Whipstock for use with a mill bit including varying material removal rates

Abstract

Provided is a whipstock and well system. The whipstock, in one aspect, includes a coupling section having a first radius of curvature, the coupling section configured to engage with a mill bit when running in hole. The whipstock, in accordance with this aspect, further includes a casing breakthrough section having a second radius of curvature, and a controlled exit section having a third radius of curvature, wherein the second radius of curvature is less than the third radius of curvature.

What is claimed is: 
     
         1 . A whipstock, comprising:
 a coupling section having a first radius of curvature, the coupling section configured to engage with a mill bit when running in hole;   a casing breakthrough section having a second radius of curvature; and   a controlled exit section having a third radius of curvature, wherein the second radius of curvature is less than the third radius of curvature.   
     
     
         2 . The whipstock as recited in  claim 1 , wherein the second radius of curvature is at least 5% less than the third radius of curvature. 
     
     
         3 . The whipstock as recited in  claim 1 , wherein the second radius of curvature is at least 10% less than the third radius of curvature. 
     
     
         4 . The whipstock as recited in  claim 1 , wherein the second radius of curvature is at least 25% less than the third radius of curvature. 
     
     
         5 . The whipstock as recited in  claim 1 , wherein the second radius of curvature is less than the first radius of curvature. 
     
     
         6 . The whipstock as recited in  claim 5 , wherein the third radius of curvature is less than the first radius of curvature. 
     
     
         7 . The whipstock as recited in  claim 1 , wherein the coupling section has a first ramp rate, the casing breakthrough section has a second ramp rate, and the controlled exit section has a third ramp rate. 
     
     
         8 . The whipstock as recited in  claim 7 , wherein the first ramp rate is less than the second ramp rate but greater than the third ramp rate. 
     
     
         9 . The whipstock as recited in  claim 8 , wherein the second ramp rate is at least six times the first ramp rate. 
     
     
         10 . The whipstock as recited in  claim 9 , wherein the controlled exit section includes a downhole portion with a downhole portion ramp rate and an uphole portion with an uphole portion ramp rate, and further wherein a downhole portion ramp rate is less than an uphole portion ramp rate. 
     
     
         11 . A well system, comprising:
 a wellbore extending through one or more subterranean formations;   wellbore casing located in at least a portion of the wellbore;   a whipstock located within the wellbore radially inside of the wellbore casing, the whipstock including:
 a coupling section having a first radius of curvature, the coupling section configured to engage with a mill bit when running in hole; 
 a casing breakthrough section having a second radius of curvature; and 
 a controlled exit section having a third radius of curvature, wherein the second radius of curvature is less than the third radius of curvature; and 
   a bottom hole assembly extending within the wellbore adjacent the whipstock.   
     
     
         12 . The well system as recited in  claim 11 , wherein the second radius of curvature is at least 5% less than the third radius of curvature. 
     
     
         13 . The well system as recited in  claim 11 , wherein the second radius of curvature is at least 10% less than the third radius of curvature. 
     
     
         14 . The well system as recited in  claim 11 , wherein the second radius of curvature is at least 25% less than the third radius of curvature. 
     
     
         15 . The well system as recited in  claim 11 , wherein the second radius of curvature is less than the first radius of curvature. 
     
     
         16 . The well system as recited in  claim 15 , wherein the third radius of curvature is less than the first radius of curvature. 
     
     
         17 . The well system as recited in  claim 11 , wherein the coupling section has a first ramp rate, the casing breakthrough section has a second ramp rate, and the controlled exit section has a third ramp rate. 
     
     
         18 . The well system as recited in  claim 11 , wherein the first ramp rate is less than the second ramp rate but greater than the third ramp rate. 
     
     
         19 . The well system as recited in  claim 18 , wherein the second ramp rate is at least six times the first ramp rate. 
     
     
         20 . The well system as recited in  claim 19 , wherein the controlled exit section includes a downhole portion with a downhole portion ramp rate and an uphole portion with an uphole portion ramp rate, and further wherein a downhole portion ramp rate is less than an uphole portion ramp rate. 
     
     
         21 . The well system as recited in  claim 11 , further including a lateral wellbore extending from the wellbore proximate the whipstock. 
     
     
         22 . The well system as recited in  claim 11 , further including a mill bit located proximate the whipstock, the mill bit including:
 a tubular having an uphole end and a downhole end;   a first cutting section having one or more first cutting surfaces disposed about the tubular, the first cutting section having a first material removal rate and configured to engage with wellbore casing disposed within a wellbore; and   a second cutting section having one or more second cutting surfaces disposed about the tubular, the second cutting section having a second material removal rate less than the first material removal rate and configured to engage with a whipstock disposed within the wellbore.