The paper reviews practical applications of geosteering to horizontal well drilling and evaluates its efficiency for horizontal drilling. On Ust-Tegusskoye filed more then 30 horizontal wells were steered using 3D geological model.

One of key problems in geosteering process is limited ability to understand the location of the wellbore relative to the target object (productive layer, sand interval). The traditional set of data – structural maps build from seismic and pilot wells does not allow building fine structural capable to ensure successful drilling. But building the modeling workflow allows to simulate many possible locations of horizontal wellbore between top and bottom of reservoir, find the most probable location and minimize risk of unsuccessful drilling. Local update of the geomodels in the relatively small regions containing newly drilled wells helps getting production forecasts from flow simulator in reasonable time.

Recently large attention is paid to developing innovative approaches to the steering of horizontal wells.

The key requirement to the geosteering process today is landing well trajectory not only into pay part of productive layer, but into most efficient part of reservoir with minimal penetration of dense sub layers. For that the whole set of technological solutions exists ranging from optimization of pilot wellbore locations and finding best possible well profiles on geological and flow simulation models to the real time geosteering.

On Ust-Tegusskoye field the number of drilled horizontal wells grows every year: in 2009 there were 3 wells, in 2010 - 5 and in 2011 - 15. At the first half of 2012 9 horizontal wells were drilled (Figure 1). Minimal thickness of target layer for horizontal wells is 2.5 m. Maximum length of horizontal part is 832 m.

In spite of continuous improvements in drilling technology the problem of finding borehole position within top and bottom of target layer is still actual. Standard set of G&G information – seismic based structural surfaces and pilot wells does not allow building geomodel with reliability required for successful steering of horizontal well. Wrong positioning of well trajectory make cause it to deviate from target layer – so effective length of the well will be significantly reduced.

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