16 PETROPHYSICS:RESERVOIR ROCK PROPERTIES TABLE 1.6 LIST OF TESTS FOR ROCK CHARACTERIZATION Disaggregated Rock Particles 1.Particle size distribution by sieve analysis 2.Sphericity and roundness of the grains by microscopic analyses 3.Chemical composition of the fraction by instrumental analyses 4.Type of grains (quartz,feldspar,older rock fragments,etc.) 5.Clay mineral analyses 6.Organic content of the particle size fractions Core Samples 1.Geologic setting and origin of the rock 2.Bedding plane orientation 3.Fluid content by retort analysis 4. Capillary pressure curves 5.Pore size distribution 6.Surface area 7.Porosity 8.Absolute permeability 9.Irreducible water saturation 10.Oil-water wettability 11.Residual oil saturation 12.Cation exchange capacity 13.Point-load strength 14.Surface mineral analyses by scanning electron microscope 15.Formation resistivity factor Chemical sediments originate from soluble cations,particularly sodium,potassium,magnesium,calcium,and silicon.They form beds of evaporites with very low to zero porosity because they have a granular, interlocking texture.Chemical sediments also serve as most of the cementing agents for sandstones by forming thin deposits between the rock grains. Sedimentary particles range in size from less than one micrometer to large boulders of several meters diameter (Table 1.7).The classification of sizes,from boulders to clay,is indicative of their source,mode of transportation,and hardness.Angular particles remain close to their source of origin whereas spherical,smooth particles indicate transpor- tation by streams.Sand,silt,and clay may be transported long distances by water and winds.Soft carbonates will rapidly pulverize in the process of transport,eventually being dissolved and later precipitated from a concentrated solution
16 PETROPHYSICS: RESERVOIR ROCK PROPERTIES TABLE 1.6 LIST OF TESTS FOR ROCK CHARACTERIZATION Disaggregated Rock Particles 1. Particle size distribution by sieve analysis 2. Sphericity and roundness of the grains by microscopic analyses 3. Chemical composition of the fraction by instrumental analyses 4. Type of grains (quartz, feldspar, older rock fragments, etc.) 5. Clay mineral analyses 6. Organic content of the particle size fractions Core Samples 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Geologic setting and origin of the rock Bedding plane orientation Fluid content by retort analysis Capillary pressure curves Pore size distribution Surface area Porosity Absolute permeability Irreducible water saturation Oil-water wettability Residual oil saturation Cation exchange capacity Point-load strength Surface mineral analyses by scanning electron microscope Formation resistivity factor Chemical sediments originate from soluble cations, particularly sodium, potassium, magnesium, calcium, and silicon. They form beds of evaporites with very low to zero porosity because they have a granular, interlocking texture. Chemical sediments also serve as most of the cementing agents for sandstones by forming thin deposits between the rock grains. Sedimentary particles range in size from less than one micrometer to large boulders of several meters diameter (Table 1.7). The classification of sizes, from boulders to clay, is indicative of their source, mode of transportation, and hardness. Angular particles remain close to their source of origin whereas spherical, smooth particles indicate transportation by streams. Sand, silt, and clay may be transported long distances by water and winds. Soft carbonates will rapidly pulverize in the process of transport, eventually being dissolved and later precipitated from a concentrated solution
PROPERTIES OF SEDIMENTARY PARTICLES 17 TABLE 1.7 STANDARD SIZE CLASSES OF SEDIMENTS Limiting Porticle Diomeler 《mm】 《中vnils) Size Closs 2048 -11- V.Lorge 1024 -10 Lorge Boulders -im Medivm 512- -9 256 Smoll -8 128—-7- Lorge Cobbies 64—-6- Smoll 01 V.Coorse 32一·5 16-4 Coarse Medium Pebbles 102 Fine 4一-2 v.Fine 2 V.Coorse O [Mcenipl Coorse o +1一500 Medium Sond +2一250 Fn自 +3一123 V.Fine 04 16一+462 V.Coarsa 32一+531 Coarsa 84一+6一18 Medium SII1 h20一◆7一 103 Fina V236一◆8一 V.Fine 12 ◆9一 Clay The phi-size classification of Table 1.7 is based on a geometric scale in which the size of adjacent orders differs by a multiple of two.The phi-scale is used as a convenient scale for graphical presentations of particle size distributions since it allows plotting on standard arithmetic graph paper.It is based on the negative base-2 logarithm of the particle diameter (d): PHI =-log2(d)=-3.322 x logio(d) (1.1) The size distribution may be represented as the cumulative curve of grains that are retained on a given sieve size "percent larger,"or the grains that pass through a given sieve,"percent finer."The cumulative curve is often represented as a histogram,which is more amenable to visual inspection. Figures 1.3 and 1.4 compare the cumulative curves and histograms of the Berea sandstone outcrop from Amherst,Ohio,to the coarse-grained
PROPERTIES OF SEDIMENTARY PARTICLES 17 TABLE 1.7 STANDARD SIZE CLASSES OF SEDIMENTS Limiting Parliclr Diameter (mml (+uni~sl Size Class 2048 - I024 - 512- 256 - 128- 64 - 32 - 16- 8- 4- 2- I- ‘4 - 14 - I/( - I/= - ha - ‘/I6 - ‘164 - ‘/OS6 - ‘1512 - The phi-size classification of Table 1.7 is based on a geometric scale in which the size of adjacent orders differs by a multiple of two. The phi-scale is used as a convenient scale for graphical presentations of particle size distributions since it allows plotting on standard arithmetic graph paper. It is based on the negative base-2 logarithm of the particle diameter (d): The size distribution may be represented as the cumulative curve of grains that are retained on a given sieve size “percent larger,” or the grains that pass through a given sieve, “percent finer.” The cumulative curve is often represented as a histogram, which is more amenable to visual inspection. Figures 1.3 and 1.4 compare the cumulative curves and histograms of the Berea sandstone outcrop from Amherst, Ohio, to the coarse-grained
18 PETROPHYSICS:RESERVOIR ROCK PROPERTIES 20 SILT SAND MEDIUM COARSE V.FINE FINE MEDIUM COARSE PHI SCALE 100 50 25 1/64 132 1/16 1/8 12 Grain Size,mm Figure 1.3.Histogram and cumulative size curves sbowing textural parameters for the Berea sandstone,Amberst,Obio.Porosity =0.219;permeability =363 mD. Elgin sandstone outcrop from Cleveland,Oklahoma [16].Although the porosities of these two sandstones are not very different(0.219 and 0.240, respectively)the permeability of the Elgin sandstone is about 10 times greater because it is composed of a relatively large amount of coarse grains,which produces a network of large pores. The sphericity and roundness of particles are two important attributes that affect the petrophysical properties of the rocks and consequently may be used to explain differences between rocks and their properties For example,these two attributes control the degree of compaction and thus can explain the differences between rocks that have the same sedimentary history but differ in porosity and permeability
18 PETROPHYSICS: RESERVOIR ROCK PROPERTIES - - 20-- c - - - io-- - 0. 1 SILT I SAND MEDIUM I COARSE I V. FINE I FINE I MEDIUM I COARSE PHI SCALE 6 5 4 3 2 0 01 I I I I I I 1 164 1 /32 1116 1 I8 1 I4 112 1 Grain Size, mm Figure 1.3. Histogram and cumulative size curves showing textural parametersfor the Berea sandstone, Amherst, Ohio. Porosity = 0.219;permeability = 363 mD. Elgin sandstone outcrop from Cleveland, Oklahoma [ 161. Although the porosities of these two sandstones are not very different (0.219 and 0.240, respectively) the permeability of the Elgin sandstone is about 10 times greater because it is composed of a relatively large amount of coarse grains, which produces a network of large pores. The sphericity and roundness of particles are two important attributes that affect the petrophysical properties of the rocks and consequently may be used to explain differences between rocks and their properties. For example, these two attributes control the degree of compaction and thus can explain the differences between rocks that have the same sedimentary history but differ in porosity and permeability
PROPERTIES OF SEDIMENTARY PARTICLES 19 20 SILT SAND MEDIUM COARSE V.FINE FINE MEDIUM COARSE PHISCALE 100 75 50 1/64 t32 1/4 12 Grain Size.mm Figure 1.4.Histogram and cumulative size curves showing textural parameters for tbe Elgin sandstone,Cleveland,Oklaboma.Porosity =0.240;permeability 3.484mD. Sphericity is a measure of how closely a particle approximates the shape of a sphere.It is a measure of how nearly equal are the three mutually perpendicular diameters of the particle,and is expressed as the ratio of the surface area of the particle to the surface area of a sphere of equal volume [17.18]. Roundness is a measure of the curvature,or sharpness,of the particle. The accepted method for computing the roundness of a particle is to view the particle as a two-dimensional object and obtain the ratio of the average radius of all the edges to the radius of the maximum inscribed circle
PROPERTIES OF SEDIMENTARY PARTICLES 30-- 20-- lo-- 0. - - - - - lI r SILT SAND I MEDIUM 1 COARSE I V. FINE I FINE I MEDIUM I COARSE PHI SCALE 6 5 4 3 2 1 0 19 1 /64 1 I32 1/16 1 /8 114 112 1 Grain Size, rnm Figure 1.4. Histogram and cumulative size curves showing textural parameters for the Elgin sandstone, Cleveland, Oklahoma. Porosity = 0.240; permeability = 3,484 mD. Sphericity is a measure of how closely a particle approximates the shape of a sphere. It is a measure of how nearly equal are the three mutually perpendicular diameters of the particle, and is expressed as the ratio of the surface area of the particle to the surface area of a sphere of equal volume 117, 181. Roundness is a measure of the curvature, or sharpness, of the particle. The accepted method for computing the roundness of a particle is to view the particle as a two-dimensional object and obtain the ratio of the average radius of all the edges to the radius of the maximum inscribed circle
20 PETROPHYSICS:RESERVOIR ROCK PROPERTIES Krumbein [19]established a set of images for visually estimating roundness,ranging from a roundness of 0.1 to 0.9.Later,Pettijohn [20]defined five grades of roundness as:(1)angular,(2)subangular, (3)subrounded,(4)rounded,and (5)well rounded.The degree of roundness is a function of the maturity of the particle.The particles are more angular near their source just after genesis and acquire greater roundness from abrasion during transportation to a depositional basin. The texture of clastic rocks is determined by the sphericity,roundness, and sorting of the detrital sediments from which they are composed.The sphericity and roundness are functions of the transport energy,distance of transport from the source,and age of the particles.Young grains,or grains near the source,are angular in shape while those that have been transported long distances,or reworked from pre-existing sedimentary rocks,have higher sphericity and roundness. DEVELOPMENT AND USE OF PETROPHYSICS The study of fluid flow in rocks and rock properties had its beginnings in 1927 when Kozeny [21]solved the Navier-Stokes equations for fluid flow by considering a porous medium as an assembly of pores of the same length.He obtained a relationship between permeability,porosity, and surface area. At about the same time the Schlumberger brothers introduced the first well logs [22].These early developments led to rapid improvements of equipment,production operations,formation evaluation,and recovery efficiency.In the decades following,the study of rock properties and fluid flow was intensified and became a part of the research endeavors of all major oil companies.In 1950 Archie [23]suggested that this specialized research effort should be recognized as a separate discipline under the name of petrophysics.Archie reviewed an earlier paper and discussed the relationships between the types of rocks,sedimentary environment, and petrophysical properties.Earlier,in 1942,Archie [24]discussed the relationships between electrical resistance of fluids in porous media and porosity.Archie proposed the equations that changed well log interpretation from a qualitative analysis of subsurface formations to the quantitative determination of in situ fluid saturations.These and subsequent developments led to improvements in formation evaluation, subsurface mapping,and optimization of petroleum recovery. The Hagen-Poiseuille equation [25],which applies to a single,straight capillary tube,is the simplest flow equation.By adding a tortuosity factor,however,Ewall [25]used pore size distributions to calculate the permeability of sandstone rocks.The calculated values matched the
20 PETROPHYSICS: RESERVOIR ROCK PROPERTIES Krumbein [19] established a set of images for visually estimating roundness, ranging from a roundness of 0.1 to 0.9. Later, Pettijohn [20] defined five grades of roundness as: (1) angular, (2) subangular, (3) subrounded, (4) rounded, and (5) well rounded. The degree of roundness is a function of the maturity of the particle. The particles are more angular near their source just after genesis and acquire greater roundness from abrasion during transportation to a depositional basin. The texture of clastic rocks is determined by the sphericity, roundness, and sorting of the detrital sediments from which they are composed. The sphericity and roundness are functions of the transport energy, distance of transport from the source, and age of the particles. Young grains, or grains near the source, are angular in shape while those that have been transported long distances, or reworked from preexisting sedimentary rocks, have higher sphericity and roundness. DEVELOPMENT AD USE OF PETROPHYSICS The study of fluid flow in rocks and rock properties had its beginnings in 1927 when Kozeny [21] solved the Navier-Stokes equations for fluid flow by considering a porous medium as an assembly of pores of the same length. He obtained a relationship between permeability, porosity, and surface area. At about the same time the Schlumberger brothers introduced the first well logs [22]. These early developments led to rapid improvements of equipment, production operations, formation evaluation, and recovery efficiency. In the decades following, the study of rock properties and fluid flow was intensified and became a part of the research endeavors of all major oil companies. In 1950 Archie [23] suggested that this specialized research effort should be recognized as a separate discipline under the name of petrophysics. Archie reviewed an earlier paper and discussed the relationships between the types of rocks, sedimentary environment, and petrophysical properties. Earlier, in 1942, Archie [24] discussed the relationships between electrical resistance of fluids in porous media and porosity. Archie proposed the equations that changed well log interpretation from a qualitative analysis of subsurface formations to the quantitative determination of in situ fluid saturations. These and subsequent developments led to improvements in formation evaluation, subsurface mapping, and optimization of petroleum recovery. The Hagen-Poiseuille equation [25], which applies to a single, straight capillary tube, is the simplest flow equation. By adding a tortuosity factor, however, Ewall [25] used pore size distributions to calculate the permeability of sandstone rocks. The calculated values matched the