How Does 1029.4 Come From?

1029.4 is used in several calculations in the oilfield and we’ve been asked about what is 1029.4, how it comes from, why it needs to be this figure so in this article, we will show you how 1029.4 comes from.

how-does-1029.4-come-from

First of all, we would like to give someone about the background of this figure. The 1029.4 is widely used for capacity calculations. The following equations utilizing 1029.4 are listed below; Continue reading

Solid Density From Retort Analysis Mud Calculation

Retort analysis is the method to determine solid and liquid components in the drilling fluid. In this article, we will adapt mass balance and retort analysis data to determine solid density in the mud.

solid-Density-In-Mud-Calculation

Mass balance for mud is listed below;

equation 1

We can rearrange the Euqation#1 in order to determine the solid density

 

equation 2

Continue reading

Volume of Cutting Generated While Drilling

While drilling, cuttings are generated every footage drilled and this topic will demonstrate how to determine volume of cutting entering into the wellbore.

Figure 1 - Cutting Generated While Drilling

Figure 1 – Cutting Generated While Drilling

 The following formula is used to calculate cutting volume generated while drilling;

vc - bbl per hour

Where;

Vc is volume of cutting in bbl/hr.

Ø is formation porosity (%).

D is wellbore diameter in inch.

ROP is rate of penetration in feet per hour.

Vc can be presented in several unit as follows;

Continue reading

Buoyancy Factor with Two Different Fluid Weights in The Well

Buoyancy Factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid and you can find more information from this article > buoyancy factor calculation .  In that article, it demonstrates the buoyancy formula only for one fluid in the wellbore. However, this time, we will have the details about buoyancy factor when inside and outside fluid are different.

Buoyancy factor with different fluid inside and outside of tubular is listed below;

equation 1

Where;

Ao is an external area of the component.

Ai is an internal area of the component.

ρo is fluid density in the annulus at the component depth in the wellbore.

ρi is fluid density in the component depth in the wellbore.

ρs is steel weight density. Steel density is 65.4 ppg.

If you can the same mud weight inside and outside, the equation 1 will be like this

equation 2

This is the same relationship as this article buoyancy factor calculation.

Let’s take a look at the following example to get more understanding.

Example

13-3/8” casing shoe was at 2,500’MD/2,000’TVD

9-5/8” casing was run to 6,800’MD/6,000 TVD.

9-5/8” casing weight is 40 ppf and casing ID is 8.835 inch.

Current mud weight is 9.5 ppg oil based mud.

The well bore diagram is show below (Figure 1).

 Figure 1 - Wellbore Diagram

Figure 1 – Wellbore Diagram

The well is planned to cement from shoe to surface and the planned cement weight is 14.0 ppg. The displacement fluid is drilling mud currently used.

Please determine the following items.

  • Air weight of casing string
  • Buoyed weight of casing in drilling mud
  • Buoyed weight of casing when cement is inside casing and drilling mud is outside casing
  • Buoyed weight of casing when cement is outside casing and drilling mud is inside casing

Air weight of casing string

Air weight of casing string, lb = length of casing, ft × casing weight, lb/ft

Air weight of casing string, lb = 6,800 × 40 = 272,000 lb

Buoyed weight of casing in drilling mud

 Figure 2 - Bouyed Weight When Submersed In Drilling Mud

Figure 2 – Buoyed Weight When Submersed In Drilling Mud

Buoyed weight = Buoyancy Factor (BF) × Air Weight of Casing

equation 2.5

Buoyancy Factor (BF) = 0.855

Buoyed weight = 0.855 × 272,000 = 232,489 lb

Buoyed weight of casing when cement is inside casing and drilling mud is outside casing

 Figure 3 - Buoyed weight of casing when cement is inside casing and drilling mud is outside casing

Figure 3 – Buoyed weight of casing when cement is inside casing and drilling mud is outside casing

 We will apply the Equation-1 for this case.

Ao is an external area of the component.

Ao = π × (Outside Diameter of casing)2 ÷ 4

Ao = π × (9.625)2 ÷ 4 = 72.76 square inch

Ai is an internal area of the component.

Ai = π × (Inside Diameter of casing)2 ÷ 4

Ai = π × (8.835)2 ÷ 4 = 61.31 square inch

ρo = 9.5 ppf (mud in the annulus)

ρi = 14.0 ppg (cement inside casing)

ρs = 65.4 ppg.

equation 3

Buoyancy Factor (BF) = 1.22

Buoyed weight = 1.22 × 272,000 = 331,840 lb

 

Buoyed weight of casing when cement is outside casing and drilling mud is inside casing

 Figure 4 - Buoyed weight of casing when cement is outside casing and drilling mud is inside casing

Figure 4 – Buoyed weight of casing when cement is outside casing and drilling mud is inside casing

We will apply Equation-1 for this case as well.

All the calculation parameters are the same.

Ao = π × (9.625)2 ÷ 4 = 72.76 square inch

Ai = π × (8.835)2 ÷ 4 = 61.31 square inch

ρo = 9.5 ppg (mud in the annulus)

ρi = 14.0 ppg (cement inside casing)

ρs = 65.4 ppg.

equation 4

Buoyancy Factor (BF) = 0.42

Buoyed weight = 0.42 × 272,000 = 114,240 lb

Conclusion: At different stage of the well, you may have different buoyed weight depending on density of fluid inside and outside of the component and it is not always that buoyed weight is less than air weight.

Reference book => formulas-and-calculationFormulas and Calculations for Drilling Operations