746 Subsurface Geologic Methods 



proved the accuracy of the unit. This type of recorder is also periodically 

 calibrated by a dead-weight tester and to temperature, as are units of other 

 types. The mechanical setup of the Bourdon gauge is such that it may be 

 adapted in the testing assembly as other recorders. Unlike the standard 

 recorder, these instruments record upon a blank chart. The recordings 

 that are made during a test are measured in inches of deflection and con- 

 verted to pressure from a calibration curve that is individually made for 

 each instrument. A chart and typical pressure changes from a standard 

 gauge are shown in figure 399. 



OIL-WELL CEMENTING 



W. D. OWSLEY 



The oil industry geologist should have a working knowledge of 

 methods and equipment used in casing and remedial oil-well cementing. 

 Such methods must usually be coordinated with subsurface information 

 and various other procedures. Frequently other departments of oil-produc- 

 ing companies are prone to consider that all cementing procedures are their 

 own special premise and are of no concern to the geologist. This is a mis- 

 taken idea since subsurface geology should always be considered in con- 

 nection with any kind of well-cementing operation. This section will be 

 devoted to some of the more important relations between cementing and 

 geologic data in a basic and elementary manner as to application, equip- 

 ment and methods of well cementing in general. 



Cementing of any casing string in a well is a primary cementing job, 

 this being the first cementing done on the casing string and, as such, it is 

 probably the most important cementing work of any kind. The successful 

 completion of the well depends to a considerable extent on the success of 

 the primary job done on any and all casing strings in the well. Cementing 

 of the production casing string is by far the most important cementing 

 operation in the life of the well. The success of this operation can fully 

 repay all the study and care expended in its performance by eliminating 

 later troubles due to incomplete sealing and the expensive, and sometimes 

 hazardous procedures necessary to correct the difficulty thus brought about. 

 The work of the geologist in connection with primary cementing lies par- 

 ticularly in proper selection of casing points, decisions as to desired pro- 

 tection of zones of production behind the casing, exclusion of zones con- 

 taining corrosive waters, advice concerning formations subject to loss of 

 returns, and selection of points of oil-water or gas-oil contact. 



The usual steps in a primary or casing cementing operation are (1) 

 The hole is circulated through the casing to obtain full returns of the drill- 

 ing fluid; (2) Cement to suit conditions of time and temperature is mixed 

 and pumped into the casing above the bottom plug separating the slurry 

 from the mud; and (3) A top plug is released and pumped down to force 

 the liquid cement slurry to the bottom and up into the annulus between 

 the bore and casing. 



