Showing papers on "Effective porosity published in 2012"

Estimation of kerogen porosity in source rocks as a function of thermal transformation: Example from the Mowry Shale in the Powder River Basin of Wyoming

Abstract: Evaluations of porosity relevant to hydrocarbon storage capacity in kerogen-rich mudrocks (i.e., source rocks) have thus far been plagued with ambiguity, in large part because conventional core and petrophysical techniques were not designed for this rock type. The growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity. This mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts (except perhaps chemically) with previously assumed matrix or mineral porosity that is dominated by bound water, and that may be largely irrelevant to hydrocarbon storage capacity in these rocks. To address this newly recognized and important nonmatrix kerogen pore system, that is arguably the dominant hydrocarbon storage and mobility network in these rocks, we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation. Kerogen porosity development is estimated within the upper Albian Mowry Shale in the Powder River Basin of Wyoming to illustrate the approach. Relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis, where we estimate that kerogen porosity does not typically exceed 3% of bulk rock volume. Modeled oil-in-place estimates are comparable to residual oil estimates from pyrolysis data (S1) at lower maturities, but exceed pyrolytic S1 yields at higher maturities. We hypothesize, therefore, that a subsurface kinetic porosity model might represent a means to account for S1 losses at surface conditions and to circumvent difficulties surrounding estimations of expulsion efficiencies that are inherent to more traditional mass balance calculations.

The Influence of Weathering on the Engineering Properties of Dunites

Abstract: Weathering processes cause important changes in the engineering properties of rocks. In this study, dunites in the Bursa region in western Turkey were investigated and the changes in engineering properties due to weathering were evaluated. The studies were initiated with field observations including measurement of the characteristics of discontinuities such as spacing, aperture, fill material, roughness, and Schmidt hammer rebound value. Subsequently, laboratory studies were conducted in two stages. The first stage comprised mineralogical, petrographic, and chemical analyses. The second stage included physicomechanical tests to determine specific gravity, unit weights, water absorption, effective porosity, uniaxial compressive strength, P-wave velocity, and slake-durability index. According to these evaluations, the changes in engineering properties were determined to be mostly related to serpentinization at every stage of weathering. The most suitable parameters for characterizing the degree of weathering of the studied dunites are loss-on-ignition values, specific gravity, unit weight, water absorption, and effective porosity.

Improved estimation of mineral and fluid volumetric concentrations from well logs in thinly bedded and invaded formations

Abstract: Calculation of mineral and fluid volumetric concentrations from well logs is one of the most important outcomes of formation evaluation. Conventional estimation methods assume linear or quasi-linear relationships between volumetric concentrations of solid/fluid constituents and well logs. Experience shows, however, that the relationship between neutron porosity logs and mineral concentrations is generally nonlinear. More importantly, linear estimation methods do not explicitly account for shoulder-bed and/or invasion effects on well logs, nor do they account for differences in the volume of investigation of the measurements involved in the estimation. The latter deficiencies of linear estimation methods can cause appreciable errors in the calculation of porosity and hydrocarbon pore volume. We investigated three nonlinear inversion methods for assessment of volumetric concentrations of mineral and fluid constituents of rocks from multiple well logs. All three of these methods accounted for the gen...

Sandstone degradation: an experimental study of accelerated weathering

Abstract: The investigated rock material belongs to the group of upper cretaceous quader sandstones which are very important construction stones in Poland and Germany. The mineral composition of the rocks is relatively uniform—they are quartzose sandstones. The most important feature is their good workability and comparatively high weathering resistance. Still, regardless of the apparent resemblance, the observations carried on buildings and monuments show differences in weathering processes. The undertaken test was an attempt to verify the proposed before rock classification, performed on the basis of parameterization of porosimetric cumulative intrusion volume curves. The aim of the experiment was the evaluation of the sandstone petrography (including the structure, texture and porosity of the rock) influence on the weathering process. The modelling of accelerated weathering was conducted in Chamber for Ageing Acceleration, where some weather circumstances were simulated (insolation, rain and frost). As the result of the weathering experiment it could be stated that the dominant mechanism of the sandstones deterioration was granular disintegration and weight loss as a consequence of sample destruction. The most important factor influencing rock deterioration is rock texture, especially the character of grain contacts. The effective porosity is a requisite of potential for the stone to take in and hold water, and hence of resistance to weathering. In case of silica-cemented sandstones, the deciding criterion influencing weathering resistance is pore structure. In case of sandstones with clay cement, the most important is mineral composition of the rock.

Dynamic Field Division of Hydrocarbon Migration, Accumulation and Hydrocarbon Enrichment Rules in Sedimentary Basins

Abstract: Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins: at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins (i.e., depths of around 1000 m), hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil (–gas)–water inversion, indicating that the oil (gas) accumulated under the water. However, the oil (gas) tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena: a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%–12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation: the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as “four high,” indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as “four low,” indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil(–gas)–water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs: there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.

The third porosity system: understanding the role of hidden pore systems in well-test interpretation in carbonates

Abstract: Well testing is a critical part of any evaluation of a carbonate reservoir discovery. Well-test interpretation in carbonate reservoirs poses additional challenges to those normally faced in the interpretation process in clastic reservoirs. The range of different boundary and crossflow relationships that are generated during well testing by the complex porosity systems are often poorly quantified and understood. The volume over which the pressure response is effective is also a source of great uncertainty and could be critical at the exploration/appraisal stage in any project. In this paper, which describes a generic modelling approach, we consider carbonate reservoirs which contain three pore sytems (or porosity types): (1) microporosity (end-member) with low permeability and high porosity; (2) macroporosity (end-member) with high permeability and high porosity; and (3) fracture porosity with high permeability and low porosity. These occur in various nested geometrical distributions and varying contrasts. The observed well-test responses (i.e. fracture flow, fracture–matrix interactions) tend to ‘obscure’ one of these systems when compared with theoretical models. Micro- (meso-) and macroporosity can merge into a single matrix porosity system where the permeability contrasts are not great and the correlation lengths short (which can often be the case in carbonates). Macroporosity can also appear in well testing to ‘merge’ with the fracture response, i.e. the contributions of flow in the fractures and (high-permeability) porous matrix are indistinguishable. As a result of the homogenizing attributes of pressure dissipation away from the well, it is not generally possible to see the effects of a ‘triple-porosity’ response (i.e. where three different pore systems have a separate and identifiable signature on the well-test response) and a classical double-porosity response in the well test, despite three different pore systems being present, is possible. The apparent double-porosity response, which might obscure a triple-porosity system, therefore needs careful interpretation in order to attribute the appropriate properties during reservoir characterization in carbonates. In this work we use ‘geological’ well testing (i.e. well testing through numerical simulation of hypothetical geological models) to systematically analyse the effects of microporosity, macroporosity and fracture porosity on pressure dissipation and their apparent homogenization. While recent studies have proposed that a triple-porosity system should result in a ‘W-shaped’ response, we do not observe this behaviour in our simulations, although we specifically designed our geological models with a triple-porosity system. Instead we observe how macroporosity merges with the fractures or micro- and macroporosity merge, creating a ‘sub-dominant’ matrix or a ‘dominant’ fracture system, respectively and follow a traditional ‘V-shaped’ double-porosity response.

Petrophysical and geochemical properties of Columbia River flood basalt: Implications for carbon sequestration

Abstract: [1] This study presents borehole geophysical data and sidewall core chemistry from the Wallula Pilot Sequestration Project in the Columbia River flood basalt. The wireline logging data were reprocessed, core-calibrated and interpreted in the framework of reservoir and seal characterization for carbon dioxide storage. Particular attention is paid to the capabilities and limitations of borehole spectroscopy for chemical characterization of basalt. Neutron capture spectroscopy logging is shown to provide accurate concentrations for up to 8 major and minor elements but has limited sensitivity to natural alteration in fresh-water basaltic reservoirs. The Wallula borehole intersected 26 flows from 7 members of the Grande Ronde formation. The logging data demonstrate a cyclic pattern of sequential basalt flows with alternating porous flow tops (potential reservoirs) and massive flow interiors (potential caprock). The log-derived apparent porosity is extremely high in the flow tops (20–45%), and considerably overestimates effective porosity obtained from hydraulic testing. The flow interiors are characterized by low apparent porosity (0–8%) but appear pervasively fractured in borehole images. Electrical resistivity images show diverse volcanic textures and provide an excellent tool for fracture analysis, but neither fracture density nor log-derived porosity uniquely correlate with hydraulic properties of the Grande Ronde formation. While porous flow tops in these deep flood basalts may offer reservoirs with high mineralization rates, long leakage migration paths, and thick sections of caprock for CO2 storage, a more extensive multiwell characterization would be necessary to assess lateral variations and establish sequestration capacity in this reservoir.

Mix Design Method for Permeable Base of Porous Concrete

Abstract: As a new material type for permeable base, porous concrete should be designed to maintain both porosity and the structural strength. Based on Talbot's formula and experience, four gradation compositions of porous concrete are designed with consideration of effective particle size and uniform coefficient as effective descriptive targets for the aggregate gradation. Three factors, including cement dosage, water cement ratio and aggregate gradation, are considered in an orthogonal test. Statistical variance analysis of the tests results showed that, at a confidence probability of 95%, the factors that significantly influence the 7-day compressive strength are gradation and cement aggregate ratio while the factor that significantly influences effective porosity at the same confidence probability is the cement aggregate ratio. In addition, when the confidence probability is 90%, gradation, cement dose and water cement ratio all have significant influence on the 7-day compressive strength and the effective porosity. Based on the test results, a series of regression relationships of 7-day compressive strength and effective porosity of porous concrete are derived. Finally, an empirical equation for mixture design of porous concrete is proposed.

The influence of depositional processes on the porosity of chalk

Abstract: Chalk constitutes challenging low-permeability reservoirs with porosity variations attributable to complex interactions between numerous processes. The influence of depositional processes, and thus the value of depositional models to predict porosity, is subject to continuing debate. In this study, a new approach is applied to investigate the influence of depositional and early post-depositional processes on chalk porosity, based on the 303 m thick Upper Cretaceous chalk succession in the Mona-1 core from the Danish North Sea. The influence of depositional processes on porosity is isolated by a mathematical correction of porosity data. Results confirm that mass-transport deposits are on average more porous than pelagites, whereas turbidites are less porous, given similar composition, burial history, and hydrocarbon migration history. The porosity variation between 12 chalk facies suggests that grain packing of the sediment in the consolidated state caused the facies-dependent porosity variation. Bioturbation caused a relatively tight grain packing compared with deposits that escaped bioturbation. Early plastic shear deformation of tightly packed bioturbated units resulted in dilative behaviour, which increased porosity, whereas more loosely packed units responded contractively, resulting in decreased porosity preservation. A firm understanding of chalk facies and thorough facies analyses are thus considered instrumental in chalk reservoir prediction.

Integration of ANFIS, NN and GA to determine core porosity and permeability from conventional well log data

Abstract: Routine core analysis provides useful information for petrophysical study of the hydrocarbon reservoirs. Effective porosity and fluid conductivity (permeability) could be obtained from core analysis in laboratory. Coring hydrocarbon bearing intervals and analysis of obtained cores in laboratory is expensive and time consuming. In this study an improved method to make a quantitative correlation between porosity and permeability obtained from core and conventional well log data by integration of different artificial intelligent systems is proposed. The proposed method combines the results of adaptive neuro-fuzzy inference system (ANFIS) and neural network (NN) algorithms for overall estimation of core data from conventional well log data. These methods multiply the output of each algorithm with a weight factor. Simple averaging and weighted averaging were used for determining the weight factors. In the weighted averaging method the genetic algorithm (GA) is used to determine the weight factors. The overall algorithm was applied in one of SW Iran?s oil fields with two cored wells. One-third of all data were used as the test dataset and the rest of them were used for training the networks. Results show that the output of the GA averaging method provided the best mean square error and also the best correlation coefficient with real core data.

Procedure for the determination of effective and total porosity of carbonated sedimentary rocks, and morphology characterization of their micro and nanopores

Abstract: The present invention is concerned with a procedure to quantitatively determine both, total and effective porosity of carbonated sedimentary rocks, and is based on the elaboration of molds of the rock pores-structure and on the determination of the volumetric and gravimetric properties of the rock and its mold. Determination of the effective porosity is achieved by using an original formula, developed by the authors of the present invention. Additionally, the structure of micro and nanopores in the rock is characterized by scanning electron microscopy (SEM), to identify relevant properties for permeability analyses such as: dimensions, shapes, type of connections, pore-structure patterns and pore throats. These and other parameters are used as indicators of the reservoir production and storage capacity.

Water seepage beneath dams on soluble evaporite deposits: a laboratory and field study (Caspe Dam, Spain)

Abstract: The paper presents analytical methods and results for assessing the variation in the concentration of sulphate (and other ions) over space and time in groundwater flowing through a soluble evaporite terrain beneath a dam. The influence of effective porosity, groundwater flow velocity and the specific rate of dissolution (K′) are considered. The theoretical analysis was tested in a scale model simulating a dam constructed on heavily karstified bedrock. A simple and useful method for assessing how much material is lost through dissolution and how the rate of dissolution changes over time is considered in the context of the Caspe Dam, Spain.

Distribution of petrophysical properties for sandy-clayey reservoirs by fractal interpolation

Abstract: . The sandy-clayey hydrocarbon reservoirs of the Upper Paleocene and Lower Eocene located to the north of Veracruz State, Mexico, present highly complex geological and petrophysical characteristics. These reservoirs, which consist of sandstone and shale bodies within a depth interval ranging from 500 to 2000 m, were characterized statistically by means of fractal modeling and geostatistical tools. For 14 wells within an area of study of approximately 6 km2, various geophysical well logs were initially edited and further analyzed to establish a correlation between logs and core data. The fractal modeling based on the R/S (rescaled range) methodology and the interpolation method by successive random additions were used to generate pseudo-well logs between observed wells. The application of geostatistical tools, sequential Gaussian simulation and exponential model variograms contributed to estimate the spatial distribution of petrophysical properties such as effective porosity (PHIE), permeability (K) and shale volume (VSH). From the analysis and correlation of the information generated in the present study, it can be said, from a general point of view, that the results not only are correlated with already reported information but also provide significant characterization elements that would be hardly obtained by means of conventional techniques.

Method for measuring overburden porosity with water in permeation fluid mechanics experiment

Abstract: The invention discloses a method for measuring overburden porosity with water in permeation fluid mechanics experiment. The method comprises the following steps of: adding ambient pressure around the core with known pore volume; injecting the single-phase fluid with known compression coefficients into the core in a saturated manner, and enabling pressure at the two ends of the core to conform to the actual conditions of the stratum; and then, sequentially increasing the ambient pressure, and sequentially measuring the change of pore pressure in the core after the ambient pressure is increased so as to determine the change of pore volume and determine the porosity change under an overburden condition. The measuring method disclosed by the invention is applicable to the overburden porosity research in the field of low-permeability and ultralow-permeability storage layer stress sensitive research; and the method can realize overburden porosity research on rock while simulating the overburden pressure on a real storage layer, pore pressure and real fluid parameters. The test equipment adopted by the method is simple, and the test principle is clear; and compared with the method for measuring overburden porosity with air, the effective porosity measured by the method disclosed by the invention can better reflect the overburden porosity characteristics of the real storage layer, and quantitative research on the overburden porosity of the storage layer can be realized.

A Physical-based Model of Permeability/Porosity Relationship for the Rock Data of Iran Southern Carbonate Reservoirs

Abstract: The prediction of porosity is achieved by using ava ilable core and log data; however, the estimation of permeability is limited to the scare core data. Hence, porosity and saturation data through the framework of flow units can be used to make an esti mation of reservoir permeability. The purpose of this study is to predict the permeability of a c arbonate gas reservoir by using physical-based empirical dependence on porosity and other reservoi r rock properties. It is emphasized that this new relationship has a theoretical background and is ba sed on molecular theories. It is found out that if rock samples with different types are separated pro perly and samples with similar fluid-flow properties are classified in the same group, then t his leads to finding an appropriate permeability/porosity relationship. In particular, the concept of hydraulic flow units (HFU) is used to characterize different rock types. This leads to a new physical-based permeability/porosity relationship that has two regression constants whic h are determined from the HFU method. These coefficients, which are obtained for several rock t ypes in this study, may not be applicable to other carbonate rocks; but, by using the general form of the model presented here, based on the HFU method, one may obtain the value of these coefficie nts for any carbonate rock types. Finally, we used the data of cored wells for the validation of the permeability results.

Hydrophilic and strength-softening characteristics of calcareous shale in deep mines

Abstract: To better understand the mechanism of the strength weakening process of soft rocks in deep mines after interacting with water, a self-developed experimental system, Intelligent Testing System for Water Absorption in Deep Soft Rocks (ITSWADSR), is employed to analyze the hydrophilic behavior of deep calcareous shale sampled from Daqiang coal mine. Experimental results demonstrate that the relation between water absorption and time can be expressed by power functions, and the soakage rate decreases while the soakage increases with time. In order to quantitatively calculate the weight coefficients of the influential factors for water absorbing capacity of rocks, a series of testing methods are adopted, including scanning electron microscope (SEM), X-ray diffraction and mercury injection test. It is demonstrated that the effective porosity has a positive correlation with the water absorbing capacity of rocks and the contents of illite and illite/smectite. The initial water content presents a negative correlation with the water absorption capacity of rocks. According to the absolute value of weight coefficients of various influential factors, the order of magnitude from high to low is captured: initial water content, illite, illite/smectite formation (S = 5%), and the effective porosity. After water absorption tests, uniaxial compressive strength (UCS) tests were performed on rock specimens allowing a linear relationship between the UCS and the water content of rock to be established, indicating that the strength of calcareous shale decreases linearly with the increasing water content.

Application of Well Log Analysis to Assess the Petrophysical Parameters of the Lower Cretaceous Biyad Formation, East Shabowah Oilfields, Masila Basin, Yemen

Abstract: 2 Abstract: Biyad Formation is mainly made up of clastic sediments that contain substantial amount of proven crude oil in the eastern Yemen. The Byiad clastic is divided into Upper and Lower Biyad clastic units. Several vertical wells have been drilled and penetrated this formation. This study is concerned with the petrophysical evaluation by means of well log data of the Lower Cretaceous rocks at the East Shabowah oilfields, Masila Basin, Yemen. Computer-assisted log analyses were used to evaluate the petrophysical parameters such as the shale volume (V ), total porosity (PHT), effective porosity (PHE), water saturation (Sw), hydrocarbon saturation sh (S ), flushed zone saturation (S ) and true resistivity (R ). Cross-plots of the Petrophysical parameters versus h xo t depth were illustrated. The Lower Cretaceous Biyad clastic reservoirs reflect that the matrix components are mainly sandstones, carbonates and shales. Moreover, the lithological-geologic model reflected that these shales are strongly affecting the porosity and consequently the fluid saturation in the Lower Biyad more than the Upper Biyad clastic units. On the basis of petrophysics data, the sediments of Biyad Formation are interpreted as a good quality reservoir rocks which has been confirmed with high effective porosity about 20 % and high hydrocarbon saturation exceeding 55%. The Biyad clastic units reveal promising reservoir characteristics especially Upper Biyad unit which should be taken into consideration during future development of the oilfields area.

Chronostratigraphic and Depth Variability of Porosity and Strength of Hard Coals in the Upper Silesian Basin

Abstract: In the article, values of porosity and compression strength of hard coals from the area of the Upper Silesian Coal Basin are presented. Change of the stage of carbonification, which results from conversion of coal substance in the process of coalification, is a source of many changes in the structure of coal. These changes exert influence on values of physical parameters, including value of porosity and strength. Porosity and compression strength change with the degree of carbonification which is a result of the depth of deposition. Presented in the article, values of effective porosity of coals and their strength have been determined considering age chronology of coal seams and depth of their occurrence. Coals of the Cracow Sandstone Series, the Mudstone Series, the Upper Silesian Sandstone Series and the Paralic Series, from depth ranging from about 350 m to about 1200 m, were examined. The authors have shown that effective porosity of the Upper Silesian coals changes for particular stratigraphic groups and assumes values from a few to a dozen or so per cent, while compression strength from several to several dozen megapascals. It has been observed, from chronostratigraphic perspective, there is a shifting of the upper and lower limit of intervals of porosity variations towards higher values for younger coals. With the increase of compression strength, value of porosity in particular stratigraphic groups generally decreases. However, no regular changes were observed of mean uniaxial compressive strength with the increase of age of subsequent stratigraphic groups. On the other hand, for bright coal and semi-bright coal, visible decrease of compression strength with the depth of deposition of strata was observed.

Petro-electric modeling for CSEM reservoir characterization and monitoring

Abstract: The controlled-source electromagnetic (CSEM) method has been successfully applied to petroleum exploration; however, less effort has been made to highlight the applicability of this technique for reservoir monitoring. This work appraises the ability of time-lapse CSEM data to detect the changes in fluid saturation during water flooding into an oil reservoir. We simulated a poorly consolidated shaly sandstone reservoir based on a prograding near-shore depositional environment. Starting with an effective porosity model simulated by Gaussian geostatistics, dispersed clay and dual water models were efficiently combined with other well-known theoretical and experimental petrophysical correlations to consistently simulate reservoir properties. The constructed reservoir model was subjected to numerical simulation of multiphase fluid flow to predict the spatial distributions of fluid pressure and saturation. A geologically consistent rock physics model and a modified Archie’s equation for shaly sandstones were th...

Petrophysics in Gas Shales

Abstract: A method is described for reservoir characterization in fine-grained and thinly bedded shales based on a probabilistic clustering procedure (PCP) of well logs followed by a forward modeling procedure that results in the calculation of profiles for porosity, water saturation (Sw), and permeability. The credibility of results relies on calibration using porosity, permeability, and mineralogy analyses of core samples. Complementary analysis using a nuclear spectroscopy log, if available, can add confidence to the results. Kerogen needs to be included during the forward modeling because it is a matrix component of the bulk rock and the matrix grain density (GD) can be significantly affected by kerogen. Kerogen profiles can be estimated if kerogen core analyses are included in the PCP. In addition, a total organic carbon (TOC) profile, which is needed to determine the amount of adsorbed gas, can be estimated based on core analyses of TOC. The relationships between TOC and kerogen, including a discussion of Rock-Eval pyrolysis, are outlined. The estimation of free gas gross pay in gas shales is fraught with difficulty because of the vagaries of estimating porosity and Sw. Although not realistic in terms of gross storage capacity, the use of the combination of total porosity (TPOR) and total water saturation (Swt) gives the same pay as the combination of effective porosity (EPOR) and effective water saturation (Swe). However, the combination of EPOR and Swt is ill-construed and results in underestimation of gross pay. The estimation of adsorbed gas in gas shales relies on a methodology and equations adopted from the coalbed methane industry. The workflow is easily implemented, but the credibility of results hinges on the assumption that the adopted methodology and equations are valid for gas shales, and on having sufficient and proper laboratory-derived gas adsorption isotherm measurements to represent the TOC heterogeneity of the reservoir. An example is given using analysis of a cored well from the Upper Jurassic Haynesville Shale of northwestern Louisiana and northeastern Texas. The analysis generated profiles for TPOR and EPOR, Swt and Swe, permeability, and net feet of pay.

Photothermal Radiometry Characterization of Limestone Rocks from the Península of Yucatán

Abstract: Limestone is a sedimentary rock composed of calcium carbonate with minor amounts of silica, iron oxide, clay, dolomite, and organic material. These types of stones have been used extensively as building materials. Due to this, determination of their thermal properties is of the utmost importance. These properties depend on the microstructure and composition of each type of rock. In this study, the effect of the thermal treatment of three different limestone rocks from the Peninsula of Yucatan were studied, in the range from 100 °C up to 600 °C, using photothermal radiometry. These studies were complemented by the characterization of the crystalline phases using X-ray diffraction and effective porosity measurements performed by the saturation technique. It is shown that the thermal diffusivity, thermal conductivity, and specific heat of the limestone decrease as the temperature increases. This behavior can be related to increases in microcracks and effective porosity due to thermal treatments.

Finding a Petro-elastic Model Suitable for Sim2seis Calculation

Abstract: The petro-elastic model (PEM) is a necessary step in simulator to seismic modelling, intended to close the loop between the seismic and engineering domains. In this work, we discuss some fundamental issues within the conventional PEM algorithm, not commonly covered by published literature. Firstly, we explain the importance of the porosity rock model for the PEM. It is shown that both total/effective porosity models are able to generate satisfactory seismic results, provided that the density and bulk/shear moduli of the solid components are set correctly using an optimisation problem. We find the underlying connections between the simulation model parameterisation and the effective porosity model from the petrophysical domain. Finally, we discuss the effect of vertical upscaling on the seismic domain. We highlight the differences between property upscaling and reflectivity upscaling, and challenge the idea of developing a scale-dependent PEM based on Backus averaging. In addition to a sim2seis analysis, the results of this work have direct impact on seismic inversion via the PEM for pressure and saturation change or impedance change onto the reservoir grid. Keywords: PEM, rock porosity model, simulation model, effective porosity, total porosity, upscaling, Backus averaging, reflectivity upscaling.

Origin of anomalously high porosity in pyroclastic reservoirs: a case study on the northern region of the east sub-sag in Nanbeier sag

Abstract: Pyroclastic rocks of Tongbomiao-Nantun Formation are an important oil reservoir in the northern region of the east sub-sag in Nanbeier sag.Vertically there are five anomalously high porosity zones at depths of 1 450~1 500m,1 560~1 775m,1 840~2 030m,2 110~2 230m and 2 330~2 520m,respectively.The origin of the anomalously high porosity zones was studied by applying various measurements,such as normal thin-section,cast thin-section,cast image analysis,scanning electron microscope and X-ray diffraction of clay minerals.The result showed that the genesis of anomalously high porosity is directly bound up with the corrosion and dissolution of tuffaceous components.The susceptibility of tuffaceous components to corrosion is a key reason for the formation of anomalously high porosity,and the organic acid generated in thermal evolution of organic matter is a main force to drive corrosion and dissolution.The suitable space relation of sedimentary facies is a primary factor controlling the distribution of anomalously high porosity zones.Besides,the inorganic acid produced during the process of transformation from kaolinite to chlorite can make a certain contribution to anomalously high porosity.

Characterizing Porosity and Diffusive Properties of Monolithic Cement-Based Solidified/Stabilized Materials

Abstract: This paper presents the application of a single reservoir diffusion test to determine both the effective porosity of a soil-cement matrix and the diffusivity of tritium through saturated, monolithic, cement solidified/stabilized wasteforms. Testing was performed on a laboratory mixture of cement paste, sand, and kaolinite. The influence of porosity on the proper interpretation of the diffusion tests was examined. Results of tests on three replicate specimens were consistent and indicate effective porosities of 0.26 to 0.28 and effective diffusive coefficients of 2.5 × 10−10 to 3.0 × 10−10 m2/s. The effect of curing time is discussed. Products of the effective diffusion coefficients and porosity (neDe) decreased by 22 % from specimens cured for 14 days to specimens cured for 28 days prior to testing while from 70 to 126 days of curing neDe only changed by 8 %. This suggests that curing should be carried out for greater than 70 days prior to conducting these tests.