Exploring Drill Holes by Sample-taking Bullets

Abstract

The search for oil has required, and without a doubt supplies, a tremendousamount of information on the structure, composition, physical properties, andhistory of sedimentary rocks. The earliest and? most complete source ofknowledge is the sample or core of the rock itself, the uses of which are wellknown. The purpose of this paper is primarily to discuss a new method forobtaining these cores, and to illustrate its use in connection with electricallogs. Most cores have been obtained through a special adaptation of rotary drilling, and the results have been remarkably good, considering the mechanical problemsinvolved. Unfortunately, because of the time and expense, this method cannot beused for the entire length of the drill hole. Even though ingeniouscontrivances have been evolved in order to reduce the time spent in roundtrips, such as wire-line coring equipment, mechanical coring still remains tooexpensive to be carried out continuously. In practice, therefore, one isfinally compelled to estimate the probable depths of the more interestinghorizons and, allowing a wide margin of safety, to core through those sectionsonly. It is true also that interesting results have been obtained by examiningthe cuttings brought to the surface by the mud circulated in the well duringthe process of drilling. Be that as it may, the inescapable fact remains thatkey horizons may be passed inadvertently, for one reason or another, while thedrilling operations are being performed. The only continuous record of theformations encountered is that furnished by electrical surveys. Obviously, it would be desirable to make the electrical survey first and totake the samples from the wall of the hole according to the indications on theelectrical log. In this way, it would be possible to core only the exactsections desired, eliminating the otherwise inevitable estimates as to thepoint at which to start coring, and thereby reducing to a minimum thisexpensive operation. At the same time this method would provide a maximum ofuseful samples. A device for taking samples of the formation from the walls of a hole thereforeoffers the possibility of recovering cores from zones otherwise lost as asource of this type of information. T.P. 1062

A New Wireline Rotary Coring Tool: Development Overview and Experience from the Middle East

“…The use of electric line sidewall coring dates from the late 1930s when retrieving small core samples horizontally from the wellbore wall were used to complement the evaluation of electric logs (Leonardon and McCann 1939). The use of electric line sidewall coring dates from the late 1930s when retrieving small core samples horizontally from the wellbore wall were used to complement the evaluation of electric logs (Leonardon and McCann 1939).…”