Gas Lift Mandrel Spacing App

You may be interested in an app for simple mandrel spacing that follows a technique that I have taught and recommended for years.

I created this app because I have previously taught that creating a gas lift mandrel spacing shouldn’t take more than 10 minutes with a pencil, graph paper, and a ruler.? I realize that people don’t have these things in their work environment anymore.?And, it would be nice to have a completed spacing in 2 minutes, or less.?I think this app might make that possible.

First, a bit of gas lift design philosophy. A good gas lift design must (in order of importance):

1)?????Avoid unstable production (heading, surging), otherwise your data will be too poor create a good design or to optimize anything.

2)?????Lift as deep as possible, to maximize drawdown, thus production and revenue.

3)?????Use the right amount of lift gas, considering this well is probably part of a larger system of wells.

Good gas lift requires careful design of gas lift valves for a given mandrel spacing, incorporating all the knowledge of the current state of the well in order to maximize production.?Gas lift designs are always a trade-off between lift depth (revenue) and risk of not working (embarrassment and maybe mechanical risk of extra wireline work to install another design if this one doesn’t work).???Experience and judgement come into play when creating gas lift valve designs for producing well completions with existing mandrels.

On the other hand, creating a new mandrel spacing for that same well completion when using side-pocket gas lift mandrels (wireline-retrievable valves) is very different:

• The mandrel design must work over the life of the completion.
• Well performance will change over the life of the completion.
• Prediction of how these conditions will change is error-prone.

Thus, there is no such thing as a perfect side-pocket mandrel spacing. If you try to optimize a gas lift design to minimize the number of mandrels, you will almost certainly fail to maximize revenue from the well.

Design of a spacing for conventional mandrels (non-retrievable valves) is somewhat in the middle, but more like gas lift valve design for existing mandrels.?The difference is?that you will have to call the rig to fix a bad gas lift design with conventional gas lift mandrels and valves. Conventional mandrels design is less forgiving and harder to optimize. I prefer gas lift mandrels with retrievable valves and a handy slickline unit.

There is such a thing as a bad mandrel spacing (sidepocket or conventional).?I have encountered many of them.?? It is sad that each harmed the value to the company many, many times more than the annual salaries of those that designed them.

In order to avoid a bad mandrel spacing make sure that you have mandrels close enough to where they are needed over the life of the completion. Use these 4 checks on any mandrel spacing:

1)?????Can unload by u-tubing completion brine back to surface.

2)?????Can unload to the operating depth expected initially.

3)?????Mandrels are spaced correctly in the operating range; never so far apart that significant revenue is lost or deferred.

4)?????Mandrels are spaced deep enough, so that later in life you can still lift as deep as possible.

Any mandrel spacing that conforms to these 4 checks is good enough.

The technique used by this app will suggest more mandrels than many people normally use.?There are two reasons I have heard to reduce the number of mandrels, neither very good:

1. Extra mandrels will cost extra money.?It is important to determine how many additional barrels of production are required to pay for a mandrel. Having a mandrel in the right place at the right time will normally be worth at least 10 barrels of oil per day at some point in time (probably at many points in the well life). ??It could be worth considerably more than this.?The revenue from 10 barrels of oil per day for a short time will pay for all the mandrels in the well.
2. The second reason I have heard is that adding mandrels introduces more leak paths.?The extra mandrels do introduce more potential leak paths, but mandrels with shop-installed dummy valves, pressure-tested in the shop, then re-tested on the rig floor, and selected with the correct elastomers rarely leak.? It’s a strange situation where that extra risk of a leak is important where the design intent is to create connections between the casing and tubing (gas lift) and to put high pressure gas into the annulus (gas lift). I suggest there is zero additional relative risk in such a situation from extra mandrels with dummy valves installed. If you are worried about additional mandrels, it would be safer to complete the well without gas lift, and wait to install gas lift until the well can no longer flow naturally.

My gas lift design spacing philosophy, derived from the masters of gas lift before me, and tested with experience is: ?install lots of mandrels, but few gas lift valves.?Having many gas lift mandrels helps you take maximum advantage of gas lift’s prime advantage: flexibility for unknown and changing situations.?But, the number of installed gas lift valves (IPO unloading valves, and an orifice with a choke) should be minimized in order to both lift deeper (fewer pressure drops with IPO valves), and to lower the chance of valves opening and closing, causing instability, and fatigue failure of tiny gas lift valve parts.

Tips for Using this App

For the packer depth, use the true vertical depth (TVD) of the packer.?This is important as this will limit the depth of the deepest mandrel(s).??If you don’t have a packer, use the end of tubing depth.?If you have a highly-deviated well, use the depth where you would install your last mandrel (+60 ft). If you have not designed the TVD depth of the packer, make a guess and the app will give you the bottom mandrel in MD and TVD. Then add 60' to that for your packer depth.

Use the expected FTP at the wellhead when flowing into the highest production system pressure that might be needed for gas lift.??

For the mandrel spacing, choose a design injection pressure (CHP) 50 psi less than the available injection pressure at the wellhead.?This is so that you can control the gas injection rate into the well and still get flow through the top gas lift valve.

Use the highest brine gradient that might be found?in the well.??If you are using a heavy completion brine, then you probably are not going to need gas lift right away.?But, consider what recourse you will have if you do have to gas lift out that completion brine on a dead well.??In normal cases, use the gradient for the density of your produced water.?A higher density is more conservative.

The gas lift gradient used in the app is a rough approximation, but fairly conservative.?If you have very light injection gas (specific gravity < 0.6) , or very hot temperatures (> 200 F), it may not be conservative enough without compensating with a higher CHP.?A lower density is more conservative.

The dP value is used in the?design is to simulate the effect of multiple pressure drops that will be needed to close successively deeper IPO valves.?A higher dP is more conservative.?If you use PPO valves, this spacing technique is probably conservative enough to ensure the valves stay closed, but you may want to check this.

You can change the minimum spacing. For example, you want to relate your spacing to the expected productivity index. The difference in lift depths between two mandrels should not be too large, because that means the difference in drawdown will be large, and with a high PI, the difference in production rates will be large.? You want to avoid the situation where lifting from the next mandrel deeper is worth an extra 500 barrels of oil per day, if you would have been willing to install a new gas lift design for a gain of 50 barrels of oil per day. A smaller minimum spacing is more conservative.?

Click Accept after you make any changes to the data.

The default , straight design line (green) is a suggestion based on experience and referenced in many gas lift design guides.?You can change it by dragging the green triangles to get a different spacing.?For example, you can create a closer spacing higher because the well will maintain a higher lift depth for longer.?If you know for certain that you will not operate near the top of the well, and maybe the well can’t produce at all without deep gas lift, you can widen the spacing at the top.?I suggest tweaking the bottom point slightly to place one mandrel right at the deepest point.

You may, of course, leave out the lower mandrels generated by this technique from your installation, if you are certain you will not lift from down there.?Be warned:?Many engineers made this assumption only to be proven wrong due to unexpectedly poor productivity or reservoir pressure performance.? Their boss was already unhappy with the poor inflow performance, and then even more unhappy with the poor lift performance. I highly recommend running mandrels as deep as possible, leaving 60’ above the packer for the ability to fish the packer, if necessary.

The graphical technique here is based on true-vertical depths (TVD), because gravity of fluids in the well are influenced only by TVD.?Folks on the rig and operating wireline do not use TVD. They use measured depth (MD), the depth measured along the hole.?Be sure that you give the rig MD values and keep the TVD values to yourself to avoid confusion.??

You can use copy and paste with this app.?You can copy your directional survey of MD, TVD pairs from a spreadsheet or other document, and paste them into the directional survey box.??I have tried this will several hundred pairs and it works.?Separate the MD value from the TVD value with a space, comma, or tab.?Excel pastes using tabs and works fine.

Clicking on the Results button calculates the mandrel depths, and it puts the depths onto the clipboard so that you can paste the results in Excel or other documents.

If you want to take a screenshot of the design, the Hide button may be of use.??You can also resize the shape of the app to get a vertical aspect if you like.

The major graph lines are 1000 feet vertically and 100 psi in pressure horizontally.

Like all of my recent apps, this app was made with the Godot Engine .?? Let me know if you want to learn how to build apps like this.

Update 2/21/22: I have made the program open in a smaller resolution to help those with small monitors. After the app opens you can resize it to whatever shape and size you like.

I have also added a Dropbox download option, as the security in some systems and browsers reports the waringworld.com site as suspicious.

Download my app here:

The html5 version (for modern browsers, perhaps not Safari):?https://waringworld.com/glmandrelspacing/html5/gasliftmandrelspacing.html

[The use of the clipboard seems to work fine with the html5 version. I'm very impressed.]

The Windows version:

https://waringworld.com/glmandrelspacing/win10/GasLiftMandrelSpacing.zip

or via Dropbox:

https://www.dropbox.com/s/dt63uuksk9xckzb/GasLiftMandrelSpacing.zip?dl=0

If you want to see more of my?creations:

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Burney Waring Copyright 2021

Burney Waring is an almost-completely retired global consultant engineer, and Director of Retirement Testing at the Waring Retirement Laboratory.