This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202661, “Combination of Radial Drilling Technology With Acid Jetting: New Approach in Carbonate Reservoir Stimulation,” by Ayrat Bashirov, Ilya Lyagov, and Ilya Galas, Perfobur, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed.
The complete paper describes an approach to stimulate carbonate formations with bedding water or a gas cap. The technique is a combination of acid jetting and a radial drilling technology that uses mechanical radial drilling with a slim mud motor. The primary advantages of the technology include controlled trajectory and the possibility of re-entry into channels. The novelty of the technology is in its ability to deploy acids in the rock far away from the wellbore through the mechanically drilled holes with known depths and azimuths.
The mature field is in central Russia in the Republic of Bashkortostan. The field contains both sandstone and carbonate reservoirs. Oil depth is from 780 to 1830 m. Six reservoirs are in development. This study concentrates on projects in a carbonate formation that is a substage of the early Pennsylvanian Period. This formation is highly heterogeneous with closely underlying water. Permeability of the reservoir is approximately 43 md; reservoir pressure is 1,000 psi, and oil density is 0.891 g/cm3. Two adjacent well candidates with identical reservoir properties were selected for the study, with a distance between wells of approximately 136 m. Net oil thickness in Well A is 4.4 m and 3 m in Well B.
The technology described by the authors uses mechanical radial drilling with a slim mud motor. The technology allows the drilling of a network of radial channels up to 15 m long with up to four channels of different trajectories on one level. The technical system features a modular construction for ease of assembly at the wellhead area and increased operational efficiency. The main elements of the technical system include the following:
- Pipe pusher connected at the top with an overflow valve module and, at the bottom, with a guiding device connected by means of a hydraulic pusher
- Flexible pipe assembly with a small (nonstandard) sectional mud motor
- Drilling bit (milling cutter for window cutting)
- Special whipstock and an anchor module with an orienting funnel connected from below to the pipe frame