Well Integrity and Pressure Control in Unconventional Reservoirs: A Comparative Study of Marcellus and Utica Shales

Abstract

Challenges associated with Utica and Marcellus shale well integrity and safety necessities further study in order to have an effective and economic drilling operations. Objectives of this comparative study are to evaluate the impact of unscheduled well control events on wellbore integrity, as well as the influence of poor drilling practices that trigger well control emergencies in shale gas wells. A realistic multiphase simulator is used to evaluate well control unexpected scenarios in Utica and Marcellus shales. Changing operational parameters such as wellbore profile, well control method, drilling fluid type and circulation rate in Marcellus and Utica horizontal wells are investigated. Further, this research studied the impact of influx type, size and intensity on well integrity. Behavior of dry gas, rich condensate and black oil influxes are compared in extended lateral wells. The impact of free gas migration in inclined downward laterals drilled with water based mud is compared to the influence of gas solubility in inclined upward wells drilled using synthetic oil based mud. Preliminary results show that deeper, over-pressurized Utica shale presents more challenges compared to Marcellus shale wells. When oil based muds are used additional challenges are presented since the surface pressures and volumes are not representative of the bottom-hole conditions. Dissolved gas in oil is liberated at the bubble point pressure complicating surface kick handling procedures. Gas influx migrates and reaches surface much quicker in water based muds and inclined downward laterals. Higher the influx circulation rate, size and intensity, higher the resultant pressures and volumes and higher the risk of exceeding casing shoe fracture pressure and risking well integrity. Drilling fluid type, properties and flow characteristics are critical for well integrity. Early detection is a key factor in minimizing kick size and properly contain pressures without violating safety and environment regulations and reduces the blowout associated risks. Accordingly, well integrity is verified by monitoring surface choke, casing shoe and constant bottomhole pressures throughout the entire well control operations.

Study on Nuclear Magnetic Resonance Logging T2 Spectrum Shape Correction of Sandstone Reservoirs in Oil-Based Mud Wells

“…Water-based mud (WBM) and oil-based mud (OBM) are considered the two types of drilling fluids that are most commonly used in the drilling process. Because shale oil reservoirs are rich in clay minerals and rock stability is poor, drilling with water-based mud will lead to water absorption and swelling in the rock, hydration expansion, borehole collapse, leakage, and so on [ 6 , 7 ]. Oil-based mud can effectively solve these problems, such as hydration expansion and wellbore instability of shale formations.…”