Methods and systems for pressurizing harsh fluids

Abstract

Methods and systems relate to a pressure exchanger which exchanges pressure energy from a high pressure clean fluid system to a relatively low pressure harsh fluid system for use in pressurizing the harsh fluid and directing the fluid to a wellbore as high pressure harsh fluid without the harsh fluid contacting identified portions of the pressure exchanger.

What is claimed is: 
     
         1 . A method of pumping an oilfield fluid from a well surface to a wellbore, comprising:
 providing a low pressure source of harsh fluid;   operating at least one high pressure pump to pump a clean fluid; and   using a piston assembly which is in contact with clean fluid in a direction of movement and which pushes the clean fluid using the pressure from the at least one high pressure pump in order to provide high pressure to the harsh fluid, thereby pushing the harsh fluid under high pressure toward the wellbore.   
     
     
         2 . The method of  claim 1 , wherein a predetermined amount of clean fluid is used to buffer the piston assembly from the harsh fluid. 
     
     
         3 . The method of  claim 2 , wherein the predetermined amount is a function of a dispersion length of the harsh fluid in the clean fluid when the piston assembly causes movement of the clean fluid and harsh fluid under high pressure. 
     
     
         4 . The method of  claim 3 , wherein the function of a dispersion length is approximately three times the dispersion length. 
     
     
         5 . The method of  claim 1 , wherein using a piston assembly comprises utilizing a system having at least two tubulars each containing a respective piston assembly, the piston assemblies working in opposite phases to continuously pump the harsh fluid into the wellbore, such that in a first half cycle, a first of the respective piston assemblies is causing harsh fluid to be ejected from a first of the two tubulars under high pressure while a second of the tubulars is being filled with harsh fluid under low pressure, and in a second half cycle, a second of the respective piston assemblies is causing harsh fluid to be ejected from a second of the two tubulars under high pressure while the first of the tubulars is being filled with harsh fluid under low pressure. 
     
     
         6 . The method of  claim 5 , wherein the respective piston assemblies are surrounded by clean fluid in both the first half cycle and the second half cycle. 
     
     
         7 . The method of  claim 6 , wherein a predetermined amount of clean fluid is used to buffer each of the respective piston assemblies from the harsh fluid in both the first half cycle and the second half cycle. 
     
     
         8 . The method of  claim 5 , wherein in the first half cycle, an increasing amount of clean fluid is used to buffer the first of the respective piston assemblies as the first of the respective piston assemblies moves under high pressure from a first end to a second end of the first of the two tubulars. 
     
     
         9 . The method of  claim 8 , wherein in the first half cycle, the harsh fluid is in low pressure contact with the second respective piston on a side opposite the direction of movement of the piston assembly. 
     
     
         10 . The method of  claim 1 , wherein the clean fluid is water. 
     
     
         11 . The method of  claim 1 , wherein the piston assembly comprises a check valve. 
     
     
         12 . The method of  claim 1 , further comprising:
 impeding movement of the piston assembly using a stop element.   
     
     
         13 . The method of  claim 1 , wherein the harsh fluid is a formation fracturing fluid. 
     
     
         14 . A system for pumping an oilfield fluid from a well surface to a wellbore comprising:
 a low pressure supply of harsh fluid;   a high pressure pump in communication with a clean fluid; and   at least two tubulars each comprising a piston assembly wherein each piston assembly is in contact with the clean fluid in the direction of movement of that piston assembly and pushes the clean fluid using the pressure from the high pressure pump in order to provide pressure to and push the harsh fluid, thereby pushing the harsh fluid under pressure toward the wellbore.   
     
     
         15 . The system of  claim 14 , further comprising:
 a plurality of valves, wherein the high pressure pump is in fluid communication with the at least two tubulars at respective first ends of the tubulars via respective first and second valves of the plurality of valves, and the harsh fluid at low pressure is in fluid communication with the tubulars at respective second ends of the tubulars via respective third and fourth valves of the plurality of valves.   
     
     
         16 . The system of  claim 15 , further comprising:
 a first storage tank for the clean fluid, wherein the respective first ends of the tubulars are in fluid communication with the first storage tank via fifth and sixth valves of the plurality of valves, and   the plurality of valves comprise seventh and eight valves respectively coupled between the respective second ends of the tubulars and the wellbore.   
     
     
         17 . The system of  claim 16 , further comprising a low pressure pump for the harsh fluid and a second storage tank for the harsh fluid. 
     
     
         18 . The system of  claim 14 , wherein each piston assembly is in contact with a predetermined amount of the clean fluid in the direction of movement of that piston assembly. 
     
     
         19 . The system of  claim 18 , wherein the predetermined amount is a function of a dispersion length of the harsh fluid in the clean fluid when the piston assembly causes movement of the clean fluid and harsh fluid under high pressure. 
     
     
         20 . The system of  claim 19 , wherein the function of a dispersion length is approximately three times the dispersion length. 
     
     
         21 . The system of  claim 14 , wherein the respective piston assemblies comprise check valves. 
     
     
         22 . The system of  claim 21 , wherein the check valves permit flow of fluid past the check valves at a defined cracking pressure. 
     
     
         23 . The system of  claim 22 , further comprising:
 a stop element located in each of the at least two tubulars, the stop elements located toward the respective second ends of the at least two tubulars, the stop elements arranged to stop movement of the piston assemblies beyond the stop elements toward the respective second ends.   
     
     
         24 . The system of  claim 21 , wherein the piston assemblies work in opposite phases to continuously pump the harsh fluid into the wellbore, such that in a first half cycle, a first of the respective piston assemblies is causing harsh fluid to be ejected from a first of the two tubulars under high pressure while a second of the tubulars is being filled with harsh fluid under low pressure, and in a second half cycle, a second of the respective piston assemblies is causing harsh fluid to be ejected from a second of the two tubulars under high pressure while the first of the tubulars is being filled with harsh fluid under low pressure. 
     
     
         25 . The system of  claim 24 , wherein in the first half cycle, clean fluid is continuously pushed past the check valve such that an increasing amount of clean fluid is used to buffer the first of the respective piston assemblies as the first of the respective piston assemblies moves under high pressure from a first end to a second end of the first of the two tubulars. 
     
     
         26 . The system of  claim 19 , wherein in the first half cycle, the harsh fluid is in low pressure contact with the second respective piston on a side opposite the direction of movement of the piston assembly.