Permanent Abandonment of a North Sea Well Using Unconsolidated Well Plugging Material

Abstract

The traditional Plug and Abandonment (P&A) method of exploration wells in the North Sea is to set a series of cement plugs to isolate the pressurised zones from each other and from surface. This paper describes a North Sea P&A field case. In this case an alternative method with a Bingham-plastic unconsolidated plugging material with high solids concentrations was used. This alternative method addresses well integrity issues like those caused by shrinking of cement or gas migration during setting, fracturing after setting, or long term degradation by exposure to temperature and chemical substances in the well.The gas tight Well Barrier Element (WBE) described here does not set up after placement and does not shrink. Furthermore it cannot fracture even when shear forces exceed its strength. When this happens the material floats and shear forces are reduced below yield strength causing the plug to reshape. Since this is a purely mechanical process the transition between solid and fluid phase is repeatedly reversible forever.The plug is thermo-dynamically stable since its sealing property is decided by the solids particle size distribution and bound water only. The closely packed particles and absence of free water means that the entire column is kept homogenous and no internal re-distribution of particles may occur. Hence, the permanent gas-tight barrier will prevent influx through the well bore forever.In the field case a successful implementation of the technology was obtained. The field case shows how the fast and efficient placement of the plug contributes to overall cost reduction. The paper explains how the well barrier element complies with governmental permanent P&A requirements and the operational procedures are also presented in some detail.

Preventing the Loss, Improving the Properties of the Circulating Material to Seal Fractures and a Depleted Section of the Well

“…Other testing equipment has been developed to evaluate the sealing efficiency of LCM treatments in sealing permeable/impermeable depleted/fractured formations. [6,14,[20][21][22] Both sand pack and total LCM concentration were found to have a significant effect on the sealing efficiency. It was also concluded that the fluid loss volume is not a good parameter to measure the sealing efficiency of LCM treatments.…”

“…However, this classification does not explain the mechanisms at which losses occur; resulting in appropriate treatments. [3,9,[16][17][18][19][20][21][22] By identifying the loss severity, proper remedial action takes place to mitigate or stop the losses. Seepage and partial losses are often cured using conventional lost circulation materials; however, when it comes to severe or total losses, special treatments are used.…”

Experimental investigation of fracture width limitations of granular lost circulation treatments

“…Other solutions that require more time for preparation and placement are used when severe losses are encountered such as cement (Messenger and McNiel 1952;Messenger 1981;Morita et al 1990;Fidan et al 2004), chemically activated cross-linked pills (CACP) (Bruton et al 2001;Caughron et al 2002), cross-linked cement (Mata and Veiga 2004), deformable-viscous-cohesive systems (DVC) (Whitfill and Wang 2005;Wang et al 2005Wang et al , 2008, nanocomposite gel (Lecolier et al 2005), gunk squeezes (Bruton et al 2001;Collins et al 2010), and concentrated sand slurries (Saasen et al 2004(Saasen et al , 2011.…”