API RP 13D (R2023)

The objective of this Recommended Practice (RP) is to provide a basic understanding of and guidance about drilling fluid rheology and hydraulics to assist with drilling wells of various complexities, including high-temperature/high-pressure (HTHP), extended-reach drilling (ERD), and highly directional wells.

Office and wellsite engineers are the target audience for this document. The complexity of the equations provided is such that a competent engineer can use simple spreadsheet programs to conduct analyses. Given that the equations used herein are constrained by this spreadsheet limitation, more advanced numerical solutions containing multiple subroutines and macros are not offered.

For this RP, rheology is the study of flow characteristics of drilling fluids and how these characteristics affect movement of the fluids. Certain properties are measured at the wellsite for monitoring and treatment, and in the laboratory for development of new additives and systems, formulation for specific applications, and diagnosis of special problems.