scope:

FOREWORD

Dimensional change after placement in oil and gas well cements, a phenomenon often referred to as shrinkage, has often been used to explain various problems (e.g., microannulus leading to bad cement bond logs, interzonal communication leading to costly remedial jobs and also lack of a seal to the gas of cement inflatable packers). Attempts have been made to find additives to decrease shrinkage, but it seems that shrinkage (as well as the exothermal reaction) are closely related to the hydration of the cement. The best solution for this shrinkage so far has been the identification of additives that favor the expansion of the cement. However, even if cement expands dimensionally, it still will shrink internally. In this case, the bulk expansion of the cement sample is simply superposed on an inner shrinkage that will affect the porosity of the sample. Shrinkage is not just one property of cement, such as rheology or thickening time that can be defined by one measurement. This is probably why little consensus has been reached today in the industry on this important issue, in spite of a large amount of work devoted to the subject.

In 1994, API proposed to open a work group on shrinkage. This report is an attempt to bring more understanding to this important area of cementing. One of the objectives of the work group was also to propose equipment to investigate shrinkage and expansion in oilwell cements. This report will address the objectives of that task group, which were:

• To develop standardized test procedures to measure expansion/shrinkage.

• To investigate possible impacts on invasion of wellbore fluids (gas, water).

• To standardize definitions of terms for cement hydration.

This report is a summary of all the background information and actual data that were generated to meet the objectives outlined above.

The equipment described in the report is the minimum recommended to measure the parameters in question.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Exploration and Production Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.