Showing papers on "Effective porosity published in 1996"
TL;DR: In this article, a new MRIL application was implemented based on the industry-standard MRIL logging tool by incorporating twice the standard sampling rate and an acquisition scheme designed to boost the signal-to-noise ratio of very fast decay modes, the tool is sensitive to transverse decay components as short as 05 ms.
Abstract: Pulsed nuclear magnetic resonance (NMR) logging has until now been limited to measurements of capillary bound water and of free fluids, the sum of which is considered the effective porosity of rock Clay-bound water and fluids trapped in micropores generally exhibit NMR relaxation times too fast to be detected, given the echo sampling rates and sensitivity limitations of current state-of-the-art NMR logging tools Core studies performed on representative clay samples confirm a linear relationship between the transverse relaxation time T 2 and the water content At 1 MHz, clays with the largest specific surface areas (smectites) exhibit T 2 's in the sub-millisecond range; illites have characteristic T 2 's of one millisecond, and kaolinites, having the smallest specific surface areas, relax with T 2 's in the range of ten milliseconds A new MRIL application was implemented based on the industry-standard MRIL logging tool By incorporating twice the standard sampling rate and an acquisition scheme designed to boost the signal-to-noise ratio of very fast decay modes, the tool is sensitive to transverse decay components as short as 05 ms During a field test campaign, the tool demonstrated the feasibility of simultaneous acquisition of effective porosity and total porosity Neither porosity measurement requires prior knowledge of rock matrix properties In shaly sands, the difference between MRIL total porosity and effective porosity can be interpreted as the clay-bound water volume, relevant as the clay correction term for resistivity analysis
86 citations
TL;DR: In this article, the authors compare profiles of reported and corrected porosities for smectite-rich Barbados abyssal plain and accretionary wedge sediments from Ocean Drilling Program Leg 110, Sites 671 and 672.
Abstract: Porosity is a fundamental parameter that must be correctly determined in order to relate physical property, hydrologic, and chemical flux studies to natural systems. Traditional porosity determinations generated from physical property or seismic data can greatly overestimate the true porosity of sediments in which hydrated minerals such as smectite are abundant. To produce a true porosity distribution such data must be corrected to account for the H 2 O residing in smectite interlayers which can make up to 25% of the total hydrated mineral mass. Such H 2 O is easily removed from the mineral by oven drying and/or exposure to low humidities. Standard physical property measurements can be corrected, provided the weight percent smectite in the sediment is known and the interlayer H 2 O content of the mineral can be estimated. We illustrate the significant consequences of this correction by comparing profiles of reported and corrected porosities for smectite-rich Barbados abyssal plain and accretionary wedge sediments from Ocean Drilling Program Leg 110, Sites 671 and 672.
84 citations
TL;DR: In this article, a combination of tension infiltrometers and dye tracers was used to investigate the extent and nature of water movement at low tensions through the well-structured subsoil of Ships clay (very-fine, mixed, thermic, Chromic Hapluderts).
Abstract: A combination of tension infiltrometers and dye tracers was used to investigate the extent and nature of water movement at low tensions through the well-structured subsoil of Ships clay (very-fine, mixed, thermic, Chromic Hapluderts). Dyed-water was placed in the reservoirs of tension infiltrometers and allowed to infiltrate into the soil under seven tension sequences to separate different size pores effective in transmitting water. Flow patterns were then revealed by exposing dye-stained soil after each infiltration sequence. The results showed that, when water was supplied at tensions <24 cm, the effective porosity (fraction of pores that were stained) in this subsoil was primarily macro- and mesoporosity, which constituted about 5% of the total soil porosity. Under flow at 0-cm tension, macropores =0.5 mm and mesopores from 0.06 to 0.5 mm (radius for cylindrical pores or width for planar pores) contributed about 89% and 10% of the total water flux, respectively. Micropores <0.06 mm contributed the remaining 1% of the total water flux, but constituted about 95% of the total soil porosity. Dye stain patterns showed that water flow at tensions <24 cm in this structured subsoil was primarily controlled by slickenside fissures, root channels, and vertical fissures. The nonuniform flow pattern caused water to penetrate to depths as much as 11 times deeper than expected from a Green-Ampt model that considered the total soil porosity to be active in transmitting water. By replacing the air-filled porosity in the Green-Ampt model with the active macro- plus mesoporosity, calculated wetting front depths were close to the observed maximum dye depths.
76 citations
TL;DR: In this article, the porosity and permeability of planar and nonplanar dolomite were determined using helium porosimetry and gas permeability, respectively, and the pore throat geometry was evaluated using capillary pressure curves and s anning electron microscope (SEM) examination of pore casts.
Abstract: Two basic textural types of dolomite exist: (1) planar dolomite, which forms in both shallow and burial diagenetic environments; and (2) nonplanar dolomite, which develops at temperatures in excess of 50°C in the burial environment by dolomitization of limestone or neomorphic recrystallization of preexisting dolomite. Variation in dolomite texture is the result of variation in the diagenetic history of the rock unit. Cambrian-Ordovician dolomites were collected from core and outcrop throughout southeastern Missouri. Effective porosity and permeability were determined using helium porosimetry and gas permeability. Total porosity and texture type were determined from thin-section analysis. Pore throat geometry was evaluated using mercury capillary pressure curves and s anning electron microscope (SEM) examination of pore casts. Two porosity-permeability populations exist for planar dolomite: (1) planar-e (euhedral) dolomite, where permeability strongly varies with porosity; and (2) planar-s (subhedral) dolomite, where permeability is lower than in planar-e dolomite and does not increase as rapidly with increasing porosity. In planar-e dolomite, capillary pressure data and SEM pore cast analysis indicate uniform pore throat sizes and well-interconnected pore systems. Uniform throat sizes and well-connected pore systems do not exist in planar-s dolomite. This most likely is due to continued cementation during diagenesis. Nonplanar dolomite shows no significant correlation between permeability and porosity. Capillary pressure curves and SEM examination of pore casts of nonplanar dolomite indicate nonexistent to very poorly interconnected pore systems and large pore to throat ratios. The petrophysical properties of dolomite petroleum reservoirs and aquifers vary depending on the petrographic texture of the dolomite. Understanding diagenetic history, and crystal textures that may result because of various diagenetic conditions, can be a predictor of petrophysical properties of dolomite reservoirs.
44 citations
TL;DR: In this paper, a model for interpreting diffusional transport in porous geological materials is developed based on a laboratory method described in a companion paper by which radial diffusion from or into a cylindrical reservoir in a core-sized sample is measured.
Abstract: A model for interpreting diffusional transport in porous geological materials is developed. The model is based on a laboratory method described in a companion paper [van der Kamp et al., this issue] by which radial diffusion from or into a cylindrical reservoir in a core-sized sample is measured. The model accounts for radial diffusion, mass balance in the reservoir, linear adsorption, decay or transformation, and periodic abstraction of samples. The model is derived using the Laplace transform method for both finite and semi-infinite domains. For conditions where solute concentrations equilibrate (i.e., in finite diameter samples), a simple expression is derived that can be used to interpret the results for effective porosity and a retardation factor. It is demonstrated that the method can provide independent measures of the effective diffusion coefficient, adsorption, and effective porosity when the results are interpreted using the model. Several real and hypothetical diffusion experiments are presented to illustrate the use of the model.
42 citations
TL;DR: In this article, an approach to model the detailed 3D distribution of lithofacies and porosity constrained to seismic data is presented, which explicitly honors the relatively coarse vertical resolution, from a reservoir modeling perspective.
Abstract: An approach to model the detailed 3-D distribution of lithofacies and porosity constrained to seismic data is presented. The simulated annealing-based approach explicitly honors the relatively coarse vertical resolution, from a reservoir modeling perspective, and the less than perfect correlation of seismic with lithofacies proportions and effective porosity. Conventional geostatistical procedures such as co-located cokriging or the Markov-Bayes model assume that the seismic attribute has the same volumetric support as the geological modeling cells. The conventional techniques are reviewed, details of the proposed methodology are presented, and a reservoir case study is shown.
37 citations
TL;DR: The porosity in the waste cork industry and when such waste product had been composted during 4, 7, and 10.5 months was determined and the ash content was highly correlated with the particle density of the finely ground material.
Abstract: The structure of cork (Quercus suber L.) bark presents a series of characteristics, suggesting that internal porosity is partly occluded. This study determined the porosity in the waste cork industry (C) and when such waste product had been composted during 4 (CC-4), 7 (CC-7), and 10.5 months (CC-10.5). The particle density of the intact and finely ground material differed significantly in all particle size ranges larger than 0.5 mm. The porosity of the cork substrates ranged from 80% to 94% of the total volume, according to granulometry and the degree of decomposition. However, large particles and less decom- posed material with a high porosity had up to 10% of the total volume as occluded pores. The material's effective porosity varied slightly between the various particle sizes and degrees of decomposition, which ranged between 80% and 89%, having an average value of 85%. The ash content was highly correlated with the particle density of the finely ground material. Nevertheless, and due to occluded porosity, we cannot estimate the "effective porosity" from the ashes; therefore, we must resort to techniques that involve the displacement of a fluid, such as liquids or gas pycnometry or submersion.
14 citations
01 Apr 1996
TL;DR: In this article, the applicability of several petrophysical techniques for the determination of effective porosity of fine-grained siliciclastic rocks was evaluated using data from the Oak Ridge Reservation (ORR).
Abstract: Effective porosity (specifically referring to the interconnected pore space) was recently recognized as being essential in determining the effectiveness and extent of matrix diffusion as a transport mechanism within fractured low-permeability rock formations. The research presented in this report was performed to test the applicability of several petrophysical techniques for the determination of effective porosity of fine-grained siliciclastic rocks. In addition, the aim was to gather quantitative data on the effective porosity of Conasauga Group mudrock from the Oak Ridge Reservation (ORR). The quantitative data reported here include not only effective porosities based on diverse measurement techniques, but also data on the sizes of pore throats and their distribution, and specimen bulk and grain densities. The petrophysical techniques employed include the immersion-saturation method, mercury and helium porosimetry, and the radial diffusion-cell method.
9 citations
01 Jan 1996
TL;DR: In this article, an integrated algorithm is provided to calculate the accurate value of shale volume from different shale indicator tools and thereafter the effective porosity is determined, and the hydrocarbon saturation profiles have been calculated using a laminated shale model.
Abstract: One of the most controversial problems in formation evaluation is the shale effect in reservoir rocks. An accurate determination of formation porosity and fluid saturation in shaly sand is subjected to many uncertain parameters, all are induced by the existence of shale in pay formation. This paper presents a comprehensive approach for handling this problem of shaly sand. An integrated algorithm is provided to calculate the accurate value of shale volume from different shale indicator tools and thereafter the effective porosity is determined. For different shale models, the water saturation and movable oil profiles are produced. The hydrocarbon saturation profiles have been calculated using a laminated shale model . Applying the present technique, two actual cases were processed, where shale volume, hydrocarbon saturation and movable hydrocarbon are determined directly for given sets of data. The validity of the values of petrophysical parameters determined by the presented integrated approach is confirmed through the comparison with measured petrophysical parameters on collected core samples from shaly sand sections from the same wells.
8 citations
TL;DR: The sandstone reservoirs in the Sava depression lost their primary porosity through compaction and cementation in the carly stage of diagenesis as mentioned in this paper, which created reservoirs that were composed mainly of secondary porosity, but some zones of these reservoirs were destroyed by precipitation of late Ferich calcite and dolomite cement.
Abstract: The sandstone reservoirs in the Sava depression lost their primaryporosity through compaction and cementation in the carly stage ofdiagenesis. Dissolution events enlarged porosity and created reservoirs that were composed mainly of secondary porosity, but some zones of these reservoirs were destroyed by precipitation of late Ferich calcite and dolomite cement. Three groups of sandstones differing in reservoir quality are identified - highly porous litharenites, litharenits with intermediate porosity, and weakly porous, highly cemented litharenites. The type of porosity depends on the clay content in sandstones, which is the result of water energy and depositional environment.
6 citations
TL;DR: In this paper, the tritium concentration of sampled groundwater was analyzed using a three-dimensional groundwater-flow and advection-dispersion code based on the finite element method.
Abstract: Effective porosity value was analyzed from the tritium concentration of sampled groundwater using a three-dimensional groundwater-flow and advection-dispersion code based on the finite element method. The effective porosity value was about 10%. Porosity values measured from core samples were 7–15%. The groundwater flow velocity estimated from the tritium concentrations was about 1 × 10−5 cm s−1. Therefore, during the low groundwater flow velocity condition, effective porosity and porosity values were the same. At the same test site, a 0.48% effective porosity value, determined by another tracer test injecting Br− solution into the aquifer during groundwater level change, was smaller than the porosity value when the flow velocity was 1.8×10−2 cm s−1. Thus the effective porosity value is concluded to be due to groundwater flow velocity. The specific yield value was calculated to be 0.6% by the total volume of tunnel seepage water and the total volume of the rock unsaturated during tunnel construction. However, as pore water continued to be drained after the groundwater level change was completed, the specific yield value became larger than 0.6%. Thus specific yield value is concluded to be due to drainage time.
TL;DR: The MRI irreducible water volume measurement was unaffected by light hydrocarbons and thus found to be a powerful tool for evaluating low-resistivity zones when integrated with conventional log analysis.
Abstract: This paper presents a case study from an offshore Gulf-of-Mexico field that illustrates some of the advantages and limitations of new gradient NMR (MRI) well log interpretation methods for evaluating light hydrocarbon-bearing reservoirs. In one well, analysis of dual-wait time MRI log data using the differential spectrum method reveals the presence of free gas in shaly sand reservoirs that was invisible by the standard neutron-density cross-over method due to shaliness effects on the nuclear logs. Well test results have confirmed the MRI log interpretation in the one zone in this well that has been perforated to date. Effective porosity and free fluid volume readings were artificially suppressed due to the well-known effects of low hydrogen density and long T 1 relaxation times characteristic of light hydrocarbons. However, the MRI irreducible water volume measurement was unaffected by light hydrocarbons and thus found to be a powerful tool for evaluating low-resistivity zones when integrated with conventional log analysis.
TL;DR: The use of petrophysical evaluation models that rely on predicting mineral composition of reservoir rocks is becoming more prevalent in the oil industry as mentioned in this paper, and a number of techniques have been proposed to obtain maximum value out of these tools by providing all possible core data as input to an integrated evaluation using total porosity.
Abstract: Use of petrophysical evaluation models that rely on predicting mineral composition of reservoir rocks is becoming more prevalent in the oil industry. Evaluation tools such as Schlumberger's Elan or Mincom's Geolog/Multimin allow prediction of variability in reservoir composition and petrophysical parameters. These are particularly useful in cases where assuming constant lithology and petrophysical parameters can result in significant variation in well evaluation, hydrocarbons in place estimates and volumetric reserves. Mineralogical evaluations have historically been questioned in cases where evaluated effective porosity differs significantly from core total porosity. Effort has been made over the last year to obtain maximum value out of these tools by providing all data as input to an integrated evaluation using total porosity. The key feature is incorporating all possible core data for calibration purposes, including:using all core total porosity, permeability and capillary pressure data, where available, to calibrate modelsusing petrological data to obtain mineral-by-mineral calibration of rock compositionoverlaying a regional total porosity curve in the absence of core data to provide a quality control on evaluated total porosity. The success of such approaches is demonstrated in an offshore WA greensand and an Eromanga shaly sand. These methods are now used on a routine basis for detailed field studies and hold the promise of both permeability evaluation and improved evaluation of wells with restricted logging suites.
TL;DR: In this paper, the relationship between velocity and effective porosity with the effects of the clay minerals was discussed and the area of the data was determined by two equations: one equation expressed the relation between the velocity and porosity for clean sandstone and another expression expressed the relations between the velocities of 100% clay minerals in the pore space.
Abstract: In this paper, we discussed the relationship between velocity and effective porosity with the effects of the clay minerals. The relation between velocity and porosity is shown on the crossplot (Fig. 1); the velocity generally increases as the porosity decreases but the data are so dispersed that we are not able to come up with an equation that exhibits strong linear relation between velocity and porosity. We supposed that the existence of clay is the cause of this dispersion. We determined the area of the data by two equations: one equation expresses the relation between the velocity and porosity for clean sandstone and another expresses the relation between the velocity and effective porosity of 100% clay minerals in the pore space. The effective porosity is moved between two lines.Using the technique of well log interpretation, we estimate the volume of bound water and show the effects of clay minerals for the relationship between velocity and effective porosity.The velocities of shale show the effects of velocity reduction due to clay minerals.
01 Jan 1996
23 Sep 1996
TL;DR: In situ geoacoustic data collected from the Dry Tortugas and Marquesas as part of the Coastal Benthic Boundary Layer Special Research Program using a new suite of in situ probes developed by the Naval Research Laboratory agree well with predicted values of shear wave velocity.
Abstract: In situ geoacoustic data collected from the Dry Tortugas and Marquesas as part of the Coastal Benthic Boundary Layer Special Research Program using a new suite of in situ probes developed by the Naval Research Laboratory agree well with predicted values of shear wave velocity. When compared with data from a number of siliciclastic environments, it is evident that for a given porosity, carbonate sediments always have a higher shear wave velocity than siliciclastic sediments. This is because the effective porosity in carbonate sediments is interparticle porosity, only part of the bulk porosity but in siliciclastic sediments, the measured bulk porosity and interparticle porosity are the same.