API OIL WELL CEMENT
OIL-WELL CEMENTING PRACTICES IN THE UNITED STATES
|Publication Date:||1 January 1959|
FOREWORD: Each year in the United States several thousand wells are drilled and completed - some productive of oil or gas and some dry - and during this drilling and completion most of these wells are cased, with the casing set in the bore hole surrounded by oil-well cement. This book has been written about the process of placing this cement and it covers how this and related operations are carried out.
The compositions used in cementing are basically portland cements or cements prepared by supplementing portland with additives or by variations in grinding or other manufacturing processes. Compositions other than portland cement are sometimes used in wells and often applied using methods closely similar to those used with portland cement. However, this book should in no way be interpreted to mean that portland-cementing methods can invariably be used with other compositions.
Indeed, no part of this book should be interpreted as an American Petroleum Institute recommendation for any procedure, method, practice, or equipment.
Some parts of the process of "cementing a well" are closely similar wherever they might be carried on; while other parts may vary widely, dependent upon geographical location. Nomenclature or terminology particularly vary from one area to the next.
One example of this variation is the expression for cement-slurry density which, like drilling-fluid density, has commonly been expressed both as pounds per gallon and pounds per cubic foot. In this one instance an API recommended unit has been devised, this being pounds per square inch per 1,000 ft of depth (psi/M ft); and this unit is used as the principal one throughout this volume with the others shown as alternative expressions.
Another of the wide variations in terminology is found in descriptions of casing strings. For example a "conductor string" is typically .a light-wall casing used only to shallow depths to prevent caving of loose earth, to bring drilling-fluid returns up through the water at marine locations, or to augment corrosion protection. It may be anything from 20 ft to a few hundred feet in depth and in the latter case is nearly identical to "surface casing".
Surface casing is one of the most uniformly used designations. Its depth may vary from 100 to several thousand feet; and its function is to protect fresh-water formations, to mount wellhead equipment, and to anchor blowout-preventer equipment.
"Intermediate strings" may range from a few thousand to over 10,000 ft in depth. In some conditions they case off salt beds of moderate depth and are called "salt strings". In others they case off troublesome shales, or zones that will not withstand high fluid pressures, and for these purposes they may be called "protection strings".
"Completion strings" have still more diversified designations. In localities where cement is used to aid such casing strings shut off water immediately above the oil production, the term "water string" is customary.
In other areas the customary term is "oil string"; and where the well may produce oil or gas or both, "completion string", "production string", or "producing string" may be used. In some instances this is also called the "long string".
Where it becomes impractical to continue drilling to the depth intended for the producing string, it is sometimes set at a lesser depth as a protection string and the hole below this is cased with a liner hung in the bottom of the original string. Thus a casing may be considered as both a protection string and producing string.
Because there is no practical method for reconciliation of these and other nomenclature differences, the text of this book has been permitted to remain as prepared by each author. Explanatory notes have been inserted in some instances but throughout most of this volume the terminology should be sufficiently self-explanatory to be understood.