Abstract

Issues associated with stuck pipe result in huge losses in the world oil industry. Historically, horizontal wells drilled in Saudi Arabia have been known to present severe stuck-pipe challenges. Thus to mitigate the problems arising due to stuck-pipe issues, a new drilling fluid has been designed which employs a combination of two different weighting agents viz. barite and manganese tetroxide (Mn3O4). The use of such a combination as a weighting material in a drilling fluid provides both operational and monetary benefits.

Manganese tetroxide is spherical in nature and has a small particle size (D50=1 µm) as compared to barite (D50=20 µm) Moreover, Mn3O4 also has a higher specific gravity (4.95 g/cm3) as compared to barite (SG= 4.20 and). This high specific gravity of manganese tetroxide makes it a good weighting material to reduce solids loading and settling in drilling fluids as compared to the conventionally used barite. Another advantage of Mn3O4 is that it is acid-soluble. This acid solubility of Mn3O4 provides more operational benefits when a fluid with a combination of barite and Mn3O4 is used as weighting agent. The acid solubility of Mn3O4 makes the use of acids or acid precursors possible in partially dissolving Mn3O4-barite based filter-cakes. This partial breakage of the filter cake is expected to free the pipe thereby mitigating the problems associated with stuck pipe incidents. Another benefit of using a combination of barite and Mn3O4 would involve reduced fluid cost as compared to a fluid formulated with Mn3O4 alone as the weighting agent.

Thus, this paper presents a solution in mitigating stuck pipe issues and 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 270°F /250°F/300°F respectively. The experimental work in this paper involves measuring rheological properties, HTHP filtration and static sagging resistance of the fluid at the specified temperature. The paper also describes the results of using different organic acid based filter-cake breaker fluids for the partial dissolution of manganese tetroxide based filter cake. Comparative studies of fluids formulated with 100% barite and a blend of manganese tetroxide and barite show that fluids formulated with a combination of barite and Mn3O4 provides increased sag resistance as compared to a drilling fluid formulated with barite alone as the weighting agent.

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