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ABSTRACT: Formation damage caused by oil-well drilling fluids components

Zein El Din, M. Y.1, F. El-Bokle2, and M. I. Abdou2
(1) Al-Azhar University, Nasr City, Cairo, Egypt
(2) Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt

This study investigates damage that may be imposed on the petrophysical properties of core samples of reservoir rocks when saturated by various types of drilling fluids.

Reservoir rocks exposed in Wadi Araba (South Sinai) area were studied. They are represented by Carboniferous sand-stones (Naqus Formation). The subsurface extension of these rocks represent very important reservoir rocks in Egypt.

The petrophysical parameters were measured for sandstone core plugs before and after saturation of the core samples by various types of drilling fluids. These measurements include effective porosity, liquid permeability, electrical resistivity, formation factor, bulk density and tortuosity. Measurements were used to calculate the damage ratio of the formation as a result of drilling fluids components. In addition, petrographical, SEM, X-ray diffraction and mechanical analyses have been carried out for the sandstone samples.

Drilling fluids testing is conducted to show that these fluids satisfy the API and OCMA specifications. Measurement of the density of drilling fluids before and after addition of local ilmenite or imported barite as weighting agents, rheological properties, filtration characteristics and material grinding and particle size distribution analysis of drilling fluids components provided good basis for proper mud selection.

The study shows that the damage ratio depends on the petrophysical parameters of the reservoir rocks and characteristics of the drilling fluids components.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia