one for pt

Hey PT

As promised here is quick post on pore and gradient pressure.

At the onset of planning a well especially in places that ERH have drilled, you would be presented with the following set of data

This data is based primarily on history of the field and surrounding areas. The data would also been put through Rehm & McClendon Correlation or Zamora Correlation, to gain the most accurate pressures.
This data allows you to do 2 things, work out your casings program and your muds weights for drilling a safe well.

This data can be logged through a scatter chart in excel.

The first thing you do is logged your pore pressure. The pore pressure is the force of the invading fluids into your well bore and you would have something that looked like this

To get the correct mud weight you simply add .5ppg to the current pore pressure. So if the weight of the invading fluids were 8.6ppg the mud weight to control this would be 9.1ppg and you would have a chart that looked like this.

You can see now we have estabished the muds weights needed for the drilling of the well.
Now that first bit is complete you need to workout your gradient pressure, the gradient pressure is basicly the maximum mud weight you can run before the rock you are drilling fractures. The gradient pressure is charted the same way

But instead of adding .5 to your ppg you take it away, in other words gradient pressure was 17.6ppg you would have a safety margin of 17.1ppg. And look like this

Now you develop your casings program. As you can see if you tried to drill the hole in one go you would have pore issues or gradient issues. So starting from the bottom and at the very edge of your pore pressure safety margin you go up to until you just touch your gradient margin. "see below".

This establishes 3 things, firstly the mud weight needed to drill the well safely and also the depth of where you production casing starts and how long it needs to be to reach total depth.
You then draw a straight line from your gradient safety margin across to your pore safety margin and and then do the same as above to work out you intermediate casing and then the same again to work out your surface casing. see below

Hope that was easy to understand mate, any issues let me know and will do my best to clear them up

cheers

ciggs