Study On The Water Control Effect And Mechanism Of Functional Nanofluids In Low Permeability Gas Reservoirs

Water control is needed for low permeability gas reservoir because production of gaswell declined rapidly by water breakthrough, however, normal polymer system can hardlymeet the need of low permeability gas reservoir to water control. Nanofluid is a newfunctional fluid with micro particle and wide application scope, and it can change theproperties and microstructure of rock surface by adorption to effect water and gas flow. In thework, a functional nanofluid composed of elastic particles and with good stability anddispersibility is prepared, and the spreadability and wettability are investigated, and its watercontrol performance and mechanism are analyzed, providing important practical support forimproving the water control and stimulation effect of low permeability gas reservoir.Based on amino-silicon oil (ASO) as the main raw materials, the reasonable formula offunctional nanofluid was optimized by the single factor and orthogonal test. The mediumparticles size of the nanofluids was30.2nm~84.2nm, well-metched with pore throat oflow-permeability rock. Infrared spectrum confirmed that amino group and Si-CH3existed innano-particles. Scanning electron microscope (SEM) showed the rock surface micro structure waschanged by nanofluid, becoming smoother and uniformer. X-ray photoelectron spectroscopy (XPS)analysis indicated that naao-fluid absorbed in rock surfaces, changing its chemical composition; Contactangle measurement suggested that ASO nanofluid was hydrophobic and the hydrophobic Si-CH3groupsprojected outward into pore, while Si-O dipole bonds as well as the polar amino groups pointed to the rockinterface. The conclusion that0.3%~0.7%was the proper nanofluid carrier cincentration wasdrawn from all the above results. Functional nanofluid can effectively inhibit the coresspontaneous imbibition, and water absorption decreased by27.2%to31.3%of the coretreated by nanofluid. The nanofluid normalized fluid resistance ratio (NFRR) was1.68~2.28with different nanofluid concentrations and different core permeabilities, and not affected by temperature under80℃.After continuous waterflood8pore volumes (PV) with brine ofdifferent salt concentrations water phase residual resistance factor (RRF) of the core treatedby nanofluid remained stable at2.0or above, showing good salt tolerance and ablationresistance. Relative permeability experiment indiceted the functional nanofluid reducedirreducible water saturation of the core, and made it easier and more efficient to displacewater in the core by gas flooding; and displacement efficiency was higher with smallerpermeability core under the same nanofluid concentration, demonstrating that the nanofluidwas more appropriate for core water control with lower permeability.