Downhole Fluid Analysis Methods For Determining Compressibility

Abstract

The present disclosure relates to methods for determining the compressibility of downhole fluids using measurements obtained during over-pressurization of a formation fluid sample. In certain embodiments, the density of the fluid may be measured as the fluid is directed through a flowline into a sample chamber. The density measurements can be employed in conjunction with pressure spikes that occur during over pressuring of a sample chamber to determine the compressibility.

What is claimed is: 
     
         1 . A downhole fluid analysis method comprising:
 directing formation fluid to a sample chamber of a downhole tool;   over-pressurizing the formation fluid within the sample chamber;   obtaining pressure and density measurements during the over-pressurization; and   determining a compressibility of the formation fluid based on the pressure and density measurements.   
     
     
         2 . The downhole fluid analysis method of  claim 1 , wherein over-pressurizing comprises operating a pump to increase a pressure in the sample chamber after the sample chamber has been filled. 
     
     
         3 . The downhole fluid analysis method of  claim 1 , wherein over-pressurizing comprises pumping the formation fluid through a primary flowline of the downhole tool, and wherein obtaining comprises measuring pressure and density of the formation fluid flowing through the primary flowline. 
     
     
         4 . The downhole fluid analysis method of  claim 1 , wherein determining comprises calculating the compressibility based on the pressure and density measurements that were obtained after a pressure spike. 
     
     
         5 . The downhole fluid analysis method of  claim 1 , wherein determining comprises calculating the compressibility based on a rate of change in density with respect to pressure. 
     
     
         6 . The downhole fluid analysis method of  claim 1 , comprising initiating sampling of the formation fluid within the downhole tool. 
     
     
         7 . The downhole fluid analysis method of  claim 6 , wherein initiating comprises opening a valve upstream of the sample chamber and closing a valve in a primary flowline of the downhole tool. 
     
     
         8 . The downhole fluid analysis method of  claim 1 , wherein determining comprises determining the compressibility as a function of pressure based on the pressure and density measurements. 
     
     
         9 . The downhole fluid analysis method of  claim 1 , comprising detecting that the sample chamber has been filled, wherein the over-pressurizing occurs within the sample chamber in response to detecting that the sample chamber has been filled. 
     
     
         10 . A downhole tool comprising:
 a density sensor to measure density of a formation fluid flowing through a primary flowline of the downhole tool;   a pressure sensor to measure pressure of the formation fluid flowing through a primary flowline of the downhole tool; and   a controller configured to execute instructions stored within the downhole tool to:
 obtain pressure and density measurements from the respective pressure sensor and the density sensor during over-pressurization of a sample of formation fluid within a sample chamber of the downhole tool; and 
 calculate a compressibility of the formation fluid based on the pressure and density measurements. 
   
     
     
         11 . The downhole tool of  claim 10  comprising a valve selectively actuated by the controller to direct the formation fluid into the sample chamber. 
     
     
         12 . The downhole tool of  claim 10 , wherein the controller is configured to execute instructions stored within the downhole tool to:
 detect a spike in the pressure measurements; and   operate a pump to over-pressurize the sample of formation fluid within the sample chamber in response to detecting the spike in the pressure measurements.   
     
     
         13 . The downhole tool of  claim 10 , wherein the density comprises a fluid density. 
     
     
         14 . The downhole tool of  claim 10 , wherein the density comprises an optical density. 
     
     
         15 . A downhole fluid analysis method comprising:
 directing formation fluid to a sample chamber of a downhole tool through a primary flowline;   inducing a pressure change in the formation fluid flowing through the primary flowline;   obtaining pressure and density measurements during the pressure change; and   determining a compressibility of the formation fluid based on the pressure and density measurements.   
     
     
         16 . The downhole fluid analysis method of  claim 15 , wherein inducing comprises restricting a flow of the formation fluid through the primary flowline. 
     
     
         17 . The downhole fluid analysis method of  claim 15 , wherein inducing comprises momentarily closing a valve disposed in the primary flowline. 
     
     
         18 . The downhole fluid analysis method of  claim 15 , wherein inducing comprises over-pressurizing the formation fluid within the sample chamber. 
     
     
         19 . The downhole fluid analysis method of  claim 15 , wherein the pressure change comprises a pressure decrease. 
     
     
         20 . The downhole fluid analysis method of  claim 15 , wherein the pressure change comprises a pressure increase.