Hydraulics Optimization - Hole Cleaning

To optimize hydraulics and achieve sufficent hole cleaning the following guidelines should be adhered to:

Pressure Losses Through System

P1= Frictional losses in surface lines

P2= Frictional losses in…

Drilling Fluid Contamination: Carbonate/ Bicarbonate

One of the most unrecognised types of contamination is that due to Carbonate and Bicarbonate ions. Usually such contamination is gradual, resulting in increased gel strengths and yield point. It is…

Alkalinity (Pf, Mf & Pm) – Water Based Mud Testing

Test to determine nature and source of alkalinity in the mud and give an indication of mud condition. Correct interpretation of the results will highlight Carbonate / Bicarbonate contamination of mud…

Drilling Fluid Contamination: Cement

Drilling Fluid Contamination: Cement

Cement contamination occurs in every well drilled. It is contamination from calcium hydroxide which can result in increased pH, severe thickening and increased fluid loss of bentonite based mud…

Sand Content - Mud Testing

This is a simple test designed to measure the level of particles in the mud of greater that 200 mesh or 75 microns.

Mud additives are generally of smaller particle size, unless specialised materials…

Gypsum/ Polymer Mud

Surface sections can be drilled with a gypsum/polymer water based mud. Attention must be paid to preserving the inhibitive properties of the drilling fluid by maintaining appropriate polymer and…

API Fluid Loss - Water Based Mud Testing

API Fluid Loss - Water Based Mud Testing

The API fluid loss test is used only with Water Based Muds. The test is used to determine the static filtration characteristics of the mud and the need for treatment with fluid loss additives.


Solids Control Equipment – Centrifuges

Solids Control Equipment – Centrifuges

Design and operating principles can be found in suppliers literature. The decanting centrifuge consists of a rotating horizontal centrifuge bowl with a conveyor turning in the same direction but at a…

High Temperature / High Pressure Test (HTHP) - Mud Testing

The HTHP test is used mainly with Oil Based Mud although it may be used with water based mud under certain circumstances such as in high temperature wells or wells which exhibit a high risk of…

Solids Content - Mud Testing

Important test for determination of the drilled solids content of the mud and therefore for identification of requirements for dilution and / or changes to solids removal equipment set-up.

In the…

Drilling Fluid Contamination: Calcium Sulphate (Anhydrite)

Contamination with Calcium Sulphate (Anhydrite) will result in flocculation of bentonite muds resulting in an increase in yield point, gel strengths and fluid loss.

Polymer muds are relatively…

Drilling Fluids Loses - Gunk Squeeze

If conventional LCM pills prove ineffective, a gunk squeeze may be attempted. The method utilises the swelling property of Bentonite in the presence of water. This method is not to be used for losses…

Drilling Fluid Contamination: Salt

If salt enters a bentonite based mud, the clay platelets will flocculate resulting in gellation and increasedfluid loss (>10ml).

Polymer systems are tolerant to salt contamination. However, the…

Solids Control Equipment - Desanders and Desilters

The hydrocyclone is an inverted conical shaped shell into which pressurised slurry is injected tangentially at the top/wide end. This induces the fluid to flow around the circumference of the shell…

Bentonite Mud

Bentonite based mud may be used to impart stability to boreholes through soft seabed sediments prior to running structural or conductor casing. 30-40ppb bentonite mud shall be used offshore to sweep…

Drilling Fluid Functions and Properties

The following table presents the main drilling fluid functions and properties.










Drilling Fluids losses - LCM in Non Reservoir Section

Drilling Fluids losses - LCM in Non Reservoir Section

If lost circulation is expected, the following recommendations should be followed:

  • Nozzles of minimum 18/32in shall be used. As a rule-of-thumb, bit nozzles must be three times larger than the…

Solids Control Equipment - Shale Shakers

The importance of shale shakers as the primary solids control equipment capable of handling the full returns from the wellbore cannot be over stressed. They must be operated as efficiently as…

Total Hardness – Water Based Mud Testing

The total hardness test gives an indication of the level of soluble Calcium and Magnesium ions present in the mud.

Such ions are considered detrimental since, under conditions of high pH (>11.5),…

Sea Water/ Flocculated Bentonite Slugs Mud

Sea Water/ Bentonite is a simple mud system for top hole drilling. Viscous bentonite slugs pumped regularly for good hole cleaning. Returns are not be taken to surface during conductor pipe cleaning/…

Calcium Hardness – Water Based Mud Testing

The Calcium test gives an indication of the level of soluble Calcium ions present in the mud.

Such ions are considered detrimental since, under conditions of high pH (>11.5), they may render…

Drilling fluids QA/QC - Quality Control of Barites

The following tests shall be carried out, or fully supervised, by the Mud Engineer, to determine the quality of barites delivered to the rig.


Barites shall be sampled using the same method as…

Drilling fluids - Best Practices

This article presents some tips for running drilling fluid systems.

PV and YP

For optimum hydraulic parameters the values of PV and YP should be as low as hole cleaning efficiency and suspension of…

Gel/Polymer Mud

Although gel/polymer muds are normally prepared as fresh water drilling fluid systems, existing bentonite spud mud or native clay mud may be converted simply by diluting the systems and adding the …

Chlorides – Water Based Mud Testing

This test may be used for determination of Chloride content in both fresh and salt water muds.

The Chloride level must be maintained at the level specified in the drilling fluids programme.


Barytes sag - treatment, prevention and causes

Generally, barytes sag is linked to a rapid change in mud properties, for operational reasons: Increase mw because of kick, reduce mw because of diff sticking pb, thinning mud at TD for the cement…

NaCl Polymer CaCO3 Mud

Reservoir sections can be drilled with a low colloidal content sodium chloride/polymer mud system weighted with calcium carbonate. The recommended formulation is to minimise formation in a sandstone…

Drilling Fluid Contamination: Hydrogen Sulphide (H2S)

H2S will have no adverse effects on the mud. However, the gas is highly poisonous and corrosive.

Sources of H2S

The gas is sometimes associated with formation fluids. (Add Biocide)



Funnel Viscosity - Mud Testing

The main use of this test is to indicate trends, and signal changes, in fluid viscosity during the drilling operation.Funnel viscosity values are dependent both on fluid type and temperature,…

Solids Control Equipment - Mud Cleaners

Design and operating principles can be found in suppliers literature. Mud cleaners consist of a desilter mounted over a fine mesh screen of 150‑240 mesh. The desilter underflow is treated mechanically…

Minimum Stock Requirements

The minimum stock requirements listed in the following tables shall be at the rig site prior to spud and maintained at all times.

Note: The approval of the Superintendent Operations is required to…

Mud Gradient - Mud Testing

Mud weight is of the utmost importance to the safety of the drilling operation. The mud gradient must be controlled at the programmed value or at the value determined by the Drilling Supervisor, to…

Mud Policy

This document describes the key elements for drilling fluids policy.

Mud Weight

The mud weight (ppg) shall be maintained as per the drilling programme and should provide a minimum overbalance of 75…

Summary Treatment of Mud Contaminants





Gypsum or Anhydrite

Calcium (Ca ++)

Soda ash if pH okay
Sodium bicarbonate if pH too high


Drilling Fluids QA/QC - Quality Control of Freshwater

The following procedures shall be carried out, or fully supervised, by the Mud Engineer to determine the salinity of freshwater delivered to the rig. This is essential to prevent inadequate yielding…

Drilling Fluids Losses: Barites Plugs

A successful Barites plug should accomplish:

  • killing of the well
  • plugging of lost circulation zone.


Barite plugs shall be applied when the following situations arise:

  • Simultaneous…

Methylene Blue Test (MBT) – Water Based Mud Testing

The MBT is a rather crude chromatographic measure of the active clay content in water based muds. The MBT value must be controlled below the maximum value specified in the drilling fluids programme.…

Solids Control Equipment - Flowlines and Settling Tanks

Flowlines, shaker header boxes (possum bellies) etc., shall be inspected regularly and cleaned out as required, in order to prevent solids build-up. Ditch magnet to be inspected as required if…

Mud Testing

A system of good laboratory practices and housekeeping shall be adopted to ensure accurate determination of mud chemistry and that safety is maintained.

All glassware shall be kept clean and washed…

Drilling Fluids: Monitoring and Reporting

1. Responsibilities for Routine Monitoring of the Drilling Fluid

The Toolpusher shall ensure that a suitably trained crew member is in attendance at the shale shaker and active pit at all times while…

Drilling Fluid Contamination

Contamination is a steady process while drilling, as drilled solids are continually entering the mud. While much of the drilled solids are inert, there are certain materials which can cause severe…

Solids Control - Introduction

Solids present in the mud will directly affect mud and well costs, and can affect drilling rates, hydraulics, rig equipment, and is also a major cause of stuck pipe and lost circulation.


Non Damaging Polymer Mud

This mud system is used to drill the reservoir section in onshore and offshore wells.  It is a sodium chloride based system, which gives inhibitions with minimal formation damage. It is…

Downhole Density Measurements

Mud density will decrease with increasing temperature, and increase with increasing pressure. Theoretical models similar to those mentioned in SPE Paper 11118 predict that temperature is the major…

Rheology - Mud Testing

Rheology is a fundamental mud property determining circulating pressures, suspension capabilities and carrying capacity. It must be checked regularly and controlled very carefully to ensure it is…

Drilling fluids QA/QC - Quality Control of Bulk Materials at Rig Site

The following tests shall be carried out by the Mud Engineer to guard against possible wrong delivery of bulk material from supply vessels/trucks:

- water/acid test
- weighing method test

The Mud…

Low Solids Non Dispersed Mud

These mud systems are used both onshore and offshore to drill the 12.1/4in hole.  This type of mud is run without the use of thinners, provided the solids content (less gravity solids) of the mud …

Drilling Fluid Contamination: Hardness

High levels of hardness will result in flocculation of bentonite with associated severe increases in viscosity. Subsequently, as the cation exchange process continues, the clay particles will…

Example Hydraulic Optimisation Programme

Example of the output from a Hydraulic Programme.

Hole Size (in)

Depth (ft)

Volume (gpm)

Jets (1/32)

Stp. Pres. (psi)




1 200

3 x 18

2 666




Drilling Fluids Losses: LCM in Reservoir Section

If losses occur in reservoir sections, the following options are available:

As a first step, the mud gradient shall be reduced, formation pressures permitting.

If the gradient reduction provides no…

Mud Products Inventory Form

In order to mix the mud for the drilling of a well it is necessary to maintain sufficient stock levels at the rigsite. It is vital that stock levels are regularly monitoring through frequent inventory…

pH – Water Based Mud Testing

pH control is important with all water based mud systems to ensure proper functioning of chemical additives and to limit the potential for corrosion.

pH must be maintained within the range specified…

Drilling Fluids Responsibilities

The correct selection, engineering and maintenance of drilling fluids is critical to the success of the drilling operations. Each member of the rig team must understand their responsibilities to…