Abstract

Horizontal wells drilled in the Marrat (lower Jurassic), Minjur and Jilh (upper and middle Triassic) formation in Saudi Arabia are known to present severe stuck-pipe challenges. Stuck pipe in a horizontal well is a problem that can result in loss of tools, non-productive time, sidetracks and loss of well thereby increasing the wellbore construction cost.

Thus to mitigate the problems arising due to stuck-pipe issues, a new drilling fluid was formulated using a combination of barite and manganese tetroxide (Mn3O4) as weighting agents. The use of such a combination as a weighting material in a drilling fluid provides both operational and monetary benefits.

Mn3O4 with a smaller particle size (D50=1 µm), spherical shape, and high specific gravity (4.95 g/cm3) makes it a good weighting material to reduce solids loading and settling compared to barite (SG= 4.20 and D50=20 µm). The fact that manganese tetroxide is also acid-soluble provides more operational benefits when a fluid with a combination of barite and Mn3O4 is used as weighting agent. In the event of a stuck-pipe incident during drilling, the use of acids or acid precursors would result in the dissolution of the Mn3O4 thereby resulting in a partial breakage of the manganese tetroxide-barite filter cake formed in a well during drilling. This partial breakage of the filter cake is expected to free the pipe thereby mitigating the problems associated with stuck pipe incidents. The use of a barite along with Mn3O4 would also result in a reduced fluid cost as compared to a fluid formulated with Mn3O4 alone as the weighting agent.

Thus, this paper showcases the benefits of using such a combination of barite and manganese tetroxide as weighting materials in 100pcf, 120pcf and 150pcf drilling fluids hot rolled at 250°F/300°F. The experimental work in this paper involves measuring rheological properties, thermal stability, HTHP filtration and static sagging resistance of the fluid at 250°F/300°F. The paper also describes the results of using different acid based filter-cake breaker fluids for the partial dissolution of manganese tetroxide based filter cake.

A blend of manganese tetroxide and barite provides increased sag resistance as compared to a drilling fluid formulated with barite alone as the weighting agent.

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