THE FIRST DEVIATED WELLBORE UNDERREAMING WHILE CLOSED HOLE CIRCULATION DRILLING

Drilling in the western part of the Karachaganak field (operator - Karachaganak Petroleum Operating b.v., KPO) presented such additional difficulties to the project as drilling horizontal wells with a low range of permissible changes in the density of the mud, catastrophic mud loss and high fracturing of the rocks. From the experience of drilling neighboring vertical wells in the Soviet era in this area, it became clear that the mud loss cannot be eliminated by conventional methods, such as pumping LCM or cementing.
Uncontrolled loss of drilling fluid prompted the use of adaptive drilling methods for further development of the field. The application of the pressure-controlled drilling method, in particular CHCD method, is not new at the Karachaganak field. “Drilling without returns” was successfully introduced, but a rotating preventer (rotating control device - RCD) was used for drilling without monitoring the well trajectory. It was imperative for the Operator to drill a horizontal well to increase the interval of the reservoir, while ensuring a possible increase in flow rate.
It was important for the company providing the directional drilling services to make sure that the technologies used would be applicable in a CHCD environment. Particular attention and approach are necessary for well planning using a rotary steerable system (Rotary Steerable System - RSS), telemetry and logging tools, the functionality of which in drilling conditions without returning the drilling fluid is associated with difficulties in transmitting telemetry data, controllability, subsequent maintenance of downhole equipment, and with the analysis of hydraulic calculations.
Close cooperation between the Operator and the service contractor has allowed to increase the efficiency of drilling operations and make significant changes to the design of the bottom hole assembly (BHA) and selection of the optimum bit. Using a special software platform, a team of engineers was able to simulate the possible behavior of the bit, underreamer, and BHA as a whole when drilling hard formation.
To prevent fatigue stress of BHA elements, at the planning stage special attention was also given to analysis of bending stresses of BHA at the expected dog leg severity of 4-8 ° / 30 m. The world’s first enlargement of the wellbore from 6 to 8 inches in the build up section under conditions of CHCD was successfully accomplished thanks to best practices and technologies.

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