Cement Transition Period in The Oil Well Can Cause Well Control Situation

When cement is in transition period (forming the bond), you will lose some hydrostatic pressure because cement becomes solid phase, therefore only water in the cement will provide hydrostatic pressure. In many cases happened, there is no issue while performing the cement job, however; once the cement is set after period of time, there is a casing pressure indicating that there is hydrocarbon in the annulus.

This example will demonstrate you why the well is in underbalance condition while waiting on cement.

Well information: Previous 9-5/8” casing shoe at 4000’ ft.

The vertical well (8.5” hole) is drilled to TD at 10,000ft with 12.1 ppg mud and the pay zone is at 9,800’ TVD with reservoir pressure of 11.6 ppg. The cement is planned to cover 3,500 ft in the annulus above the casing shoe. Water used to mix cement is 8.3 ppg weight.

 cement Transition Period

Continue reading

Applied Drilling Engineering (Spe Textbook Series, Vol 2) Review

If you would like to learn about drilling engineering, this book, Applied Drilling Engineering – Spe Textbook Series, is my recommendation. The book contains various topics regarding drilling engineering.

What will you learn from this book?

Rotary drilling – basic of drilling rigs, rig power system, hoisting system, circulating system, etc.

Drilling fluids – Mud test, pilot test, water based mud and oil based mud.

Cements – composition of cement, cement testing, cement additives, and cement placement techniques used in the drilling field.

Drilling hydraulics – Hydrostatic pressure, annular pressure during well control operation, buoyancy factor, non static well condition, flow through jet bits, rheology models, laminar and turbulent flow, surge/swab pressure and particle slip velocity.

Continue reading

Minimum strength to support casing string

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.

Continue reading

Hydraulicing Casing Calculation Example

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?

Continue reading

Balanced Cement Plug Calculation

You already learn about balance cement plug and I would like to show how to calculate balance cement plug.

 Let’s start with the concept so you can imagine how the calculation should be.

1. Determine volume of cement that you need.

2. Determine height of cement and spacer when pipe in hole.

3. Determine displace volume to balance the hydrostatic both sides. When the displacement is completed, you should have equal height of cement/spacer/mud. You can see the figure below for more understanding.

4. When you pull cement stinger, you will have the balance set properly like this.

Continue reading