Downhole tools having non-toxic degradable elements
Downhole tools for use in oil and gas production which degrade into non-toxic materials, a method of making them and methods of using them. A frac ball and a bridge plug comprised of polyglycolic acid which can be used in fracking a well and then left in the well bore to predictably, quickly, and safely disintegrate into environmentally friendly products without needing to be milled out or retrieved.
1. A downhole article comprising:
a non-composite body configured to block a downhole conduit in an initial configuration, wherein the non-composite body is stable in a dry condition at ambient temperature, and, when exposed to a downhole fluid having a temperature of at least about 136° F., the non-composite body will change within about 48 hours to a subsequent configuration that does not block the downhole conduit and, in its changed configuration, is then capable of passing through the downhole conduit; wherein:
the non-composite body is hard and prepared from high-molecular weight polyglycolic acid (PGA), namely Kuredux or its equivalent, which is suitable for high-pressure downhole fracking operations, has at least short-term term stability in ambient conditions, and will lose compression resistance and structural integrity due to hydrolysis in the downhole fluid in the wellbore;
the non-composite body is spherical, and is in the range of between about 0.75 inches to about 4.625 inches in diameter;
the non-composite body is homogenous;
the non-composite body will degrade into glycerin and environmentally non-toxic substances within about one month of being exposed to the downhole fluid; and
the downhole conduit is in a downhole tool useful for zonal isolation dimensioned on an outer side to engage casing in the wellbore and dimensioned on an inner side to engage the non-composite body, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degradation in the downhole fluid in the wellbore, causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
2. The downhole article of claim 1 , wherein the PGA is a semi-crystalline material having a density of between about 1.50 grams per cc and about 1.90 grams per cc.
3. The downhole article of claim 1 , wherein the subsequent change in configuration results, at least in part, from a decrease in non-composite body mass, which mass decrease is at least about 18% of the initial configuration within about 4 days of being exposed to the downhole fluid with a temperature of at least about 150° F.
4. The downhole article of claim 1 , wherein the subsequent change in configuration results, in part, from non-composite body deformation due to downhole fluid pressure on an increasingly malleable non-composite body, increasing malleability being due in part to continued exposure of the non-composite body to the downhole fluid with a temperature of at least about 150° F. causing some outer portions of the non-composite body to become less crystalline and more amorphous.
5. The downhole article of claim 1 , wherein the non-composite body in its initial configuration can withstand compression of at least about 6600 psi upon the non-composite body against a seat with a diameter of about ⅛-inch smaller than the non-composite body without deforming sufficiently to pass through the seat.
6. The downhole article of claim 1 , wherein the non-composite body is prepared by machining PGA stock into the non-composite body.
7. The downhole article of claim 6 , wherein the PGA stock is prepared from PGA pellets placed under heat and pressure.
8. The downhole article of claim 1 , wherein the non-composite body is prepared by milling substrate PGA into the non-composite body.
9. The downhole article of claim 8 , wherein the substrate PGA is prepared from PGA pellets placed under heat and pressure.
10. The downhole element of claim 1 , wherein the degradation occurs in a downhole fluid such that after about 91 days the ball weighs less than about 90% of its initial weight.
11. The downhole article of claim 1 , wherein the PGA is grade 100 R60 Kuredux® from Kureha, Inc.
12. A downhole article suitable for high-pressure downhole fracking operations comprising:
a non-composite hard body configured to block a downhole conduit in an initial configuration, wherein the non-composite body is stable in a dry condition at ambient temperature, has a compressive strength between 50 and 200 MPa and is suitable for high pressure downhole fracking operations, and when exposed to a downhole fluid having a temperature of at least about 136° F., the non-composite body will lose compression resistance, at least partially change to a subsequent configuration that does not block the downhole conduit and is then capable of passing through the downhole conduct; wherein:
the non-composite hard body is prepared from high molecular weight polyglycolic acid (PGA);
the non-composite body is spherical, and is in the range of between about 0.750 inches to about 4.625 inches in diameter;
the non-composite body is homogenous;
the non-composite body degrades into environmentally non-toxic substances in the presence of the downhole fluid within about one month; and
the downhole conduit is in a downhole tool useful for zonal isolation dimensioned on an outer side to engage casing in the wellbore and dimensioned on an inner side to engage the non-composite body, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degradation in the downhole fluid in the wellbore, causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
13. A downhole article suitable for high-pressure downhole fracking operations comprising:
a non-composite body configured to block a downhole conduit in an initial configuration, wherein the non-composite body is stable in a dry condition at ambient temperature, and, when exposed to a downhole fluid having a temperature of about 250° F. for about 48 hours, the non-composite body will at least partially change to a subsequent configuration that does not block the downhole conduit and is then capable of passing through the downhole conduit; wherein:
the non-composite body is hard and prepared from high molecular weight polyglycolic acid (PGA);
the non-composite body is spherical, and is in the range of between about 0.750 inches to about 4.625 inches in diameter;
the non-composite body is homogenous;
the non-composite body degrades into environmentally non-toxic substances in the presence of the downhole fluid within about one month; and
the downhole conduit is in a downhole tool useful for zonal isolation dimensioned on an outer side to engage casing in the wellbore and dimensioned on an inner side to engage the non-composite body, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degradation in the downhole fluid in the wellbore, causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
14. A downhole article suitable for high-pressure downhole fracking operations comprising:
a non-composite body configured to block a downhole conduit in an initial configuration, wherein the non-composite body is partly amorphous and partly crystalline and stable in a dry condition at ambient temperature, and, when exposed to a downhole fluid having a temperature of at least about 136° F., the non-composite body will at least partially change to a subsequent configuration that does not block the downhole conduit; wherein:
the non-composite body is hard and prepared from high molecular weight polyglycolic acid (PGA);
the non-composite body is spherical, and is in the range of between about 0.750 inches to about 4.625 inches in diameter;
the non-composite body is homogenous;
the spherical non-composite body degrades into environmentally non-toxic substances within about one month in the presence of a downhole fluid; and
the downhole conduit is in a downhole tool useful for zonal isolation dimensioned on an outer side to engage casing in the wellbore and dimensioned on an inner side to engage the non-composite body, the downhole isolation tool containing a structural element that will lose compression resistance and structural integrity due to hydrolysis in the downhole fluid in the wellbore , causing the downhole isolation tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
15. A downhole article suitable for high-pressure downhole fracking operations comprising:
a non-composite body configured to block a downhole conduit in an initial configuration, wherein the non-composite body is in a dry condition at ambient temperature, and, when exposed to a downhole fluid having a temperature of 275° F., the non-composite body will at least partially change to a subsequent configuration that does not block the downhole conduit at a degradation rate of at least 0.033 in/hr.; wherein:
the non-composite body is hard and prepared from high molecular weight polyglycolic acid (PGA);
the non-composite body is spherical, and is in the range of between about 0.750 inches to about 4.625 inches in diameter;
the non-composite body is homogenous;
the spherical non-composite body degrades into environmentally non-toxic substances within about one month in the presence of a downhole fluid; and
the downhole conduit is in a downhole tool useful for zonal isolation dimensioned on an outer side to engage casing in the wellbore and dimensioned on an inner side to engage the non-composite body, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degradation in the downhole fluid in the wellbore, causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
16. A ball for use in a downhole tool, wherein the ball is hard and made from high molecular weight polyglycolic acid, namely Kuredux or its equivalent, which is suitable for high-pressure downhole fracking operations, and will lose compression resistance and structural integrity due to hydrolysis in the downhole fluid in the wellbore; and has a diameter of about 0.75 inches to about 4.625 inches;
wherein the ball is stable in a dry condition at ambient temperature for at least one year, is capable of withstanding compression of the ball upon a seat which seat has a diameter about ⅛-inch smaller than the ball under a pressure of at least about 6,600 psi, and is capable of changing to allow the ball to pass through the seat about ⅛-inch smaller than the ball within about four days of being immersed in a downhole fluid at a temperature of at least about 150° F.;
wherein the ball is degradable into environmentally non-toxic substances within about one month in the presence of the downhole fluid; and
the downhole tool and the ball dimensioned to engage each other to block flow of downhole fluid through the downhole tool from at least one direction, the downhole tool dimensioned on an outer side to engage the casing in the wellbore, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degradation in the downhole fluid in the wellbore, causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products.
17. A downhole article for use in a wellbore comprising:
a homogenous, non-composite round hard polyglycolic acid ball between about 0.750 inches to about 4.625 inches in diameter, wherein the ball is stable in a dry condition at ambient temperature, and is capable of blocking a downhole conduit within a downhole tool located in a well bore,
the downhole tool dimensioned on an outer side to engage casing in the wellbore, the downhole tool containing a structural element that will lose compression resistance and structural integrity due to degrading in the downhole fluid in the wellbore causing the downhole tool to release from the casing without being drilled out and to thereafter degrade in the wellbore fluid into degradation products,
the downhole tool and the ball are dimensioned to engage each other to block flow of downhole fluid through the downhole tool from at least one direction,
wherein the ball is:
(a) at least about 1-½ inches in diameter;
(b) stable in a dry condition at ambient temperature for at least one year;
(c) capable of withstanding up to about 15,000 psi of pressure upon the ball seated on a seat which is at least about ⅛-inch smaller in diameter than the ball without the ball incurring deformation or cracking, and
wherein when the ball is exposed to a downhole fluid at a temperature of at least about 150° F. the ball will at least partially change in configuration so the ball ceases to be capable of blocking the downhole fluid from flowing through the down hole conduit, wherein the change in configuration, at least in part, results from a decrease in mass from the ball of at least about 18% within about 4 days and at least in part results from an increase in malleability of the ball, and wherein the ball is degradable into glycerin and other environmentally non-toxic substances within one month of being exposed to a downhole fluid.