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.

Effect of temperature on the adsorption of water in porous carbons.

Abstract: We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298-600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption-desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption-desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure-density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor-liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid.

Analysis of Induced Seismicity for Stress Field Determination and Pore Pressure Mapping

Abstract: The focal mechanisms of some one hundred microseismic events induced by various water injections have been determined Within the same depth interval, numerous stress measurements have been conducted with the HTPF method When inverted simultaneously, the HTPF data and the focal plane solutions help determine the complete stress field in a fairly large volume of rock (about 15×106 m3) These results demonstrate that hydraulically conductive fault zones are associated with local stress heterogeneities Some of these stress heterogeneities correspond to local stress concentrations with principal stress magnitudes much larger than those of the regional stress field They preclude the determination of the regional stress field from the sole inversion of focal mechanisms In addition to determining the regional stress field, the integrated inversion of focal mechanisms and HTPF data help identify the fault plane for each for each of the focal mechanisms These slip motions have been demonstrated to be consistent with Terzaghi's effective stress principle and a Coulomb friction law with a friction coefficient ranging from 065 to 09 This has been used for mapping the pore pressure in the rock mass This mapping shows that induced seismicity does not outline zones of high flow rate but only zones of high pore pressure For one fault zone where no significant flow has been observed, the local pore pressure has been found to be larger than the regional minimum principal stress but no hydraulic fracturing has been detected there

Permeability of the Montney Formation in the Western Canada Sedimentary Basin: insights from different laboratory measurements

Abstract: Permeability is a critical parameter for evaluating unconventional shale or tight gas and oil reservoirs such as the Montney Formation in the Western Canada Sedimentary Basin. Permeability is also one of the most difficult parameters to be accurately and consistently determined in the laboratory and field as it is a second-order tensor and is dependent on many factors (e.g. test methods, sampling or testing scales, heterogeneities in fabrics, pore networks and pore-throat size distribution, transport mechanisms, pore pressure and confining stress). Although laboratory permeability measurement is limited to samples on the scale of centimeters or less, it provides valuable insights on hydrocarbon transmissibility of the reservoir matrix rock. Several methods have been developed for permeability measurements of unconventional reservoirs but each method has limitations and specific applications and often yields different permeability values even for the same sample. In this study, various permeability measurements on samples from 46 Montney wells in Alberta and British Columbia are examined. The permeability data set has primarily been obtained using transient pressure fall-off and pressure pulse-decay methods due to the relatively low permeability seen throughout the Montney Formation. A unique data set of permeability determined from canister desorption tests is also analyzed and compared to other permeability measurements. Direct permeability measurements obtained using different techniques are further compared with permeability values predicted using models based on mercury intrusion capillary pressure (MICP) data. The results show that the pressure fall-off (kpf) or GRI (kgri) permeability to helium correlates strongly with porosity. The kpf of crushed samples (20/35 meshes) ranges from 1e-3 md with porosity increasing from 3% to 13%. The pressure fall-off permeability (kpf) of plug samples is about two orders of magnitude higher than kpf of crushed samples. Pressure pulse-decay permeability (kpdp) under initial in-situ effective confining stress conditions is generally higher than the pressure fall-off permeability of crushed samples but lower than that of core plugs. Pressure pulse-decay permeability (kpdp) of visually intact samples varies over two orders of magnitude for a given porosity, which is likely a result of variable sample characteristics (e.g. with or without micro fractures, net confining stresses applied due to different sample depths and regional locations, mineralogy, amount and type of organic matter, and pore-throat size). The pulse-decay permeability of fractured samples varies widely over three orders of magnitude and is up to three orders of magnitude higher than kpdp of intact samples, indicating favorable enhancement of permeability by unpropped fractures in the Montney Formation. Out of eight MICP-based permeability models tested in this study, the Winland model (Kolodzie, 1980) and the modified Winland model by Di and Jensen (2015) predict the most comparable permeability to the pulse-decay permeability measured on intact samples, and the rest models also predict acceptable values if proper conformance and compaction corrections are done to MICP data. The permeability from these models has stronger correlations with pressure fall-off permeability measured on both intact and fractured core plugs than the other models. For the Montney Formation, the strong dependence of gas permeability on pore pressure and confining stress is also highlighted. The pore pressure and stress dependence of permeability is characterized by a modified Klinkenberg effects correction equation. Liquid permeability to decane or oil is about one order of magnitude lower than gas permeability under similar confining stresses. Variable permeability from different methods, even on the same Montney samples, underlines the limitations and specific applications of each method, and implies the strong heterogeneities in mineralogical fabrics, organic matter distribution and pore size distributions of the Montney samples. The implications of different laboratory methods for formation evaluation are further discussed, and a practical fit-for purpose approach is recommended for the measurement of permeability, which allows for a more rigorous evaluation of in-situ matrix permeability of the Montney Formation and other unconventional shale and tight reservoirs.