Muzarabani drilling will answer a lot of questions

10 Jun, 2022 - 00:06 0 Views
Muzarabani drilling will answer a lot of questions

eBusiness Weekly

Invictus Energy is now getting ready to move drilling equipment from East Africa to Zimbabwe to start the planned drilling of two test wells in the Muzarabani area where the Mukuyu prospect underlies the Cabora Bassa basin.

But until test wells hit gas-condensate there is no guarantee that there is anything trapped in the rock formations, and even if there is the test wells are crucial to find out just what sort of natural gas and condensate is trapped and the percentage of each component and impurity.

Seismic data has already established that there are the anticlines, the domed structures that can trap gas, deep underground. These would at some stage have trapped the gas condensate, but now the critical point has been reached to see if that gas is still there or if it has leaked out over the last 75 million years.

The Cabora Bassa basin is basically an arm of the sea that appeared fairly early on in the break-up of the giant Gondwanaland continent that once included South America, Africa, Madagascar, India, Australia and Antarctica. But the arm never developed into a rift that split southern Africa from eastern Africa and so was just there.

Over time, a lot of time, a lot flowed into that arm and was filling it, with the organics hopefully still largely trapped as petroleum products but layers of eroded rock and the like also flowing in.

Some of this rock would have formed hard layers, and as geological processes continued these were twisted and folded, forming the domes that we all hope trapped the organics.

The seismic surveys have confirmed the domes, and even measured how big they are and what sort of area they cover. But they have not been able to tell if the domes are fractured and if they continue to trap the gas and condensate.

Because the original filling was under the sea the result should be natural gas and petroleum condensates, rather than the peat bogs turning into coal fields that we have seen when vegetation was trapped in the freshwater swamps and shallow lakes inland.

The threat of leaks is real and this is the most important reason for the test wells, to find out if it has or if a reasonable amount remains trapped, and Invictus has identified this potential leakage as the biggest single risk.

If the two wells are both dry then Invictus reckons there are probably other sites that can be drilled to check, although this will push the exploration process in both time and cost.

The second important point, once gas condensate has been found, is to find out exactly what it comprises and in what sort of quantities, with the percentages of each type of hydrocarbon plus the percentages of each of the impurities, some of which can be commercially viable if they can be fairly easily separated out and others that have to be removed and disposed of without creating environmental risks.

What is almost certainly absent is the crude oils, the heavier hydrocarbons that are liquid in almost all circumstances.

Invictus is fairly sure that whatever is there is a mixture of natural gas and gas condensates, very largely a range of the lighter gases and hydrocarbons and this will determine what sort of processing is required to separate out what must be separated out and then how the products must be processed at the well-head, or even underground, how those compounds can be processed at other locations and how they can be pumped along what sort of pipeline.

Clean natural gas for a power station will be largely methane, the hydrocarbon with one carbon atom, and ethane, the hydrocarbon with two.

Both are gaseous at almost any pressure and in any pipeline and the mixture can be fed into a power station without much trouble.

The next pair of hydrocarbons are propane, with three carbon molecules, and the butanes, with four, although what for convenience is still called iso-butane, a row of three carbon atoms with a fourth branching off the middle one, is in more modern nomenclature called methyl propane but for once the older name makes more sense since the two gases with four carbon atoms are so similar.

Propane and the butanes liquefy at room temperature but under pressure.

They are the liquefied petroleum gases we use in cylinders to cook with, although propane will predominate, and can be moved in a pipeline mixture if the pressure is moderate.

We then move up the scale to pentanes, where we start seeing more condensation and hexane, the six carbon chains, which are the prime chemical used to extract vegetable oils in modern processing plants, and that would be from soya bean, sunflower and cotton seed.

Once we start seeing pentanes and above in the mixture of what comes out of a well we move away from raw natural gas to what are known as the condensates, since some of what comes out of the ground will be liquid, even if largely in droplets.

Higher carbon chains can be found, along with cyclic components, but it is extremely likely that these will be in very low quantities. The precise percentages will be important.

If almost everything is methane with some ethane and very small quantities of other gases and contaminants including water, it is dry and raw natural gas and can be fed into a power station without too much processing.

Degrees of purity required can vary quite a bit. There is what is called enough processing to create gas that is acceptable in a pipeline; there is no absolute standard for this.

Contaminants vary. One of the most important is hydrogen sulphide, and if this is around the gas is known as sour natural gas and above some very low levels needs to be removed. We can also have quite a bit of other stuff, but again it depends on just how much.

One reason for hoping that at least some of the gas that can be pumped is almost all methane with perhaps some ethane is that this can be fed into a power stations fairly quickly without much extra processing.

Natural gas power stations can be built fairly quickly. Basically they are a jet engine running a generator and unlike hydro stations with their dams and thermal stations with their cooling towers and other civil engineering they do not need much in the way of a structure.

Grossly oversimplifying they have been described as a jet engine in a shed, but that is largely the concept and as the engine-generator sets are largely off the shelf a gas station can be built in months rather than years.

This would allow Zimbabwe to catch up fairly quickly on the electricity generating shortfalls we will be facing for some years.

That is even with Hwange Thermal Extension, the major maintenance, amounting to replacing a lot of the components of the boiler-turbine-generator sets, for the first two 1980s phases of Hwange, and some of the smaller private generating stations.

The second giant thermal station, planned as a major independent station, and Batoka will take a lot longer.

They will be needed but are not going to finished in the next three years even if we started pouring concrete tomorrow.

The other major importance of natural gas finds will be our chemical industry. The first critical industry will be ammonia production.

At present in the world the cheapest way of making ammonia, a vital fertiliser component that chews up more than 80 percent of global production is fertiliser, so the importance is obvious, is from natural gas.

The industrial process is not that simple, but the process requires bringing together methane, air and steam with the result being ammonia, carbon dioxide, which needs to be scrubbed and preferably not released, and oxygen, which can be sold or vented.

This requires a lot less energy, now expensive, that is used in countries with surplus cheap hydro power, such as Norway, to make ammonia from air and water.

This was used in Zimbabwe when we had a Kariba surplus.

With plenty of energy, liquefaction of air to get nitrogen and electrolysis of water to get hydrogen can provide the raw materials.

Others of the impurities can be used in chemical industries.

The condensates can be processed and pushed together to get petrol and diesel, but this requires a large plant and refinery, which would be different from the sort of refinery used to break up longer chains from crude oil, and might not be that viable.

The world is moving to the electric car over the next decade and a bit, and while older vehicles will still need petroleum the quantities will be diminishing and so in the end natural gas running power stations might be more valuable.

A natural gas station burns produces less than half the carbon dioxide as a coal station for every unit of electricity generated.

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