Practices Implemented to Achieve Record Performance in Narrow-Margin Drilling in Bass Strait Extended Reach

Abstract

Abstract This paper discusses the successful application of the operator's drilling performance management process in the Australia Snapper / Moonfish platform drilling program. Snapper performance has historically been limited by shale instability, collapsing coal seams, lost returns, and other narrow margin drilling challenges. The design and execution practices implemented achieved record performance while simultaneously addressing the borehole behaviors that prevented the previous extended reach drilling (ERD) campaign from fully developing significant Moonfish resources. The operator's performance management process ensures both bit and non-bit limiters, such as borehole instability, are addressed with equal rigor, technology, and workflow. Issues that were previously viewed as trouble costs are treated as drilling performance limiters so solutions are pursued that both eliminate the trouble time and increase footage per day. The performance and borehole management practices implemented by the multifunctional team included:–Wellbore profile optimization to maximize shale and coal stability;–Specialized rig equipment and operational practices for equivalent circulating density (ECD) management;–Unique coal drilling practices to improve borehole stability;–Application of specialized hole cleaning equipment and surveillance;–Bit and bottomhole assembly (BHA) design to manage borehole quality while maximizing rate of penetration (ROP) and tool life;–Contingency planning for execution flexibility to respond to borehole limiters;–Office and field team training and alignment for flawless execution. The Moonfish M33a and Moonfish A26a extended reach wells were drilled to total depths of 20,341 and 21,180 ft, respectively. Both wells were completed under budget and are among the highest oil producers in the Bass Strait. The performance management process ensured that the borehole behaviors which had lowered the results of previous wells were addressed, while simultaneously achieving record setting performance. Interests in the Snapper and Moonfish fields are held by Esso Australia and BHP Billiton in a 50:50 joint venture arrangement. Esso Australia Pty Ltd provides services to the joint venture and is a subsidiary of the Exxon Mobil Corporation. Introduction The Snapper and Moonfish fields are located in the Bass Strait Gippsland Basin, offshore Southeast Victoria Australia. See Fig. 1 for a map of the Bass Strait region. The Snapper field was initially discovered in 1968, and later developed in 1981 when drilling commenced from the Snapper production platform. The platform is set in 200 ft of water and is centrally positioned over the Snapper field. A second development phase was conducted in 1986. The Moonfish field is located 3.25 miles to the North of the platform, and was first discovered in 1992. Three extended reach wells were drilled from the Snapper platform in 1997 to develop Moonfish, however, due to drilling problems only two were completed as successful oil producers with just one reaching all geological objectives. The Snapper and Moonfish fields are anticlinal structures characterized by significant faulting and a deep igneous intrusion. The reservoir intervals are overlaid with a thick and mostly homogeneous Gippsland Limestone interval, followed by a thinner Lakes Entrance shale sequence. At Snapper and Moonfish, the upper reservoir interval consists of highly interbedded Latrobe Group sands, shales and coals seams. The Golden Beach sub-volcanic reservoir is primarily lower quality sands and shale intervals. Fig. 2 shows the Snapper and Moonfish structures along with the local stratigraphy.