High Density Drilling Fluids for Managed Pressure Drilling

摘要

Drilling with high density water-based muds invariably increases the chances of a stuck pipe. Stuck pipe significantly increases the cost of drilling and decreases the chances of successfully drilling a well within the stipulated time. Drilling fluids formulated with a combination of manganese tetroxide and barite as weighting agents are expected to have the following advantages: a) Better sag resistance b) Lower equivalent circulating density (ECD) c) Lower fluid cost d) Stuck pipe mitigation due to acid solubility of manganese tetroxide. This paper describes the formulation of 100pcf, 120pcf and 150pcf drilling fluids formulated with a combination of barite and Mn3O4 as weighting materials and hot rolled at 270o F/250o F/300o F respectively. The experimental work involves measuring rheological properties, HTHP filtration and static sagging resistance of the fluid at the specified temperature. The paper also describes the data obtained from the field trial of 160pcf fluids formulated with barite and Mn3O4 for wells with a BHST of 300o F. Details are shed on the high-pressure, high-temperature (HPHT) operations across naturally fractured formations with 0.5 – 1.0 pcf mud window. The paper discusses the advantage of using such drilling fluids in mitigating stuck pipe issues and showcases their benefits in terms of better barite sag resistance and lower equivalent circulating density as compared to conventional drilling fluids formulated with barite as weighting agent. The 100pcf, 120pcf and 150pcf fluids showed superior rheology, thin filter-cake and better sag resistance as compared to fluids formulated with only barite as the weighting agent. The drilling fluids formulated with a combination of barite and manganese tetroxide showed good rheology, barite-sag resistance and resulted in successful drilling of wells having a BHST of 300o F. 160pcf fluid formulated with a combination of barite and manganese tetroxide when field trialed showed good rheology, better sag-resistance thereby resulting in successful drilling of the well. In fact, managed pressure drilling (MPD) operations became more practical with such high mud weights as this novel formulation facilitates mud management and treatment when compared to the conventional recipes. MPD control algorithms are absolutely dependent on the mud system consistency and durability which is a feature provided by this innovative fluid formulation.