# Estimated mud weight required to safely drill the well

I have an interesting question to share with you about how to estimate minimum mud weight required to safely TD the well.

The question is shown below.

7” casing shoe was set at 6,500’MD/5,000’ TVD. The geologist team in town expects 2 hydrocarbon reservoirs and information is listed below;

Formation sand A: Expected depth 5,500’ TVD, pressure gradient is 0.48 psi/ft.

Formation sand B: Expected depth 8,800’ TVD, pressure gradient is 0.49 psi/ft.

The planned TD is 9200’MD/9000’TVD and the drilling team requires 250 psi overbalance while drilling.

What is the mud weight required to drill the well with 250 psi overbalance?

First of all, let’s draw a simple diagram like this.

Knowledge required for this example:

Calculate formation pressure from pressure gradient

Convert pressure in to equivalent mud weight

Let’s take a look at each point.

Formation sand A:

Formation pressure of sand A = 0.48 x 5500 = 2,640 psi

With over balance of 250 psi, the hydrostatic pressure required is 2,890 (2640 + 250) psi.

Convert pressure into mud weight = 2890 ÷ (0.052 x 5500) = 10.2 ppg.

Formation sand B:

Formation pressure of sand B = 0.49 x 8800 = 4,312 psi

With over balance of 250 psi, the hydrostatic pressure required is 4,562 (4312 + 250) psi.

Convert pressure into mud weight = 4562 ÷ (0.052 x 8800) = 10.0 ppg

Please always use round up number for the mud weight.

For this case, you must use 10.2 ppg mud weight in order to drill to TD safely.

The point that I would like to emphasize on this topic is that you need to calculate how much pressure required for all sands. Please do not use only the sand that has the maximum pressure gradient.

### Related Post

Maximum Surface Pressure from Gas Influx in Water ... When a well is shut in due to well control operation, the casing pressure will increase due to gas migration and gas expansion. In water based mud, yo...
Boyle’s Gas Law and Its Application in Drilling Understand Boyle’s Gas Law Boyle’s law states that at constant temperature, the absolute pressure and the volume of a gas are inversely proportiona...
Reserve Fluid System and Pumping System in Koomey ... Reserve Fluid System in Koomey According to API RP53, each closing unit should have a fluid reservoir tank with a capacity equal to or at least twi...
Learn The Basic About Drilling Rig Types from VDO ... This is another training VDO that is very good for entry level personnel who are working in the oilfield industry especially drilling part. This VDO w...
Share the joy
• 87
•
•
•
•
•
•
•
•
87
Shares

Working in the oil field and loving to share knowledge.

### 10 Responses to Estimated mud weight required to safely drill the well

1. eduardo says:

hola soy eduardo de argentina trabajo en un perforador deceo aprender mas sobre mi trabajo y siemper me matan con las formulas en especiar cuando estan con herramientas en el pozo por ej: cuanto tarda un tapon en llegar a la punta del trepano y salir tengo que calcular los diametros interiores y los exteriores pero no tengo las formulas me las podrian enviar por correo si las tienen? atte gracias

• Can you ask the question again in English? I try to use a translation program but your massage cannot be interpreted clearly.

2. Obi Anselm says:

How can you determine pore pressure at the depth about 10 to 15ft from the last casing shoe using d-exponent in a known blowout recorded zone assuming if the mud weight was just increased from 10.5 to 13.5 ppg. The last caing shoe was 9183, the casing was 9 5/8 inches.
Mr. A.C. Obi

• From the information that you give me, I can tell only that the formation pressure must be more than 13.5 ppg.

If you give more information, I may have better ideas on this issue.

Regards,
Shyne

3. Xavier says:

Can someone tell me how to calculate Pore pressure and Fracture Pressure using only D’exponent realtime during drilling.

4. Leonardo Santana says:

Hi Obi,
you can determine the pore pressure with you corrected d-exponent using Eaton approach. You need the normal pressure gradient of the area. Please take note that you will miscalculate the pore pressure using the d-exponent without correction.

As Shyne said, the pressure in the kick zone has to more than 13.5 ppg because you already got a kick.

5. sakai laut solero says:

Hi,

Is it normal if mudweight that I calculate keep decreasing?

For example,

Conductor = 9.8 ppg
Surface = 9.8 ppg
Intermediate = 8.9 ppg
Production = 8.6 ppg

• It can be normal because it depends on formation pressure. If you convert it into PPG, it can be lower that the top section.

Regards,
Shyne.

This site uses Akismet to reduce spam. Learn how your comment data is processed.