Formation Temperature Calculation

Formation temperature is one of the most critical parameters in drilling and workover operation and it varies by true vertical depth of wellbore.

The following formula shows relationship between formation temperature and true vertical depth of well.

Formation temperature = (ambient surface temperature ) + (temperature gradient x  Well TVD)

Where:

Formation temperature in F (Fahrenheit)

ambient surface temperature in F (Fahrenheit)

temperature gradient in F/ft (Fahrenheit / ft)

Well TVD in ft

Example: The temperature gradient in a specific area is 0.015 °F/ft of depth and the ambient surface temperature is 90 °F.

Determine the estimated formation temperature at a TVD of 12,000 ft:

Formation Temperature, °F = 90 °F + (0.015 °F/ft x 12,000 ft)

Formation Temperature, °F = 90 °F + 180 °F

Formation Temperature = 270 °F (estimated formation temperature)

Please find the Excel sheet used for estimating formation temperature.

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

Hydraulic Horse Power (HHP) Calculation

Hydraulic Horse Power is a measure of the energy per unit of time that is being expended across the bit nozzles. It is commonly calculated by this equation, HHP=P*Q/1714, where P stands for pressure in pounds per square in., Q stands for flow rate in gallons per minute, and 1714 is a conversion factor necessary to yield HHP in terms of horsepower. Bit manufacturers often recommend that fluid hydraulics energy across the bit nozzles be in a particular HHP range, for example 2.0 to 7.0 HHP, to ensure adequate bit tooth and bottom-of-hole cleaning (the minimum HHP) and to avoid premature erosion of the bit itself (the maximum HHP).

Hydraulic Horse Power (HPP) formula:

 

HHP= (P x Q) ÷1714

where;

HHP = hydraulic horsepower
P = circulating pressure, psi
Q = circulating rate, gpm

Example : Determine Hydraulic Horse Power with these following data:

circulating pressure = 3500 psi
circulating rate = 800 gpm
HHP= (3500 x 800) ÷1714
HHP = 1633.6

Please find the Excel sheet for calculating Hydraulic Horse Power (HHP)

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

Hydrostatic Pressure (HP) Decreases When POOH

When pulling out of hole, volume of steel will be out of hole and mud volume will replace the steel volume.  If we don’t fill hole, hydrostatic pressure will decrease. There are 2 cases of pulling pipe which are pull dry and pull wet. Each condition is different in calculation concept because mud volume to displace pipe volume is different.

This topic shows you how to calculate hydrostatic pressure loss for both cases of pulling pipe, pull dry and pull wet. Moreover, there is the Excel sheet for calculating pressure decrease due to pulling out of hole.

Case#1: When pulling DRY pipe

When pulling dry, we will consider volume of steel out of hole only.

Step 1: Determine Total Pipe Volume

Step 2: Determine Hydrostatic Pressure Decrease

Example: Determine the hydrostatic pressure decrease when pulling DRY pipe out of the hole:

Number of stands pulled = 10
Pipe displacement = 0.0055 bbl/ft
Average length per stand = 91 ft
Casing capacity = 0.0873 bbl/ft
Mud weight = 12.0 ppg

Step 1: Determine of pipe displacement in Barrels = 10 stands x 91 ft/std x 0.0055 bbl/ft displaced
Barrels displaced = 5.01 bbl
Step 2: Determine HP, psi decrease = 5.01 barrels x 0.052 x 12.0 ppg ÷ (0.0873 bbl/ft – 0.0055 bbl/ft)
Hydrostatic pressure decrease = 38.2 psi

Case#2: When pulling WET pipe

When pulling wet, we will consider volume of steel out of hole and volume of mud in drillpipe as well. Therefore, pulling wet will decrease hydrostatic more than pulling dry pipe.

Step 1: Barrels displaced = number of stands pulled per stand in ft
x average length x {pipe disp inbbl/ft + {(% volume in drill pipe out of hole ÷ 100) x pipe cap in bbl/ft)}

Step 2: Determine hydrostatic pressure in psi decrease = barrels displaced x 0.052 x mud weight, ppg ÷ ((casing capacity in bbl/ft) – (Pipe disp in bbl/ft + pipe cap in bbl/ft))

Example: Determine the hydrostatic pressure decrease when pulling WET pipe out of the
hole:

% of volume in drill pipe out of hole = 100
Number of stands pulled = 10
Pipe displacement = 0.0055 bbl/ft
Average length per stand = 91 ft
Pipe capacity = 0.01876 bbl/ft
Mud weight = 12.0 ppg
Casing capacity = 0.0873 bbl/ft

Step 1: Barrels displaced = 10 stands x 91 ft/std x {(.0055 bbl/ft + (100 ÷ 100) x 0.01876 bbl/ft)}
Barrels displaced = 22.08 bbl

Step 2: hydrostatic pressure in psi decrease = 22.0766 barrels x 0.052 x 12.0 ppg ÷ ((0.0873 bbl/ft) – (0.0055 bbl/ft + 0.01876 bbl/ft))
HP decrease, psi = 218.52 psi

Please find the Excel sheet for calculating pressure decrease due to pulling out of hole.

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

Buoyancy Factor Calculation

Buoyancy Factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid.

Before explaining any further, I will explain you about the basic concept of Buoyancy. Buoyancy is the upward force that keeps things afloat. The net upward buoyancy force equals to the amount of the weight of fluid displaced by the body volume. This force will make objects lighter when it immerses in fluid. For example, we feel ourselves lighter when we are in swimming pool because this is the effect of buoyancy.

bouyancy-factor

In drilling operation, we need to know how much weight of string of drill pipe, completion string, etc in drilling fluid. Therefore,  Buoyancy Factor is value that we need to know and be able to calculate this value. Please follow the formulas below to calculate Buoyancy Factor in different mud weight units, ppg and lb/ft3.

Buoyancy Factor using mud weight in ppg

Buoyancy Factor (BF) = (65.5 – mud weight in ppg) ÷65.5

Note: 65.5 ppg is density of steel.

Example: Determine the buoyancy factor for a 13.0 ppg fluid:
BF = (65.5 – 13.0) ÷ 65.5
BF = 0.8015

Buoyancy Factor using mud weight in  lb/ft3

Buoyancy Factor (BF) = (489 – mud weight in lb/ft3) ÷489

Note: 489 lb/ft3 is density of steel.

Example: Determine the buoyancy factor for a 100 lb/ft3 fluid:
BF = (489 – 100) ÷489
BF = 0.7955

How to use the Buoyancy Factor

In order to figure out the actual weight of drilling string in mud, the air weight of drilling string times the buoyancy factor equal to actual weight in mud, called buoyed weight.

Example: Determine the string weight in 13.0 ppg mud. Air weight of string is 350 klb.

The buoyancy factor for a 13.0 ppg fluid:
BF = (65.5 – 13.0) ÷ 65.5
BF = 0.8015

Buoyed weight of drill string = String weight in the air x BF

The buoyed weight of drill string in 13.0 ppg mud = 350 x 0.8015 = 280.5 Klb.

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

Amount of cuttings produced per foot of hole and total solid generated

After learning about capacity calculation, we can apply the capacity calculation to determine how much barrels of cutting produced per foot of hole drilled and total solid generated in pounds.

Please read and understand the following formulas:

Use formula#1 and #2 for calculating amount of cutting generated per feet drilled.

Formula#1 for BARRELS of cuttings drilled per foot of hole drilled:

 

Barrels of cutting per foot drilled = Dh2 x (1 – % porosity) ÷1029.4

Where: Dh is hole diameter in inch.

Example: Determine barrels of cuttings drilled for one foot of 6-1/8 inch hole with 25% (0.25) porosity:

Barrels/footage drilled = 6.1252 x (1 – 0.25) ÷1029.4
Barrels/footage drilled = 0.02733 bbl/footage drilled

Formula#2 for CUBIC FEET of cuttings drilled per foot of hole drilled:

Cubic feet of cutting per foot drilled = Dh2 x 0.7854 x (1 – % porosity) ÷144

Where: Dh is hole diameter in inch.

Example: Determine barrels of cuttings drilled for one foot of 6-1/8 inch hole with 25% (0.25) porosity

Cubic feet/footage drilled = 6.1252 x 0.7854 x (1 – 0.25) ÷144
Cubic feet/footage drilled = 0.153462 cu ft/footage drilled

Moreover, you also apply sample density and volume relationship to determine total solids generated. Use the following formula to calculate total solid generated.

Wcg = 350 x Ch x L x (l – porosity) x Cutting density

Where;

Wcg = solids generated in pounds
Ch = capacity of hole in bbl/ft
L = footage drilled in ft
Cutting density = cutting density in gm/cc

Example: Determine the total pounds of solids generated in drilling 100 ft of  6-1/8 inch hole (0.03644 bbl/ft).

Density of cuttings = 2.20 gm/cc.

Porosity = 25%:
Wcg = 350 x 0.03644 x 100 x (1 – 0.25) x 2.2
Wcg = 2104.41 pounds

Please find the excel sheet how to calculate how much cuttings drilled per foot of hole drilled and total solids generated

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.