Applicability of Managed Pressure Drilling MPD in a High Sulfur Content Fractured Reservoir

Abstract

Objectives/Scope: In this study, Managed Pressure Drilling (MPD) is investigated in a naturally fractured Iranian oil field as a tool to mitigate under balanced drilling hazards due to its high Sulfur content; and fluid losses and other problems that are inherent to conventional over balanced drilling. Methods, Procedures, Process: MPD was identified, planed, and applied in an already drilled well, as an alternative technology, to calculate the increase in its rate of penetration (ROP). The calculations were made by Schulumberger Drilling Office package and quality checked by using Signa ERDS software. The software simulates drilling fluid dynamics to investigate application of drillind hydraulics to better chose the optimum drilling technique. Well drilling fluid properties, bottom-hole assembly, casing/completion design and rock formation properties are implemented as an input to the software to start calculations. Results, Observations, Conclusions: The subject of this study was drilled in south west of Iran. Drilling experiences in this area identified the rock formation as a brittle, highly fractured, which negatively impacts drilling time and cost. Also, in certain instances, elevated mud weights are required to deal with high-pressure high sulfur content gas and/or water flows. Calculation shows that in shallow depths (0-470.8 ft, dd) due to low pore pressure, drilling mud is in balance and within pressure window. At deeper depths (470.8-7211.3 ft, dd) drilling is MPD and increase in mud pressure is required. At (7211.3-9530.8 ft, dd) depths, sharp changes in reservoir pore-pressure cause different increases in mud pressure (from 90 to 600 psi). At deeper depths (9530.8-13154.5 ft, dd) an increase in mud pressure may cause formation fracture, so it is suggested to continue overbalance drilling or separate the well bore by casing. If the formation is separated in previous section, drilling from 9530.8 to 13154.5 ft, dd, pressure management can be continued with an increase in applied back pressure in order to stop toxic gas hazards. At deeper depths (more than 13154.5 ft) according to high depth and dramatic pressure increase, it is suggested to continue MPD to prevent formation damage or induced fracturing and also prevent H2S influxes into annulus. Novel/Additive Information: Tts the first time to apply MPD technique in a drilling well design in this filed as a solution to challenging drilling conditions like narrow pressure window, Toxic gas hazards, sever mud loss problems, differential stocking and blow out risks. Such results may result in a significant improvement in drilling economics.