--> Reducing Risk By Inclusion Of Robust Subsurface Analysis For Plugging And Abandonment Campaigns

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Reducing Risk By Inclusion Of Robust Subsurface Analysis For Plugging And Abandonment Campaigns

Abstract

Currently there is a disaggregated technical (and commercial) response in Plugging and Abandonment (P&A) procedures by operators which results in: higher risks, higher costs, sub-optimal operational performance and lack of improvement by learnings. A way forward would be to develop a risk-based verification service to drive safe efficient and affordable P&A (major component of decommissioning and restoration activity/risk exposure/cost) process founded on a risk assessment matrix. A common platform/framework is needed to describe what needs to be verified and how, based on best practice in pore pressure and geomechanical prediction, risks can be quantified and managed to an acceptable level. To help improve the process we present a way to re-think the plugging and abandonment process given the geology, both regional and local, will control the distribution of fluids and pressures, hence impacting the placement of well plugs. The challenge for the industry is the growing surge in asset abandonment with the current low oil price. The main objective is, therefore, to maximize efficiencies and reduce costs during the plugging and abandonment operations whilst maintaining an operationally and environmentally safe strategy. The current cost of such an operation on a single well is commonly not a concern for an operating company, but considering the amount that will need to be abandoned in the near future, new or novel technologies and methods are needed to be developed. The P&A process itself is simple to summarise; to isolate and seal a well forever. However, the long term success of these abandoned wells is dependent on the sealing requirements, which become critical since the cost risk and environmental impact of returning to re-abandon the well is a major concern. Designing a well abandonment program to deal with the virgin pressures may not be cost effective or required given the complex effects of production on the sub-surface pore pressures within neighbouring fields. A geological assessment of the field, and its surrounding area, is needed to understand the potential for communication within reservoir horizons and the possibility for fluid movement. At the pre-drill stage much of this information should be known, given the assessment of the formation pressures, overburden and fracture strength are required for well planning, but this assessment may only be applicable on a well by well basis. Throughout the life cycle of a field the state of a reservoir will change; pore pressures may become depleted and/or recharged potentially leading to fault reactivation, overburden may compact, and thermal changes may also occur. Therefore, having an understanding of the current pore pressures, recharge pressures, and the timescales over which these may occur, on both a regional and local scale, during the abandonment planning procedure should be invaluable. A case study from the North Sea is presented as this is a mature area for oil and gas with numerous successful fields now entering the final stages of production requiring a P&A strategy. However, the same process will be required for any well due to undergo P&A.