Plan For The Unexpected

Let's talk about the oilfield for a minute. The heart of the oil and gas industry takes place out in the field, where there are a lot of uncertainties. First, all the work is done outdoors, in all types of weather, which means that there is a massive force impacting our work, which we have no control over. Secondly, much of our work is downhole, where we can't see what is happening. Downhole is a harsh environment with high pressure, high temperature, chemicals, scales, and a variety of fluids. Finally, in the oil patch we like to move really fast because, well, there's usually a lot of money on the line. All of this together creates a recipe for unexpected events to derail our plans.

In my time in the oil and gas industry, I've seen all kinds of bizarre, unexpected things happen, some small and some major. In fact, this kind of thing happens so often that you actually come to expect it. You learn to expect the unexpected. Plans rarely go perfectly as planned and thus we should not be surprised when unexpected things happen. Despite this, I'm always amazed when I see projects that are planned so precisely that everything has to go perfectly or else chaos ensues.

What does this mean? Well, it means that our plans should include some margin of error. When you go out to the field, pack some extra tools just in case. If you expect a project to last 5 days, plan for 7. Add a little extra money to your budget just in case. The worst thing that happens is that things go as planned and your margin of error goes "unused". If you do this, I promise you that you'll be a lot less stressed out. You can thank me later.

Remember, it's the oilfield and nothing goes as planned. Plan accordingly.

A Helpful Formula For Gas Hydrostatic Pressure

Calculating the hydrostatic pressure of a liquid column is straight-forward. In case you need a refresher, the equation is:

P-hyd [psi] = 0.052 * (Fluid Density [ppg]) * (Fluid Depth [ft])

The above equation calculates the exact hydrostatic pressure of a liquid column. But what about for a gas column? The answer is far less straight-forward because the gas is compressible and therefore the density is changing with the depth. There are iterative methods for calculating the hydrostatic pressure of gas, but these methods take some effort. With that said, someone once showed me a simple formula to estimate the hydrostatic pressure of gas, and it gets you surprisingly close to actual data. Here it is:

P-hyd-gas (psi) = 0.25 * (Depth [ft]/100) * (Surface Pressure [psi]/100)

The equation above works for 0.6 gravity gas and if you compare it to actual bottomhole data you will find that it's remarkably close.

Try To Avoid Packers Downhole

As you may or may not know, I spent the first third of my career so far in production. In that time I learned a lot about producing oil and gas wells, and one thing I learned is that downhole packers (between casing and tubing) really have a way of limiting your production options. The reason is that it cuts off your access to the annulus, thereby leaving your only downhole access through the tubing, which is where your reservoir fluids are being produced up. When a well has a packer, there is no easy way to provide continuous chemical injection into the well. This means that soap, corrosion inhibitor, salt inhibitor, and a whole slew of other valuable production chemicals cannot be easily injected into the well without shutting in the well. This leads to expensive capillary strings and/or other non-desirable options. For this reason, I don't like packers and I recommend trying to avoid them.

With that said, packers do serve a purpose and sometimes they are necessary. In these situations you will obviously have to install them and deal with the consequences. However, I've seen far too many times where a packer is installed as a part of the completion process, with no regard to the production impacts. I think this is silly. Production is the only point where you make money on a well, and therefore great consideration should be taken when making drilling or completion decisions that will negatively impact production. My advice is to use packers where absolutely necessary, but nothing more.

For those of you in drilling or completions, this may sound silly. Just trust me on this. Your production folks will appreciate it.

Understand The Limitations Of Echometers

Echometers are a neat tool that uses sound to determine (among other things) the depth of fluid downhole in a well. Similar to radar or seismic, an echometer sends a sound pulse down a well and measures how quickly that sound bounces back. Coupling this data with some math, we can estimate the depth of fluid in a well. It's a cheap, fast and neat way to answer the question, "How much fluid is in my well?" With that in mind, it's important to understand that echometers have limitations. The fluid level calculated by an echometer has some error in it. I've shot echometers on the same well, back to back, and received different fluid level calculations, sometimes off by 50 feet!

This is not an indictment on echometers, but rather my point is to say that you need to understand the limitations of this technology and only use it when appropriate. If you are simply trying to get an estimate of fluid level, or perhaps just trying to figure out if any fluid is downhole at all, then an echometer is a great tool for this application. However, if you are trying to determine your bottomhole pressure for a reserve analysis, then an echometer is simply not going to cut it. In this case you need a lot more accuracy than +/- 50 ft of fluid. If this is the case, then I'd recommend running bottomhole gauges in the well and performing a static pressure gradient, which will result in a much more accurate pressure measurement.

In short, echometers are a cheap and easy way to estimate your fluid, but it's important that you understand their accuracy and make sure sure you are using the appropriate tool for the job.