Nanoparticle dispersions (NPDs) are an emerging new technology in the oil and gas industry which can be applied to EOR, well remediation, and formation damage removal to stimulate hydrocarbon production using the unique properties that colloidal particles possess. Nanoparticles have a high surface area to volume ratio allowing a greater efficiency for chemical interactions to occur. However, nanoparticle dispersions are often difficult to stabilize in harsh downhole environments. The dispersion can quickly become unstable and agglomerate when the fluid is subjected to changes in pH, or encounters increased salinity and/or temperature. Agglomeration renders the fluid ineffective, and at worst can cause severe damage to the formation. The development of highly concentrated nanoparticle dispersions stable in high TDS brine at high temperatures has been achieved and verified in the laboratory with imbibition tests and dynamic core flow experiments.
NPDs can be stabilized in the reservoir by altering charge density, hydrodynamic diameter, and the zeta potential of the particles. This is accomplished by surface modification, as well as with the addition of stabilizing chemistry.
This paper presents solutions to the destabilizing elements encountered in the reservoir, that until now have inhibited the downhole utilization of nanoparticle dispersions. Stability research of NPD fluids in brines empirically illustrates that by chemically modifying the particle surface and the surrounding aqueous environment, the fluids will remain properly dispersed and active in destabilizing bottomhole conditions. This will further pave the way for industry research into new applications of nanoparticle based fluid systems.
Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE International Oilfield Nanotechnology Conference held in Noordwijk, The Netherlands, 12-14 June 2012. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited.
Hydraulic fracturing of oil and gas wells requires high volumes of water. Often these waters originate from rivers, lakes, ponds, and recovered water from previous fracturing treatments. These waters are often infested with aerobic and anaerobic bacteria that can cause multiple problems. These include degradation of fracturing chemicals, down-hole corrosion, biological-based H2S generation, and down-hole flow-impairment due to slime producing bacteria. Historically, these waters have been treated with biocides such as tetrakis (hydroxymethyl) phosphonium sulfate (THPS), glutaraldhyde or quaternary ammonium-based surfactants. Lately, oxidizing biocides such as peracetic acid, chlorine dioxide and hypochlorous acid have been used as environmental alternatives.
Recently, tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (Dazomet) has been used as a biocide with good results in the Barnett, Marcellus, Eagle Ford and Haynesville gas shale basins in the US. This biocide is effective against most aerobic and anaerobic bacteria encountered in water sourced for fracturing applications. Although not a fast-killing biocide, it is effective for long-term maintenance of the formation and well with loadings normally about 0.4 L/m3 of 24% active solutions.
Further investigation has now discovered that the combination of this biocide with others has significantly reduced necessary loadings of these biocides to values less than 0.2 L/m3. These Dazomet-combinations also tend to show much higher degrees of efficacy, showing superior bacteria management over the single or oxidizing biocides. This enhanced performance also allows for reduced chemical exposure to the environment. The performance of these Dazomet biocide-combinations and field trials will be presented and discussed.