FORMATION EVALUATION

CHAPTER 1PART 119/09/20131CGE 674 FORMATION EVALUATION Role and Function of PetrophysicistIntroduction to Well LoggingLogging HistoryPrinciples of Openhole Logging Tools GR, SP, Neutron, Density, Acoustic, Resistivity, InductionOther Sources of Subsurface Data

OUTLINE19/09/20133LEARNING OUTCOMEAfter completing this chapter, you should be able to:

1. Describe the basic principle of formation evaluation and well logging

2. Explain the logging tools and their operating principles.

3. Discuss the basic log response of respective logging tool.

19/09/20134ROLE OF PETROPHYSICIST5Rock property and fluid type identifier.Petrophysical data are derived mostly from indirect measurements.

Example: Hydrocarbon intervals are related to high formation resistivity measured by logging tools.Oil is differentiated from gas based from neutron response and neutron respond is related to hydrogen counts in the formationProductive rocks are differentiated from non-productive rocks based from a number of different log data like gamma ray, density and neutron.

Thus, due to indirect measurements, petrophysics requires interpretation of the data available to arrive at defining the reservoir properties and the types of fluid in the borehole drilled.

Interpreted Log

Bedding scale

Slab core scale

Cuttings

Pore scaleWHO ARE PETROPHYSICIST?

Net to Gross Porosity Fluid Saturation Lithology Rock Types Fluid Type/Contacts Edited Sonic Log Edited Density Log Fluid Contents Cased Hole Logs Well Composite Saturation vs Height Permeability Flow Units Fluid Type/Contacts Elastic Moduli Cement Evaluation Casing Evaluation Perforating Intervals19/09/20136ROLE OF PETROPHYSICIST

19/09/20138INTRODUCTION TO WELL LOGGING19/09/20139THE WELL LOGSData records of formation rock properties

Continuously recorded versus well depth

Measured by logging tools lowered into the well

Conveyed by electric cable (called Wireline Logging)

Recorded during drilling (called Logging While Drilling).

Recorded by means of resistivity, nuclear, acoustic or magnetic measuring devices

19/09/201310Two main types of well logs

Open hole logs

Well logs run inside a well while the formation is still exposed or open

Cased hole logs

Well logs run inside a casing or tubing, mainly for production/injection profiling and reservoir monitoring purposes

Casing and cement evaluation logs, corrosion monitoring logsTYPE OF WELL LOGS19/09/201311Wireline conveyed logging

Drill pipe conveyed logging (TLC/PCL)

Logging While Drilling (LWD)

Coiled tubing conveyed logging

Slick line (piano wire) conveyed logging

CONVEYANCE METHODS19/09/201312WIRELINE LOGGING

Well logging tools are loweredinto the well by means of anelectric cable attached tothe head of the tool string.

Power and tool commands aresent downwards and data is transmitted upwards, by meansof a telemetry tool.

IDW (Integrated Depth Wheel) measures the length of cablelowered into the well, thusproviding depth measurement19/09/201313PIPE CONVEYED LOGGING

Normal wireline logging tools are attached to the drill pipe by means of a side-entry sub and lowered into the well.

Pipe Conveyed Logging System is used in wells where the logging tools cannot be lowered into the well using a logging cable, due to hole conditions.19/09/201314LOGGING WHILE DRILLING

19/09/201315COILED TUBING CONVEYANCE

Logging tools, usually cased hole logging tools, can be attached to the end of a coiled tubing and lowered into the well.

A special coiled tubing, with an electric cable inside, is required to transmit power and data to and from the logging tools.19/09/201316WHY DO WE RUN LOGSTo derive input parameters for calculating hydrocarbon volumes as follows:

HCIIP = GRV x N/G x F x Sh x 1/FVF

GRV = Gross Rock VolumeN/G = Net to Gross Ratio = Formation PorositySh = Hydrocarbon SaturationFVF = Formation Volume Factor (Bo or 1/Bg)

Hydrocarbon volume calculation

Definition of Net to Gross Ratio

19/09/201321THE ESSENTIALS WELL LOGSGamma Ray logs: to differentiate reservoir rock from non-reservoir rock

Porosity logs: to determine net reservoir rock with potential to store hydrocarbons

Resistivity logs: to calculate water saturation, which in turn provides hydrocarbon saturation

19/09/201322GAMMA RAY LOG

GR Log measures natural Gamma Rays and is used to differentiate between reservoir and non-reservoir rock19/09/201323GAMMA RAY LOGDiscrimination between reservoir and non-reservoir rocks

Computation of clay content in reservoir rocks

Well to well correlation in a field

Identification of reservoir characteristics

Determination of depositional environment

19/09/201324POROSITY LOG

Bulk density log measures formation density and is used to compute formation porosity19/09/201325POROSITY LOGPorosity can be computed using various porosity logs

Three main types of porosity logsBulk Density LogNeutron Porosity LogSonic Porosity Log

Porosity logs can be used to determine the Net Porous Reservoir Thickness

Determination of hydrocarbon type based on the combination of various porosity logs

19/09/201326RESISTIVITY LOG

Resistivity log measures formation resistivity and is used to identify hydrocarbon bearing zones and compute hydrocarbon saturation19/09/201327RESISTIVITY LOGIdentification of hydrocarbon bearing reservoirs

Determination of Net Pay thicknesses

Calculation of hydrocarbon saturation

Identification of productive reservoirs

Estimation of formation permeability

19/09/201328LOGGING HISTORY

YearDescription1927First electrical log was recorded in a well in the small oil field of Pechelbronn, in Alsace, a province of north-eastern france.Single graph of electrical resistivity of rock formations was recorded by station method.sonde was stopped at periodic intervals in borehole, measurements made, and calculated resistivity was hand-plotted on a graph this procedures was carried out from station to station until entire log was recorded.Resistivity log was used to detect HC present in the formation.1929Electrical resistivity logging was introduced on a commercial basis in Venuzuela, US, Russia and Dutch East Indies.Usefulness: for well to well correlation and identification of potential HC-bearing strata. 1931Include SP measurement with Resistivity curve on electrical log. Schlumberger brothers (Marcel & Conrad) perfected a method of continuous recording1936Photographic-film recorder was introducedElectrical log consisted of SP curve, short normal, long normal & long lateral resistivity curves, was predominant in logging activity from 1936 to late 1950s (curves were recorded simultaneously after about 1946).Electrical LoggingLOGGING HISTORYYearDescription1930sThe development of dipmeter began with the anisotropy dipmeter tool.

1943Three-arm dipmeter device, with an associated photoclinometer was introduced permitted both direction and angle of formation dip to be determined (SP sensor at each arm).1946SP sensors were replaced by short resistivity devices made dip measurements possible in wells where SP had little correlatable detail.Mid-1950sFirst continuously recording electrical dipmeter sonde (used 3 microresistivity arrays and contained a fluxgate compass) was introduced.TodayA 4-arm dipmeter tool records 10 microresistivity curves simultaneously, and a triaxial accelerometer and magnetometers provide highly accurate info on tool and deviation azimuth.Processing data done exclusively with electronic computers.Dipmeter LogLOGGING HISTORYYearDescription1941Neutron log was first described by Pontecovo.In combination with GR log, neutron log enhanced lithological interpretations and well-to-well stratigraphic correlations.1949Attention to neutron log as a porosity indicator.1962SNP sidewall neutron porosity tool was introduced.1936CNL* compensated neutron tool was introduced.Dual Porosity neutron tool combines those 2 neutron measurements into a single tool.GR and Neutron Tools (first use of radioactive properties in well logging)LOGGING HISTORYYearDescription1950sMicrolog tool was introduced used a miniature linear array of 3 electrodes imbedded in the face of an insulating pad, which is applied to the borehole wall.Microlog recording is also useful to delineate permeable beds, and other microresistivity devices help establish resistivity profile from the invaded zone near the borehole to the non-invaded virgin formation.1951Laterolog tool was introduced (the first focused deep-investigating resistivity device) focused resistivity logs are well adapted for investigating of thin beds drilled with low-resistivity muds (eg. Salt muds & highly resistive formations)1953Microlaterolog tool was developed for salt muds. The MicroProximity log and MicroSFL* log have followed.TodayDLL* dual lateral log tool (deep laterolog and shallow laterolog measurements) is the standard.Usually run with a MicroSFL device as wellEarly Porosity Determination & Microresistivity MeasurementLOGGING HISTORYYearDescription1949Induction log was developed, as an outgrowth of wartime work with mine detectors, for use in oil-based mud.However, its superiority over electrical log in freshwater muds was soon recognized.1956Combine a five-coil induction device with SP curve and a 16-in normal to make induction electrical tool.1959Five-coil device was replaced by one with a six-coil array with deeper investigation.1963DIL* dual induction log was introduced, now is the standard deep induction, medium induction, and shallow resistivity-measurements.The shallow resistivity-measuring device is now a focused resistivity device a Laterolog 8 on the 1963 tool and an SFL device on current toolsA new dual induction log, the Phasor* induction, provides improved thin-bed response, deeper depth of investigation, and greater dynamic resistivity range.Induction Log (replace original electrical log in freshwater muds)LOGGING HISTORYYearDescriptionSince 1930Logging cables have been used to lower geophones into wells to measure long-interval acoustic travel times from sound sources at the surface.Late 1950sSonic log was accepted as a reliable porosity logs its measurement responds primarily to porosity and is essentially independent of saturation.Sonic log, coupled with focused resistivity logs (laterolog and induction) made possible modern formation evaluation from well logs.Sonic log measure porosity; focused resistivity logs measure true resistivity of non-invaded virgin formation.Subsequent improvements in sonic logging BHC borehole compensated sonic, LLS* long-space sonic, and the Array-sonic* tools.Sonic LogLOGGING HISTORYYearDescriptionEarly 1960sLogging of formation bulk density (measurement of formation porosity), was commercially introduced.1964An FDC* compensated formation density log (compensated for the mudcake), was quickly followed.1981Litho-Density* log provided an improved bulk density measurement and a lithology-sensitive photoelectric absorption cross section measurement.Density LogLOGGING HISTORYYearDescription1937Sidewall coring, using a hollow, cylindrical bullet shot into formation and retrieved by pulling it out, has existed since 1937.1957A formation tester was introduced recovered a sample of formation fluids and pore presure was measured during the sampling process.FIT formation interval tester and RFT* repeat formation tester have followed (RFT tool can make unlimited number of pressure measurements and recover two fluid samples per trip.1978 & 1985Dielectric measurements have been developed to handle formation with freshwater formation, or varies in salinity, or in which salinity is unknown.EPT* electromagnetic propagation log was introduced in 1978DPT* deep propagation log was followed in 1985.

Recovery of Physical Rock Samples & Formation Fluid Samples with Wireline ToolsLOGGING HISTORY19/09/201345THANK YOU!