This year there have been a number of instances that the natural gas transmission and distribution system of Pakistan was under strain due to an increase in “line pack”, which is a critical operational parameter. It is basically the total volume of natural gas stored in the pipes of a transmission or distribution system. If it crosses the threshold of approximately 5 BCF (Billion Cubic Feet) mark, then there is a risk to pipeline integrity as the pressure in the pipelines begins to exceed the value on which it has been designed. The recent surges have been attributed to a drop in demand of RLNG (Regasified Liquified Natural Gas) by the power sector and also a drop in consumption of system gas by the fertilizer sector owing to their ATA (Annual Turn Around). The reduction in consumption by the bulk sector forces a shift to the retail sector due to which gas is offloaded to the distribution system leading to increased leakages. Another step which is taken is to request reduction in production from indigenous resources which puts their wells at risk and can cause contractual penalties to the gas utilities. This begs the question, is there a solution?
Natural gas can be stored underground under pressure in three types of facilities: depleted oil/natural gas reservoirs, aquifers and salt caverns. These storage facilities have their own physical characteristics as well as economics associated with them which can be leveraged for an application. Depleted oil/natural gas reservoirs are advantageous due to their wide availability and we can utilize the existing infrastructure like wells and gathering lines for connection to the transmission system.
Natural aquifers can be converted to natural gas storage reservoirs, however, its suitability can be determined by the presence of an impermeable cap rock on the water-bearing sedimentary rock formation. The development costs are also high as compared to depleted gas and oil reservoirs as it requires installation of allied infrastructure like wells, pipelines and dehydration facilities. It also requires higher levels of “cushion gas” or “base gas”, which is the volume of gas that is necessary to maintain the required pressures during withdrawal when there is peak demand.
The third type of facility are salt caverns which provide very high levels of withdrawal and injection rates and require lower levels of cushion gas to maintain the desired pressures. Although salt cavern construction is more expensive in contrast to depleted reservoirs on the surface as cost per thousand cubic foot (MCF) of gas is high, keeping in view their ability to perform multiple withdrawal and injection cycles the cost per MCF of gas reduces.
The ability to store natural gas underground in these formations will give the natural gas transmission and distribution companies the flexibility to balance the flow in pipelines and maintain line pressures within designed parameters. It builds enhanced operational resilience in the system to respond to seasonal variations like low demand during summers and high demand in winters and gives the utility companies the ability to take advantage of global LNG spot-market fluctuations. Underground storage facilities also mitigate energy security risks which arise out of global conflict as has been witnessed in the on-going Russia-Ukraine conflict.
It is the need of the hour to build a strategic natural gas reserve by identifying suitable underground storage sites throughout the country with the necessary physical characteristics like porosity, permeability and stability. The economic feasibility and return on investment need to be carried out. The private sector can be encouraged to invest through incentives for which the government needs to delineate a policy framework. This will help address pressing issues of gas price volatility and supply disruptions, while also reducing the strain on the grid during peak demand periods. By investing in natural gas underground storage facilities, Pakistan can join the ranks of countries like US & Russia, which have successfully leveraged underground storage to manage pipeline integrity and insulate themselves against any shocks to the global economy. Recently, Pakistan had to defer LNG cargo shipments from Qatar and the upstream gas sector has also complained of losses to the tune of millions of dollars due to curtailment from local gas fields. We are dealing with the paradox of oversupply due to demand side suppression. If we invest in natural gas underground storage systems, we can add inherent flexibility in the system and add a new dimension to the energy security of our country.
Hussam Mehboob
The writer is an electrical engineer and works in the downstream natural gas sector.
