Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Method and apparatus for drilling a borehole into a subsea abnormal pore pressure environment

Abstract: An apparatus for controlling a subsea borehole fluid pressure is proposed for use with a conductor casing (110) positioned below the mudline (57) and within a normal pore pressure environment. The apparatus includes a pump (53) for moving a fluid through a tubular into a borehole. The fluid, before being pumped, exerts a pressure less than the pore pressure of an abnormal pore pressure environment (10). The fluid in the borehole is then pressurized by the pump (53) to at least a borehole pressure equal to or greater than the pore pressure of an abnormal pore pressure environment (10). A pressure housing assembly (15) allows for the drilling of a borehole below the conductor casing (110) into an abnormal pore pressure environment (53) while maintaining the pressurized fluid between a borehole pressure equal to or greater than the pore pressure of the abnormal pore pressure environment (10), and below the fracture pressure of the abnormal pore pressure environment (10).

Porosity and permeability evolution during hot isostatic pressing of calcite aggregates

Abstract: Porosity, permeability, and storativity were measured during isostatic hot-pressing of fine-grained calcite aggregates at temperatures of 633 to 833 K, confining pressures of 200 to 300 MPa, and argon pore pressures of 100 to 250 MPa. The progressive changes in total porosity were measured in situ by monitoring the sample length changes. The connected porosity and the permeability and storativity were measured in situ by incrementing and oscillating pore pressure techniques, respectively. In a given test, there was a decrease with time in the rate of reduction of porosity, the rates being higher at higher temperature and effective pressure. The permeability k was nonlinearly related to the total porosity ϕ in the form k ∝ ϕn. The exponent n was approximately equal to 3 and thus consistent with the prediction of the “equivalent channel” model, in the range of porosity from 0.18 down to 0.07. Below 0.07, n became much larger (around 14), an effect that can be attributed to loss of connectivity and which is qualitatively similar to that observed by Bernabe et al. [1982] in post-hot-pressing measurements. However, a cube law continues to apply below 0.07 total porosity if the permeability is related to the connected porosity itself. The storativity is also nonlinearly related to the porosity. Model analyses of the permeability and storativity results indicate both that the pore apertures decrease and that the pore shapes become more equant as the porosity decreases. The marked downturn in the permeability-porosity relationship at total porosities below 0.07 appears from microscopical observation to correspond to a change in pore geometry from largely connected, irregular pores between grains to isolated, tubular pores at junctions of several grains. Application of the “Swiss-cheese” continuum percolation model indicates a percolation threshold of about 0.04 porosity. Microstructural evidence, the apparent activation energy for densification, and the stress dependence of densification rate suggest that porosity reduction has occurred mainly by dislocation creep.

Comparison of methods for conducting marine and estuarine sediment porewater toxicity tests—extraction, storage, and handling techniques

Abstract: A series of studies was conducted to compare different porewater extraction techniques and to evaluate the effects of sediment and porewater storage conditions on the toxicity of pore water, using assays with the sea urchin Arbacia punctulata. If care is taken in the selection of materials, several different porewater extraction techniques (pressurized squeezing, centrifugation, vacuum) yield samples with similar toxicity. Where the primary contaminants of concern are highly hydrophobic organic compounds, centrifugation is the method of choice for minimizing the loss of contaminants during the extraction procedure. No difference was found in the toxicity of pore water obtained with the Teflon® and polyvinyl chloride pressurized extraction devices. Different types of filters in the squeeze extraction devices apparently adsorbed soluble contaminants to varying degrees. The amount of fine suspended particulate material remaining in the pore water after the initial extraction varied among the methods. For most of the sediments tested, freezing and thawing did not affect the toxicity of porewater samples obtained by the pressurized squeeze extraction method. Pore water obtained by other methods (centrifugation, vacuum) and frozen without additional removal of suspended particulates by centrifugation may exhibit increased toxicity compared with the unfrozen sample. The toxicity of pore water extracted from refrigerated (4°C) sediments exhibited substantial short-term (days, weeks) changes. Similarly, sediment pore water extracted over time from a simulated amphipod solid-phase toxicity test changed substantially in toxicity. For the sediments tested, the direction and magnitude of change in toxicity of pore water extracted from both refrigerated and solid-phase test sediments was unpredictable.

Pore space hydrate formation in a glass bead sample from methane dissolved in water

Abstract: [1] An experimental device designed and developed to grow methane hydrate in the pore space of a sediment was successfully used with a glass bead sample. The underlying idea for the experiment is that methane dissolved in water is transported with upward moving fluids from its place of origin at greater depths to formations within the hydrate stability field where the methane is removed from the pore water to form hydrate. This process is simulated in a closed loop flow system where methane charged water from a gas/water reservoir outside the hydrate stability field is pumped into the sediment sample cell in the stability field for methane hydrate. The fluid depleted of methane, then flows back into the gas/water reservoir to be recharged with methane. When the experiment was terminated due to blockage of flow by hydrate formation, hydrate saturation was about 95%.