Drilling the Deepest High-Pressure High-Temperature (HPHT) Onshoreexploration Well Using a Combination of Mud Cooling and Managedpressure Drilling (MPD) Techniques: A Field Case Study from the Nile Deltaof Egypt Targeting Mesozoic Carbonate Platform

Abstract

Abstract This paper reviews the successful application of a Mud Cooling and Managed Pressure Drilling (MPD) system in a HPHT well to explore the potential of the Mesozoic Carbonate Platform with pressure ramp and Narrow Mud Weight Window (NMWW) in the Nile Delta of Egypt. The Constant Bottom Hole 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 around 50°C. Drilling this well is challenging due to the uncertainty of pressure and temperature regimes and the lack of data in this area. This paper will discuss the application of the MPD and Mud Cooling combination. Also, the challenges encountered while drilling and how they were tackled will be explained, besides the best practices and recommendations for similar applications. 10 in. × 12 in. section completed the pressure ramp, then entered and drilled through the NMWW. The hole was drilled and enlarged simultaneously to 12 in. to section target depth (TD) at 5118 m. Losses at a rate of 3.5 to 5m3/h were encountered (lost 26m3) when circulating to increase mud weight from 2.16 to 2.20 sg to follow the pressure ramp. Then the mud weight was cut back to 2.16 sg, and drilling continued with active use of the MPD system to maintain a CBHP at 2.22 sg. Equivalent Mud Weight (EMW) both equivalent circulation density (ECD) while drilling and with surface back pressure (SBP) during connections. A dynamic formation integrity test (FIT) and a static Pore pressure Test were performed with the MPD to re-assess the drilling window and adjust mud weight accordingly. The mud cooler was running at 100% capacity keeping mud-in temperature 50°C while mud-out temperature ranging from 60 to 70°C and annular temperature from MWD was recorded while drilling at a maximum temperature of 139°C at TD. The 8 in. hole was drilled through the primary objective from 5118 to 5585 m. The MPD detected two well control events early at 5585 m which alleviated their consequences. Difficulties were experienced to regain control of the well, facing a kick and losses scenario due to NMWW. The open hole was plugged back with cement to secure the well after a fragile control was regained. The mud-in temperature was maintained at around 40°C. T-1 well was the first well to reach that deeply buried Mesozoic carbonate structure. The Mesozoic carbonate platform has never been reached in this area. This paper provides an in-depth study for an innovative combination of utilizing MPD along with mud cooling technique to drill a HPHT exploratory well with a NMWW providing guidance for similar applications.