   the preset first and second rings' outer perimeters do not obstruct movement of the tool in the well;   a non-separable portion of the preset first ring is adjacent the preset second ring's separable portion;   a non-separable portion of the preset second ring is adjacent the preset first ring's separable portion;   a first expander located about the mandrel in a preset position, the tool configured and comprised so setting the tool will move the first expander toward the first ring and expand the first ring radially outward to press the first ring's outer perimeter against the casing;   a second expander located about the mandrel and a preset position, the tool configured and comprised so setting the tool will move the second expander toward the second ring and expand the first ring radially outward to press the first ring's outer perimeter against the casing;   the first ring is configured and comprised so radial expansion of the first ring during setting of the tool will cause the first ring to circumferentially separate or further separate at the separable portion, the post-set ring's separation space or further separation space being a first ring gap;   the second ring is configured and comprised so radial expansion of the second ring during setting of the tool will cause the second ring to circumferentially separate or further separate at the separable portion, the post-set ring's separation space or further separation space being a second ring gap;   the tool is configured and comprised and the preset rings' separable portions are located relative to each other so radial expansion of the rings by the expanders and circumferential expansion of the rings at the ring's gaps produce a post-set tool and rings configuration, namely:   the first ring's post-set gap is adjacent the casing;   the second ring's post-set gap is adjacent the casing;   a non-gap portion of the post-set first ring is adjacent the post-set second ring's gap;   a non-gap portion of the post-set second ring is adjacent the post-set first ring's gap;   the upper side of the post-set first ring is adjacent the lower side of the post-set second ring; and   the post-set first ring and the post-set second ring are configured to cooperatively seal against axial fluid flow through any of the first ring gap, the second ring gap, and between the first and second rings and the casing, and the tool isolates the zone above the tool from the zone below the tool to permit fracing in a zone above the tool in isolation from a zone below the tool.   
     
     
         9 . The tool of  claim 8 , comprising: the tool does not have an elastomeric sealing element for sealing the tool to the casing when the tool is set against the casing. 
     
     
         10 . The tool of  claim 8  comprising: the outer perimeter of the preset first ring has a greater axial width than the inner perimeter of the preset first ring and the outer perimeter of the preset second ring has a greater axial width than the inner perimeter of the preset second ring. 
     
     
         11 . The tool of  claim 8  comprising: the first and second rings are the only rings in the tool which in the tool's post-set configuration cooperatively seal the tool to the casing against axial fluid flow through the casing. 
     
     
         12 . The tool of  claim 8 , comprising: the metallic post-set first and second rings press against the inner wall of the casing creating a metal ring to metal casing seal. 
     
     
         13 . The tool of  claim 8 , comprising: the rings are comprised essentially of metal, the metal comprising aluminum or magnesium which will degrade in a natural aqueous downhole fluid from the formation in the well having a pH less than toward 7. 
     
     
         14 . The tool of  claim 8 , comprising: the tool and the rings are configured and comprised to be interventionless, namely, within less than five days after the tool and the rings are immersed in a natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than 7, the tool and the rings degrade enough so the tool ceases to isolate the zone above the tool from a zone below the tool, and hydrocarbons can be produced from a zone below where the tool was set in the well without milling out the tool, retrieval of the tool from the well or other intervention on the tool from the surface. 
     
     
         15 . The tool of  claim 8 , comprising: the tool and the rings are configured and comprised to be interventionless, namely, within less than two days after the tool and the rings are immersed in a natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than 7, the tool and the rings degrade enough so the tool ceases to isolate the zone above the tool from a zone below the tool, and hydrocarbons can be produced from a zone below where the tool was set in the well without milling out the tool, retrieval of the tool from the well or other intervention on the tool from the surface. 
     
     
         16 . The tool of  claim 8 , comprising: the rings' outer perimeters are malleable enough to conform to the inner wall of the casing, and provide a more fluid tight seal with the casing than similarly configured non-malleable steel rings. 
     
     
         17 . The tool of  claim 8 , comprising: the rings' outer perimeters are comprised of a material which is more malleable than the rings' inner perimeters. 
     
     
         18 . The tool of  claim 8 , comprising: in the tool's pre-set configuration, one of the first ring or the second ring has a circumferential groove on a side, and the reciprocal second ring or first ring has a circumferential tongue on a side adjacent the circumferential groove, and the groove and tongue are adjacent and engage each other. 
     
     
         19 . The tool of  claim 8 , comprising: one of the first ring or the second ring has a radial groove on a side, and the reciprocal second ring or first ring has a radial tongue on its side is adjacent the radial groove, the groove and tongue are adjacent and engage each other, and the engaged adjacent tongue and groove facilitate nonalignment of the rings' separable portions. 
     
     
         20 . The tool of  claim 8 , comprising: the first ring's separable portion is linear, and the second ring's separable portion is linear. 
     
     
         21 . The tool of  claim 8 , comprising:
 the preset first ring has a first end at a first side of the first ring's separable portion and has a second end at a second side of the first ring's separable portion, the first ring's first end and second end are reciprocally nonlinear, the first ring's first end has an extended circumferential portion and a retracted circumferential portion, and the first ring's second end has a reciprocal retracted circumferential portion opposite the first end's extended portion and has a reciprocal extended circumferential portion opposite the first end's retracted portion;   and a first ring's first end extended portion circumferentially overlaps a first ring's second end extended portion, and   the preset second ring has a first end at a first side of the second ring's separable portion and has a second end at a second side of the second ring's separable portion, the second ring's first end and second end are reciprocally nonlinear, the second ring's first end has an extended circumferential portion and a retracted circumferential portion, and the second ring's second end has a reciprocal retracted circumferential portion opposite the first end's extended portion and a reciprocal extended circumferential portion opposite the first end's retracted portion; and a second ring's first end extended portion circumferentially overlaps a second ring's second end extended portion.   the post-set first ring's first end extended portion and the post-set first ring's second end extended portion circumferentially overlap, and the post-set first ring's first end retracted portion and the post-set first ring's second end retracted portion do not circumferentially overlap;   the post-set second ring's first end extended portion and the post-set ring's second end extended portion circumferentially overlap, and the post-set second ring's first end retracted portion and second end retracted portion do not circumferentially overlap; and   the post-set first ring and the post-set second ring are configured to cooperatively seal against axial fluid flow through any of the first ring gap, the second ring gap, and between the first and second rings and the casing, so the tool isolates the zone above the tool from the zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool.   
     
     
         22 . The tool of  claim 8 , comprising:
 the preset first ring has:   a first end at a first side of the first ring's separable portion and a second end at the other side of the first ring's separable portion;   the first end has an extended circumferential portion and a retracted circumferential portion;   the second end has a reciprocal retracted circumferential portion opposite the first end's extended portion and has a reciprocal extended circumferential portion opposite the first end's retracted portion;   the post-set first ring's first end extended portion and second end extended portion circumferentially overlap, and the post-set first ring's first end retracted portion and second end retracted portion do not circumferentially overlap;   the preset second ring has:   a first end at a first side of the second ring separable portion and a second end at the other side of the second ring separable portion;   the first end has an extended portion and a retracted portion, the second end has a reciprocal retracted portion opposite the first end's extended portion and a reciprocal extended portion opposite the first end's retracted portion;   the post-set second ring's first end extended portion and second end extended portion circumferentially overlap, and the post-set second ring's first end retracted portion and second end retracted portion do not circumferentially overlap; and   the post-set first ring and the post-set second ring are configured to cooperatively seal against fluid flow through the first ring gap, through the second ring gap, and between the first and second rings and the casing, and the tool isolates the zone above the tool from the zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool.   
     
     
         23 . The tool of  claim 8 , comprising:
 a portion of the first ring's inner perimeter is canted relative to the mandrel's axis;   the first expander has an outer face facing the first ring canted relative to the mandrel's axis;   the first ring's canted inner perimeter portion and the first expander's canted face are canted in the same direction relative to the mandrel's axis;   the tool is configured so moving the first expander toward the first ring moves the first expander's canted face toward the first ring's canted inner perimeter portion and radially expands the first ring away toward the casing; and   a portion of the second ring's inner perimeter is canted relative to the mandrel's axis;   the second expander has an outer face facing the first ring canted relative to the mandrel's axis   the second ring's canted inner perimeter portion and the second expander's canted portion are canted in the same direction relative to the mandrel's axis; and   tool is configured so moving the second expander toward the first ring moves the second expander's canted portion against the second ring's canted inner perimeter portion and radially expands the second ring toward the casing.   
     
     
         24 . The tool of  claim 8 , comprising:
 the first ring has a flat upper or lower side;   the second ring has a flat upper or lower side; and   the flat sides are approximately perpendicular to the mandrel and adjacent each other.   
     
     
         25 . The tool of  claim 8 , comprising:
 the first ring's separable portion is a full separation through the first ring from the ring's outer perimeter through to the ring's inner perimeter; and   the second ring's separable portion is a full separation through the second ring from the ring's outer perimeter through to the ring's inner perimeter.   
     
     
         26 . The tool of  claim 8 , comprising:
 the first ring's separable portion is a separation only part way through the first ring between the first ring's outer perimeter and the first ring's inner perimeter; and   the second ring separable portion is a separation only part way through the second ring between the second ring's outer perimeter and the second ring's inner perimeter.   
     
     
         27 . The tool of  claim 8 , comprising:
 the first ring separable portion is a weakening groove or frangible portion extending at least part way between the first ring's outer perimeter and inner perimeter; and   the second ring separable portion is a weakening groove or frangible portion extending at least part way between the second ring's outer perimeter and inner perimeter.   
     
     
         28 . The tool of  claim 8 , comprising: the rings are comprised of metallic materials which are more electrically negative than the mandrel and the casing so the rings will be sacrificial anodes relative to the mandrel and the casing when the tool is in the casing and immersed in acidic natural downhole fluids, the resulting galvanic corrosion speeding degradation of the rings and speeding release of the rings from the casing relative to similar rings not subject to the galvanic corrosion. 
     
     
         29 . The tool of  claim 8 , comprising: the first and second rings are comprised of metallic materials with different electrochemical potentials, namely, one ring being an anode ring which is more electrically negative than the other ring, the other ring being a cathode ring, so the anode ring will be a sacrificial anode relative to the cathode ring when the rings are in the casing and immersed in acidic natural downhole fluids, so the resulting galvanic corrosion will speed degradation of the rings and speed release of the rings from the casing relative to similar rings not subject to the anode ring/cathode ring galvanic corrosion. 
     
     
         30 . The tool of  claim 8 , comprising:
 the first and second rings each have multiple predetermined separable portions;   non-separable portions of the preset first ring are adjacent the preset second ring's multiple separable portions;   non-separable portions of the preset second ring are adjacent the preset first ring's multiple separable portions; and   the rings' separable portions and non-separable portions are located so in the tool's post set configuration:   non-gap portions of the post-set first ring are adjacent the post-set second ring's multiple gaps; and   non-gap portions of the post-set second ring are adjacent the post-set first ring's multiple gaps.   
     
     
         31 . The tool of  claim 28 , comprising: the first ring and the second ring, each has at least three separable portions, each ring's separable portions being at least thirty degrees apart. 
     
     
         32 . The tool of  claim 8 , comprising:
 at least one of each rings' preset separable portions is a first preset separable portion with a full separation of 3/32 inches or more and the tool is configured so the first separable portions have a post-set gap of at least 1.5 inches.   
     
     
         33 . The tool of  claim 8 , comprising the first ring's gap and the second ring's gap each has substantially the same tangential angle relative to the mandrel's axis and each has a tangential angle of 45 degrees to 70 degrees relative to the mandrel's axis. 
     
     
         34 . The tool of  claim 8 , comprising: the first and second rings are located, configured and sized to circumferentially expand at their separable portions responsive to being radially expanded by the first and second expanders respectively, each ring's circumferential expansion at each ring's separable portion or portions causing the rings to circumferentially slide against each other during radial expansion of the rings when the tool is being set. 
     
     
         35 . The tool of  claim 32 , comprising: an anti-seize agent located between the first ring and the second ring which anti-seize agent facilitates the rings circumferentially sliding against each other during the radial expansion of the rings when the tool is being set relative to similar rings without an anti-seize agent between the rings. 
     
     
         36 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well having a wellbore fluid, the tool comprising:
 a mandrel;   a first split metallic ring located about the mandrel, and a second split metallic ring located about the mandrel, the first and second rings each having an inner perimeter and an outer perimeter, and an upper side and a lower side;   the first ring and the second ring each has a pre-set configuration in which each ring's outer perimeter does not obstruct movement of the tool in the well;   a first expander located about the mandrel for moving axially on the mandrel and wedging the first ring radially outward toward a post-set configuration when the tool is set in the well, and a second expander located about the mandrel for moving axially on the mandrel and wedging the second ring radially outward toward a post-set configuration when the tool is set in the well;   the tool is configured and comprised so the first ring and the second ring each has a post-set configuration in which:   the first and second rings are radially expanded from their pre-set configurations so the first and second rings' outer perimeters press against the casing;   the first ring has an outer perimeter gap adjacent the casing, the second ring has an outer perimeter gap adjacent the casing, the first ring has a non-gap portion adjacent the casing and adjacent the second ring's gap, and the second ring has a non-gap portion adjacent the casing and adjacent the first ring's gap, and the non-gap portions of the first ring and second ring seal against the casing enough to isolate a zone above the tool from a zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool; and   the rings are configured and comprised to dissolve quickly enough in a natural aqueous downhole fluid from the formation in the well having a pH less than toward 7 so within less than five days after the tool is immersed in the well's wellbore fluid, the rings dissolve enough so the tool ceases to isolate the upper zone from the lower zone, without milling out the tool, retrieval of the tool from the well or other intervention on the tool from the surface.   
     
     
         37 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, comprising:
 a mandrel;   a sealing element located about the mandrel for impeding fluid flow between the tool and the casing, the sealing element comprising a metallic ring;   wherein the ring has a pre-set configuration in which its outer perimeter does not obstruct movement of the tool in the well, and a post-set configuration in which its outer perimeter seals against the casing;   an expander located about the mandrel, configured and comprised so setting the tool will move the expander toward the ring so the expander will expand the ring toward the casing and against the casing;   the metallic ring is malleable enough so upon setting the tool, the expanded ring against the casing will seal the tool against radial flow of fluid between the sealing element and the casing;   the ring is configured and comprised to dissolve quickly enough in a natural aqueous downhole fluid from the formation in the well having a pH less than toward 7 so within less than five days after the tool is immersed in the well's wellbore fluid, the ring dissolves enough so the tool ceases to isolate the upper zone from the lower zone, without milling out the tool, retrieval of the tool from the well or other intervention on the tool from the surface; and   the tool does not have an elastomeric sealing element for sealing the tool to the casing when the tool is set against the casing.   
     
     
         38 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, comprising:
 a mandrel;   a first non-elastomeric ring which will degrade in an aqueous fluid in the well having a pH less than 7, the first ring being in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   a second non-elastomeric ring which will degrade in an aqueous fluid in the well having a pH less than 7, the second ring in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   the outer perimeter of the preset first ring has a greater axial width than the inner perimeter of the preset first ring and the outer perimeter of the preset second ring has a greater axial width than the inner perimeter of the preset second ring;   the preset first and second rings' outer perimeters do not obstruct movement of the tool in the well;   a non-gap portion of the preset first ring is adjacent the preset second ring's gap;   a non-gap portion of the preset second ring is adjacent the preset first ring's gap;   a first expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the first expander toward the first ring and expand the first ring radially outward to press the first ring's outer perimeter against the casing, the first ring's expanded configuration being the first ring's post-set configuration, and expanding the first ring radially outward will circumferentially expand the first ring's preset gap to a wider first ring post-set gap;   a second expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the second expander toward the second ring and expand the second ring radially outward to press the second ring's outer perimeter against the casing, the second ring's expanded configuration being the second ring's post-set configuration, and expanding the second ring radially outward will circumferentially expand the second ring's preset gap to a wider second ring post-set gap;   a portion of the first ring's inner perimeter is canted relative to the mandrel's axis;   the first expander has an outer face facing the first ring which outer face is canted relative to the mandrel's axis;   the first ring's canted inner perimeter portion and the first expander's canted outer face are canted in the same direction relative to the mandrel's axis;   the first ring and the first expander are configured and located so moving the first expander toward the first ring when setting the tool moves the first expander's canted outer face toward the first ring's canted inner perimeter portion and radially expands the first ring outward against the casing; and   a portion of the second ring's inner perimeter is canted relative to the mandrel's axis;   the second expander has an outer face facing the first ring which outer face is canted relative to the mandrel's axis   the second ring's canted inner perimeter portion and the second expander's canted portion are canted in the same direction relative to the mandrel's axis; and   the second ring and the second expander are configured and located so moving the first expander toward the first ring when setting the tool moves the second expander's canted outer face against the second ring's canted inner perimeter portion and radially expands the second ring outward against the casing;   the tool is configured and comprised so in the tool's post-set configuration:   the first ring's post-set gap is adjacent the casing;   the second ring's post-set gap is adjacent the casing;   a non-gap portion of the post-set first ring is adjacent the post-set second ring's gap;   a non-gap portion of the post-set second ring is adjacent the post-set first ring's gap;   the upper side of the post-set first ring is adjacent the lower side of the post-set second ring;   the post-set first ring and the post-set second ring are configured to cooperatively seal against axial fluid flow through any of the first ring gap, the second ring gap, and between the first and second rings and the casing, so the tool isolates a zone above the tool from a zone below the tool to permit fracing in the zone above the tool in isolation from the zone below the tool;   the tool and the rings are configured and comprised to be interventionless, namely, the tool and the rings will degrade enough within less than five days after the tool is immersed in a natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than 7 and hydrocarbons can be produced from a zone below where the tool was set in the well, without milling out the tool, retrieval of the tool from the well, or other intervention on the tool from the surface; and   the tool does not have an elastomeric sealing element for sealing the tool to the casing when the tool is set against the casing.   
     
     
         39 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, the tool comprising:
 a mandrel;   a non-elastomeric sealing element comprised of aluminum or magnesium located about the mandrel for impeding fluid flow between the tool and the casing, the sealing element comprising a first split metallic ring, and a second split metallic ring, the first and second rings each having an inner perimeter and an outer perimeter;   each first and second ring has a pre-set configuration in which its outer perimeter does not obstruct movement of the tool in the well;   each of the first and second rings has one or more outer perimeter gaps, and the gaps in the first ring are not adjacent the gaps in the second ring;   each first and second ring has a post-set configuration in which its outer perimeter presses against the casing;   each of the first and second rings has one or more outer perimeter gaps, and the gaps in the first ring are not adjacent the gaps in the second ring;   the post-set first and second rings' perimeters press against the casing, the rings' outer perimeters are malleable enough to conform to the inner wall of the casing enough to provide a more fluid tight seal with the casing than similarly configured non-malleable steel rings and to impede axial fluid flow between the tool and the casing enough to isolate a zone above the tool from a zone below the tool to permit fracing in the zone above the tool; and   the tool does not have an elastomeric sealing element for sealing the tool to the casing.   
     
     
         40 . A settable downhole tool for temporarily isolating a zone above the tool from a zone below the tool in a cased well, comprising:
 a mandrel;   a first non-elastomeric ring comprised of metal in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   a second non-elastomeric ring comprised of metal in a retracted preset configuration located about the mandrel, having an outer perimeter, an inner perimeter, an upper side, a lower side, and a preset gap from the outer perimeter to the inner perimeter;   the outer perimeter of the preset first ring has a greater axial width than the inner perimeter of the preset first ring and the outer perimeter of the preset second ring has a greater axial width than the inner perimeter of the preset second ring;   the preset first and second rings' outer perimeters do not obstruct movement of the tool in the well;   a non-gap portion of the preset first ring is adjacent the preset second ring's gap;   a non-gap portion of the preset second ring is adjacent the preset first ring's gap;   a first expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the first expander toward the first ring and expand the first ring radially outward to press the first ring's outer perimeter against the casing, the first ring's expanded configuration being the first ring's post-set configuration, and expanding the first ring radially outward will circumferentially expand the first ring's preset gap to a wider first ring post-set gap;   a second expander located about the mandrel, configured and comprised so setting the tool in the cased well will move the second expander toward the second ring and expand the second ring radially outward to press the second ring's outer perimeter against the casing, the second ring's expanded configuration being the second ring's post-set configuration, and expanding the second ring radially outward will circumferentially expand the second ring's preset gap to a wider second ring post-set gap; and   the tool is configured and comprised so in the tool's post-set configuration:   the first ring's post-set gap is adjacent the casing;   the second ring's post-set gap is adjacent the casing;   a non-gap portion of the post-set first ring is adjacent the post-set second ring's gap;   a non-gap portion of the post-set second ring is adjacent the post-set first ring's gap;   the upper side of the post-set first ring is adjacent the lower side of the post-set second ring;   the rings are configured and comprised so the post-set rings pressed against the casing leave unsealed areas between the rings and the casing, and the rings do not seal against the casing enough to prevent the axial flow of fluid through between the rings and the casing and do not isolate the zone below the tool from the zone above the tool enough to enable fracing the zone above the tool in isolation from the zone below the tool, and the rings are configured and comprised so the flow of wellbore fluid through the unsealed areas between the rings and the casing degrades the rings' outer perimeters, and the degraded rings' outer perimeters will further conform to the casing and further seal against the casing enough to isolate the zone below the tool from the zone above the tool to enable fracing the zone above the tool in isolation from the zone below the tool;   the tool and the rings are configured and comprised to be interventionless, namely, the tool and the rings will degrade enough within less than five days after the tool is immersed in a natural aqueous downhole fluid in the well produced from formation flow in the well having a pH less than 7 and hydrocarbons can be produced from a zone below where the tool was set in the well, without milling out the tool, retrieval of the tool from the well, or other intervention on the tool from the surface; and   the tool does not have an elastomeric sealing element for sealing the tool to the casing when the tool is set against the casing.