Abstract

An innovative two-well Low Cost Drilling (LCD) programme has been executed to exploit small, un-drained oil targets in the Andrew field. The wells have been drilled with 10% fewer offshore drilling crew, enabling critical back-to-back inspection and fabric maintenance to continue. Reserves targets have been met and costs reduced by 35%, allowing access to other smaller targets and extending field life.

Three questions needed to be satisfied throughout the program. Is the oil there; can we access it cost effectively and can the platform accommodate the work? In 2004, we accepted the challenge to identify and develop these targets and embarked on a 3-point program to:

  1. Better define oil targets using 4D seismic and Top Down Reservoir Modelling (TDRM) techniques to address uncertainty;

  2. Minimize offshore drilling support by using an Onshore Operations Centre (OOC). Only 80 beds are available for managing the delivery of all aspects of the business.

  3. Minimise drilling cost through sidetracking, de-scoping and executing preparatory well work prior to full rig mobilization. Highlights include drilling the 6″ hole section in a single run using agitators to maximize ROP by maintaining WOB transfer and simplifying completions to use pre-drilled liners, isolating the production zones using swell packers.

This success has been achieved through innovation, technology and adopting industry best practice, with meticulous planning and outstanding teamwork between operations, subsurface and drilling, both onshore and offshore.

Introduction

The Andrew field, comprising a Palaeocene turbidite reservoir overlaying a Lower Cretaceous prospect was discovered in 1974 by well 16/28–1. Development of the Paleocene reservoir commenced in 1993 and continued through 1997 using horizontal technology to access the thin oil column1,2. A total of 10 producing wells, radiating from a single, central platform location were drilled and completed during this period. Reservoir pressure is maintained by the strong natural water drive and by injecting gas into the crest of the existing gas cap. Infill drilling took place during the periods 1998 - 99 and 2001 - 04, culminating in the successful drilling of the A16 and A17 wells. Up to this point; economics supported drilling all the wells from surface.

The un-drained targets are located between the radial spokes formed by the existing wells, Fig. 1. These volumes, containing 2 million bbls or less, no longer support the costs of drilling a well from surface.

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