Rock Failure Mechanism

Evseev V.D. Samochvalov M.A.

VICTOR D. EVSEEV, Doctor of Technical Sciences, Professor, Department of Drilling, е-mail: evseevvd@mail.ru 
MICHAEL A. SAMOCHVALOV, Associate Professor, Department of Drilling, е-mail: samochvalovma@ignd.tpu.ru. 
National Research Tomsk Polytechnic University, Tomsk. 30 Lenina Ave, Tomsk, Russia, 634034.

The possibilities of early detections of oil show in the course of oil and gas drilling

The paper deals with the possibility of using electromagnetic precursors of intensive rock failure in the bottom hole under the action of additional filtration loading when an oil-bearing formation shows itself in the well being drilled. The electromagnetic precursors occur when free electricity is generated on the walls of the growing cracks of normal fracture caused by the failure of dielectric minerals. The only electromagnetic precursors observed in well drilling are the electric currents flowing from the source of electric charges in the bottom hole to the surface. The electromagnetic fields that accompany the generation of free electric charges in growing cracks are screened by highly conductive drilling fluids. The electric current flowing through the drill pipe string and the casing string is registered as voltage drop. The specific electric current variations are precursors of the oncoming oil show. They may manifest themselves both in the alteration of the absolute current value and in current reversals. The observed variations are due to the changes in the nature and electrochemical properties of drilling fluid resulting from the oil inflow into the well being drilled. This provides a new communication channel with the borehole bottom which sends an early warning about the beginning oil show.

The registration of the electric current increases also the accuracy of determining the time when the borehole penetrates the producing formation.

Key words: oil inflow, drilling, electromagnetic precursors, electric current, variation, control.

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