Drilling Fluid Systems For Deep Drilling - An Interrelated Approach
Authors: McCaskill J.N. 
Published: December 2007

This paper was prepared for the 1972 Deep Drilling Symposium of the Society of Petroleum Engineers of AIME to be held in Amarillo, Tex., Sept. 11–12, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The safe economical drilling of an ultradeep well depends upon several interrelated factors. Drilling fluid is one of the key factors. It contributes to, or eliminates, hole problems. It is a tool of the hydraulic program, influences bit performance and rate program, influences bit performance and rate of penetration. It is a vital communication link with the dictates of the hole. Its performance and maintenance contributes directly performance and maintenance contributes directly to safety and economy. It must be designed to perform with stability and predictability as an perform with stability and predictability as an integral tool in the total drilling operation.
To design an interrelated program for casing, mud, bit hydraulic, monitoring, and drilling; a pore pressure-fracture gradient profile for the drill site must be developed. profile for the drill site must be developed. This requires the compilation, cross checking, and verification of all possible data including records from seismic, bits, DST, production, wireline logs, recaps, and well histories. The distilled pressure-fracture information is then plotted by depth and formation against pressure plotted by depth and formation against pressure expressed as mud density. The profile will indicate desirable casing seats and show maximum-minimum mud density requirements throughout the hole. Add hole size requirements and formation characteristics and the profile is the basis for the bit and hydraulic profile is the basis for the bit and hydraulic programs. Hole size, geometry, and hydraulics programs. Hole size, geometry, and hydraulics determine any special rheological considerations. Low pressure permeable zones determine filtration characteristics. Water or chemically sensitive formations, contaminants, and temperature determine mud type. Thus, anticipated conditions determine the physical and chemical requirements of a drilling fluid. The mud that will most satisfactorily give these requirements determines the type system needed.
The monitoring program will continually confirm or immediately note any deviation from the expected profile. Mud properties should be closely monitored, as well as flow rates, mud volume, drilling variables, pressure losses, and geological data. Changes in these variables can indicate adjustments to be made in mud properties to insure best performance characteristics for prevailing conditions.

Introduction
In recent years the design of a mud program as a key part of the drilling systems program as a key part of the drilling systems has been given considerable attention. This is especially true in regard to maximum-minimum density requirements.