Vincent Quad-Lateral: Use of Hi-Tech Geo-Steering, Drilling, Completion and Anti-Collision Technology to Re-Develop a Thin Oil Field, Offshore Carnarvon Sub-Basin, Australia

Abstract

The Vincent oil field has a thin, low API oil column and gas cap in unconsolidated sands of the Lower Barrow Group delta. It is typical of other shallow, low-relief oil fields in the basin, with economic development requiring multi-lateral horizontal wells. Vincent has 39 cased or completed holes including: vertical and pilot holes, gas and water injectors, and horizontal producers drilled 150m apart in 2007–12. An infill program began in 2015 to enhance oil recovery with the Quad-lateral VNB-H1ST1. This requires stringent geosteering and anti-collision criteria only possible using the latest hi-tech Geosteering, Surveying, Drilling and Completion technology. Initial development in 2007–09 focused on the main part of the field below the gas cap. The mostly bi-laterals were drilled geometrically below the GOC, some 1/3 down in the oil column, to mitigate gas and water ingress, because the geosteering tools could not see the roof through the gas cap. The survey errors after drilling >4km allowed large vertical drift and the rotary steerable tools struggled to maintain constant height in the dipping reservoir. Many open-hole sidetracks resulted exposing the holes for long periods. Together with synthetic drilling fluids for hole stability, the result was low productivity wells and slow sweep. Wells drilled outside the gas cap were geosteered to stay 2–3m below Top Reservoir but had similar outcomes. In 2011–12 a combination of new drilling technology and better completion concepts, Geosteering and High Definition Surveying (HDS) was successful. Three tri-lateral wells were drilled on the flanks of the field, yet the productivity and sweep is much higher and these wells are the best producers in the field. The main part of the field was re-assessed to see if infill wells could capture unswept oil above and between the existing laterals. This requires precise well placement 2–4m below the GOC and anti-collision measures to place wells over and under existing laterals. VNB-H1ST1 is one of the first quad-laterals drilled offshore. Geosteering uses Deep Directional Resistivity tools to see through the gas cap and down to the OWC below combined with HDS to reduce drift. High dogleg capable rotary steerable tools control the build and drop tendencies and reduce torque and drag to maximise length. The latest completion techniques minimise formation damage and allow installation of long screens with inflow-control-devices.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015