The last word on non-condensable gas injection?

How do you cut the costs of steam generation for SAGD projects? That's a SAGD riddle that would even baffle the sphinx.

Here's another sphinx riddle: Which is cheaper, injecting methane or generating injection steam with it?

When his steam chambers reach 60% recovery, one SAGD operator proposes to completely replace steam injection with methane.

In his regulatory application you can see his plans for leading up to this point. And you can see his proposed methane injection rates. You can get his application documents within moments by clicking the blue button labelled "Get this application now" at the bottom of this post.

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You can think of a SAGD scheme as a two dimensional graph with axes of Steam injection and Methane injection. Some schemes are inject steam only. Many schemes are injecting both steam and methane. And now some schemes are proposing methane injection only. Primary production embraces no injection.

This quick methane-steam primer doesn't cover all the in-depth technical considerations. But it discusses high level concepts of methane co-injection.

Do you have a different opinion about steam/methane co-injection? Almost everyone does. Let's agree to disagree and see if that can take us somewhere new.

Sphinx riddles

Although the Great Sphinx of Giza is a very well known monument in Egypt, the sphinx symbol wasn't limited to that country. It was also found in ancient Phoenician, Syrian, and Greek societies. In Greek legend, the sphinx devoured all travelers who could not answer the riddle it posed:

"What is the creature that walks on four legs in the morning, two legs at noon and three in the evening?"

The Greek hero Oedipus gave the correct answer, "Man. For he crawls on all fours at the dawn of his life and he walks on two legs at the mid-day of his existence. But when he is old, he uses a cane and therefore walks on three."

The Egyptian monument itself has many riddles as to its construction, purpose and history. Geologists believe that the Great Sphinx started out as an outcrop that was carved into the lion body. Head, shoulders and paws were added to complete the statue which measures 73m at its longest dimension.

Adding steam to heavy oil increases recovery

Steam and methane injection can be represented on a two dimensional grid.

Primary recovery to bitumen can earn you 3-5% recovery -- perhaps a bit more.

Recovery depends of course on the rock properties, bitumen viscosity and reservoir pressure. If those are all working in your factor and if you drill many wells cheaply and close together, you'll get high production rates.

If you add enough heat to the reservoir to reduce the viscosity of the bitumen, you can increase recovery.

Many different methods of heating bitumen reservoirs have been tried. Microwave emitters, electrical heating elements, radio waves, hot water injection, hot propane injection, and many others. But the most popular heating method is steam injection.

Steam injection has been tried in vertical wells, in horizontal wells, and in horizontal well pairs (SAGD). In general, steam injection increases bitumen production rate and recovery.

Adding methane to steam reduces cost

But generating steam is expensive. Boilers have a high capital cost and require costly operation and maintenance.

Delivery of steam to the wellhead requires capital. Somehow you need to make sure the steam doesn't lose all its heat before it gets to the well.

Keeping up steam temperature during it's delivery down the wellbore is also a challenge. Some operators have tried insulated well strings, but many rely on raising the steam temperature at the boiler to great heights. Start out really hot so after all the heat losses, you still have enough temperature at the reservoir.

Some try to generate steam in a distributed way closer to the well head. But that also requires operating equipment people and costs at several points rather than at a central facility.

If you can deliver less steam to the reservoir and still get the same recovery you reduce the effort to generate steam at a boiler.

Adding a non-condensable gas (like methane) to the injection mix tends to reduce the amount of steam you inject. Many field trials have shown that gas injection works well in SAGD. In many cases it reduces the amount of steam you need but still keeps the SAGD chambers producing.

Almost every SAGD operator has experimented with methane injection. Many believe that injecting steam keeps the temperature up to reduce bitumen viscosity. They also believe that adding methane can keep the pressure up so production rates can stay high.

After steam, methane alone keeps recovery going

Although almost all SAGD owners are trying to add methane to steam at some ratio, some are resorting to methane injection only.

Some SAGD owners believe that they can totally replace steam with methane and keep their projects producing. After a steam chamber in the reservoir has enough heat, methane injection alone can keep the pressure up and allow production to continue.

Of course the temperature of the reservoir will drop off after steam injection has stopped. But the additional methane pressure will keep the recovery alive for a while after the heat has been shut off and the temperature slowly drops.

Many operators have been experimenting with methane injection. Some feel that they should inject methane during pad start-up. Some feel they should add methane when a steam chamber is nearing the end of its life. Some operators are trying to temporarily suspend their operations by injecting methane to keep the pressure up.

Where is your SAGD scheme in the steam-methane Cartesian grid?

Future of methane and steam?

What's the next step for methane injection? Perhaps cyclic steam stimulation (CSS) operators will look at methane injection to reduce the cost of steam injection. Huff and puff operators may find the SAGD field tests will help them determine the benefits of methane injection.

You can find all the thermal operations that are trying methane injection through AppIntel. AppIntel has a google-like search that allows you to search through application documents. You can type into the KiP search box sagd methane or non-condensable gas injection.

Tags: Thermal, Heavy Oil

Granger Low   6 Sep 2016

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