Home arrow News arrow Microbial Fouling of Oil and Gas Wells can Cause Plugging
Microbial Fouling of Oil and Gas Wells can Cause Plugging

Plugging means the well is losing its production because there is not enough conductivity into the well as a result of biofilms growth with subsequent encrustation and slime formations. It is a common experience for oil and gas wells to begin to lose their production capacity long before the reserves around the well have become exhausted.

The general thought of bacterial plugging around an oil or gas well would sound far fetched given the extreme environments that exist at those locations. However, what would appear extreme to humankind may not, in fact, be extreme for the bacteria that have an almost infinite ability to adapt as a community.

The bottom line for plugging is that liquid water has to be available for bonding into the complex slime structures to form the "living quarters" for the microbes involved in the plugging. Oil even if it has only 0.1% water content can be literally "mined" for the water by the bacteria that grow within the oil in complex structures. Under some circumstances, the bacteria also use the paraffins and anthracenes (P/A) from the oil to coat these complex structures. When this P/A builds up (like a black goop), the wells production shuts down. To illustrate this, an example is given from some oil well fields in western Saskatchewan, Canada. Here, the rods going down the wells clog up with the P/A. This black goop gets thicker and thicker until the well stops functioning. In some experiments ran in 1997 and 1998, there was a body of evidence that shows this P\A black goop was really supporting structures for bacterial growth.

The P/A problem
It was postulated that the P\A was simply a mass of paraffins and anthracenes that had become bioaccumulated around and within biofilms. To determine this, some P/A plugged 2" steel distribution pipe was treated with the surfactant CB-4. This surfactant has been used for years in the water well industry as a part of a technology to rehabilitate plugged water wells.

Image of Clean pipeCB-4 has a superior ability to attack and destroy the polymeric structures that support the biofilm particularly when the temperatures are elevated 40 or 50oC. The other factor is that the CB-4 becomes biocidal once the concentrations are raised above 0.7%. This technology therefore used a combination of heat and biocidal strength surfactant to attack the P\A black goop. At 57oC it was found that the P\A (left) become unstable and sheared away from the walls leaving the pipe clean again (right).

Image of Examine the potential to clean upTo examine the potential to clean up the rods coated with P/A from a well, two coated rods were treated. One (right) with just water that was heated up and the second with a CB-4 solution (left) heated at the same rate.

Image of The rod being heated with the CB-4 solution The rod being heated with the CB-4 solution discolored quickly and there was a significant swelling of the P/A compared to control. By 48°C, there was signs that the P/A was beginning to collapse and oil was oozing out from the black goop.

Image of Rods at 57oCBy the time the temperature reached 57°C, all of the black goop (P/A) appeared to have been stripped from the rods which were now clean. In field trials the treatment was so successful that the original manufacturers markings could be read.

Image of P/A had been stripped from the rodsWhat was surprising was the thick P/A plug that collected on the water lines as a thick disc. This disc was twice as thick where CB-4 had been used compared to the control indicating that the CB-4 had indeed increased the rate at which the P/A had been stripped from the rods.

Even more remarkable was the fact that on the underside of the plug, there was a mass of bacterial debris that had floated up the water column more slowly than the P/A and so collected on the underside. Photomicrography revealed structures that have also been seen in rusticles from the RMS Titanic and also from plugging water wells. Three basic structures were observed in the biological debris under the P/A disc. These included:

Image of Thread like structures
Image of Basic structures in the biological debris under the P/A disc

 

  • Thread like structures
  • Sheath (Tube-like) structures
  • Clusters of spherical (wax-like) structures

This work suggests that bacteria may play a major role in the plugging of oil wells. CB-4 and the application of chemicals with heat is patented as the blended chemical heat treatment (BCHT™, ARCC Inc., Daytona Beach, FL) and this research was conducted under the sponsorship of Nautilus Explorations and Associates Ltd., Regina, Saskatchewan, Canada.

Reference: www.dbi.ca