Pakistan produces around 4 bcf per day (bcfd) natural gas out of which 3.2 bcfd is available to the two Gas Utility companies viz SSGC and SNGPL. The balance is a dedicated supply for fertiliser and power that is direct and not supplied through the utility companies. SSGC and SNGPL in turn supply gas to consumers categorised as power (42%), industries and captive power (27%), domestic (20%), CNG (8%) and commercial (3%).
The natural gas demand has a wide seasonal variation between the summer and winter months. For example, the gas demand for Quetta is four times more in the winter than in the summer. This mainly arises due to the space heating and geyser load that sets in during the winter months. A similar situation arises in Punjab and KPK. Since almost all this increase demand, in winter, is generated from the domestic sector the gas is curtailed from the Industry, CNG and power to service the domestic consumer.
Historically, the demand has outstripped the supply since 2008 and the gap has been widening ever since. Although a variety of figures are quoted in the press but a more realistic estimate would be about 500 mmcf per day (mmcfd) in the summer and 1000 mmcfd in the winter that is growing by at-least 10% every year.
The government has been striving to bridge the gap by working on import options such as LNG and Interstate pipelines. This will augment the supply side and help in mitigating the gas shortages. However there is a need for examining the demand side as well. The increase in natural gas demand predominantly arises from the growth in the consumer base. However it is the un-accounted for gas (UFG) or gas losses that enhances the demand and aggravates the supply demand gap, more so in winters.
The main reasons for Unaccounted for gas (UFG) have been well understood in the two gas companies and are:
-- Line Leakages
-- Measurement and billing errors
-- Theft
Theft has always been singled out as the main reason of UFG and both the companies have focused on its prevention and control. However, not as much effort has been made to control line leakages arising out of insufficient maintenance, interrupted corrosion prevention and falling workmanship,
It has now been well established that the Gas distribution network of both the companies has dilapidated resulting in gas leakages also termed as line losses. The deterioration in the gas pipelines have occurred due to insufficient maintenance, poor corrosion protection, falling standards of workmanship and use of under spec materials. Natural gas is a colourless and odorless substance. In order to avoid gas-related accidents and detect leaking gas an odorizer is introduced in the gas stream. It appears that not enough odorizer is introduced, or the quality of the odorizer needs to be checked, to highlight the leakage of gas. It may be emphasised that the companies must carry out periodic leakage surveys to analyse the health of distribution system.
The leakages become more pronounced in winters because of higher gas withdrawals from the distribution network requiring the system to be operated at bigger pressures. The higher the system pressure the higher is the leakage from the pin holes and crevices in the distribution lines. This is further explained below.
The volume of gas leakage is directly proportional to the pressure in the gas distribution system and square of the diameter of the orifice through which the leakage occurs. Mathematically this is expressed as Volume 'V' = pd2. In the winter time the pressure in the SNGPL system triples or quadruples as it does in Quetta for SSGC. The leakage rate also increases accordingly. This is only the effect of pressure. The corrosion holes found in the pipeline also enlarge with time due to erosion and have an exponential growth effect on leakage as the volume is directly proportional to the square of the diameter of the hole. To illustrate the effect of diameter and pressure, a pin hole of 1/16" dia at a pressure of 15 pounds per square inch will leak at a flow rate of 0.11 mcf/hour. In other words, if the size of the hole doubles to say 1/8" and the pressure increases say 4 times to 60 pounds per square inches the leakage will increase 16 folds to 1.76 mcf/hour. In winters, the leakage factor is compounded and becomes very critical because the gas distribution system is operated a 3 to 4 times the summer pressures.
What happens to the natural gas distribution in winter? As winter sets in the domestic demand begins to increase, due to space heating and hot water requirement. In order to compensate this demand the system pressure is increased so as to push more gas into the system. The bigger cities and towns have had a population growth over the years that have developed serious bottlenecks in the gas distribution system laid some 20 years or more ago. In order to supply gas at the terminal ends the system pressures are further jacked up. This is a very serious action that is necessitated in order to supply gas to all the consumers during winter. It has serious consequences as the leakage rate increases manifold and further creates more shortages. This is a catch-22 situation that arises every winter more so on the SNGPL system. Thus in the winter time there are pockets in the city complaining of low pressure and no gas.
The average Unaccounted For Gas for the two companies is 10% and climbs up to as high as 20% for SSGC and 25% for SNGPL; in the peak winter months. At 20% the UFG is around 650 mmcfd. Compare this with the summer month figure of 250 mmcfd. If the line leakage contributes 50% to the total UFG in summer it touches around 80% in winter, due to high system pressure. So in winter the gas losses due to pipeline leakage mount to 520 mmcfd. This is more than 50% of the total shortages in the winter. This gas is lost in the air and unlike theft is never used.
It may be noted that methane has a 23-time larger carbon footprint on the environment than carbon-dioxide emissions. This is why in the developed world the unaccounted for gas is kept at 1% to 2% level, beyond which the utility companies are penalised by the EPA. Neither Ogra nor the utility companies have any cognisance of this as they believe that all the UFG is theft.
It is heartening to note that SSGC has recognised this phenomenon; it has been gradually working for more than 10 years in system augmentation, rehabilitation and removing bottlenecks by replacing leaking lines and increasing the diameters of distribution mains to operate the system at lower/optimum pressures whenever the demand for gas in the system rises. For example, the natural gas distribution pressures, in Karachi, have been brought down to 15 pounds per square inches in the summer and 35 pounds per square inches in winter. This has been accomplished by dividing Karachi into three zones and replacing the old distribution mains by higher diameter pipeline (opening up the arteries). Although, this is but a symptomatic relief as operating gas distribution systems below the design pressures has other technical complications of line choking and creates gas distribution inefficiencies. However, compare this with SNGPL where they operate at 60 pounds per square inches in the summer and 200 pounds per square inches during the winter, which is achieved by activating the bypasses at the Sales Meter Stations (SMSs) resulting in the depletion of the line packs in the Transmission lines.
This is a major reason that there is no outcry of gas shortages in the SSGC franchise. If the distribution pressures were to be kept as high as that of SNGPL, during the winter months, the gas shortages in Karachi and other cities would have reflected the same trend as in Faisalabad and other cities in the SNGPL franchise. SSGC now has the World Bank funded "Natural Gas Efficiency Project" (NGEP) that has its focus on reducing Natural Gas Losses. It is a very well planned and thought after project that can bring the much desired efficiency in the usage of natural gas- a very precious energy resource.
The government plan of augmenting gas supply is laudable and extremely essential but conserving the natural gas by reducing line leakages is also very necessary. (The writer is a mechanical engineer with a Masters in Production Management and a PhD in Metallurgy from United Kingdom)