September 7, 2016 by Taylor Miles
Liquefied Petroleum Gas (LPG) and Other Natural Gas Liquids (NGL)’s The Family of Orphaned Hydrocarbons
Without the proper infrastructure these hydrocarbons are vaporized into the atmosphere.
The definition of Orphaned according to dictionary.com:
Verb – (used with object) Informal. to deprive of commercial sponsorship, an employer, etc.
The definition of Commercial also from dictionary.com:
Adjective – prepared, done, or acting with sole or chief emphasis on salability, profit, or success
Over 90% of the oil and gas production as well as midstream compression locations around the world have a huge emission problem. Unfortunately, the industry and the regulators are not addressing these emissions. Here is the problem. Liquefied Petroleum Gas (LPG) and Natural Gas Liquids (NGL) cannot be sold as gas due to the fact that under pressure these hydrocarbons coalesce into a volatile liquid, therefore they are no longer a gas. Oil is stored and sold at atmospheric pressure and since these hydrocarbons re-gasify at atmosphere they also can’t be sold with the produced oil. LPG and NGL may also contain over 30% methane and 20% ethane and are disguised as a leak so they can be vented or otherwise wasted into the atmosphere.
Specifically, these hydrocarbons that we will reference as NGL’s consist in varying quantities of propane, butane, pentane and heavier hydrocarbons. These NGL’s are the most valuable of all hydrocarbon gases, whose total average BTU heating value is 4,380 per standard cubic ft. As a comparison the total average BTU of methane and ethane is 1,390 per standard cubic ft. If you filled your car with the methane and ethane mixture and could travel 500 miles, the same tank filled with the NGL mixture could travel 1,575 miles.
To provide some additional context, methane, ethane, and some propane will not become a liquid at most pipeline pressures, temperatures, and concentrations. However, gases are soluble in liquids proportional to partial pressure. Partial pressure is found by multiplying the mole fraction of the component in the gas phase with the system pressure (see Dalton’s Law of Partial Pressure). Therefore, in the presence of the heavier NGL’s the lighter gases dissolve into the NGL’s more readily at higher pressures. The quantity of methane and ethane is based on the partial pressure, the higher the partial pressure the higher the concentration of these gases in the liquid phase. Oil and gas wells, as well as pipelines, commonly operate at very high pressure and up to 1,400 pounds per square inch gauge (psig) thus increasing the partial pressure. For example, a bottle of soda has a pressure of around 50 psig. When the cap is opened CO2 is released into the atmosphere due to the decrease in the partial pressure. Now compare that with a pipeline operating at 1,250 psig or about 20 times that partial pressure (on an absolute pressure basis). As with the soda when the oil solution containing the dissolved gases are dumped into the atmospheric tanks the gases naturally flash into a vapor.
Due to these phase characteristics (liquefaction/vaporization) of NGL’s they lack salability and are deprived of commercial sponsorship. Simply, this natural resource is wasted because NGL infrastructure is nonexistent in the majority of the facilities around the world. The reason it is nonexistent is a commercial one and the fact that it is not a crime to intentionally waste a natural resource, regardless of the effect on the environment. In the beginning of the shale oil and gas boom, we justified the waste due to the fact that the US was dependent on foreign countries for our oil so it was disguised as a national security issue. The truth was that the oil was valuable enough that it could be produced, the gas and NGL’s were flared and or vented, and the project was still profitable. Compounding the issue, due to the low value of the gas and the continued high value of the oil, natural gas pipeline construction projects were slow to develop so the waste continued and the infrastructure for the NGL’s were never even considered.
We understand the magnitude of this issue is difficult to grasp but make no mistake it is real. While the debate on the impact of methane and other hydrocarbon gases in the atmosphere continue, this problem must be logically discussed and addressed.
We know there are environmental specialist as well as oil and gas industry experts who are willing to work together to solve these problems. All of us at One Step In hope you will join us in this discussion and please follow us on FB @OneStepInOrg , Twitter @OneStepIn_ , and LinkedIn at One Step In.
Wiley Rhodes, Founder