CHEN 490 Notes Log Examples (Final), Fall 2014

In the late 1950’s, the sonic log gained acceptance as areliable porosity log; its measurement responds primari- ly to porosity and is essentially independent of saturation. The sonic log, coupled with the focused resistivity logs — laterolog and induction — made possible modern for- mation evaluation from well logs. The sonic log provid- ed a measurement of porosity; the focused resistivity logs, a measurement of true resistivity of the noninvaded virgin formation. Subsequent improvements in sonic logging included the BHC borehole compensated sonic, the LSS* long-spaced sonic, and the Array-Sonic* tools. The latter tools per- mit the recording of the entire sonic wavetrain. From an analysis of the wavetrain, the shear and Stoneley transit times can be extracted as well as the compressional tran- sit time. The logging of formation bulk density, another measurement primarily dependent on formation porosi- ty, was commercially introduced in the early 1960’s. An FDC* compensated formation density log, which com- pensated for the mudcake, quickly followed in 1964. In 1981, the Litho-Density* log provided an improved bulk density measurement and a lithology-sensitive photoelec- tric absorption cross section measurement. The recovery of physical rock samples and formation fluid samples with wireline tools also has a rich history. Sidewall coring, using a hollow, cylindrical ‘‘bullet’’ shot into the formation and retrieved by pulling it out, has existed since 1937. Obviously, this technique has undergone continuous improvement over the one-half century since its introduction. For very hard rocks, downhole mechanical coring tools exist that actually drill out the rock samples. In 1957, a formation tester was introduced. It recovered a sample of the formation fluids and the pore pressure was measured during the sampling process. The FIT for- mation interval tester and the RFT* repeat formation tester have followed. The older tools could make only one pressure measurement and recover only one fluid sample per trip into the well; the RFT tool can make an unlimited number of pressure measurements and recover two fluid samples per trip. To handle those formations in which the formation water is fresh, or varies in salinity, or in which the salini- ty is unknown, dielectric measurements have been developed. The EPT* electromagnetic propagation log was introduced in 1978; the DPT* deep propagation log, in 1985. The preceding historical sketch has not, by any means, covered all the measurements now made with wireline well logging devices. Other logging measurements include nuclear magnetic resonance, nuclear spectrometry (both natural and induced), and numerous cased hole parameters. INTRODUCTION Fig. 1-2—Wireline logging operation. THE FIELD OPERATION Wireline electrical logging is done from a logging truck, sometimes referred to as a ‘‘mobile laboratory”’ (Fig. 1-3). The truck carries the downhole measurement in- 1-3 LOG INTERPRETATION PRINCIPLES/APPLICATIONS struments, the electrical cable and winch needed to lower the instruments into the borehole, the surface instrumen- tation needed to power the downhole instruments and to receive and process their signals, and the equipment need- ed to make a permanent recording of the ‘‘log.”” Fig. 1-3—A typical CSU wellsite mobile laboratory. The main winch contains up to 30,000 ft of seven-conductor logging cable; the optional small winch at the rear contains 24,000 ft of slim monoconductor cable for servicing producing wells under pressure. Data acquisition and computer equipment are inside the logging cab. For offshore-remote locations, the cab and winch assemblies are mounted on a skid. The downhole measurement instruments are usually composed of two components. One component contains the sensors used in making the measurement, called the sonde. The type of sensor depends, of course, upon the nature of the measurement. Resistivity sensors use elec- irodes or coils; acoustic sensors use transducers; radioac- tivity sensors use detectors sensitive to radioactivity; etc. The sonde housing may be constructed of steel and/or fiberglass. The other component of the downhole tool is the car- tridge. The cartridge contains the electronics that power the sensors, process the resulting measurement signals, and transmit the signals up the cable to the truck. The cartridge may be a separate component screwed to the sonde to form the total tool, or it may be combined with the sensors into a single tool. That depends, of course, upon how much space the sensors and electronics require and the sensor requirements. The cartridge housing is usually made of steel. Today, most logging tools are readily combinable. In other words, the sondes and cartridges of several tools can be connected to form one tool and thereby make many measurements and logs on a single descent into and ascent from the borehole. The downhole tool (or tools) is attached to an electrical cable that is used to lower the tool into and remove from the well. Most cable used in openhole logging today con- 1-4 tains seven insulated copper conductors. New cable developments include a fiber optics conductor in the center of six copper conductors. The cable is wrapped with a steel armor to give it the strength to support the tool weight and provide some strength to pull on the tool in case it becomes stuck in the borehole. The cable and tools are run in and out of the borehole by means of a unit-mounted winch. Well depths are measured with a calibrated measuring wheel system. Logs are normally recorded during the as- cent from the well to assure a taunt cable and better depth control. . Signal transmission over the cable may be in analog or digital form; modern trends favor digital. The cable is also used, of course, to transmit the electrical power from the surface to the downhole tools. The surface instrumentation (Fig. 1-4) provides the electrical power to the downhole tools. More important- ly, the surface instrumentation receives the signals from the downhole tools, processes and/or analyzes those signals, and responds accordingly. The desired signals are output to magnetic tape in digital form and to a cathode- ray tube and photographic film in analytical form. The photographic film is processed on the unit, and paper prints are made from the film. This continuous recording of the downhole measurement signals is refer- red to: as the log. FIELD UNITS This special-purpose unit is equipped with a mast. The standard offshore unit is used for Production Service operations on drilling platforms. Smaller transportable units are available for other applications. The standard Production Services field units have the computerized CSU* instrumentation system. *Mark of Schlumberger U LEGEND ‘Loceins ENomEER_JOHN DOE __uniT wo. 100_} arm nceco 2880 yo10.820 yom _a40_rx| Neo New Cone art weet -@uasra OLosieu FT Ost ont sren rest fo seccnos DATE LOGGED_5-2-55 _TO_7-3-55 ___| wR wore TURNS API CC'S: se ERO ata | 1s Taras earn cr ore or same sr_o000 | bo ncouae our RETURNS Zz __AT. KB_265.5 DEPTH CORRESPONDS TO DRILL PIPE MEASUREMENTS. — EMERG + OL EMULSION. LOW LITHOLOGY POROSITY J sano EEE] umestone ESSE ag x sHace_E ==) vocomme EZ eee 24 cnert_EEEERE crane ve fain 7 a85e Lowe Famed orpamvonite SQ 9000 a = 2335 TOTALGAS seeceees METHANE —= [DRILLING RATE. MUD ANALYSIS. CUTTINGS ANALYSIS. Gre ren nn. Lar NS aE [THOLC OL GAS. ot GAS. 190 190. % pag ee A. BIT AND CORE RECORDS B. DRILLING RATE CURVE C. LITHOLOGY D. OIL CURVE (MUD) E. METHANE CURVE (MUD) F. TOTAL GAS CURVE (MUD) G. MUD CHARACTERISTICS H. OIL CURVE (CUTTINGS) I. METHANE CURVE (CUTTINGS) J. TOTAL GAS CURVE (CUTTINGS) Fig. 11.2. Mud logging report. Courtesy Baroid Sales Division, National Lead Company. 196 WELL LOGGING Vv [Chap. 11 Line in drilling operations column Thanae Chania AT 9.00 ANAND #0O;P =) A rations. @ phe GEOLOGRAPH, CHART moves to the left indicating that 40 7, ‘orenaton LLIN ‘O- driller got on bottom with new bit and a = en Lease oe) started drilling at 11:26. Total trip time, ——— ee NE-MWn BE sec. 12. JEN »2W as indicated by “Trip Action”, 3 hours vs = coun LW/COLA/ state and 17 minutes. : aate ot toon JOS rue on Bern: ro.orf: omg Time DRG OPERATIONS. vores te) B This is the way a connection looks on the Geolograph chart. The drill- er raised the drill pipe from bottom at 12:03, broke out the kelly, picked up a single pipe (adding it to the drilling string), picked up the kelly and resumed drilling. This operation required 11 min- utes, and the driller has written the depth of the hole, at that time, on the chart. Thus, every connection is a con- venient datum for determining the depth of any drilling or down-time break, either immediately above or below. — 20 20 0 9:00 os 10 20 [ A 4-foot hard streak was encount- ih 2s ered at 5,235 feet, as indicated by : 20 the increased spacing of the foot marks 3s on this time chart. 40 4s ° D A connection was made at 5,259 lone _ feet and a vertical test was run at this point to determine the vertical devi- ation of the hole. The driller has noted on the chart that the test was actually taken at 5,250 feet and the deviation was ¥% degree. The vertical test and connec- tion required 34 minutes. o E Soft bed was drilled from 5,266 to 20 5,269 feet. Because of the thinness ss of this bed, no core or drill stem test 11:00 was attempted. a F This section represents 5 feet of drilling. Note that every 5 feet the base line is offset for 1 foot, making a convenient marker for determining the depth of significant drilling changes. 3s G Connection was made at 5,287 feet. ¥2100 Note similarity to the record at “B”. 1s H A hard streak was encountered 20 from 5,288 to 5,290 feet. = | At 5,290 feet, the formation soft- ” ened, drilling continued to 5,300 oa feet where the driller was given orders *e to cease drilling and circulate for ss samples. 1:00 os J Circulating for samples started at 6:39 as indicated by movement of the line to the right. After circulating for 35 minutes, samples showed stain 30 and odor, and a drill stem test was 88 ordered. Fig. 11.1. Typical mechanical drilling log record. Courtesy Geolograph Mechanical Well th Logging Service. Deters L 45 OEPTH 4615 4626 4625 4630 4835 | 4640 4645 4685 4655 4666 4665 46706 4675 | 4680 4685 46396 4635 4769 4796S DOWDCO SPONGE CORE DATA GRAPHICS MAJOR OIL COMPANY SPONGE WELL #1 SAN ANDRES FORMATION ECTOR COUNTY TEXAS OIL SATURATION WATER POROSITY PERMEABILITY PROOUCT ION CORE, SPONGE, TOTAL SATURATION INDEX <G---------- 2G---- 2 S6--------— 2S~--------- 28 6¢------- 2106 — 7 7 — —= 1 a —— | | | Wy —_- = i t--lH AVERAGE CORE OIL: 21.5 AVERAGE SPONGE OIL: 8.3 AVERAGE POROSITY: 6.7 FORMATION VOLUME FACTOR: PAGE: 1 AVERAGE TOTAL OIL: 29.8 RVERAGE WATER SATUR. : AVERAGE PERMEABILITY: 1,1 $0.7 .? d 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 engimeering 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 cae, TABLE 1—Geological data obtained by core analysis e 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 © Presence or absence of oil (fluorescence) © 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 e@ 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 4665 4670 4675 | 4680 | 4685 | 46390 4635 4760 $7958 DOWDCO SPONGE CORE DATA GRAPHICS MAJOR OIL COMPANY SAN ANDRES FORMATION SPONGE WELL #1 ECTOR COUNTY TEXAS WATER SATURATION OIL SATURATION CORE, SPONGE, TOTAL POROSITY PERMEABILITY PRODUCTION HH ee a a ! 4 =H AVERAGE CORE OIL: 21.5 AVERAGE SPONGE OIL: 8.3 AVERAGE POROSITY: 6.7 FORMATION VOLUME PAGE: 1 AVERAGE TOTAL OIL: 29.8 AVERAGE WATER SATUR. : AVERAGE PERMEABILITY: FACTOR: 1.1 so.? 2?