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THE EFFECT OF BARITE DRILLING MUD ON THE PERMEABILITY OF TIGHT GAS IN CRACKED SHALES OF DEEP WELLS

Rail Kadyrov

Abstract

In the conditions of depletion of traditional energy resources, the development of hard-to-recover hydrocarbon resources is becoming increasingly important in the world economy. One of these potential sources of tight gas can be in carbonate-clay fractured reservoirs of the Cambrian deposits of Kazakhstan, located at the depth of about 6 km. The reservoir rocks consist of quartz, muscovite, albite, calcite, mixed layered clays, and chlorite. It is assumed that, the deposited particles from barite mud, which are used in deep drilling, can clog the cracks, thereby blocking the gas outlet. The X-ray computed microtomography of mud-saturated shale sample has showed that the cracks width in these compacted rocks varies up to 20-25 ?m, which corresponds to the size of the particles of the weighted drilling mud, as a result of significant penetration of the mud particles is not observed. Cracks, acting as a filter, pass water, but block the particles from getting inside, causing a thick crust to form up to 5 mm of drilling fluid on the surface of the reservoir in the well, which makes it difficult to escape the gas. Experimental upbuilding of 5-mm mud crust on the shale sample has led to decreasing of gas permeability from 3.182 mD to 0.418 mD. In this case, the porosity of the sample increases from 0.669% to 4.688% due to the porosity of the crust. The action on the barite mud crust of an aqueous solution of the Arten B-Solv complexing agents at a temperature of 100пїЅ C and background pressure of 20 MPa for 24 hours, almost completely dissolves the crust, partially leaving a clay fraction on the surface. As a result, the gas permeability increases to 1.166 mD, the porosity of the sample decreases to 0.331%.

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DOI resolver: doi.org/10.5593/sgem2017h/15/s06.064

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