Controlled variable density fluid for wellbore operations

Abstract

Fluid systems may contain elements to provide changes in bulk fluid density in response to various environmental conditions. One environmental driver to the variable density is pressure; other environmental drivers include, but are not limited to, temperature or changes in chemistry. The variable density of the fluid is beneficial for controlling sub-surface pressures within desirable pore pressure and fracture gradient envelopes. The variability of fluid density permits construction and operation of a wellbore with much longer hole sections than when using conventional single gradient fluids.

1 . A fluid of variable density comprising: 
 a base fluid; and    a plurality of elements that change their volume/weight ratio in response to a condition selected from the group consisting of pressure, temperature, and chemical composition of the base fluid.    
   
   
       2 . The fluid of  claim 1  where the average particle size of the elements is about 100 microns or less.  
   
   
       3 . The fluid of  claim 1  where the elements each comprise a spring-like component.  
   
   
       4 . The fluid of  claim 1  where the elements each comprise at least one gas-filled void.  
   
   
       5 . The fluid of  claim 1  where the elements each comprise a non-deformable core, a compliant shell, and at least one gas-filled void between the core and compliant shell.  
   
   
       6 . The fluid of  claim 1  where the elements each comprise a compliant shell surrounding at least one gas-filled void.  
   
   
       7 . The fluid of  claim 1  where the elements each comprise a non-deformable body including at least one cellular, compliant component.  
   
   
       8 . The fluid of  claim 1  where the elements have an average expanded state size and an average contracted state size, and where the volume ratio of the average expanded state size to the average contracted state size is at least about 2.5.  
   
   
       9 . The fluid of  claim 1  where the base fluid is selected from the group consisting of a wellbore operation fluid, a produced fluid and a sealant.  
   
   
       10 . A fluid of variable density comprising: 
 a base fluid; and    a plurality of elements that change their volume/weight ratio in response to a condition selected from the group consisting of pressure, temperature, and chemical composition of the base fluid, where the elements have an average expanded state size and an average contracted state size, and where the volume ratio of the average expanded state size to the average contracted state size is at least about 2.5, and where the average contracted state size is about 100 microns or less.    
   
   
       11 . A method of constructing a wellbore comprising: 
 drilling a wellbore using a variable density wellbore operation fluid within the wellbore;    subjecting the wellbore operation fluid to a condition where the density of the fluid is changed in response to the condition, the condition selected from the group consisting of pressure, temperature, and chemical composition of a base fluid, where the variable density wellbore operation fluid comprises: 
 the base fluid; and  
 a plurality of elements that change their volume/weight ratio in response to the condition.  
   
   
   
       12 . The method of  claim 11  where the wellbore has a longer hole section as compared with a wellbore drilled with a fluid otherwise identical except the elements are absent.  
   
   
       13 . The method of  claim 11  where the average particle size of the elements is about 100 microns or less.  
   
   
       14 . The method of  claim 11  where the elements each comprise a spring-like component.  
   
   
       15 . The method of  claim 11  where the elements each comprise at least one gas-filled void.  
   
   
       16 . The method of  claim 11  where the elements each comprise a non-deformable core, a compliant shell, and at least one gas-filled void between the core and compliant shell.  
   
   
       17 . The method of  claim 11  where the elements each comprise a compliant shell surrounding at least one gas-filled void.  
   
   
       18 . The method of  claim 11  where the elements each comprise a non-deformable body including at least one cellular, compliant component.  
   
   
       19 . The method of  claim 11  where the elements have an average expanded state size and an average contracted state size, and where the volume ratio of the average expanded state size to the average contracted state size is at least about 2.5.  
   
   
       20 . The method of  claim 11  where the base fluid is a sealant, and the method further comprises sealing at least a portion of the wellbore.  
   
   
       21 . A method of improving the lift of a produced fluid comprising injecting into the produced fluid at a subsurface point an effective amount of a plurality of elements that change their volume/weight ratio in response to a condition selected from the group consisting of pressure, temperature, and chemical composition of the produced fluid to increase the lift thereof.  
   
   
       22 . The method of  claim 21  where the elements each comprise a spring-like component.  
   
   
       23 . The method of  claim 21  where the elements each comprise at least one gas-filled void.  
   
   
       24 . The method of  claim 21  where the elements each comprise a non-deformable core, a compliant shell, and at least one gas-filled void between the core and compliant shell.  
   
   
       25 . The method of  claim 21  where the elements each comprise a compliant shell surrounding at least one gas-filled void.  
   
   
       26 . The method of  claim 21  where the elements each comprise a non-deformable body including at least one cellular, compliant component.  
   
   
       27 . The method of  claim 21  where the elements have an average expanded state size and an average contracted state size, and where the volume ratio of the average expanded state size to the average contracted state size is at least about 2.5.  
   
   
       28 . An element that changes its volume/weight ratio in response to a condition comprising: 
 a non-deformable core;    a compliant skin surrounding the core; and    at least one gas-filled space between the non-deformable core and the compliant skin,    where the condition is selected from the group consisting of pressure, temperature, and chemical composition of a base fluid in which the element is present.    
   
   
       29 . An element that changes its volume/weight ratio in response to a condition comprising: 
 a non-deformable pseudo-porous body; and    at least closed cell compliant component,    where the condition is selected from the group consisting of pressure, temperature, and chemical composition of a base fluid in which the element is present.    
   
   
       30 . An element comprising: 
 a hollow, rigid external shell having at least one cavity therein and at least one opening into the cavity; and    an inner material within the cavity that changes its volume/weight ratio in response to a condition, where the condition is selected from the group consisting of pressure, temperature, and chemical composition of a base fluid in which the element is present.