西安石油大学：《油藏物理（油层物理学）Petro-physics》精品课程教学资源（PDF电子书）油藏物理（英文）.pdf_P31-P35

MINERAL CONSTITUENTS OF ROCKS-A REVIEW 11 reactions that are responsible for rock degradation.One of the processes that takes place is leaching,which is the transfer of chemical constituents from the rock to the water solution.Some minerals react directly with the water molecules to form hydrates.Carbonic acid,formed from biogenic and atmospheric carbon dioxide dissolved in water,plays an important role in the chemical weathering process by reacting with the minerals to form carbonates and other minerals such as clays.The feldspars react with carbonic acid and water forming various clays,silica,and carbonates,as illustrated in the reaction below for potassium feldspar: 2KAlSisOs+H2CO3+H2O-Al2SiOs(OH)4+4SiO2+K2CO3 The sedimentary deposits that make up the large variety of rocks are continually altered by tectonic activity,resulting in deep burial of sediments in zones that are undergoing subsidence.Uplift of other areas forms mountains.The continual movement and collisions of conti- nental plates cause folding and faulting of large blocks of sedimentary deposits.This activity forms natural traps that in many cases have accumulated hydrocarbons migrating from the source rocks in which they were formed.The geologic processes of sedimentation,subsidence, compaction,cementation,uplift,and other structural changes occur continuously on a gradual scale and are intrinsically associated with the physical properties of the rocks as well as the migration and accumulation of hydrocarbon reserves.The physical properties of rocks, such as density,rate of sound transmission,compressibility,and the wetting properties of fluids,are the consequence of the mineral compo- sition of the rocks.Thus the basic materials that make up the rocks and their chemistry are associated with the petrophysical characteristics of rocks. Siltstones (mud-rocks) Quartz grains (originating from weathering of igneous and meta- morphic rocks)are very hard;they resist further breakdown,but are winnowed by currents of winds and water and distributed according to size.Larger grains accumulate as sandstones,and grains having an average size of 15 um mix with clays and organic materials in turbulent aqueous suspensions that are transported and later deposited in quiet,low energy, valleys from flooding rivers,lakes,and the continental shelves.Tidal currents on the continental shelves effectively sort the grains of sand, silt,and clay once more until they settle in quiet regions,forming very uniform thick beds.Bottom-dwelling organisms burrow through the mud,kneading and mixing it until the depth of burial is too great for this to happen.The material then undergoes compaction and diagenesis, with the clay minerals changing composition as they react with chemicals

MINERAL CONSTITUENTS OF ROCKS-A REVIEW 11 reactions that are responsible for rock degradation. One of the processes that takes place is leaching, which is the transfer of chemical constituents from the rock to the water solution. Some minerals react directly with the water molecules to form hydrates. Carbonic acid, formed from biogenic and atmospheric carbon dioxide dissolved in water, plays an important role in the chemical weathering process by reacting with the minerals to form carbonates and other minerals such as clays. The feldspars react with carbonic acid and water forming various clays, silica, and carbonates, as illustrated in the reaction below for potassium feldspar: 2KAlSijO8 + H2COj + H2O + AlzSi05(0H)4 + 4SiO2 + K2CO3 The sedimentary deposits that make up the large variety of rocks are continually altered by tectonic activity, resulting in deep burial of sediments in zones that are undergoing subsidence. Uplift of other areas forms mountains. The continual movement and collisions of continental plates cause folding and faulting of large blocks of sedimentary deposits. This activity forms natural traps that in many cases have accumulated hydrocarbons migrating from the source rocks in which they were formed. The geologic processes of sedimentation, subsidence, compaction, cementation, uplift, and other structural changes occur continuously on a gradual scale and are intrinsically associated with the physical properties of the rocks as well as the migration and accumulation of hydrocarbon reserves. The physical properties of rocks, such as density, rate of sound transmission, compressibility, and the wetting properties of fluids, are the consequence of the mineral composition of the rocks. Thus the basic materials that make up the rocks and their chemistry are associated with the petrophysical characteristics of rocks. Siltstones (mud-rocks) Quartz grains (originating from weathering of igneous and metamorphic rocks) are very hard; they resist further breakdown, but are winnowed by currents of winds and water and distributed according to size. Larger grains accumulate as sandstones, and grains having an average size of 15 pm mix with clays and organic materials in turbulent aqueous suspensions that are transported and later deposited in quiet, low energy, valleys from flooding rivers, lakes, and the continental shelves. Tidal currents on the continental shelves effectively sort the grains of sand, silt, and clay once more until they settle in quiet regions, forming very uniform thick beds. Bottom-dwelling organisms burrow through the mud, kneading and mixing it until the depth of burial is too great for this to happen. The material then undergoes compaction and diagenesis, with the clay minerals changing composition as they react with chemicals

12 PETROPHYSICS:RESERVOIR ROCK PROPERTIES in the contacting water.The compacted mud forms the siltstones and beds of shale that are encountered throughout the stratigraphic column, making up two-thirds of the sedimentary deposits.Where they overlie hydrocarbon reservoirs,the compacted layers of mud provide seals for the petroleum traps. Beds of mud containing organic materials that are deposited in anaerobic environments,such as swamps,form siltstones and shales that are gray to black in color.Many of these are the source rocks of petroleum hydrocarbons.Red deposits of mud were exposed to oxygen during burial and the organic material was lost to oxidation while iron compounds formed ferric oxide (Fe2O3)that produced the bright red coloration.Brown muds underwent partial oxidation with iron constituents,forming the hydroxide geothite [FeO(OH].If the mud does not contain iron,it will exhibit the coloration of the clays (biotite, chlorite,illite,etc.)that range in color from beige to green. Sandstones The quartz grains and mixed rock fragments resulting from mechanical and chemical degradation of igneous,metamorphic,and sedimentary rocks may be transported to other areas and later transformed into sandstones. After the loose sediments of sand,clay,carbonates,etc.,are accu- mulated in a basin area they undergo burial by other sediments form- ing on top.The vertical stress of the overlying sediments causes compaction of the grains.Transformation into sedimentary rocks occurs by lithification,or cementation,from minerals deposited between the grains by interstitial water.The main cementing materials are silica, calcite,oxides of iron,and clay.The composition of sandstones is dependent on the source of the minerals (igneous,metamorphic, sedimentary)and the nature of the depositional environment. Theodorovich [11]used the three most general constituents of sandstones to establish a scheme of classification which is useful in petroleum engineering because it encompasses the majority of the clastic petroleum reservoirs (Figure 1.2).Only the three most important classifications are shown;many other subdivisions of these were devel- oped by Theodorovich and other investigators,and are summarized by Chilingarian and Wolf [12]. A distinctive feature of sandstones is the bedding planes,which are visible as dark horizontal lines.The bedding planes are the consequence of layered deposition occurring during changing environmental conditions over long periods of deposition in the region.Layering introduces a considerable difference between the vertical(cross-bedding plane direction)and horizontal (parallel to the bedding planes)flow

12 PETROPHYSICS: RESERVOIR ROCK PROPERTIES in the contacting water. The compacted mud forms the siltstones and beds of shale that are encountered throughout the stratigraphic column, making up two-thirds of the sedimentary deposits. Where they overlie hydrocarbon reservoirs, the compacted layers of mud provide seals for the petroleum traps. Beds of mud containing organic materials that are deposited in anaerobic environments, such as swamps, form siltstones and shales that are gray to black in color. Many of these are the source rocks of petroleum hydrocarbons. Red deposits of mud were exposed to oxygen during burial and the organic material was lost to oxidation while iron compounds formed ferric oxide (Fe2O3) that produced the bright red coloration. Brown muds underwent partial oxidation with iron constituents, forming the hydroxide geothite [FeO(OH)] . If the mud does not contain iron, it will exhibit the coloration of the clays (biotite, chlorite, illite, etc.) that range in color from beige to green. Sandstones The quartz grains and mixed rock fragments resulting from mechanical and chemical degradation of igneous, metamorphic, and sedimentary rocks may be transported to other areas and later transformed into sandstones. After the loose sediments of sand, clay, carbonates, etc., are accumulated in a basin area they undergo burial by other sediments forming on top. The vertical stress of the overlying sediments causes compaction of the grains. Transformation into sedimentary rocks occurs by lithification, or cementation, from minerals deposited between the grains by interstitial water. The main cementing materials are silica, calcite, oxides of iron, and clay. The composition of sandstones is dependent on the source of the minerals (igneous, metamorphic, sedimentary) and the nature of the depositional environment. Theodorovich [ll] used the three most general constituents of sandstones to establish a scheme of classification which is useful in petroleum engineering because it encompasses the majority of the clastic petroleum reservoirs (Figure 1.2). Only the three most important classifications are shown; many other subdivisions of these were developed by Theodorovich and other investigators, and are summarized by Chilingarian and Wolf [ 121. A distinctive feature of sandstones is the bedding planes, which are visible as dark horizontal lines. The bedding planes are the consequence of layered deposition occurring during changing environmental conditions over long periods of deposition in the region. Layering introduces a considerable difference between the vertical (cross-bedding plane direction) and horizontal (parallel to the bedding planes) flow

14 PETROPHYSICS:RESERVOIR ROCK PROPERTIES is composed of accumulated deposits of skeletal or shell remains of microscopic animals;and coquina is fossiliferous limestone composed almost entirely of fossil fragments cemented by a calcareous mud. Dolomite forms in areas where sea water has been restricted,or trapped,by land enclosure where the concentration of salts increases due to evaporation.As the concentration of magnesium increases it reacts with the calcite that has already been deposited to form dolomite by the following reaction: 2CaCO3 Mg2+CaMg(CO3)2 +Ca2+ In some cases the limestone formations are changed to dolomite by reaction with magnesium which is dissolved in water percolating through pores and fractures in the limestone.Porous carbonate rocks derived from chemical and biogenic precipitation of calcium carbonate form a large portion of the petroleum reservoirs [13]. Evaporites Evaporites are salts that are deposited in isolated marine basins by evaporation of the water and subsequent precipitation of salts from the concentrated solutions.Salt Lake in Utah,United States,and the Dead Sea in the Middle East,are examples of lakes that are gradually forming beds of evaporites as the water evaporates.Anhydrite (CaSO),sodium halite (NaCl),sylvite (KCl),and other salts are associated with evaporites. Table 1.5 contains a general description of the rocks that have been discussed.The principal rock-forming minerals are feldspars,olivine, pyroxene,amphibole,mica,and quartz.Almost all coarse-grained rocks contain feldspars.There are three feldspars:calcium-,potassium-,and sodium-aluminum silicates.Other descriptive names that are used for them are placed in parentheses. PROPERTIES OF SEDIMENTARY PARTICLES There are a large number of tests that can be made to obtain quantitative and qualitative data for characterization of sedimentary rocks.All of the methods listed in Table 1.6 are discussed in various locations in the book and can be found by reference to the Index.The loose particle analyses are made on disaggregated rock particles that are obtained using a crushing apparatus,or by carefully breaking the rock with a hammer.The other analyses are obtained from core samples of rock which are oriented parallel to the bedding planes.Tests of the vertical fluid flow properties can be useful for analyses of gravity drainage of oil,vertical diffusion of gas released from solution,and transport

14 PETROPHYSICS: RESERVOIR ROCK PROPERTIES is composed of accumulated deposits of skeletal or shell remains of microscopic animals; and coquina is fossiliferous limestone composed almost entirely of fossil fragments cemented by a calcareous mud. Dolomite forms in areas where sea water has been restricted, or trapped, by land enclosure where the concentration of salts increases due to evaporation. As the concentration of magnesium increases it reacts with the calcite that has already been deposited to form dolomite by the following reaction: 2CaCO3 + Mg2+ += CaMg(C03)~ + Ca2+ In some cases the limestone formations are changed to dolomite by reaction with magnesium which is dissolved in water percolating through pores and fractures in the limestone. Porous carbonate rocks derived from chemical and biogenic precipitation of calcium carbonate form a large portion of the petroleum reservoirs [ 13 J . Evaporites Evaporites are salts that are deposited in isolated marine basins by evaporation of the water and subsequent precipitation of salts from the concentrated solutions. Salt Lake in Utah, United States, and the Dead Sea in the Middle East, are examples of lakes that are gradually forming beds of evaporites as the water evaporates. Anhydrite (CaSO4), sodium halite (NaCl), sylvite (KCl), and other salts are associated with evaporites. Table 1.5 contains a general description of the rocks that have been discussed. The principal rock-forming minerals are feldspars, olivine, pyroxene, amphibole, mica, and quartz. Almost all coarse-grained rocks contain feldspars. There are three feldspars: calcium-, potassium-, and sodium-aluminum silicates. Other descriptive names that are used for them are placed in parentheses. PROPERTIES OF SEDIMENTARY PARTICLES There are a large number of tests that can be made to obtain quantitative and qualitative data for characterization of sedimentary rocks. All of the methods listed in Table 1.6 are discussed in various locations in the book and can be found by reference to the Index. The loose particle analyses are made on disaggregated rock particles that are obtained using a crushing apparatus, or by carefully breaking the rock with a hammer. The other analyses are obtained from core samples of rock which are oriented parallel to the bedding planes. Tests of the vertical fluid flow properties can be useful for analyses of gravity drainage of oil, vertical diffusion of gas released from solution, and transport

PROPERTIES OF SEDIMENTARY PARTICLES 15 TABLE 1.5 GENERAL DESCRIPTIONS OF ROCKS DISCUSSED IN CHAPTER 1 Andesite:fine-grained extrusive igneous rock:intermediate color between rhyolite and basalt. Basalt:fine-grained extrusive igneous rock;dark colored. Coquina:a form of limestone that is composed of shells and shell fragments. Diotrite:coarse-grained intrusive igneous rock intermediate in color between granite and gabbro;composed principally of potassium feldspar(~25%), sodium plagioclase (~35%),biotite (20%),and hornblend (~20%). Evaporite:sedimentary rock originating from the evaporation of water. Gabbro:coarse-grained intrusive igneous rock;dark colored with an approx- imate composition of calcium plagioclase (40%),augite (~50%),and olivine (~10%). Gneiss:coarse-grained,foliated metamorphic rock.Contains feldspar and is generally banded.The rock has recrystallized under pressure and temperature with growth of new crystals in bands. Granite:coarse-grained intrusive,quartz-bearing rock.The coarse texture implies that it came from a large,slowly cooled,intrusive body and has been exposed by uplift and deep erosion (light-colored to dark).Granite is generally composed of a mixture of quartz(35%),potassium feldspar(~45%),biotite (~15%),and hornblende (5%). Marble:originates from metamorphosis of limestone or dolomite;the fine crystals of limestone grow bigger and develop an interlocking texture to yield marble. Rhyolite (felsite):fine-grained,extrusive igneous rock;light colored. Schist:coarse-grained,foliated,metamorphic rock containing mica:derived from high temperature and pressure metamorphosis of shale. Shale:fine-grained,sedimentary rock composed of clay and silt Slate:fine-grained,metamorphic rock derived from shale. properties using mathematical simulation.More recent microgeometry analyses are discussed by Ceripi et al.[14]and Talukdar and Torsaeter [15]. A simplifying theme resulting from the analysis of the sources of sedimentary rocks is that they are composed of materials from two different sources:(1)detrital sediments are composed of discrete particles.having a wide range of sizes,that are derived from weathering of pre-existing rocks;(2)chemical sediments are inorganic compounds precipitated from aqueous solutions,and may be subdivided into carbonates and evaporites as shown in Figure 1.2.The detrital sediments form beds of unconsolidated sands,sandstones,and shales.In the process of being transported from the source to a depositional basin,the grains are reduced in size and rounded,and as a result they cannot pack together without having pore spaces between the grains

PROPERTIES OF SEDIMENTARY PARTICLES TABLE 1.5 GENERAL DESCRIPTIONS OF ROCKS DISCUSSED IN CHAPTER 1 15 Andesite: fine-grained extrusive igneous rock; intermediate color between Basalt: fine-grained extrusive igneous rock; dark colored. Coquina: a form of limestone that is composed of shells and shell fragments. Diotrite: coarse-grained intrusive igneous rock intermediate in color between granite and gabbro; composed principally of potassium feldspar (-- 25%), sodium plagioclase (- 35%), biotite (- 20%), and hornblend (- 20%). rhyolite and basalt. Evaporite: sedimentary rock originating from the evaporation of water. Gabbro: coarse-grained intrusive igneous rock; dark colored with an approximate composition of calcium plagioclase (- 40%), augite (- 50%), and olivine (-- 10%). Gneiss: coarse-grained, foliated metamorphic rock. Contains feldspar and is generally banded. The rock has recrystallized under pressure and temperature with growth of new crystals in bands. Granite: coarse-grained intrusive, quartz-bearing rock. The coarse texture implies that it came from a large, slowly cooled, intrusive body and has been exposed by uplift and deep erosion (light-colored to dark). Granite is generally composed of a mixture of quartz (- 35%), potassium feldspar (- 45%), biotite (- 15%), and hornblende (- 5%). Marble: originates from metamorphosis of limestone or dolomite; the fine crystals of limestone grow bigger and develop an interlocking texture to yield marble. Rhyolite (felsite): fine-grained, extrusive igneous rock; light colored. Schist: coarse-grained, foliated, metamorphic rock containing mica; derived from high temperature and pressure metamorphosis of shale. Shale: fine-grained, sedimentary rock composed of clay and silt. Slate: fine-grained, metamorphic rock derived from shale. properties using mathematical simulation. More recent microgeometry analyses are discussed by Ceripi et al. [14] and Talukdar and Torsaeter [ 151. A simplifying theme resulting from the analysis of the sources of sedimentary rocks is that they are composed of materials from two different sources: (1) detrital sediments are composed of discrete particles, having a wide range of sizes, that are derived from weathering of pre-existing rocks; (2) chemical sediments are inorganic compounds precipitated from aqueous solutions, and may be subdivided into carbonates and evaporites as shown in Figure 1.2. The detrital sediments form beds of unconsolidated sands, sandstones, and shales. In the process of being transported from the source to a depositional basin, the grains are reduced in size and rounded, and as a result they cannot pack together without having pore spaces between the grains