Dual service compressor system for conditioning hydrocarbon gas

Abstract

A system for compressing gas from a wellbore that uses a single reciprocating compressor unit to boost pressure of the gas to an intermediate stage, and from the intermediate stage to a final stage. The final stage is at a destination pressure for distribution. Between the intermediate and final stages the gas is treated to remove water and higher molecular weight hydrocarbons so that the gas pressurized to the final stage is compressed natural gas. The reciprocating compressor is made up of a series of throw assemblies that are all driven by a single shaft. Each throw assembly includes a cylinder with a piston that reciprocates within the cylinder to compress and pressurize the fluid therein. The reciprocating compressor can be a non-lube design thereby eliminating lube oil contamination of downstream compressed natural gas or higher molecular weight hydrocarbons.

What is claimed is: 
     
         1 . A method of producing compressed natural gas, the method comprising:
 providing a reciprocating compressor having a booster cylinder and a compressed natural gas (CNG) cylinder;   directing an amount of gas from a wellbore to the compressor;   compressing the amount of gas in the booster cylinder to an intermediate stage pressure to define an amount of intermediate stage gas;   directing the intermediate stage gas to the CNG cylinder; and   compressing the intermediate stage gas in the CNG cylinder to a destination pressure to form compressed natural gas.   
     
     
         2 . The method of  claim 1 , further comprising treating the intermediate stage gas prior to directing the intermediate stage gas to the second one of the cylinders. 
     
     
         3 . The method of  claim 2 , wherein treating the intermediate stage gas comprises separating higher molecular weight hydrocarbons from the intermediate stage gas. 
     
     
         4 . The method of  claim 2 , wherein treating the intermediate stage gas comprises removing moisture from the intermediate stage gas. 
     
     
         5 . The method of  claim 4 , wherein removing moisture from the intermediate stage gas comprises adding a hygroscopic agent to the intermediate stage gas. 
     
     
         6 . The method of  claim 1 , wherein the booster cylinder comprises a first booster cylinder and a second booster cylinder, and wherein a discharge of the first booster cylinder connects to a suction in the second booster cylinder. 
     
     
         7 . The method of  claim 1 , wherein the CNG cylinder comprises a first CNG cylinder and a second CNG cylinder, and wherein a discharge of the first CNG cylinder connects to a suction in the second CNG cylinder. 
     
     
         8 . The method of  claim 1 , wherein the reciprocating compressor comprises a body, a shaft extending axially through the body, pistons in the booster and CNG cylinders coupled to the shaft, and a motor connected to the shaft, the method further comprising activating the motor to rotate the shaft and to reciprocate the pistons in the cylinders. 
     
     
         9 . The method of  claim 8 , wherein the reciprocating compressor further comprises a control panel on the body, the method further comprising manipulating the control panel to operate the motor. 
     
     
         10 . The method of  claim 1  further comprising removing moisture from the gas from the wellbore before directing the gas from the wellbore to the compressor. 
     
     
         11 . The method of  claim 1 , wherein the reciprocating compressor is a non-lube design. 
     
     
         12 . The method of  claim 11 , wherein the motor comprises an internal combustion engine powered by gas from the wellbore. 
     
     
         13 . A method of producing compressed natural gas, the method comprising:
 providing a reciprocating compressor having a body, a shaft in the body, a series of cylinders that extend radially outward from the body, and pistons in the cylinders;   supplying fluid from a wellbore to a one of the cylinders that is designated as a booster cylinder;   creating intermediate stage fluid by pressurizing the fluid in the booster cylinder;   removing moisture from the intermediate stage fluid to form intermediate stage gas; and   forming an amount of compressed natural gas by pressurizing the intermediate stage gas in another one of the cylinders.   
     
     
         14 . The method of  claim 13 , further comprising removing higher molecular weight hydrocarbons from the intermediate stage fluid. 
     
     
         15 . The method of  claim 13 , wherein the series of cylinders comprises a multiplicity of booster cylinders. 
     
     
         16 . The method of  claim 13 , wherein the another one of the cylinders comprises a compression cylinder, and wherein the series of cylinders comprises a multiplicity of compression cylinders. 
     
     
         17 . A compression system for generating compressed natural gas comprising:
 a body;   cylinders mounted on the body and pistons in the cylinders that comprise a booster compressor and a compressed natural gas compressor;   a feed line containing fluid from a wellbore and having an end connected to a suction side of the booster compressor;   a suction side on the compressed natural gas compressor that is in fluid communication with a discharge side on the booster compressor via an intermediate circuit; and   a discharge line containing compressed natural gas and connected to a discharge side of the compressed natural gas compressor.   
     
     
         18 . The compression system of  claim 17 , further comprising a dehumidification system disposed in the intermediate circuit. 
     
     
         19 . The compression system of  claim 17 , further comprising a tank disposed in the intermediate circuit for removing higher molecular weight hydrocarbons. 
     
     
         20 . The compression system of  claim 17 , further comprising a crankshaft coupled with each of the pistons, and a motor coupled with the crankshaft. 
     
     
         21 . The compression system of  claim 20 , further comprising a control system mounted on the body and in signal communication with the motor.