Filter Cake Thickness inch

These two properties shall be dealt with together, as it is the filtration of mud that causes the build up of filter cake. Loss of fluid (usually water and soluble chemicals) from the mud to the formation occurs when the permeability is such that it allows fluid to pass through the pore spaces. As fluid is lost, a build up of mud solids occurs on the face of the wellbore. This is the filter cake.

Two types of filtration occur; dynamic, while circulating and static, while the mud is at rest. Dynamic filtration reaches a constant rate when the rate of erosion of the filter cake due to circulating matches the rate of deposition of the filter cake. Static filtration will cause the cake to grow thicker with time, which results in a decrease in loss of fluids with time.

Mud measurements are confined to the static filtration. Filtration characteristics of a mud are determined by means of a filter press. The test consists of monitoring the rate at which fluid is forced from a filter press under specific conditions of time, temperature and pressure, then measuring the thickness of the residue deposited upon the filter paper.

Excessive filtration and thick filter cake build up are likely to cause the following problems:

  1. Tight hole, causing excessive drag.
  2. Increased pressure surges, due to reduced hole diameter.
  3. Differential sticking, due to an increased pipe contact in filter cake.
  4. Excessive formation damage and evaluation problems with wireline logs.

Most of these problems are caused by the filter cake and not the amount of filtration because the aim is to deposit a thin, impermeable filter cake. A low water loss may not do this, as the cake is also dependent upon solids size and distribution.

The standard fluid loss test is conducted over 30 minutes. The amount of filtrate increases with direct proportion to the square root of the time. This can be expressed by the following;

Where: Q2 is the unknown filtrate volume at time T2

Q1 is the known filtrate volume at time T1

Pressure also affects filtration by compressing the filter cake, reducing its permeability and therefore reducing the filtrate. Small plate-like particles act as the best filter cake builders and bentonite meets these requirements.

Increased temperature has the effect of reducing the viscosity of the liquid phase and hence increasing filtration. With all other factors being constant, the amount of filtrate will vary with the square root of time.

Proper dispersion of the colloidal clays in the mud gives a good overlap of particles, thus giving good filtration control. A flocculated mud, which has aggregates of particles, allows fluid to pass through easily. The addition of chemicals to act as dispersants will increase the efficiency of the filter cake.

The standard test is conducted at surface temperature at 100 psi and is recorded as the number of ml's of fluid lost in 30 minutes. An API high pressure/high temperature (Hp/Ht) test is conducted at 300° F and 500 psi. The tests may be conducted using a portable filter press that uses CO2 cartridges or using a compressed air supply.

The high pressure and high temperature test is conducted to simulate downhole conditions, since the degree of filtration may vary, depending upon the compressibility of the filter cake. A mud sample may be tested at standard temperatures and pressures, increased temperature and 100 psi, or at high temperatures and pressures. Increased pressure will indicate if the filter cake is compressible.

The primary fluid loss agent in most water based muds are the clays. These solids should have a size variation with a large percentage being under 1 micron. This will produce a filter cake with low porosity and permeability. The use of centrifuges or cyclone solids removal equipment may cause filtration problems by removing the small size solids. Starch is also used as a fluid loss agent, the starch being treated is so that it will easily gelatinize and swell. Water soluble polymers are commonly used as viscosifiers, acting on the fluid phase which also reduces fluid loss.

Sodium Carboxyl-Methyl Cellulose (CMC) is an organic colloid with a long chain structure that can be polymerized into different lengths or grades. It is thought to act by either the long chains plugging narrow openings in the filter cake, curling into balls to act as plugs, or by coating the clay particles with a film. It will however, lose its effectiveness as salt concentrations rise above 50,000 ppm. A polyanoinic cellulose is used as the fluid loss agent in high salt concentration, low solids drilling fluids.

Alkalinity or acidity of a mud is indicated by the pH. The pH scale is logarithmic and hence a high pH mud may vary considerably without a noticeable change in pH. The filtrate and mud can both be measured to show the phenolphthalein alkalinity.

The test for filtrate is carried out by putting 1 or more milliliters of filtrate into a titration dish and adding 2 or 3 drops of phenolphthalein indicator solution. Drops of 0.02 normal nitric or sulfuric acid solution are then added until the pink coloration just disappears. The alkalinity is measured as the number of milliliters of acid per milliliter of filtrate. The test for mud is similar except that to one milliliter of mud, 25 to 50 milliliters of water are added for dilution and 4 or 5 drops of phenolphthalein are added. The result is measured the same as for the filtrate.

The salt or chlorides concentration of the mud is monitored as an indicator of contamination. The salt contamination may come from water used to make mud, salt beds or from saline formation waters. The test is conducted on mud filtrate.

One or more milliliters of filtrate is added to a titration dish and 2 or 3 drops of phenolphthalein solution is added. Drops of 0.02 nitric or sulfuric acid solution are then added while stirring to remove the pinkish color. One gram of pure calcium carbonate is then added and stirred. Next, 25 - 50 ml

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Responses

  • Alastair McMillan
    How to remedy high mud cake build up?
    3 years ago
  • roddy
    How to remedy high mud cake build up as a mud engineer?
    3 years ago
  • jaakko
    How can a high filter cake be remedied?
    3 years ago
  • Rose
    How do you control high rate of mudcake buildup on the well?
    3 years ago
  • Eva
    How to reduce mud cake build up that occur during drilling operations?
    3 years ago
  • RALPH
    How to remedy mud cake build up on a wellbore?
    3 years ago
  • deodata
    How to control mud cake buildup?
    3 years ago
  • Duilio
    How do you as a mud engineer remedy the high rate of mud cake build up on the wall of the wellbore?
    2 years ago
  • iiro
    How do mud engineers remedy the high rate of mud cake build up on the wall of the wellbore?
    2 years ago
  • Clara
    How can we control high mud cake build up?
    2 years ago
  • ashleigh
    How to reduce high mud cake build up in drlling opeation?
    2 years ago
  • patricia darosa
    How to reduce high mud cake build up in drilling operation?
    2 years ago
  • Gianni Padovano
    How can a wall cake be build during drilling?
    2 years ago
  • tommi
    What mud engineer tool would be used to measure cake thickness?
    2 years ago
  • Ernest
    How does the rate of filtration become constant in mud engineering?
    2 years ago
  • Idris
    How to measure filter cake thickness?
    2 years ago
  • sinit
    What happens to pressure when theres increase in filter cake?
    2 years ago
  • Olga
    What are the problems that could occur when mud cake is too thick?
    2 years ago
  • bilbo
    What does it imply when a mud cake has a thickness of 2/32 inches?
    1 year ago
  • lara
    How does starch thin filter cake?
    1 year ago
  • sandro
    How to test mud cake formation in drilling operations?
    1 year ago
  • Dirk
    What are the four basic problems caused by excess filter cake?
    1 year ago
  • laura groop
    How to read a filter cake?
    1 year ago
  • lavonda
    How to break the bentonite filter cake?
    10 months ago
  • amy
    How thick should a mud cake be for effective drilling operation?
    10 months ago
  • HONEY MACLEOD
    What tool measures cake thinkness?
    8 months ago
  • COSIMO
    Does mud filtrate have bentonite in it?
    8 months ago
  • Gringamor Boffin
    How o calculate mudcake thickness?
    8 months ago
  • carol yoder
    How to reduce filter rate in mud?
    8 months ago
  • anneli
    How long it take to build filter cake?
    6 months ago
  • kathrin koehler
    What is the api recommended filter cake thickness?
    18 days ago

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