THE EFFECT OF CEMENT ON THE STRENGTH OF GRANULAR ROCKS

Relatively neglected by the oil industry in the past, the rock mechanics approach is now routinely applied to production problems such as subsidence or wellbore stability. As a result, there is a growing need for a better understanding of the strength of porous rocks. In addition to porosity, composition and amount of cement are two important parameters controlling the strength of granular rocks. In order to investigate their effect we prepared synthetic granular materials in which the amount and composition of cement could be varied. Synthetic materials are more reproducible and better characterized than natural rocks but do not always possess properties realistically imitating those of natural rocks. Here, we propose procedures to fabricate satisfactory materials that could also be fruitfully used in other experimental studies. We performed a series of triaxial tests on samples of cemented and uncemented material. We observed that cement, even in very small quantity, significantly increased the strength of granular materials. Our results suggest that the amount of cement was less important than the location where it was deposited. Strengthening was due to precise deposition of the cement at the grain-to-grain contacts, thus preventing sliding and rotation of grains.