MUDLOGGING, CORING, AND CASED HOLE LOGGING BASICS COPYRIGHT. Coring Operations Basics. By the end of this lesson, you will be able to:

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1 LEARNING OBJECTIVES MUDLOGGING, CORING, AND CASED HOLE LOGGING BASICS Coring Operations Basics By the end of this lesson, you will be able to: Understand why cores are justified and who needs core data Identify which type of core is most suitable based on data requirements and budget Identify three types of cores and explain the advantages and disadvantages of each type Understand the basic components of a whole coring equipment string 1

2 OBJECTIVE: REVIEW CORING OPERATIONS OBJECTIVE: REVIEW CORING OPERATIONS Coring process and types/equipment Core handling at wellsite Value of Core Information 2

3 CORE ANALYSIS Why Core? Usually the responsibility of the subsurface team to justify the expense and risk of taking cores Need cores to determine the basic petrophysical parameters including reservoir porosity and permeability Information needed is subtle and complex Obtaining high quality cores requires careful planning Usually services of a consultant coring expert are required Special attention must be paid to mud properties to minimize alteration of the cores INTRODUCTION: WHY CUT A CORE? Calibrating core derived properties with log response is critical Calibrating core-derived properties with log response is critical! 3

4 THE ROCKS HAVE A STORY TO TELL YOU NEED TO KNOW THE RIGHT QUESTIONS! Reservoir Potential Depositional Environment Diagenetic history Quality (production potential) of the rocks Correlate lithologic characteristics to log properties Fluid sensitivities to completion chemicals How to maximize production and minimize formation damage using proper exploitation procedures RESERVOIR ROCK SPECIMENS (CORES) Reasons core data are important: Fundamental information for reservoir exploration, description and exploitation. Positive evidence of hydrocarbon presence, storage capacity (porosity), flow capacity (permeability). Interpretation of the probable production of oil, gas or water. Understand reservoir performance, well treatment responses, calibration of well logs, a basis for reservoir estimation, modeling and exploitation. 4

5 WHY CORE AND FLUID SAMPLES? UNCERTAINTY = RISK WHY CORE AND FLUID SAMPLES? UNCERTAINTY = RISK 5

6 WHY CORE AND FLUID SAMPLES? UNCERTAINTY = RISK Reservoir Characterization and Modeling require a quantified and realistic description of formation properties Reservoir geometry, internal structures and heterogeneities, impact on fluid flow Size of reservoir, reservoir producing mechanisms, field development strategy and COSTS Maximize field returns Rule of Thumb: Obtain at least one good quality whole core from each significant reservoir that is developed WHO NEEDS CORE DATA? Geology Core description Facies analysis Stratification Lithology Diagenesis Geologic age Pore geometry Petrophysics Porosity, perm, Sw Capillary pressure pore geometry, saturation Electrical properties CEC Acoustic properties Reservoir Engineering Relative permeability Capillary pressure curves Critical gas saturation Pore volume compressibility Waterflood parameters 8 inches Carbonate breccia contains low gravity oil Production Technology Well injectivity Rock mechanical data Mineralogy/lithology for cementing, stimulation 6

7 THE CORING EQUIPMENT AND PROCEDURES FULL DIAMETER CORE BIT VS. SIDEWALL CORING Percussion Sidewall Cores Whole Cores 7

8 SIDEWALL CORING TYPES Percussion Lowest cost alternative Explosive charges for each hollow bullet Significantly disturbs the rock sample Best recovery in unconsolidated lithologies SIDEWALL SAMPLE GUN Rotary Drilled with small diamond bit Recovers virtually undisturbed sample Rotating head cuts horizontal plug Multiple samples per run Sample Bullet Wire cables Igniter Power charge Formation 8

9 SIDEWALL CORE RETRIEVAL Chronological Sample Taker (CST) Procedure at the surface Samples are pressed from bullets at surface Placed into plastic bottles with screw-on tops, tight gas seal Labeled for depth PERCUSSION SIDEWALL CORING (SWC) Advantages: Disadvantages Highest quality sidewall samples recovered from unconsolidated sand formations Typically Miocene and younger geologic age sediments Usable rock samples may also be recovered from hard rocks Including carbonates and consolidated sandstones Samples from the harder formations may be shattered and disturbed, but are still useful for petrographic studies and making thin sections for geologic examination 9

10 PERCUSSION SIDEWALL CORING (SWC) Advantages: Large number of samples in single trip (e.g., 90) Coring points are individually selected using wireline logs Available for temp up to 500 o F Faster and more cost effective Good in soft rocks ROTARY SIDEWALL CUTTER AND PLUGS Disadvantages Sample quality degraded Tumbling Partial penetration Sample damage due to impact Large washed out holes cause poor recovery Sample size is small Plugs up to 2 inches long, to 1 inch diameter 10

11 FULL DIAMETER OR WHOLE CORING CORING BIT Formation Samples Bit Coring or Cuttings? Core Bit and Barrel 11

12 FULL DIAMETER CORE FULL DIAMETER (WHOLE) CORE Advantages: Disadvantages: Whole cores provide the best quality and least disturbed samples for most petrophysical and geomechanical analysis. 12

13 FULL DIAMETER (WHOLE) CORE Advantages: Long, continuous sample of formation Selection of plug, whole core depths of core optimized Can maintain saturations better Wider spectrum of observations and tests Depositional facies and sequence determination Vertical plugs possible CORING TYPES: WHAT ARE TRADE-OFFS? Percussion Sidewall Coring (SWC) Relatively inexpensive Depths more precise based on previous logging runs (open hole or LWD) Typically more shattered or compacted by the impact Disadvantages: Typically taken in multiplies of 30 ft. sections Coring done while drilling not afterwards Requires one to several special trips in hole Typically slower drilling to enhance recovery Mudlog gas not reliable through cored intervals More expensive than sidewall options Higher potential for getting stuck while coring Higher potential for swabbingin while POOH with core Rotary SWC (RSWC) Sample quality better, more expensive than percussion Good in consolidated lithologies Full Diameter Whole Cores Cut more or less blind ; open hole logs missing Larger rock volume for analysis Requires special well site handling, transportation beyond that required by SWC processes No matter what the type of core, remember to make description and subsample core before leaving location! 13

14 LEARNING OBJECTIVES Understand why cores are justified and who needs core data Identify which type of core is most suitable based on data requirements and budget Identify three types of cores and explain the advantages and disadvantages of each type Understand the basic components of a whole coring equipment string 14