Amount of cuttings produced per foot of hole drilled
Annular Pressure Loss
Annular-Capacity
Annular-velocity
Bulk Density Calculation
Buoyancy Factor Oilfield
Convert Pressure to Equivalent Mud Weight
Convert-Specific-Gravity
Cost Per Foot Calculation
Critical RPM
D Exponent Calculation
D Exponent Corrected Calculation
Decrease Oil Water Ratio
Density of Oil Water Mixture
Depth of Washout
Dilution LGS control
Dilution LGS control – adding mud
Directional Survey Calculation – Angle Averaging Method
Directional Survey Calculation – Radius of Curvature Method
Dogleg Severity Calculation – Radius of Curvature Method
Dogleg Severity Calculation – Tangential Method
Drilling or Connection Ton-Mile
Drill-pipe-pulled-to-lose-certain-hydrostatic-pressure
Equivalent Circulating Density Calculation
Equivalent Circulating Density with engineering formula
Formation Integrity Test
Formation Temperature
Free Point Constant Calculation
Hydraulic Horse Power
Hydrostatic Pressure Calculation
Hydrostatic Pressure Decreases When POOH
Increase mud weight adding Barite
Increase mud weight adding calcium carbonate
Increase mud weight adding hematite
Increase Oil Water Ratio
Internal Capacity
Lag Time Calculation
Leak off test calculation
Light Weight Spot Pill
Loss hydrostatic due to filling water into annulus
Mix Different Fluid Density – Limit Space
Mix Different Fluid Density – Unlimit Space
Mud Volume Increase Due to Adding Barite
Mud Volume Increase Due to Adding Calcium Carbonate
Mud Volume Increase Due to Adding Hematite
Oil Water Ratio from a Retort Analysis
Pipe Displacement Calculation
Pressure and Force Calculation
Pressure Gradient Calculation
Pressure Required to Break Circulation In Annulus
Pressure Required to Break Circulation Inside Drill String
Pump Output (Duplex and Triplex)
Pump Pressure and Pump Stroke Relationship
Reduce Mud Weight by Dilution
Slug Calculation – Barrel of Slug Required
Slug Calculation – barrels of slug required for a desired length of dry pipe
Slug Calculation – Weight of Slug Required
Specific Gravity Calculation
Starting Volume for Weighting Up with Bartie
Starting Volume for Weighting Up with calcium carbonate
Starting Volume for Weighting Up with Hematite
Stuck Pipe Calculation – Not Know Free Point Constant
Stuck Pipe Calculation – Use Table for Free Point Constant
Temperature Conversion Formulas
Ton-Mile (TM) for Coring Operation
Ton-Mile (TM) for Making Short Trip
Ton-Mile (TM) for Round Trip
Ton-Mile (TM) for Setting Casing
Ton-Mile (TM) for Drilling or Connection

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Data Given

Reverse circulate total of 3 time bottom up from annulus to tubing with 12.7 ppg mud at 10,000′MD/10,000 TVD.

Pump pressure = 1000 psi

Annulus friction loss = 50 psi

Inside tubing friction loss = 925 psi

Surface line friction loss = 25 psi

Determine pressure at bottom hole.

We still apply the concept of frictional pressure so reverse circulation is calculated by this following equation:

Pressure at bottom hole (reference at annulus side)  = Hydrostatic Pressure + Pressure from pump- Annular Pressure Loss

Note: Hydrostatic pressure and pressure from pump force downward to bottom hole but annulus pressure forces upward direction.

Pressure in the well at 10,000’ = 1000 + (0.052×10,000×12.7) – 50 = 7554 psi

OR you can referrence to the tubing side as well.

Pressure at bottom hole (reference at tubing)  = Hydrostatic Pressure +  Annular Pressure Loss in tubing + surface line pressure loss
Note: All pressure force downward to bottom hole so all pressure term must be sum together.

Pressure at bottom hole (reference at tubing)  = (0.052×10,000×12.7) + 925+25 = 7554 psi.

Determine Equivalent Circulating Density at bottom hole.

ECD = Current mud weight in PPG + (annular pressure loss /(0.052xTVD)) = Total Pressure at Bottom Hole /(0.052xTVD)

ECD =7554 / (0.052 x 10,000) = 14.53 PPG.

The point that I want you to think of between this example and the previous example, Pressure Loss and Equivalent Circulating Density Review, is about the different of bottom hole pressure and ECD between forward circulation and reverse circulation.
You will see that reverse circulation results in a lot of pressure at bottom hole. Hence, you must keep in mind this concept and try to figure out how much pressure at bottom hole should be for both forward circulation and reverse circulation. Otherwise, you can accidentally break wellbore due to high ECD.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Information given is listed below;

Circulate at 3 bottom up through open end tubing (Down tubing and up annulus) with 12.7 ppg mud.

Pump pressure = 1000 psi

Annulus friction loss = 50 psi

Inside tubing friction loss = 925 psi

Surface line friction loss = 25 psi

Calculate the pressure in the well at 10,000’ (tubing tail). What would ECD at 10,000’ TVD be?

The concept of calculation that you should know : total pressure at bottom = pumping pressure + hydrostatic pressure – pressure loss in the opposite way of fluid flowing.

Then,

If I reference to tubing site, I will get the equation like this.

Pressure at bottom hole= Hydrostatic Pressure at bottom hole + Pressure from pump- Pressure Loss in surface line – Pressure loss in tubing

Pressure in the well at 10,000’ = 0.052×12.7×10000 + 1000 – 25 – 925 = 6654 psi

If I reference to annulus site, I will get the equation like this.

Pressure at bottom hole= Hydrostatic Pressure at bottom hole +Annular pressure loss

Note: Hydrostatic pressure and annular pressure loss force downward.

Pressure in the well at 10,000’ = 0.052×12.7×10000+ 50 = 6654 psi

Note: It doesn’t matter which site of u-tube you refer to the bottom hole pressure is still the same.
ECD (Equivalent Circulating Density) is calculated by this following equation:

ECD = Current mud weight in PPG + (annular pressure loss /(0.052xTVD))

ECD = 12.7 + (50/(0.052 x 10000))

ECD = 12.8 ppg

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Given situation as shown in figure above.  This situation is in vertical well.

1) Inside 16” shoe, from 0’ to 1975’ = 9.3 ppg mud

From 1975’ to 2000’ = 16.0 ppg mud

2) Outside 16” shoe, From 0’ to 1500’ = 11.6 ppg cement (lead)

From 1500’ to 2000’ = 16.0 ppg cement (tail)

Given the conditions above and assuming the cement is still liquid, how much pressure will we see at cement head in case of float shoe fail?

** Note : you need to understand how to calculate hydrostatic pressure in order to fully understand this question **

Using U-tube concept: Bottom hole pressure both sides are the same.

Let’s work out at annulus side which is heavier due to cement in the annulus

Pressure at bottom hole in annulus = hydrostatic pressure of lead cement + hydrostatic pressure of tail cement

Pressure at bottom hole  in annulus = 0.052×11.6×1500 + 0.052x16x(2000-1500) =1320.8 psi

Since, hydrostatic pressure in the annulus is more than hydrostatic pressure in 16″ casing; therefore, there will be pressure in the cement head in order to balance u-tube.

We can simply write equation as follows;

Bottom hole pressure = hydrostatic pressure inside 16” casing + surface pressure at cement head

1320.8 = 0.052x16x(2000-1975) + 0.052×9.3×1975 + surface pressure at cement head

Surface pressure at cement head = 1321 – 976 = 345 psi

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Referring to the figure below, the well is shut in and there are 2 gauges showing different numbers. Gauge#1 shows 600 psi and gauge#2 shows 100 psi.

One side we have water (8.5 ppg ) and mud 10.7 ppg and anther side has mud 10.7 ppg and mud 13.3 ppg. All depths are in TVD.

You know that the gauge #1 is reading correctly.

(1) Is gauge #2 correct?

In order to check the function of the gauge no.2, the concept of U-tube pressure balance is utilized.

Pressure at the bottom hole is calculated by this following equation:

BHP = Pressure gauge#1+ Hydraulic Pressure at gauge#1 side

BHP = 600 + 8.5×0.052×2500 + 10.7×0.052x(4000-2500)

BHP= 2539.6 psi

Pressure at the gauge#2 must balance BHP and is calculated by this following equation:

Pressure gauge2 = BHP – Hydraulic Pressure at gauge#2 side

Pressure gauge2 =2539.6-13.3×0.052×1,000-10.7×0.052×3,000

Pressure gauge2 =178.8 psi

Pressure gauge#2 must be about 180 psi; however, pressure gauge#2 is only 100 ps for this reason the Gauge #2 is not correct.

(2) If not, what should it read?

It should read about 180 psi.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Lag time is traveling time interval required for pumping cuttings from each particular depth to surface. It can be expressed in terms of time (minutes) and pump strokes.

The lag time always changes when a well becomes deeper and/or pumping speed change. Two factors, affecting lag time calculation, are annulus volume of drilling fluid in and drilling mud flow rate.

With certain annular volume, the lag time, normally expressed in minutes, can be determined by dividing the annular volume (bbls) by the flow rate (bbl/min).

If there are changes in mud flow rate, the lag time figure will be changed as well. In order compensate for any changes, the lag time is transformed into pump strokes too; therefore, a change in speed of pump will not affect the lag time.

How to Calculate Theoretical Lag Time

There are 3 steps to do in order to calculate lag time as listed below;

1. Calculate pump output
2. Calculate annular volume at certain depth of hole
3. Calculate the theoretical lag time

Example – Determine lag time from bottom to surface with the following information;

Bit depth = 9500’ MD
Pump rate = 300 GPM
Annular volume at 9500’ MD = 250 bbl
Pump details: Triplex pump, 97% efficiency, liner size 6” and stroke length 12”

Solution;

Triplex Pump Output Formula is listed below;

Triplex Pump Output in bbl/stk = efficiency x 0.000243 x (liner diameter in inch) ² X (stroke length in inch)

Triplex Pump Output in bbl/stk = 0.97x 0.000243 x (6) ² X (12)
Triplex pump output = 0.102 bbl/stroke

Pump rate = 300 GPM ÷ 42 = 7.14 bbl / minute

Lag time in minutes = 250 bbl ÷ 7.14 bbl / minute = 35 minutes
Lag time in strokes = 250 bbl ÷ 0.102 bbl/stroke = 2451 strokes

Please find the lag time calculation sheet

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

The ton-miles of work done in making a short trip is equal to the difference between round ton-miles of end depth and starting depth. The formula for short trip ton-miles is listed below;

Tst = T6 – T5

Where; Tst = ton-miles for short trip
T6 = ton-miles for one round trip at the deeper depth
T5 = ton-miles for one round trip at the shallower depth

Example;

Please determine short trip ton-miles from 8000 ft to 8050 ft
Ton-miles @ 8050 ft = 200
Ton-miles @ 8000 ft = 190
Tst = (200 – 190)
Tst = 10 ton-miles

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Ton-miles for setting casing can be determined from the following formula:

Tc = {Wp x D x (Lcs + D) + D x Wb} x 0.5 ÷ (5280 x 2000)

Where; Tc = ton-miles setting casing
Wp = buoyed weight of casing in lb/ft
Lcs = length of one joint of casing in ft
Wb = weight of travelling block assembly in lb
D = depth of casing in ft
2000 = number of pounds in one ton
5280 = number of feet in one mile

Example: Ton-Miles for Setting Casing

Mud weight = 10.0 ppg
Casing weight = 25.0 lb/ft
Depth of casing = 5200 ft
Travelling block assembly = 95,000 lb
Length of one joint of casing = 42 ft

Solution:

a) Buoyancy factor:
BF = (65.5 – 10.0) ÷ 65.5
BF = 0.8473

b) Buoyed weight of casing in mud, lb/ft (Wp):
Wp = 25.0 lb/ft x 0.8473
Wp = 21.18 lb/ft

c) Casing ton-miles
Tc = {21.18 x 5,200 x (42 + 5,200) + 5,200 x 95,000} x 0.5 ÷ (5280 x 2000)
Tc = 50.73 tone-miles

Ton-Mile (TM) for Setting Casing Calculation Sheet

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

The formula for calculating ton-mile for coring operation is shown below;

Tc = 2 x (T4 – T3)

Where;

Tc = ton-miles for coring operation
T4 = ton-miles for one round trip at depth where coring operation stopped before coming out of hole
T3 = ton-miles for one round trip at depth where coring get started

Example – Please determine coring ton-mils from 8000 ft to 8050 ft.

Ton-miles @ 8050 ft (end of coring operation) = 200
Ton-miles for trip @ 8000 ft (start of coring operation) = 190

Tc = 2 x (T4 – T3)
Tc = 2 x (200 – 190)
Tc = 20 ton-miles

Ton-Mile (TM) for Coring Operation Calculation Sheet

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

Drilling or Connection ton-miles is  ton-miles of work in drilling operations. These are the actual ton-miles of work in drilling down the length of a section of drill pipe, usually around +/- 31 ft, plus picking up, connecting, and starting to drill again. In order to figure out connection or drilling ton-miles, it takes 3 times of ton-miles for current round trip minus ton-miles for previous round trip. The formula for calculating drilling ton mile is listed below;

Td = 3 x (T2 – T1)
Where;
Td = Ton-miles for drilling
T2 = Ton-miles for one round trip of last depth before coming out of hole.
T1 = Ton-miles for one round trip of first depth that drilling is started.

Example;
Please determine drilling tome-miles from 8000 ft to 9000 ft.
Ton-miles for trip @ 9000 ft = 230
Ton-miles for trip @ 8000 ft = 195
Td = 3 x (T2 – T1)
Td = 3 x (230 – 195)
Td = 3 x 35
Td = 105 ton-miles
Download the Excel sheet for calculating drilling or connection ton-mile.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition