Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells

Abstract

SbstractNowadays more and more unexpected uses for common materials have been observed, especially when recycled polymers are concerned. In this work, the viability for application of virgin and recycled poly(ethylene terephthalate) (PET vir and PET rec , respectively) and also poly(methylene oxide) (PMO) as granular materials (gravel) for gravel packing in sand control systems for unconsolidated sandstone reservoirs was studied. Polymer samples were tested in conditions similar to those observed in Campos Basin sandstone formations, in Brazilian Southwest (70 °C and 24.1 MPa). Samples were individually confined in roller cells with chemicals used in formation treatment: hydrochloric acid, pentapotassic DTPA salt (chelant Trilon CK) and in a mixture of diesel, xylene and butyl glycol. Mass loss was measured and the changes in molecular mass verified by size exclusion chromatography (SEC). Physical shape and grain size distribution were verified by scanning electron microscopy (SEM) and sieving tests. The effects over the polymeric gravel pack confinement resistance and permeability were evaluated using an API permeability cell. PMO proved to have a limited use, whereas PET rec and PET vir samples were not significantly affected, suggesting the viability of applying that recycled polymer in gravel packing for sand control in petroleum wells.

Degradation profiles of poly(methylene oxide) and poly(glycolic acid) for inflow control devices in oil wells

“…However, the DSC results indicate that the glass‐transition temperature of PGA (37 °C) was below the tests conditions, so the acceleration of PGA hydrolysis with temperature was not likely to have been especially related to the T g parameter in the performed tests . Similar effects were observed in previous studies that compared the behavior of PMO and PET exposed to HCl at lower temperatures and pressures with the same exposure time; this resulted intense degradation of the polyacetal and just mild hydrolysis of the polyester at relatively low temperatures …”

“…This structure suggested a relatively uniform and progressive degradation process at the polymer surface; this created a porous media made of partially attacked and probably more crystalline PMO . The hydrolysis process seemed to be dominated by the mass transport of HCl through the porous layer to the sample core; this favored the continuous degradation of the core surface and the growth of the porous layer thickness, despite its own hydrolysis…”

“…The polymer samples were exposed to chemical products in a cylindrical cell made of steel N316 and Hastelloy C276, with capacity for 443 mL, with prototypes developed by Petrobras . Cells, polymer samples and chemical solutions were preheated to the test temperature to reduce temperature variation during the experiments.…”

“…Each cell was filled with approximately 100 g of polymeric samples and the respective liquid media. After that, the cells were closed and pressurized to 41.4 MPa with 20 mL of mineral oil with manual pumps . Upon retrieval, samples exposed to 15% w/w HCl and a saturated 26% w/w NaCl neutral solution (NaCl brine) were washed with water over slow filtration with Vetec filter paper.…”

“…PMO is known for its mechanical resistance and sensitivity to strong acids such as HCl . It has enough resistance to brine and could probably be removed by acid hydrolysis during stimulation operations.…”