Investigations into the coiled tubing partial underbalanced drilling (CT-PUBD) technique for drilling hard formations

Abstract

To improve the rate of penetration (ROP) in drilling deep and hard formations, this paper proposes a new drilling method called coiled tubing partial underbalanced drilling (CT-PUBD). As a preliminary investigation into the new drilling method, this paper presents predictions of hole cleaning efficiency, drilling speed, cuttings migration and pressure loss in the drilling process with CT-PUBD. Based on numerical simulation and full-scale experimental studies, we conclude that using CT-PUBD, an underbalanced drilling condition can be achieved near the bit while maintaining wellbore safety at the same time. This condition can be achieved using a cuttings discharge device, a rotary packer and a backflow controller. According to the numerical simulations performed in this study, CT-PUBD can achieve high efficiency of hole cleaning. Along the cuttings migration process, the fluid velocities can reach the maximum values in the backflow holes. A full-scale laboratory experimental system was used to test the hydraulic characteristics and obtain the drilling performance of the new technology. The result shows that CT-PUBD significantly improves the ROP compared to the conventional drilling method. Keywords Partial underbalanced drilling Á Coiled tubing Á Flow fields Á Cuttings removal Á Rate of penetration (ROP)

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“…With the rising demand for energy, oil and gas exploration and extraction have deep, usually hard rock formations. 10 A low penetration rate (ROP) and a long drilling time are driven by hard workouts, leading to high drilling costs compared to soft rocks with a high content of clay. Different techniques have been developed to enhance the ROP for hard training drillings like under-balanced drilling (UBD), Reelwell drilling, and coiled wire.…”

“…The prediction and selection of best drilling scenarios for the performance of the drilling process would, therefore, constitute an important challenge in the oil industry that needs to be considerably addressed. With the rising demand for energy, oil and gas exploration and extraction have deep, usually hard rock formations 10 . A low penetration rate (ROP) and a long drilling time are driven by hard workouts, leading to high drilling costs compared to soft rocks with a high content of clay.…”

Application of Implicit Pressure-Explicit Saturation Method to Predict Filtrated Mud Saturation Impact on the Hydrocarbon Reservoirs Formation Damage

“…These parameters would be of importance during the design of the drilling fluid before drilling performances to reduce the formation damage effect [25]. Shi et al (2018) proposed a new experimental and numerical method which is known as coiled tubing partial underbalanced drilling (henceforth; CT-PUBD) to enhance the penetration rate in the hard rock formation. They estimated the considerable influence of drilling speed, pressure loss, cutting migration, and cleaning hole efficiency in UBD operations to optimize the procedures.…”

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