A Silicate Based Process for Plugging the Near Well Bore Formation

International audienceA method for treating the surrounding of a well using a reactive suspension is studied, using silicate based solutions. They present the following key qualities: high performance, long term chemical stability, good injectivity, little environmental impact. We present an experimental investigation of the precipitation of commercial low-cost potassium silicate solutions, using a weak acid to lower the pH. Experiments were performed between 20°C and 60°C, by adding a non-hazardous acidic compound to the silica based solution. Bulk gelation times were estimated between a few minutes to 4 days. A coreflood injection experiment was then performed on an analog sandstone sample, representative of CO 2 formation, by using an optimum mixture with viscosity close to water. After a few days, a breakthrough experiment was performed by increasing gradually the differential pressure across the sample. Preliminary results indicate a very large strength of the order of 600 bar/m

Influence of hydrothermal alteration on the elastic behaviour and failure of heat-treated andesite from Guadeloupe

International audienceStudies on the mechanical behaviour of rocks, including volcanic rocks, usually seek for unaltered and simple material: rocks without macroscopic defects. However, volcanic rocks are often naturally altered due to the circulation of hydrothermal fluids. This alteration may influence mechanical and physical properties. Here, we study the effect of hydrothermal alteration on the elasticity and failure properties of andesite. A homogeneous block of natural andesite was retrieved from a quarry. Three samples were first heat-treated and then artificially altered at different temperatures by soaking them in a brine for one month at a pressure of 20 MPa and temperatures of 80, 180 and 280 • C. Heat-treated unaltered and altered samples were hydrostatically loaded up to 50 MPa and unloaded, while strains and elastic wave velocities were recorded. Samples were also triaxially deformed to failure at a constant strain rate and a confining pressure of 15 MPa. At ambient pressure, increased alteration temperature resulted in increased wave propagation velocity, thus increased dynamic elastic moduli. During hydrostatic loading, volumetric deformation at a given effective pressure decreased with alteration temperature denoting increased static elastic moduli. During triaxial loading, the degree of alteration decreased elastic compaction and peak stress at failure. These observations are interpreted as the result of microcracks in-filling by alteration minerals, and in particular smectite, a swelling-clay mineral with a low friction coefficient. The mechanical behaviour of a volcanic rock subjected to triaxial loading was modelled with a damage model based on crack propagation from pre-existing flaws. A decreasing friction coefficient within the flanks of the cracks leads to a decrease of the peak stress and explains the experimental observations

The effect of silica coatings on the weathering rates of wollastonite (CaSiO3) and forsterite (Mg2SiO4): an apparent paradox?

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