Patent Application
20220228079
The invention relates generally to conditioning of rich natural gas and natural gas liquid (NGL) recovery.
Rich natural gas is produced along with crude oil when oil is produced by horizontal drilling and fracking. The produced natural gas is called associated gas and is comprised primarily of methane but also has heavier hydrocarbons including ethane, propane, butane, heptanes and hexane. The heavier hydrocarbons are often collectively called NGL. Unused gas-phase components are often wasted by the practice of flaring.
The rich natural gas causes two problems for the oil industry. First, the heavier hydrocarbons cause the gas energy content to be too high for internal combustion in engines. Specifically, the high energy content causes internal combustion engines to knock. Second, the high energy content makes the rich natural gas unsuitable for use as a compressed natural gas (CNG) fuel. The NGC process removes the valuable NGL hydrocarbons for sale and distribution while concurrently producing a lean natural gas suitable for internal combustion and CNG. Consequently, the associated gas may be put to good use instead of wasted up a flare stack.
Competing processes include mechanical refrigeration and Joule Thompson refrigeration. Mechanical refrigeration is relatively expensive and has reliability issues, particularly in cold weather. Mechanical refrigeration is also bulky and difficult to move from site to site as is often needed in oil fields. Conventional Joule Thompson refrigeration has the disadvantage of emulsifying the three-phase mixture from the depressurization valve. Consequently, NGL is often emulsified with the water.
A natural gas conditioning process (NGC) described herein conditions rich natural gas for use as a fuel while simultaneously recovering valuable natural gas liquids (NGLs). Natural gas from a well at about 50 psig is compressed by a compressor, and then cooled in multiple steps, such as through cooling with conditioned natural gas, heat exchanged with an air cooler, heat exchanged with an expanded gas from a separator, and heat exchanged by an expanded NGL stream from a separator. Some embodiments do not include all of the coolers. Subsequently, gas, NGL liquid, and water are separated in a primary separator. NGL from the primary separator is expanded and cooled. The cooled gas/liquid mixture is then separated in a second separator.
The compressor, usually provided on a separate skid, is modified to work as an integrated part of the NGC system in two ways. First, the gas from the second separator is connected by piping to allow the second separator gas to be recycled to the compressor skid to improve recovery of NGL. Second, hot gas from the compressor is piped to the condition gas cooler to provide a heat sink upstream of an ambient air cooler. The resulting pre-cooled gas is returned to the ambient air cooler (the compressor aftercooler), allowing the ambient air cooler to operate closer to the ambient air temperature.
The NGC process is differentiated by traditional mechanical refrigeration or Joule Thompson cooling systems by several features. For example, inlet gas is indirectly cooled by a Joule Thompson expansion of the separator gas and separator NGL to preclude emulsification problems that are common in traditional Joule Thompson systems. Further, the heat integration of the conditioned gas cooler upstream of the ambient air cooler is different than traditional processes. Finally, no mechanical refrigeration system is required, which simplifies the process and lowers capital cost.
Up to 80% of propane and heavier components are recoverable, depending on the rich gas composition. The intensity of the flare can be reduced by up to 50%.
(modified)
(modified) Referring now to
Three streams exit the first separator 90. Water 102 flows from a bottom of the first separator 90. The water 90 can be then be put to other uses downstream directly or after treatment to remove any residual components from the separation.
Conditioned gas 91 exits the first separator 90 and flows through a gas expansion valve 92. The gas expansion valve 92 facilitates keeping pressure inside the first separator 90 at a working pressure approximately between 600 psig and 1200 psig depending on a composition and characteristics of the inbound gas/NGL/water mixture 89. Gas 93 from the gas expansion valve 92 flows through the cold side of the gas expansion cooler 86. The conditioned gas 64 from expansion cooler 86 exits at a pressure approximately between 50 psig and 400 psig and at a temperature between 50 and 200 deg. F. Conditioned gas 105 flows into a cold side of the conditioned gas cooler 103 and leaves the system as conditioned gas 94.
NGL 95 exits the first separator 90 and flows through a NGL valve 96. A cooled NGL/gas mixture 97 from the NGL valve 96 flows into the cold side of NGL expansion cooler 88. NGL/gas mixture 98 from the NGL expansion cooler 88 flows into a second separator 99 where gas 100 is separated from an output stream of NGL 101. The NGL 101 exits at a pressure approximately between 100 psig and 250 psig and at a temperature between 20 and 80 deg. F. The recycle gas 100 exits at a pressure approximately between 100 psig and 250 psig and at a temperature between 20 and 80 deg. F. The gas 100 may be recycled to the compressor 81 or put to another use downstream directly or after treatment. Relative ratios of the three streams 91, 95 and 102 vary according to a composition of the rich natural gas 81.
Embodiments and variations thereof, illustrated in the accompanying figure(s) are not to scale. The technical subject matter described above is merely illustrative, and, along with the figures, is not meant to limit the scope of the invention. It is to be appreciated that numerous other variations of the invention have been contemplated, as would be obvious to one ordinary skilled in the art given the benefit of the disclosure. All variations of the invention that read upon appended claims are intended and contemplated to be within the scope of the invention.
The present application is related to and claims priority to the following co-pending application, the entirety of which is incorporated by reference herein: U.S. Provisional Patent Application Ser. No. 62/846,789, titled “NATURAL GAS CONDITIONING,” filed May 13, 2019.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 62846789 | May 2019 | US |
| Child | 16576394 | US |
