In the drilling process, mud materials (barite, water, treating chemicals, etc) are mixed almost continuously to maintain desired mud properties. Drilling mud usage is defined as the volume of mud that is lost with the
drilling operation. This should be contrasted with mud consumption which is the total volume of mud created to support the drilling operation.
In a stable drilling environment where mud costs are controlled by the solids generation/removal cycle, the major loss of mud occurs in the removal of solids. In other situations such as loss of circulation or unstable mud properties, mud consumption is not related to the removal of solids and a material balance approach for mud system solids control evaluation is not appropriate.
One of the easiest methods of determining mud usage for a drilling situation is to monitor the additions of a material to the mud system and to monitor the concentration of that material in the mud. Weighting
agents such as barite are ideal for monitoring mud consumption and usage. Every mud check can be analyzed and barite volume in the system determined. Calculation of mud volume usage from barite additions and barite volume remaining in the system can proceed directly. In most weighted muds, barite costs usually are the highest single component of the mud cost. Additionally, other product usage can generally be related to barite consumption.
When whole mud losses with solids removal occur as in screening equipment, mud usage is a clear concept. In cases where solids removal occurs with the fractionating of the mud into different components (liquid phase and solid phase in a barite recovery centrifuge, for example), mud usage and solids removal is not as clear a concept. Even in systems where a barite recovery centrifuge is operating, barite consumption is still a major factor and mud volume usage remains a useful concept. Directly relating a calculated volume usage, however, to actual mud volume usage is not possible in these situations. For purposes of calculation and comparison, volume usage from barite consumption can be used. This paper utilizes mud usage calculated from barite consumption for all example calculations. Dilution mud or water consumption can also be used to determine mud usage and, when these concepts are extended with
additional data, can be tools for further system analysis.
Like the solids removal efficiency, mud usage can be measured instantaneously. In most cases, the usage is calculated on a daily basis or by. interval.
Relating mud usage to the volume of solids generated is preferable to just calculating volume usage. A mud usage factor, F m , can be calculated by taking the ratio of the mud usage volume and the theoretical drilled hole volume based on bit size. When oil mud is in use, mud usage factors of 0.50 to 1.50 are typical. With water muds, values of 1.50 to 5.00 are typical. With the calculation of a mud usage factor this way, the evaluation becomes independent of bit size and the results can be used to compare wells drilled with different bit sizes.
Hole enlargement will cause the mud usage and mud usage factor to increase. When signifigant hole enlargement occurs, usage factors and removal efficiencies can be calculated based on calipered hole volume. Comparison of the usage based on a theoretical gauge hole with usage based on the actual enlarged wellbore can be used to illustrate the costs
associated with wellbore enlargement. An example is given later that illustrates how this analysis can be used.