Closed Loop Nitrified Foam MPD Delivers Unprecedented Drilling Performance in a Mature Sour Gas Field in Pakistan

Abstract

As oil and gas reserves mature the world over, operators are looking towards advanced methods of increasing the ultimate recovery from their ageing fields. An energy deficient country of Pakistan relies heavily on oil and gas imports. The country was once self sustaining in at least natural gas needs. A major portion of this gas was produced from the Field-X which was discovered in the 1950’s. The primary reservoir in Field-X is the YZ-Limestone reservoir which bears sour gas. Due to extensive production from the YZ-Limestone formation, the reservoir pressure has depleted to a mere 2.0 PPG in equivalent mud weight, and it being a naturally fractured limestone formation presents numerous drilling challenges. The operator has evaluated a potential higher pressured formation in the deeper horizons of sui field but that requires drilling through approximately 650-690 meters of the YZ-Limestone formation. This feat when attempted conventionally is plagued with numerous problems like, total lost circulation, differential sticking, influxes due to the loss of a sufficient hydrostatic head, and stuck pipe following well control events. To mitigate these challenges the operator, need an effective method to drill through this depleted formation without pumping heavy LCM pills, and multiple cement plugs across the massive cavernous thief zones in the YZ-Limestone formation which could have been detrimental to the production of nearby wells. Moreover, such remedies with specialized LCM’s and acid soluble plugs would have resulted in excessive material cost and non-productive time, which in some instances extended to a period of more than a month. To address the aforementioned challenges in drilling the YZ-Limestone formation, a multiphase managed pressure drilling system was suggested to drill the formation with minimal non-productive time and cost. Multiphase hydraulics were performed to assess appropriate pumping parameters for a near-balanced condition across the YZ-Limestone formation. A closed loop MPD equipment system was designed to help maintain near-balanced conditions in pumping and static (non-circulating) periods. The designed equipment system would also ensure that the risk of H2S exposure to the atmosphere was eliminated. The application of a closed loop nitrified mpd system on a recently drilled well proved to be highly successful and reduced the drilling time to just 28 hours by not only eliminating fluid lost circulation but by also delivering an extremely high rate of penetration of 39.2 m/hr. The successful and exemplary application of nitrified MPD has opened up a new horizon for the development of deeper prospects in the Field-X and similar neighboring fields. The paper outlines the design and execution of the closed loop nitrified MPD system.