摘要
Due to the high demand for plugging and abandonment(P&A)of wells,concerns have been raised regarding existing solutions in terms of their capability of long-term sealing-such as cement,which is the only qualified barrier material for downhole plugs.Therefore,alternative materials that can ensure better long-term sealability than cement are sought.Metal plugs have been actively researched and tested in the field,especially the ones made of bismuth alloys,due to their characteristics of impermeability and expansion upon solidification.This work focuses on the numerical modeling of bismuthtin plugs for potential field applications.Bismuth is unique due to its expansion upon solidification,a beneficial characteristic that achieves better sealability.However,due to the low melting point of bismuth alloys,they can be susceptible to creep and aging effects if the plug is placed in high-temperature wells.In this work,the mechanical behavior of the eutectic bismuth-tin alloy is modeled using commercial finite element analysis software and then validate this model with available laboratory data.Such modeling includes expansion,creep,and aging effects of the alloy;expansion data is taken from manufacturers,while creep and aging use data found in the literature.The sealability is then checked by carrying out numerical push-out tests.The results obtained do not agree completely with laboratory data,especially at lower temperatures,highlighting the uncertainties in the input data used,especially on creep parameters.The conclusion from this validation procedure is that it is fundamental to acquire good input data for the model to match experimental results accurately.In particular,the creep parameters-for whichever fitting model is adopted-and the friction coefficient are the major sources of uncertainties,while being the main drivers of the sealability mechanism of metal plugs.This leads to a recommendation for thorough sample testing,under test conditions that replicate actual field conditions to obtain more accurate parameters.Further,this work contributes by providing a working numerical model that can be used to simulate different laboratory and field scenarios,thus assessing the sealing capabilities of any bismuth-based alloy.
基金
funded by the Research Council of Norway
The authors acknowledge the Research Council of Norway(RCN)for financing the Centre for Research-based Innovations"SWIPA Centre for Subsurface Well Integrity,Plugging and Abandonment",RCN project no.309646,for which the work has been carried out
The center is also financed by the operating companies AkerBP,Equinor ASA,and Wintershall Dea Norway,and includes in addition more than 20 in-kind contributing industry partners.
