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…
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…
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…
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…
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…
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.
The following table presents the main drilling fluid functions and properties.
OF MUD AND RIG
EFFECT OF PROPERTY
ON PENETRATION RATE
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…
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…
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…
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…
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…
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.
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…
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…
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…
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)
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…
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…
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…
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),…
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…
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…
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/…
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…
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.…
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…
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.
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…
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…
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:
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…
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…
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…
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: 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…
CONCENTRATION PER 100 ppm
Gypsum or Anhydrite
Calcium (Ca ++)
Soda ash if pH okay
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…
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.
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,…
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…
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…
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 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…
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…
Example Hydraulic Optimisation Programme
Example of the output from a Hydraulic Programme.
Hole Size (in)
Stp. Pres. (psi)
3 x 18
Low Solids Non Dispersed MudThese 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 …
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…
This document describes the key elements for drilling fluids policy.
The mud weight (ppg) shall be maintained as per the drilling programme and should provide a minimum overbalance of 75…
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
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…
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…