Drilling is a disruptive process. As drillers and equipment operators, we have the opportunity to control the disruptive process and guarantee a successful bore. What if the damage done while finishing that bore prevents you from starting the next?
Think about how often you perform maintenance on the mud pump, fluid lines, valves and swivel. Do you keep a record? It is expected that undesirable solids will have an impact on downhole conditions and slow the drilling process. However, do you expect abrasive solids loading on that job to affect your next job? If your dilling rig is down to replace the mud pumps every three months then yes, solids are affecting you more than just in the drilling phase.
What is an acceptable amount of solids, or percent solids content, in a drilling fluid? It depends on whom you ask in the industry. If you ask a mud engineer what an acceptable solids content is, he or she is going to say, "As low as possible, but less than 1 percent." If you ask a mud pump engineer, they will say, "Zero. I want the fluid to be as close to water as possible." Moreover, if you ask the rig manufacture the answer will be, "How often do you want to do maintenance?" There is not a standard answer, but more of a guideline. The more solids in a drilling fluid, the harder the pump has to work to clean the hole and the more horsepower required to pump the solids-laden fluid through the entire system. From a maintenance standpoint, the increase in horsepower is also “sand blasting” the inner workings of your fluid system.