The present work describes not only the main aspects related to planning and executing six multilateral (ML) horizontal branches drilled underbalanced (UB) in Carmópolis field, but also presents an analysis of the initial productive life of this well. All the main engineering information used for making decisions while planning and at well site, drilling performance and production evaluation are included.

As the targeted formations are consolidated, UBD did not bring any special concern in terms of wellbore collapse. In order to achieve the required bottomhole pressure, nitrogen was mixed with a synthetic base mud (SBM) after flowing down through the annular space between the 9 5/8″ and 7″ casings and passing through a 1″ aperture in the 7″ casing. After that, the mixture went up through the annulus between the 7″ casing and the drill string. This concentric casing approach for injecting gas made possible the use of conventional MWD, but it brought some concerns about the maintenance of the UB condition while operating.

The first ML well UB drilled in Brazil successfully combined the following different technologies: (1) ML level 2; (2) UB condition, and (3) medium radius build-up drilling system. It also involved four different parties where the operating company worked together with three service companies to build a team and achieve operational goals.

As the reservoir pressure was not sufficient to sustain the flow of oil to the surface, this paper also addresses the design of the pilot well, which was specifically prepared for operating with a sucker rod pump (SRP). Finally, from the perspective of the reservoir engineers in charge of developing this field, the oil production is presented and evaluated.

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