mudlogging, coring, and cased hole...

Coring Operations Basics

MUDLOGGING, CORING, AND CASED HOLE LOGGING BASICS

LEARNING OBJECTIVES

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

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© PetroSkills, LLC., 2016. All rights reserved._____________________________________________________________________________________________

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OBJECTIVE: REVIEW CORING OPERATIONS

Coring process and types/equipment

Core handling at wellsite

Value of Core Information

OBJECTIVE: REVIEW CORING OPERATIONS

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© PetroSkills, LLC., 2016. All rights reserved.

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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 petrophysicalparameters 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!

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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.

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WHY CORE AND FLUID SAMPLES?UNCERTAINTY = RISK


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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

Production Technology Well injectivity Rock mechanical data Mineralogy/lithology for

cementing, stimulation8 inches

Carbonate breccia contains low gravity oil

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THE CORING EQUIPMENT AND PROCEDURES

FULL DIAMETER CORE BIT VS. SIDEWALL CORING

Percussion Sidewall Cores

Whole Cores

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SIDEWALL CORING TYPES

Percussion Lowest cost alternative Explosive charges for

each hollow bullet Significantly disturbs the

rock sample Best recovery in

unconsolidated lithologies

Rotary Drilled with small

diamond bit Recovers virtually

undisturbed sample Rotating head cuts

horizontal plug Multiple samples per run

SIDEWALL SAMPLE GUN

Sample

Formation

BulletIgniter

Power charge

Wire cables

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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

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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 500oF

Faster and more cost effective

Good in soft rocks

Disadvantages Sample quality degraded Tumbling Partial penetration Sample damage due to

impact

Large “washed out” holes cause poor recovery

Sample size is small

ROTARY SIDEWALL CUTTER AND PLUGS

Plugs up to 2 inches long, 0.875 to 1 inch diameter

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FULL DIAMETER OR WHOLE CORING

Coring or Cuttings?

Core Bit and BarrelFormation SamplesBit

CORING BIT

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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.

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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

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 “swabbing-

in” while POOH with core

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

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

Rotary SWC (RSWC) Sample quality better, more

expensive than percussion Good in consolidated

lithologies

No matter what the type of core, remember to make description and subsample core before leaving location!

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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

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