Method of determining reservoir pressure

Abstract

A well test method for use in tight gas reservoirs prior to hydraulic fracture stimulation. The method can use injection of water using low-rate surface pumps into the reservoir below parting pressure. The measured rates and pressures are converted to sandface rate and pressure datasets for each stage. The technique can utilize either surface or bottom-hole pressure sensors. The resulting sandface datasets are analyzed using the baseline/calibration method or other analysis appropriate to stage data to determine reservoir flow properties. The small-volume, staged well test enables estimation of the flow properties of reservoir, including pressure and permeability, in hours rather than days.

What is claimed is: 
     
         1 . A method for testing a reservoir, comprising:
 causing a volume of liquid to be injected into or produced out of the reservoir, wherein the reservoir is accessed via a well and the reservoir has not been stimulated;   measuring one or more parameters indicative of flow properties of the reservoir over a first predetermined period of time to form a first stage dataset, wherein the one or more parameters includes pressure;   inducing a change in an injection rate, a production rate, an injection pressure, or a production pressure of the liquid into or out of the reservoir;   measuring the one or more parameters indicative of flow properties for at least a second predetermined period of time to form a second stage dataset;   determining sandface rate and pressure based on the first stage dataset and the second stage dataset.   
     
     
         2 . The method of  claim 1 , wherein:
 the first predetermined period of time is no more than 30 minutes and the second predetermined time is no more than 30 minutes; or   the first predetermined period of time is no more than 10 minutes and the second predetermined time is no more than 10 minutes.   
     
     
         3 . The method of  claim 1 , wherein the change in rate comprises a change in injection rate or a change in production rate, and the change in pressure comprises a change in injection pressure or a change in production pressure. 
     
     
         4 . The method of  claim 1 , further comprising, after forming the second stage dataset, performing iterations of:
 inducing a change in the injection rate, the production rate, the injection pressure, or the production pressure of the liquid into or out of the reservoir;   measuring the one or more parameters indicative of flow properties for at least a predefined period of time to form an iteration stage dataset; and   after a final one of the iterations: performing the determining based on each iteration stage dataset.   
     
     
         5 . The method of  claim 1 , wherein the volume of liquid is no more than 40 gallons. 
     
     
         6 . The method of  claim 1 , further comprising selecting a rate of injection for the liquid to prevent fracturing of formations of the reservoir during the testing. 
     
     
         7 . The method of  claim 1 , wherein the determining comprises correcting for ballooning of wellbore casing and weepage of the wellbore casing due to an increase in pressure caused by the testing. 
     
     
         8 . A method for testing a reservoir, comprising:
 in a first stage:
 injecting into, or producing from, the reservoir a liquid at a first rate or first pressure and measuring one or more parameters indicative of flow properties of the reservoir over a first time period to form a first stage dataset; 
   in one or more additional stages:
 injecting into, or producing from, the reservoir a liquid at a given rate or given pressure and measuring the one or more parameters indicative of flow properties of the reservoir over a given time period to form one or more additional stage datasets, wherein the given rate is different from the first rate, and the given pressure is different from the first pressure; and 
   determining sandface rate and pressure based on the first stage dataset and the one or more additional stage datasets.   
     
     
         9 . The method of  claim 8 , wherein a total time spent in the first stage and additional stages is no more than 12 hours. 
     
     
         10 . The method of  claim 8 , wherein each of the first time period and the each given time period is between 10 and 30 minutes. 
     
     
         11 . The method of  claim 8 , wherein a volume of the liquid injected in each of the first stage and each of the additional stages is between 10 and 40 gallons. 
     
     
         12 . The method of  claim 8 , further comprising selecting the first rate and additional rate to prevent fracturing of formations of the reservoir during the testing. 
     
     
         13 . The method of  claim 8 , wherein the determining comprises correcting for ballooning of wellbore casing and weepage of the wellbore casing due to an increase in pressure caused by the testing. 
     
     
         14 . A system for testing a reservoir, comprising:
 one or more sensors configured to measure parameters indicative of flow properties of the reservoir, wherein the one or more parameters comprise pressure, and the reservoir has not been stimulated;   a pump configured to deliver liquid in a wellbore, the wellbore fluidically coupled to the reservoir;   a controller configured to:
 cause the pump to inject a volume of liquid into the reservoir; 
 cause the sensors to measure one or more parameters indicative of flow properties of the reservoir over a first predetermined period of time to form a first stage dataset, wherein the one or more parameters includes pressure; 
 cause the pump to change a rate or pressure of injection of the liquid into the reservoir after completion of the first stage dataset; 
 cause the sensors to measure the one or more parameters indicative of flow properties for at least a second predetermined period of time to form a second stage dataset; 
   a processing unit configured to process the first stage dataset and the second stage dataset to determine sandface rate and pressure.   
     
     
         15 . The system of  claim 15  wherein the pump is a surface pump, and further comprising a length of coiled tubing coupled to the pump and running into the wellbore. 
     
     
         16 . The system of  claim 15 , wherein the pump is a downhole pump, and further comprising a wireline or a length of coiled tubing coupled to the pump to deploy the pump in the wellbore. 
     
     
         17 . The system of  claim 15  wherein the sensors comprise one or more of a pressure sensor, an acoustic sensor, and a fluid level sensor. 
     
     
         18 . The system of  claim 15 , wherein the controller is configured to:
 set the first predetermined period of time to be no more than 30 minutes and the second predetermined time to be no more than 30 minutes; or   set the first predetermined period of time to be no more than 10 minutes and the second predetermined time to be no more than 10 minutes.   
     
     
         19 . The system of  claim 15 , wherein the controller is configured to inject the liquid at rate that prevents fracturing of formations of the reservoir during the testing. 
     
     
         20 . The system of  claim 15 , wherein the processing unit is configured to correct for ballooning of wellbore casing and weepage of the wellbore casing due to an increase in pressure caused by the injection of liquid during the testing.