Yearly Archives: 2011

Slow Circulation Rate (SCR)

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Slow Circulation Rate is a circulation rate which will be used in well kill operation. Typically, slow circulation rate pressure (SCR) is recorded from each particular flow rate and the pressure represents pressure loss of the system while circulating. Since there are so many pressure gauges on the rig, you may get confused on the figures. In order to be at the same page for every personnel on the rig, the SCR should be recorded by the pressure gauge that we will use for killing the well.

 

There are a lot of reasons why we should kill the well with slow rate rather than a drilling rate as follows:

 

• To minimize friction pressure

• To allow time to weight up mud if you use wait and weight method

• To reduce pressure on surface equipment

• To allow degasser to separate gas from the mud

• To reduce needs for fast choke operation

• To allow personnel to think if something goes wrong

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Cutting Slip Velocity Calculation Method 2

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This is another method to determine cutting slip velocity. The process of calculation is quite different from the first method however it is still straight forward calculation. It still gives you the following answers: annular velocity, cutting slip velocity and net velocity.

 

Let’s get started with this calculation method.

 

1. Determine n

Where;

n is the power law exponent.

Θ600 is a value at 600 viscometer dial reading.

Θ300 is a value at 300 viscometer dial reading.

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Cutting Slip Velocity Calculation Method 1

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Cutting slip velocity is velocity of cutting that naturally falls down due to its density. In order to effectively clean the hole, effect of mud flow upward direction and mud properties must be greater than cutting slip velocity (settling tendency of cuttings). Otherwise, cutting will fall down and create cutting bed.

You can learn more detail about it via this topic -> Cutting Slip Velocity

This calculation will show annular velocity, cutting slip velocity and net velocity so you can use as a reference for you hole cleaning indication.

There are 2 calculation methods and I will show the first method via this topic.

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Minimum strength to support casing string

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One function of cement is to support casing string and the shear strength of cement holds casing string once cement is set. You may think about other load supporting casing as compressive loading at coupling areas or thermal movement. They are the part of the supporting force as well but the most support is from the cement shear strength.

(Diagram above shows how shear strength of cement supports casing string)

We don’t normally measure shear strength of cement but we can apply knowledge from Civil engineer to estimate the shear strength from the compressive strength. Generally, cement has the shear strength approximately 1/12 of compressive strength. For instant, if the cement 1000 psi compressive strength, its shear strength is 83.3 (1000 x 1/12) psi.

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Hydraulicing Casing Calculation Example

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For the previous topic, Hydraulicing Casing (pressure to lift the casing while cementing), you already know the concept. This topic will demonstrate you how to figure out if the casing will be hydraulically lifted while pumping cement.

 

Example:

Casing 9-5/8”, 40 ppf (pound per foot), ID of casing = 8.835”

Casing is set at 3,200’MD/3,000’TVD

Top of cement at 600’MD/550’TVD

Previous casing shoe (13-3/8”) = 1000’MD/900TVD

Cement weight = 14.0 ppg

Mud weight = 9.5 ppg

Displacement fluid weight (Brine) = 8.4 ppg

 

What is the condition at the static condition after cement in place?

What is the maximum pressure that we can apply before the casing is hydraulically pumped out of the well?

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