RIASSUNTO
Abstract
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.
Introduction
Nanofluids have a large range of potential applications in the oil and gas industry including damage remediation, EOR, and water recovery. Inherent challenges for oilfield chemistry include carrier water quality, bottom-hole temperature, high salinity formation water, varying geochemical lithology, and hydrocarbon compatibility. A variety of traditional fluids designed to overcome these challenges exist, however, often the price of gaining fluid stability is paid by compromising performance. NPD solutions also fall victim to these inherent fluid stability challenges. This work examines different methods for stabilizing NPD based fluids in order to maintain product integrity and performance.
Background
There are two types of fluids that are commonly referred to as nano fluids. Micellular solutions, which include surfactants and microemulsions, are soft particle nano fluids that can fluctuate between a micellular and free floating surfactant state. There are also hard nanoparticle solutions which are distinctly different in that they are solid colloidal particles, and even in a diluted state they maintain their structural integrity. Historically, nano micellular fluids (micro emulsions) have been used for EOR, improved flow back during hydraulicfracturing, and to alter reservoir wettability. Current research indicates promise for these applications utilizing hard particle nano fluids. However, in extreme environments the stability of hard particle systems can be compromised leading to agglomeration and subsequent damage to the reservoir. The consequences of a soft particle nano fluid destabilizing are less than the consequences of a hard nanoparticle system doing the same. For this reason the industry has been hesitant to employ hard particle systems in treatment additives. However, the potential positive impact of stable hard particle systems fueled our interest in researching the necessary components of hard particle stabilization.