The conceptual idea of chemical sand consolidation is to give the formation some additional residual strength in order to enhance the maximum sandfree rate (MSFR).
Sand production in weakly consolidated reservoirs will occur when stresses in the well/perforation tunnel walls are large enough to disrupt the binding between the individual sand grains. This will generate a plasticised layer of sand in the near well bore area. The layer will erode by the produced fluid and may be transported to the surface. The rate of erosion will depend on the residual strength of the plastified material and the fluid rate.
There is field evidence indicating a residual strength corresponding to the capillary force in water-wet sand to be sufficient in stopping or limiting the sand production substantially. Thus, only a small increase in residual strength of the plastified sand would make large contribution for enhancing the MSFR. This will have large economical implications in fields with wells controlled by MSFR.
As the criteria for strength are quite low, search for potential treatment chemicals could be done in areas completely different from the traditional chemicals used in sand consolidation. Three different chemicals have been investigated and one has been brought further for laboratory qualification and field use.
An important property is that the treatment system is oil soluble. In contrast to water soluble systems, it will not alter the relative permeability in the oil bearing zones, thereby reducing the risk of increased skin due to changes in saturation. This oil-soluble system will be beneficial in fields with low reservoir pressure. The method is employed by simple bull-heading and will have a kind of self-diverting property.
A team of engineers and scientists from different Statoil organizations were put on the job. New challenges regarding high water contamination, wells with difficult placements and zonal coverage, and a complex polymerization mechanism in the carrier fluid had to be solved. These experiences will be presented and discussed to gain valuable knowledge for future chemical sand consolidation operations.
In this paper, the experimental data and field applications will be presented. In one well, oil production was doubled as a result of the treatment.