QUESTION: In a multi stage frac job are all the stages opened for production at one time or do they open a stage or two then wait a period of time before they open the next few stages? I appreciate your help in understanding this process.
They can, and do, open either way.
There are companies that have completed 50 to 100 wells in, for example, the Eagle Ford shale. A company may have several other wells nearby. They will have records of these wells and if the new one has fracture pressures, amount of propant injected, final pressures, etc. that are in line with the prior wells there is really no need to incur the added expense of selective opening unless it was needed on the other wells.
When starting in a new area and still in an exploratory phase, these meticulous, step-by-step operations will be followed in all, not just well opening, steps. As development progresses and data is collected it is easier to recognize "normal" and to be less conservative>
If a stage was to fracture early then it may be decided to check that spot. Packers or plugs can be run in to isolate other areas.
A well that is drilled into different formations at different depths will need a multiple completion that has each zone isolated from each other. The different formations will have different pressures and flow rates and if they mingled, a higher pressure zone would "snuff out" a lower pressure zone.
Shale drilling is different in that the well bore is horizontal and so the formation strength and formation pressure will be uniform along the length of the well bore. This allows the oil or gas to flow in along the length of the perforated sections at the same pressure and rate at each section.
During the fracture and packing phase, each section should be equal. The reason for fracing in stages is not because they are different. If the casing was perforated along its entire length and then pumped into it, it would fracture at a point and all the remaining fluids would go into the first fracture. The frac job is done in stages in order to insure the formation is fractured along the entire length of the casing.
It is the operations at each of these stages that may determine how the well is cleaned up.
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QUESTION: Sorry, I now see that my question was not detailed enough. The procedure I am trying to understand is a 9 stage (4,500)frac job on a new horizontal well all in the same pay zone. Every 11 days the pressures and production drop 80% and then reestablish over 3-5 days. It appears that they may be opening a new stage, or 2, at those times but I don't really know. Trying to explain it to my kids (college age)and need to understand it more completely before I start down that road. I appreciate your help very much.
That is what it sounds like Ed, pulling individual plugs.
When the plug is pulled frac fluids will flow back and when the zone is cleaned up the pressure will increase as the production oil/gas that is in the area closest to the casing surges into it. Then as this production must start flowing through the pack material and flow further to reach the casing, the flow rate will decrease. Then the production techs will begin using different size orifices to maintain sufficient back pressure to minimize water production and gas loss (it is the gas pressure that pushes it to the surface.
I have included some links I have bookmarked. One is a narrative of the frac process, the next is a collection of public domain images that I sometimes use to illustrate something during a meeting. The last one is from Halliburton and is a video showing well opening and simultaneous clean up. I donít have one for plug operations as I no longer do that.
This one shows some plug setting.
This is the video