Abstract

Seventeen horizontal wells have been drilled in the Widuri, Intan and neighboring satellite fields of the Maxus SES Production Sharing Contract area in Indonesia, over the period from mid 1996 until end 1997. The horizontal wells produce from dominantly high permeability (multi-Darcy) fluvial sandstones of the Talang Akar Formation, which are often laterally restricted in the form of sandstone bodies having a meandering channel-like form. The horizontal wells give more efficient oil recovery than deviated or vertical wells, and provide additional recoverable reserves. Optimum well design for the Widuri reservoirs relies on an integration of all relevant disciplines from the outset. The interpreted three dimensional reservoir geometry, reservoir behavior, preferred well completion and efficient drilling practices, all contribute to the well plan. 3D seismic is fundamental, and provides detailed images showing gross sandstone body geometry and in some cases details of the sandstone body's internal architecture. A pilot borehole is drilled, prior to a sidetracked horizontal borehole in most cases, due to an uncertainty of sandstone versus mudstone fill, height of local oil-water contacts, and the desire to set casing into the top of the reservoir prior to drilling the completion interval. Widuri reservoirs range from strong water-drive to dominantly pressure depletion-drive.

An open-hole gravel-pack with a wire weave membrane screen, and electric submersible pump (ESP) is the preferred completion method for the Widuri horizontal wells. The planned well trajectory contains tangent sections for ESP placement, potential errors in depth prognosis, unexpected build rates, unstable zones and potential recompletions. Curvature restrictions often become critical in the design of horizontal wells targeted below pre-existing platforms.

The planning and coordination stage for drilling the horizontal well is important in ensuring that the well meets its objectives. The type of bottom-hole-assemblies required, need for additional survey frequency in high build-rate sections, type of measurement-while-drilling (MWD) tools required to discriminate lithologies and potential swept zones, use of stratigraphic and petrophysical modeling for geosteering, and clear communication with the relevant rig-site personnel, are factors which help ensure the success of a horizontal well.