API RP 13D : 2026

The objective of this recommended practice 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. This standard has been designed such that office and wellsite engineers can implement complex topics and equations sets into a standard spreadsheet program to conduct hydraulic 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. This limitation does not suggest that only the results given by the spreadsheet methods are valid engineering solutions but are a basic determination of them as their order of magnitude.