Combined Mud-Cooling, MPD Techniques Enable HP/HT Drilling in Egypt

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210252, “Drilling the Deepest HP/HT Onshore Exploration Well Using a Combination of Mud-Cooling and MPD Techniques: A Field Case Study From the Nile Delta of Egypt Targeting a Mesozoic Carbonate Platform,” by Mahmoud El-Husseiny, Egyptian Natural Gas Holding Company, and Taher Elfakharany, Al-Azhar University. The paper has not been peer reviewed. _ The complete paper reviews the successful application of a mud-cooling and managed-pressure-drilling (MPD) system in a high-pressure/high-temperature (HP/HT) well to explore the potential of the Mesozoic carbonate platform with a pressure ramp and narrow mud-weight window (NMWW) in the Nile Delta. The constant bottomhole pressure (CBHP) variation of MPD in combination with mud cooling was used to drill from the middle of the pressure ramp to the target depth, maintaining the mud-inlet temperature at approximately 50°C. Geological Targets and Geohazards The primary objective of Well T-1 is the edge of a Mesozoic carbonate platform. These carbonates are expected to be high-energy shallow marine deposits with fair reservoir properties (20–50% net-to-gross, 5–10% porosity). The secondary objectives are turbiditic sandstone channels of the Oligocene. These sandstones are expected to have 9–20% porosity and 50–300 md permeability. Potential Middle and Late Miocene geohazards include pressure rampup associated with losses, kicks, and borehole degradation, including tight holes, overpull, and caves; and reported sticking and hangup events. The HP domain begins below approximately 4000 m. Potential Oligocene to Paleocene geohazards include NMWWs associated with losses, kicks, and simultaneous gains and losses (ballooning); borehole degradation, including tight holes, overpull, and caves; and sticking and hangup events. The HP and HT domains begin below approximately 4500 m. Potential Mesozoic carbonate geohazards include possible losses of fractured and pressure-regressed carbonates. Mud-Cooling Technique Concept and Equipment The mud cooler consists of two circuits. In the first, hot mud is circulated through a dual mud cooler using a centrifugal pump. Because of heat exchange through the plate heat exchanger, the mud is cooled and transferred back into the active mud system. The discharge of cold mud takes place upstream of the point where the suction of hot mud occurs. In the second circuit, a fluid mixed with water and glycol is circulated between a dual air cooler and the dual mud cooler using a dedicated pump. When passing through the plate heat exchanger, this mixture of water and glycol is evacuated. When this mixture returns to the dual air cooler, it is cooled using high-performance ventilators. The mud-cooling system features 16 ventilators. The efficiency of the mud-cooling system is adjusted with a number of operated ventilators. The mud-cooling units used in this well consist of two dry air coolers and two sets of air fans (Fig. 1), with each set containing 24 fans. A mixture of 10% glycol and water was used as a cooling fluid.