The key to a successful abandonment is the selection of seals that will secure the well long after the abandonment is complete, reducing corporate liability and potential environmental impact. Traditionally elastomer and cement plugs have been used with varying degrees of success and reliability. Over time, they may deteriorate, particularly in corrosive environments, due to the materials from which they are manufactured. Conventional bridge plugs also have very small expansion ratios, limiting them for use in wells with restrictions. Alternatively, high expansion plugs, as inflatable packers, do not have the differential pressure capabilities required for many well abandonments, nor do they provide a gas tight seal.
BiSN has developed multiple tools utilizing their patented Wel-lok M2M™ technology to be used in well abandonment. These tools are known as the Wel-lok M2M TS™ (Tubing Seal) and Wel-lok M2M MXD™ (Maximum Drift). Both tools offer higher expansion rations than conventional bridge plugs and higher differential pressure ratings than inflatable packers, all while providing a V0 rated, gas tight seal that cement cannot provide. Though their designs are different, the proven BiSN technology behind them is the same.
BiSN Wel-lok M2M™ technology consists of utilizing a modified thermite heater to melt a bismuth based alloy that cools and expands on solidification. Some of the advantages of this technology are:
Seals wells with patented metal to metal technology
Heater uses a thermite chemical reaction that is non-explosive, no special licenses or handling permits required
Can be deployed on any standard wireline without special connection
Bismuth has a viscosity similar to water when melted in the liquid state allowing it to flow into the smallest of areas including cement micro-annuli
Bismuth has a density 10 times that of water allowing the alloy to displace wellbore fluids
Bismuth expands on solidification which creates a V0 gas tight seal in accordance with ISO 14310
Bismuth is non-corrosive, environmentally friendly and is not affected by H2S, CO2 or acid washes
The seal is created within minutes and ready to test within one hour
This Wel-lok M2M™ application was the first use of this new technology. It was developed to overcome the shortcomings of traditional methods of bridge plugs using cement. It quickly became apparent that this innovative technology is superior to the standard methods both when compared by speed and cost. It can be run on a wire line or a slick line and can pass through small restrictions such as damaged or crushed casing, yet still set the gas tight plug due to the larger drift than conventional bridge plugs.
In an effort to increase the expansion ratio beyond even that of the original TS without compromising pressure differential and gas tight sealing capabilities, BiSN developed the Wel-lok M2M™ MXD tool. The use of a bailer to carry the bismuth based alloy downhole in shot form allows for a smaller diameter tool to be run in hole while increasing the expansion ratio of the tool up to 3 times the tool OD.