The stimulation of carbonate oil deposits


A new solution to stimulate carbonate formations with bedding water or a gas cap was proposed. It is a combination of acid jetting and Perfobur radial drilling technology. Perfobur is a technology of a mechanical radial drilling with using of slim mud motor. The main advantages of the technology are controlled trajectory and the possibility of re-entry into the channels. After channel drilling, a jetting gun with four nozzles is run into the drilled channel. Acid is injected through these nozzles at a flow rate of 100 m/s (328 ft/s). In addition to the effect of dissolving the formation, the additional caverns, which in theory are up to one meter long, are washed out.

This technology was applied on the carbonate reservoir of Bashkirian stage, which is characterized by high heterogeneity and close location of the underlying water. Two adjacent well candidates with identical reservoir properties were selected. Acid fracturing was performed on well-A. Two channels 46 feet long each were drilled on well-B using the Perfobur technology. Then acid was injected through the jetting gun. In each channel, acid was injected at two points. In total, 48 m3 of acid were injected. The productivity index of well-A was 0.4 m3/day/atm and on well-B - 1.07 m3/day/atm. Watercut on well №1 was 28%, and on well №2 - 10%.The experience of combination Perfobur technology and acid jetting showed a number of advantages. Firstly, it is an increased acid penetration length. Secondly, controlled acid injection minimizes the risk of breakthrough into the water. Thirdly, it is high productivity of wells after the workover.

The novelty of this technology is in ability to deploy acids far out in the rock away from wellbore through the mechanically drilled holes with known depths and azimuths. Precise locations of drilled channels allow to stay away from contacting the water or gas zones. The different chemicals can be deployed through the channels to treat the wells with various challenges, for example the heave oils and others.

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