Do you have too much slug in the well?

Slug is heavy drilling mud that is used to pump when you want to pull pipe dry. However, excessive volume of slug in the well can create higher mud weight and cause the problem. Today I would like to share my experience regarding slug in the well.

The situation happened on the drilling rig like this.

The well was TD with 13.0 ppg mud and circulation was conducted until the shale shakers. After that we pull 10 stands wet and pumped 40 bbl of 15.0 ppg slug and came out of hole without any problem. Then we run the logging and we got stuck. We picked the fishing gear and grabbed the fish. We pulled out 10 stands wet and hole was taking proper fill. We pumped same amount of slug 40 bbl of 15.0 ppg and came out of hole. The decision was made by town to trip in hole to do the wiper trip.

Tripping was done with caution and break circulation was conducted every 3000 ft to break the gel. Prior to TD 100 ft, we made up top drive and slowly washed down to TD. While we were circulating, the mud weight out was varied from 13.2 ppg to 14.2 ppg. Additionally, we start losing mud while circulating.

Do you know what went wrong?

The two slugs in the well cause us trouble.

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Power Law Constants (n and K) Calculation

Many types of drilling mud are classified as non-Newtonian fluid which is the behavior between Newtonian fluid model and Bingham Plastic model. The relationship between shear rate and shear stress is defined by the power law model shown below:


 = shear rate

K = consistency factor

 = shear rate

n = flow behavior index

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Cutting Carrying Index – Simple Tool To Determine Hole Cleaning

To get the good idea on how good of the hole cleaning is, the another method called Cutting Carrying Index (CCI) is utilized. The CCI is an empirical relationship from real data and the equation is below:

CCI = (K × AV × MW )÷(400,000) — Equation 1


AV is annular velocity in ft/min.

MW is mud weight in ppg.

K is a Power Law Constant.

The Power Law constant (K) can be calculated from the equation below:


PV is plastic viscosity in centipoises.

YP is yield point in lb/100sqft

n is flow behavior index.

The flow behavior index (n) can be determined by the following equation:


PV is plastic viscosity in centipoises.

YP is yield point in lb/100sqft

How will the CCI tell you about hole cleaning?

If CCI is equal to 0.5 or less, the hole cleaning is poor and the hole problem may be seen.

If CCI is equal to 1.0 or greater, it indicates that the hole cleaning is good.

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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.

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Drilling Formula Excel Sheet Version 1.2 Free Download

This is the second up date of drilling formula spread sheet, Drilling Formula Excel Sheet Version 1.2. distributed the first version of drilling formula spread sheet on 28 March 2011 and another update on 18 May 2011. The calculation sheet has been downloaded over 8,300 times around the world since the fist distribution.

Today, the lasted up date of drilling formula spread sheet, Drilling Formula Excel Sheet Version 1.2 is available for you to download. It is still totally FREE !!!.

Click here to get the drilling formulas spread sheet.

What new drilling formulas are added into this version?

Cutting Slip Velocity Method#1

Cutting Slip Velocity Method#2

Surge and Swab Pressure Method#1

Surge and Swab Pressure Method#2

Total Flow Area Table

Calculate Influx Height

Hydrostatic Pressure Loss Due to Gas Cut Mud

Kill Weight Mud

Maximum pit gain from gas kick in water based mud

Maximum Surface Pressure from Gas Influx in Water Based Mud

How many total useful drilling formulas in this version?
There are a total of 75 formulas which are divided into 7 categories (Applied Drilling Formulas, Basic Drilling Formulas, Directional Drilling Calculation, Drilling Fluid Formulas, Engineering Formulas, Hydraulic Formulas and Well Control Formulas).

How much will it cost?

Nothing. The spread sheet is totally FREE for everybody.