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.
Volume, size and type of solids present in the mud can influence the:
- mudgradient
- viscosity and gel strengths
- fluid loss
- filter cake.
Mechanical Treatment
Solids contamination of drilling fluids is the single most costly mud control problem. Mechanical treatment is the most economical means of treatment and must begin immediately drilling commences rather than to delay until the mud properties start to deteriorate as this will result in the requirement for dilution or treatment with costly chemicals.
Solids Removal Equipment
The following table lists solids removal equipment which is commonly used, along with the range of mud gradient with which each may be applied.
|
Equipment |
LGS Particle Size (Microns) |
Mud Gradient (ppg) |
|
Linear Motion Shaker |
1150 down to 74 |
All |
|
Desander |
Down to 75 |
Unweighted |
|
Desilter |
Down to 50 |
Unweighted |
|
Mud Cleaner |
74 (200 mesh) discarded |
All |
|
Centrifuge |
3 - 5 |
All |
|
Hole Size |
Shaker Screen Size |
|
16” |
60 - 100 |
|
12 ¼” |
100 - 140 |
|
8 ½” / 6” |
140 - 200 |
Solids Removal Guidelines
The main problem is to remove undesirable drilled solids without removing those solids, such as Barites, which are added to maintain the mud properties. The amount of solids removed must be maximised but to achieve complete removal of undesirable solids is not practically feasible.
Highest solids removal efficiency is made possible by adhering to the following guidelines:
- All applicable equipment shall be switched on immediately as drilling begins.
- Equipment shall be maintained to its highest standards.
- Efficiency checks shall be made at regular intervals and parameters adjusted accordingly.
- Mechanical and electric maintenance and operating instructions found in manufacturers manuals shall be strictly adhered to.
Solids Content of Drilling Fluids
Inefficient use of the solids removal equipment will be reflected in the solids content as measured on a routine basis by the Mud Engineer. In the event of any increase in solids content, above those indicated in the Drilling Fluids Programme, being reported, steps shall be taken to improve the efficiency of the solids control system, in accordance with the operational guidelines.