During the last seven years in the Changbei gas wells of China, operator utilized heavy-set roller-cone bits in the 8 ½-in.lateral wells because of the hardness and abrasiveness of the rocks. After the project moved from the southern to the northern part of the block, the formation became more heterogeneous, and the ROP of the roller-cone bits dropped 40% on average. This challenged the project economically because 60% of the operating time is spent drilling this interval.
To improve performance in these wells, a hybrid bit combining PDC and roller-cone was proposed. The intention was to improve ROP through the hard-to-drill intervals in the northern block and reduce bit consumption. Claystone and other soft and plastically behaving rocks are drilled farther using PDC bits; hard and abrasive sandstone, meanwhile, are drilled farther using roller-cone bits.
Field trials in Changbei gas wells were very successful. The client saved multiple standard Tungsten Carbide Insert (TCI) runs and drilled 100% farther, achieving a rate of penetration (ROP) two times faster than the best TCI bit run in the same well and area. Stable tool face control was also observed because of the lower torque fluctuations which enabled the operator to reduce the amount of time sliding by up to 15% versus using offset bits. The paper will present an analysis of the drilling data from the field and provide a detailed description of the application's achievement by comparing the performance of the roller-cone, PDC and hybrid bits.
The paper will describe the planning and operational execution of drilling an 8½-in. horizontal lateral with a hybrid bit in a challenging application, and conclude with the technical and economic benefits and the potential of the new drill-bit technology.