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In praise of the mapmaker: Why they’re more vital than you might think

In praise of the mapmaker: Why they’re more vital than you might think

When the world was less thoroughly travelled, cartographer’s maps allowed ships to arrive safely at their destinations. Maps of hydrocarbon accumulations deep below ground serve a similar purpose in the oil and gas business, preventing investors from getting lost at sea.

Only a handful of people might be involved in creating and checking a subsurface map, but their work will affect thousands of people involved in downstream processes, from exploration drilling to refining. If a map says there’s a hundred million barrels in the ground, engineers, lawyers, managers, and investors rely on it to be accurate. If the map is poor — decisions based on it will be poor too.

Because millions of working hours and billions of dollars can be invested as a result of decisions based on a single map, it’s vital to get that map right. Anyone familiar with the art and science of depth conversion will know that a map can integrate well and seismic data in both good and bad ways. But that doesn’t mean the goal of a mapmaker is necessarily perfection. A seismic interpreter knows their map can’t always be 100% correct so the question really is, how wrong can it be? If you can quantify the uncertainty, those making investment decisions will be much more able to account for risk.

 

Map-making is vital at each stage of the oil and gas cycle

 

1. Maps are vital at the exploration stage

 When mapmaking is done right, great things can happen. For instance, if you trace the sea bed 20km offshore Nigeria to the well known Aje field, you’ll encounter a shelf edge, where the seabed disappears into much deeper water. Subsurface rocks, where we hope to find oil and gas, dip monoclinally into the abyss.

Looking at the seismic images of this field you won’t see a time structure that could be drilled. But that picture changes once you complete a depth conversion. Then you’ll notice the monocline has become an anticline – a structure that’s home to a considerable amount of oil.

An exploration well was drilled and discovered this field because the explorers had confidence in their map, resulting from confidence in their depth conversion velocity model.

 

2. Maps are vital at the investment stage

 Another example we can look at is in the Southern North Sea – a region where maps of the reservoir are notoriously difficult to make.

On one occasion, a company brought us in on a gas field discovery they’d made in the area. They wanted us to understand the depth conversion sensitivities, and to understand the uncertainty in the field structure map. The company was being sold, and the gas field was a key asset. The more work we did to understand sensitivity and improve the velocity model, the more the discovery seemed to balloon. Almost every improvement we made to our working map revealed a greater quantity of gas.

As a result, the potential size of the asset increased and it became a more valuable bargaining chip in the corporate sale.

On this occasion, the map maker added value by providing confidence in understanding the uncertainty in the map, and increasing the most likely stored volumes.

 

3. Maps are vital at the development stage

We know of one large development in Asia that was believed to have several hundred BCF of gas in the ground. The owners had already invested significantly in field development, but production was declining much more rapidly than expected.

Recreating field structure maps we predicted far less gas than originally expected, and realised that the field development had been unnecessarily gold plated. The key to field mapping was understanding that seismic told us where the gas-water contact was, at the edge of the strong reflections. This gave us new information in areas where there were no wells to tell us reservoir depth, over the flanks of the structure. The extra control led to steeper flanks and smaller gas volumes.

Here the map maker used deep understanding of the seismic image to improve the depth map using seismic attributes, leading company management to develop a deeper reservoir rather than throw good money after bad in the depleted shallower rocks.

 

4. Maps are vital at the production stage

Let’s look at another North Sea case – a development that was already in full swing by the time we arrived to begin mapmaking.

In this instance, the operator had a map of the mature field already, but they wanted to be doubly sure they were on the right track before they sunk tens of millions of dollars into drilling two new wells. They were renewing their asset strategy and margins mattered.

They’d wisely reprocessed their seismic data, using state-of-the art techniques. Following a review, we could see that the seismic velocities were high quality and making depth maps directly from the seismic was a better option than depth converting time maps. This meant that the spot they were planning to drill was deeper than previously thought and the structure contained less oil and gas than expected.

Although unhappy that they had fewer hydrocarbons than previously thought, management were able to switch drilling strategy and invested in only one well, saving unnecessary cost and keeping the development profitable.

The map maker’s judgement in evaluating the quality of the data on which to make the map was key to making a sound investment decision here.

 

You need to be confident in your maps – so assurance is essential

Every geoscientist aims to be a proficient map maker, but while they may interpret seismic data every week, other steps in the map making process such as depth conversion may come up only once per project. This means they may not acquire enough experience to temper the optimism of their calculations or be confident they’re not dismissing an opportunity out of hand.

This lack of experience is not a problem in and of itself – so long as you have management or an internal QC who can help. But even at management and QC level, the understanding required isn’t as widespread as it could be – and so it’s often worth prioritising external quality assurance early. As we’ve explored in our article on how to make assurance less costly, it’s hard to put the brakes on a project right before it’s due to be greenlit.

Navigating the choppy seas of oil and gas investment is much safer using a robust map.  Ultimately, if you don’t invest in assurance early in the map making process, your project might end up on the rocks.

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