Well abandonment is becoming a frequent activity in the oil and gas industry as aging fields reach their productive economic limits. In fact, the cost of decommissioning the world’s 6500 offshore platforms is estimated at $29-40bn over the next 30 years.
In this fledgling service industry, the issue of a rig versus rigless approach is at the centre when planning activity. A rig-based approach uses mobile vessels or platform-based rigs to recover downhole equipment and plug the wells. Rigless alternatives however can be used for plug and abandonment operations to reduce expensive rig day costs.
The condition and type of well dictates or limits the potential use of rigless intervention. Costs can increase dramatically if unexpected conditions are encountered and a rig needs to be deployed to complete the abandonment.
Due to cost implications, operators are being driven to maximise oil recovery from existing wells. As well as optimising production, late life reservoir management includes evaluating aging wells which present complex issues. Safety, environmental and legislative requirements must also be considered when permanently isolating the reservoir.
It is therefore vital to effectively plan late-life asset operations to realise the full potential of a well prior to full decommissioning. Part of this planning involves forecasting, integrity assessment, well maintenance and interventions as well as data acquisition.
Prior to the removal of topside and seabed facilities, individual wells must be made safe, reservoirs isolated and permanent barriers installed throughout the wellbore. Permanent reservoir abandonment accounts for a significant proportion of overall abandonment costs.
A rigless approach which could include reservoir isolation, wellbore and wellhead remediation working towards a hydrocarbon free facility, can offer significant savings – in both time and cost.
Finally, when the well has been successfully abandoned, it is important to monitor the long term integrity of permanent barriers via well integrity software and wireless monitoring systems.
Expro have previously worked with major operators to develop engineered solutions for successful rigless abandonment – most notably with BP on the Miller Platform in the UK North Sea.
Combining proven technology and best practice, Expro performed pre-abandonment logging operations to establish well integrity prior to finalising the abandoned design for each well. The project included drift runs to ascertain through-bore access, and the acquisition of pressure and temperature data – crucial in defining the final well abandonment methodology.
The reservoir was first isolated through the installation of wireline set mechanical bridge plugs, run-though tubing and then set in the liner above the main reservoir. The subsurface knowledge of well construction and completion design provided valuable insight into potential hazards including the ‘eccentric’ casing.
Expro’s perforating gun strings were then developed to perforate the tubing and casing strings prior to cementing. This meant that the guns were orientated to sit on the low side and with adjusted charge penetration, could perforate selective tubing and casing. During the project, 235 runs were performed with 92% efficiency.
Well abandonment is the natural conclusion to the lifecycle of a well and in the current offshore environment, there is an ever expanding list of wells that require abandonment and decommissioning.
As well abandonment costs are not directly related generating revenue via production, it is important that the challenges associated with re-entry are understood, legislation is adhered to in order to safeguard the environment, and that technology-driven solutions offer cost-effective abandonment.
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