Characteristics and Application of an Oil-base Mud

Abstract

This paper presents the ingredients composing a type of oil-base mud thathas been successfully used in drilling oil horizons in California, the effectof ingredient concentrations on physical properties, methods of handling at thewell and possible advantages of a waterless drilling fluid with excellentplastering properties. Introduction An oil-base mud is a rotary drilling fluid in which oil has been substitutedfor water as the principal liquid ingredient. In recent years such a mud hasbeen developed and used successfully for drilling the oil horizons of wells invarious California fields. There are several types of oil-base mud, but onlythe type that is currently used to any appreciable extent will be considered atthis time. The oil-base drilling-mud compositions used by Shell Oil Company, Incorporatedhave been covered by several patent applications on which patents are expectedto issue at an early date. The purpose of this paper is to present data on the fundamental design of themud; the ingredients used and their specifications; the effect of ingredientconcentration on physical properties; the selection of the proper mud; thefacilities needed for handling the mud; and a general discussion on drillingwith oil-base mud. In view of the early stage of development of oil-base mud, the great number ofvariables, and the almost unlimited possible combinations of these variables, which in turn require extensive laboratory study, there are certainirregularities and omissions in the data presented here. However, it isbelieved that sufficient data are at hand to permit a fairly complete analysisof the characteristics of oil-base muds. In view of the excellent plasteringproperties of oil-base mud when properly proportioned, its use should:minimize the possibility of impairing the natural flow potentialities of theproducing horizon such as that resulting from infiltration of water fromwater-base mudspermit smaller clearances for setting liners, since themud sheath has no appreciable thicknesseliminate the possibility ofclogging the perforations of the liner with thick mud sheathfacilitatethe removal of the mud sheath from the walls of the hole, for its mud sheathhas no appreciable strengthassist in drilling through formations, such as "heaving shale," where water wetting appears to be a source ofdifficultypermit cores to be obtained without contamination from drillingwater. Fundamental Design of an Oil-Base Mud In the design of any rotary drilling mud it is necessary to select materialsthat will fulfill the following requirements:act as the liquid medium andregulate the viscosity;impart initial and final plastering properties;give gel strength and structure in order to prevent settling;serve as aweighting material. T.P. 1322