One of the factors influencing the development and use of the rotary drill 

 was its ability to cut through young, unconsolidated sediments and still have the 

 bore hole tend to stand up. Nevertheless, numerous problems connected with 

 rotary drilling and oil producing were a direct result of hole caving in rotary 

 wells. The exact nature and extent of this caving was unknown. Every driller 

 and every geologist had a theory, but there was no exact knowledge. Subsurface 

 bore-hole caving was likened to surface erosion, but owing to the different 

 character of the sediments and the greatly accelerated subsurface erosional 

 forces, this parallel could not be drawn too far. 



Present knowledge indicates three major reasons for differential hole size 

 in a hole drilled with rotary tools: (1) action of the drilling fluid, (2) action 

 of the bit, and (3) action of the drill pipe. Of these, it is believed that the 

 action of the drilling fluid is most important. 



The hole change caused by mud or any conventional drilling fluid is due 

 either to a chemical effect (hydration) or a mechanical effect (attrition or dis- 

 solution). Of these two, it is believed that the former is the more important 

 cause. 



Water-base muds must have a tendency to cause many shales to swell and 

 heave or to disintegrate. Many shales disintegrate beyond the 32-inch range of 

 the modern caliper tool. Interestingly enough, a mud cake may be built up on 

 the face of a formation, causing a hole to caliper smaller than bit size. 



In order to reduce hole change, many muds other than water-base muds 

 are used. Oil-base, oil-emulsion, silicate-base, and salt-base muds are all com- 

 monly used to prevent the caving of shales or soluble formations. It is not the 

 purpose of this chapter to discuss the merits of various types of muds. The effect 

 of these muds on hole size has been clearly shown to the industry by caliper logs. 

 Figure 16-1 shows caliper logs on offset wells, one drilled with oil-base mud and 

 one with water-base mud. 



In 1932, M. M. Kinley made a successful attempt to caliper a hole. A few 

 years later R. B. Bossier measured the enlargement of a hole caused by shooting. 

 These early tools measured a short section of the well and were used mostly in 

 shallow areas. The original Kinley caliper had four separately actuated arms, 

 each arm giving a separate record. A stylus-recorded strip chart was obtained. 



The present modern caliper used by the oil industry was developed from 

 the original M. M. Kinley tool by the Halliburton Oil Well Cementing Company 

 in 1940. 



The present caliper is a chrome-plated tool three inches in diameter and 

 approximately five feet long. It consists of an oil-filled chamber containing the 

 electrical components, the four caliper arms, and the releasing mechanism. The 

 tool itself is standard equipment on an electrical-service truck and is run in a 

 well on a 5/16-inch logging line. 



347 



