An Analysis of Rotary Steerable Systems for Sidetracking in Open Hole Fishbone Multilateral Wells in Vostochno-Messoyakhskoye Field

Abstract

Vostochno-Messoyakhskoye and Zapadno-Messoyakhskoye fields are the northernmost of the known onshore oil fields in Russia. Under severe climate and geological conditions in the field, an operator planned initially to construct horizontal wells with sidetracks with the use of fishbone drilling.

This paper describes the results of construction of four fishbone wells. A comparative analysis of horizontal sidetracks as well as different downhole conditions and their impact on performance are discussed. Recommendations on effective performance of works are given.

The technology of sidetracking in open hole with a rotary steerable system (RSS) was tried while drilling four wells.

Fourteen sidetracks of different complexity were drilled: the distance from a casing shoe to a kickoff point (KOP) varied from 50 to 720 m; in this case the sidetrack intervals were affected by formations of different densities. The distinctive features of each of the wells are taken into account in the analysis: a number of horizontal wellbores—from 3 to 5, and a total length of the laterals—from 1980 to 3544 m. An accumulated experience made it possible to compare the sidetracking conditions and results against each other as well as make a list of practical guidelines for drilling similar wells in future. Based on performance results, the optimal conditions for sidetracking with an RSS were determined under geological conditions imposed at Vostochno-Messoyakhskoye field. The experience has shown that in case a sidetrack interval falls on dense rocks, then the duration of work increases three/fourfold.

In this context, 3 levels of sidetracking difficulty were identified on the basis of the rock density. Individual recommendations related to drilling process were compiled for each level.

Geosteering in mother bore plays an important role in locating a KOP. Interpretation of LWD data in real time allows identifying the level of difficulty for the upcoming sidetrack and locating a proper KOP for the next sidetrack. Apart from that, the requirements for the sidetrack interval were drawn up. It is necessary to build a tangent section in the main hole, which matches the bottomhole assembly (BHA) length. A build up interval ("ramp up") should follow immediately after the tangent section, where sidetracking is to be performed. Provided that the recommended conditions are met, it is possible to drill several horizontal sidetracks over one run, resulting in reduction of well construction time.

Based on the operator company’s estimates, the fishbone drilling application made it possible to increase an initial oil production rate by 40% in average, versus conventional horizontal wells. Due to RSS usage during sidetracking and drilling horizontal holes, an overall length of horizontal sections of four wells totaled 10 kilometers (horizontal section of a conventional well is about 1000 m).

After testing under challenging conditions of Vostochno-Messoyakhskoye field the fishbone drilling is ready to be applied in other regions as well.