CHEN 490 Notes Logging (Final), Fall 2014

11 21 Determines fracture orientation and 3-D geometry of reservoirs \G Establishes environment: of deposition of carbonates Qualifies amount, type, character and distribution of porosity in sediments Fig. 6—A number of factors are involved in understanding a depo: analysis takes into account these factors and can give the operator a virtual three-dimensional a TABLE 3—Engineering data obtained by core analysis : © Porosity distribution and magnitude (histogram) e Permeability distribution and magnitude (histogram) e Permeability heterogeneity (Lorenze coefficient, variance factor) ® Porosity vs. permeability relationships e Reservoir water saturations (oil-base cores) Reservoir residual oil saturations and distribution (pressure and sponge core) i Data for calibration and refinement of downhole log calcula- tions Grain density Calcimetry (limestone/dolomite ratio) Acoustic velocity A Gamma ray characteristics (core gamma and core spec- tral) Electrical properties (‘m" and “n") - Mineralogy and clay type, distribution and quantity e Special core analysis ~ Relative permeability Formation wettability / Capillary pressure (water-retention properties) J Pore volume compressibility -Rock-injected fluid compatibility /Residual gas {trapped by water) erformance evaluations Water flood Enhanced oil recovery e Oil shale assay Hydrocarbon yield Water recovered Spent shale Geotechnology (rock mechanics) Compressive strength Poisson's ratio Young’s modulus Hardness Tensile strength Oil or bitumen quantity/unit volume of reservoir (tar sands) WORLD OIL, March 1985 aa Explains and quantifies tight sand zones Helps with study of mineralogy, texture, diagenisis and porosity of sands sitional environment and evaluating its exploration potential. A detailed basin | picture of the kind of geology wells will encounter. with audio lithologic description is another new and innova- tive means of recording and presenting core data. Special core analysis. This field consists of several more complex and time-consuming measurements that extend and supplement the more commonly available information. A number of these tests are utilized in reservoir engineering applications, as they furnish information to quantify oil-in- place (capillary pressures), fluid flow characteristics (rela- tive permeability —see Fig. 3) and recovery anticipated with various improved recovery schemes (waterflood and en- hanced oil recovery). Log-related parameters such as forma- tion factor-porosity and acoustical properties are also mea- sured, and these relieve the need to use published, average values that may be inappropriate. Drilling, completion, ‘workover and injection fluid reac- tions with the reservoir rock can be evaluated with special core analysis so that suitable fluids can be selected that will not damage the formation or reduce productivity. These spe- cial tests are generally made on fewer samples than used for routine measurements, yet the variation noted in the routine data forms the basis of subsequent special core analysis sam: ple selection. Petrology. The study of rock composition, characteristic and. origin of sediments, adds depth to information gener ated by both conventional and special core analysis. Its use ha expanded as instrumentation has improved and been re duced in cost, and as operator awareness of the cost benef from utilizing the information has increased. Detailed cor descriptions are aided by microscopic examination that ii cludes thin section analysis, X-ray diffraction analys (XRD) and scanning electron microscopy (SEM). The data yield information on depositional environmen diageneses, reservoir potential, porosity type and contr‘ potential completion damage OF production problems a! authigenic (formed-in-place) minerals. An example SEM photograph illustrating the presence montmorillonite in the pore space is shown in Fig. 4. It fo warns of the potential formation damage that may occur permeability reduction from freshwater drilling, complet or injection fluids. The potential also exists for high irred ible water and abnormally low resistivity in hydrocarl productive zones. Permeability damage can be quantifiec sensitivity studies utilizing special core analysis fluid f tests, and irreducible water can be determined from cz 1121 _ aiaiperpmeresrmrorresemas mses ae Determines mineralogy and organic content of potential source beds Determines fracture orientation Se and 3-D geometry of reservoirs 3 Establishes environment of deposition of carbonates Qualifies amount, type. character and distribution of porosity in sediments analysi v TABLE 3—Engineering data obtained by core analysis © Porosity distribution and magnitude (histogram) e Permeability distribution and magnitude (histogram) e Permeability heterogeneity (Lorenze coefficient, variance factor) Porosity vs. permeability relationships e Reservoir water saturations (oil-base cores) Reservoir residual oil saturations and distribution (pressure and sponge core) Data for calibration and refinement of downhole log calcula- tions Grain density Calcimetry (limestone/dolomite ratio) Acoustic velocity f Gamma ray characteristics (core gamma and core spec- tral) Electrical properties (‘m" and “n”) - Mineralogy and clay type, distribution and quantity e Special core analysis . _/ Relative permeability VY Formation wettability / Capillary pressure (water-retention properties) / Pore volume compressibility Rock-injected fluid compatibility /Residual gas (trapped by water) Performance evaluations - Water flood Enhanced oil recovery e Oil shale assay Hydrocarbon yield Water recovered Spent shale Geotechnology (rock mechanics) Compressive strength Poisson's ratio Young’s modulus Hardness Tensile strength e Oil or bitumen quantity/unit volume of reservoir (tar sands) WORLD OIL, March 1985 Explains and quantifies tight sand zones Helps with study of mineralogy, texture, diagenisis and porosity of sands Fig. 6—A number of factors are involved in understanding a depositional environment and evaluating its exploration potential. A detailed basin s takes into account these factors and can give the operator a virtual three-dimensional picture of the kind of geology wells will encounter. with audio lithologic description is another new and innova- tive means of recording and presenting core data. Special core analysis. This field consists of several more complex and time-consuming measurements that extend and supplement the more commonly available information. A number of these tests are utilized in reservoir engineering applications, as they furnish information to quantify oil-in- place (capillary pressures); fluid flow characteristics (rela- tive permeability—see Fig. 3) and recovery anticipated with various improved recovery schemes (waterflood and en- hanced oil recovery). Log-related parameters such as forma- tion factor-porosity and acoustical properties are also mea- sured, and these relieve the need to use published, average values that may be inappropriate. Drilling, completion, workover and injection fluid reac- tions with the reservoir rock can be evaluated with special core analysis so that suitable fluids can be selected that will not damage the formation or reduce productivity. These spe- cial tests are generally made on fewer samples than used for routine measurements, yet the variation noted in the routine data forms the basis of subsequent special core analysis sam: ple selection. Petrology. The study of rock composition, characteristic and. origin of sediments, adds depth to information gener ated by both conventional and special core analysis. Its use ha expanded as instrumentation has improved and been re duced in cost, and as operator awareness of the cost benefir from utilizing the information has increased. Detailed con descriptions are aided by microscopic examination that cludes thin section analysis, X-ray diffraction analys (XRD) and scanning electron microscopy (SEM). The data yield information on depositional environmer diageneses, reservoir potential, porosity type and contri potential completion damage or production problems a! authigenic (formed-in-place) minerals. An example SEM photograph illustrating the presence montmorillonite in the pore space is shown in Fig. 4. It fo warns of the potential formation damage that may occur permeability reduction from freshwater drilling, complet or injection fluids. The potential also exists for high irred ible water and abnormally low resistivity in hydrocart productive zones. Permeability damage can be quantifiec sensitivity studies utilizing special core analysis fluid f tests, and irreducible water can be determined from cz vl ments of rock properties, such as those obtained from down- hole logs, pressure build-up analysis and seismic surveys. In general, however, these formation evaluation techniques yield average properties over several feet to several hundred feet of vertical section. All can determine properties at a greater distance from the wellbore than seen by a single core, but none yields as detailed information on vertical section properties and heterogeneity as may be obtained from core studies. In fact, gathering core data enhances the under- standing of response in these other important formation study tools. Thick formations of constant and known chemical compo- sition that have undergone little alteration after deposition, that contain no mineral impurities within the pore space, or that have water of constant salinity, can likely be evaluated adequately without cores for completion purposes or to de- termine oil-in-place. Unfortunately, this ideal case is seldom encountered in the real world, and core data are still re- quired to evaluate subsequent improved recovery schemes. CONSIDERATIONS PRIOR TO CORING When sampling a particular reservoir, coring operation objectives should be clearly defined and established early. These objectives influence the type of core to be cut, its size, coring fluid to be used and the analysis to follow. Most cor- ing devices require that a coring point be predetermined so that the tool may be attached to the bottom of the drillstring. Unless a total section in the well is to be cored, some geologic control is required. Otherwise, data such as gas shows, oil shows or drilling breaks supplied by a hydrocarbon well log- ger are used to indicate the coring point. One type of wireline coring tool allows a center plug to be recovered from the drill bit so that coring can be done at any selected depth. Another tool allows recovered cores to be spatially oriented, while others allow reservoir pressure to be maintained during core recovery. All of these, run at the bot- tom of the drillstring, supply a continuous vertical section of core from 2 to 8 in. in diameter from which needed informa- tion may be derived. Percussion sidewall and the sidewall drilled cores now un- der development have a unique advantage in that coring points are selected after the well is drilled and downhole logs have been run to identify zones of interest. Unfortunately, these devices do not furnish a continuous core, since they sample small portions of the reservoir at selected intervals. While they are of tremendous value in formation evaluation and for petrographic studies, alteration of percussion side- wall cores makes them unsuitable for the special core analysis tests that furnish hard engineering data. It is anticipated, however, that tools such as the new sidewall device designed to drill 1-in.-diameter core§ at right angles to the wellbore will overcome this latter limitation. . CORE.ANALYSIS Conventional core analySis. Of all commonly available cor- ing methods, this is the most important source of informa- tion in that it furnishes measured values of basic rock prop- erties. Porosity, permeability, residual fluids, lithology and texture are some of the parameters that characterize a core vertically, and representative samples are commonly taken every foot (and more frequently when core examination in- dicates the need). A quick look at these cores and their tabulated and plotted data identifies zones of greatest storage capacity (porosity), greatest flow potential (permeability) and the presence of and magnitude of residual oil (Fig. 1). Relative changes in these properties with depth are easily observed, and average properties of selected zones can be compared for relative quality. Grain size, an indication of sorting, color of the rock, presence of laminations and other important structures WORLD OIL, March 1985 TABLE 1—Geological data obtained by core analysis ¢ Formation lithology (sandstone, limestone, dolomite, etc.) Texture (grain size, distribution, and orientation) © Sedimentary structures (laminations, cross-bedding, root casts, worm burrows) Porosity type (storage capacity) intergranular intragranular intercrystalline © Permeability (flow capacity) © Rock color e Presence or absence of oil (fluorescence) e Formation presence and thickness (tops and bottoms) © Formation sequence © Formation age, facies and correlation (biostratigraphy) © Depositional environment ¢ Fracture definition vugular-moldic fracture microporosity depth and occurrence width length mineralization dip angle staining dip azimuth © Diagenesis (chemical, physical and biologic changes after deposition) © Geochemical (source bed studies) organic richness thermal maturity type of organic matter —_ liquid hydrocarbon potential © Trace elements and insoluble residues @ Paleomagnetism Permanent record of core appearance and fluorescence (core photo) - TABLE 2—Completion data obtained by core analysis © Mineralogy (fabric and pore filling minerals type and occur- rence) © Clay morphology (form and structure) © Clay distribution and quantity © Porosity magnitude and distribution ¢ Residual oil quantity and distribution Type of fluid production expected Gas-oil and oil-water contacts ® Grain size distribution (gravel pack selection) © Formation-rock compatibility with completion and workover fluids ¢ Vertical permeability (define need for frequency of perfora- tions and cross flow expected) © Horizontal permeability (selection of perforation intervals) © Critical water estimates (quantity of water held immobile) ¢ Acidization susceptibility and fracture treatment design are described. Fractures, vugs, and color, intensity and dis- tribution of oil fluorescence are also reported. Supplemen- tary data such as grain density, grain size distribution, cation exchange capacity and acid solubility typically are furnished on request. Core photography offers a permanent and objective rec- ord of both the core’s appearance and fluorescence (Fig. 2). The presence of oil-saturated rock and non-fluorescing shale zones are thus documented, and a record of the preserved core is established. This is of particular value for needs that may occur years after the core is cut (i.e., net pay determina- tion) or when well participants are located at prohibitive travel distances from the point of analysis. Color videotape — DOWDCO SPONGE CORE DATA GRAPHICS MAJOR OIL COMPANY SPONGE WELL #1 SAN ANDRES FORMATION ECTOR COUNTY TEXAS OIL SATURATION WATER POROSITY PERMEABILITY PRODUCTION CORE, SPONGE, TOTAL SATURATION | INDEX DEPTH} <G@---------- 2$--------- @ | «Q------» 1] ’G----------~- > 16 | O¢------- 2106 4615 ay “. ; ; <2 | 46625 | i) | | | H | i | Ht : == = =F == = ia fe me we 1 L 2 AVERAGE CORE OIL: 21.5 AVERAGE SPONGE OIL: 8.3 AVERAGE POROSITY: 6.7 FORMATION VOLUME FACTOR: PAGE: 1 LL + AVERAGE TOTAL OIL: 29.8 AVERAGE WATER SATUR.: 50.7 AVERAGE PERMEABILITY: .? isl ancl M weet fi a Oh tw ane - | USE FOR ANSWER rT = \* ube FOR ANSWER | her S| | | ip aa bat rsa faut S| > | ogee \ iat chet ater Wn eee va Ge an oh rapa 5 fom $ ( Bo \S ola fe es Tho wily Aha UW Caw b 3 ues alti xt Re is Waed fo lis! Ape Pe ro RE) nid 2g Bg SpAst: ' MELGCAESO RTT ey Ve wes sh Hapa gg ape: rat fs ae “Patsy Ss an co | cy [_ “peg oe be a a REG 7 2 Tistiaty Sf | = cl va: +31 tel ifehs gsr eee ey Hf f ea nl ) | | Tiel | |i ron _| rt EH ried fo siinabaty | aoc 04 9) > Obtew Sy, R 0 | is Nepyeng | 1 | | | \.1 . | | | | i | i r ce eee co vr ts i PCR AAW lon | r = | weber hare \\ — “IZ AL ede, tk WoW KWo “pp ne agente ae Piet Teehas <alions ye Wihtoe Z Z| ll —_ 1 | im FOR ANSWER | 25 _2- The. therium Senes |_| 1a 4- “The naw Senes | | Cc Cer Coco | | T_T | | | | TA J Pa “the pot ss tum Hotep ap Lae CI Percfeteapuscisas canter traces a ie | Selle a, a5 a cnsegrenta, eet méassobl ingercsareaee —] ES 5 Qywe Si ive Saasty af Ath we vodldelion, wo Et