In order to drill a successful oil well, most drilling operators will use a good drilling fluid or mud (figure 1).

Mud cools and lubricates the drilling tool, helps to attack the rock by injection under pressure, and cleans out the hole, carrying away the pieces of crushed rock [1].

These mud systems are usually WBM (Water-Based Mud), OBM (Oil-Based Mud) or SOBM (Synthetic Oil-Based Mud).

One of the major problems with these systems, particularly when reused on different wells, is the build-up of very fine micron solids (less than 5 microns) known as Low Gravity Solids (LGS).

The generation of LGS in the mud creates:

– Slower penetration rates
– High pump pressures
– Increased solids surface area, plastic viscosity
– Increased yield point and gel strengths

The use of Particle Size Analysis (PSA) for drilling in the petroleum industry

imgg65Particle Size Analysis (PSA) based on laser diffraction is an easy-to-use technique to measure liquids and dry products. All mud systems with their different carry liquids can be tested, from WBM and OBM to SOBM. This analysis makes it possible to detect the presence of 5-μm particles in drilling fluids in order to avoid the cementing process in the well

The use of Particle Shape Analysis for drilling in the petroleum industry

imgg66imgg67Size and shape analysis is performed with an optical microscope (figure 4) with a CILAS particle size analyzer and Expert Shape software.

Thresholding treatment makes it possible to reduce the noise inside the picture and erase particles touching the border.

Moreover, each particle can be identified to determine size and shape factors such as compactness factor or aspect ratio (figure 5).

The size distribution is determined from more than 6,000 particles, according to the method described in ISO 13322-1.

imgg68A specific design makes it possible to perform a shape analysis with the same sample analyzed by laser diffraction and to compare these two techniques.

The determination of particle size by laser diffraction and optical microscopy can be correlated with excellent accuracy. Particle shape factor determination can also provide important information on the process quality and specific properties.

The use of Particle Size Analysis (PSA) in drilling petroleum industry

imgg69Along with drilling mud, the particle size measurement of LCM (Lost Circulation Material), such as calcium carbonate and barium sulphate (figure 3), is significant.

The latter are used as a weighting material to increase the apparent density of the mud and can be measured with adapted dispersion protocols. By adjusting the viscosity of the carrying liquid, the stabilisation of weighting materials makes it possible to take the particle size measurement without sedimentation.

The influence of shape factor in drilling efficiency

In addition to particle size distribution, shape parameters provide much information on the drilling fluid’s properties.

The morphology of particles plays a role in the thixotropic behaviour of drilling fluids. Thixotropy is the property of some fluids to show a timedependent change in viscosity.

For example, the intrinsic viscosity [h] of particles with the same volume is directly related to their aspect ratio (figure 5) [1–2].

Furthermore, the rheological properties of some clays are of great importance in structural and geotechnical engineering.


The measurement of particle size is a key point for drilling fluid formulation, which itself plays an important role in the efficiency of drilling wells.

CILAS Particle Size Analyzers are easy to use, fast, accurate and very reliable with liquid and dry formulations.

With their robust design, they enable testing and analysis to be performed in the field without being affected by dust or vibration, and provide reliable analysis even under adverse industrial conditions for routine analysis.

From this information, the condition of the drilling fluid can be quickly and accurately assessed. Shape analysis makes it possible to control the particle morphology to complete knowledge of the material’s properties.

Decisions can be made based on this accurate data to correct the problem in the most efficient way before a serious incident occurs.

By employing robust analytical methodologies, formulators can use this tool to generate reproducible particle size data rapidly, which in turn facilitates the development of formulations suitable for drilling in diverse geologies.


[1] Alteration of permeability by drilling fluid invasion and flow reversal Journal of Petroleum Science and Engineering Volume 58, Number 1–2, p. 227–244, (2007)

[2] Rheology modification in mixed shape colloidal dispersions. Part I: Pure components Soft Matter Volume 3, p. 1145–1162, (2007)

[3] Rheology modification in mixed shape colloidal dispersions. Part II: Mixtures Soft Matter Volume 4, p. 337–348, (2008)