INFLUENCE OF THE MINERAL COMPOSITION OF CLAY ROCKS IN THEWELLBORE STABILITY

Abstract

In the oil companies, the operation of drilling wellbore could be more expensive if the composition of the rocks is clay, the cost could increase between 10 and 15% from the starting budget. In order to decrease this problem, the oil industry has spent too much money for developing mechanisms that can provide better controland stability in clay formations during the drilling. The Society Petroleum Engineers (SPE) in some researches have published that the main chemical effects that are involved in the interaction of perforation fluids and the clay formation are: 1) chemical osmosis; and 2) hydration stresses, although, there are others like: Capillary effects, dehydration, differences in pressure and cationic exchange. These factors are not present generally in independent form. At “Piedemonte Llanero” the problem of the wellbore stability represents a high spending of money for oil companies, caused in this region by chemical factors between fluid/rock and mechanical factors as resulted of the stresses in the area. Metil Blue Testing (MBT) and X-ray Difraction (DR-X) were made in samples of clay; these were taken from cuts extracted of boreholes drilled in some places of the Colombian Llanos. It was found that these samples had a moderate content of reactive and low content of swell minerals.The samples main component was kaolinite, this mineral does not let the rock get swell, but it produces cavingin the hole. However, it is necessary to do other tests to quantify the damages and evaluate the influence of there gime of the stress during the perforation of wellbore.

Keywords: Wellbore, Instability, Clay minerals, “Piedemonte Llanero”.