Abstract

Multilateral drilling technology is difficult and risky, especially if the target is a naturally fractured carbonate abnormally pressured formation. Even drilling of simple wells in such formations risks severe mud losses and loss of circulation, which is why most of these wells have not been drilled to total depth (TD). Yurubcheno-Tokhomskoe oil field, located in west Siberia, is a notable example where such problems are observed. To reduce mud losses and make it possible to reach the TD, multiphase managed-pressure-while-drilling (MPD) technology was applied in Yurubcheno-Tokhomskoe field, and the results exceeded all expectations.

MPD is an adaptive drilling process used to dynamically control the bottomhole pressure (BHP), either with friction pressure losses or with applied surface backpressure. It requires thorough planning of the entire preparation and drilling phases. Implementation of MPD gives a proven technological advantage in these cases where, even though reducing mud weight helps to manage the equivalent circulating density (ECD) while circulating, during static periods, BHP is lower than pore pressure, which leads to well control events. Pumping lost circulation material (LCM) does not solve the losses problem; rather, the addition of LCM increases formation damage and affects well productivity.

The first application of multiphase MPD technology in Russia was in 2016 at Yurubcheno-Tokhomskoe field for drilling of a simple horizontal well. Compared to conventional drilling, multiphase MPD enabled reducing mud losses by 80% and increasing average rate of penetration (ROP) by 40%. Furthermore, no LCM pills or oil-water mixture was applied for handling mud losses, which positively affected formation production properties. The initial production potential of wells drilled with MPD was 65 to 180% more than expected.

In September 2017, multiphase MPD technology was applied for drilling first horizontal multilateral well at Yurubcheno-Tokhomskoe. It enabled drilling all six planned laterals, of which the overall length was 2571 m. Furthermore, compared to a conventionally drilled multilateral well at this field, mud losses were reduced by approximately 80% (1619 m3 instead of 9354 m3) and average ROP was increased. It is also important to note that no LCM or oil-water mixture was used during drilling this well. No lost circulation or well control incident was incurred, which materially reduced net drilling days.

Successful drilling of the first multiphase MPD multilateral well showed the high potential of this technique for drilling 4-in. horizontal sections in highly fractured carbonate formations. One main and five laterals were drilled. Each of drilled laterals required an individualized approach due to the completely different behavior of the wells. Such results open new horizons for drilling and completion of complicated wells in Yurubcheno-Tokhomskoe oil field. Because of this project, it was decided to drill more complicated multilateral wells with MPD technology in future.

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