Coring Operations Basics

Petrophysical Data Acquisition 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

Objective: Review Coring Operations

Coring process and types/equipment

Core handling at wellsite

Value of Core Information

Core Analysis

OUTLINE Why Core? Wellsite Requirements for High Quality Core Early Core Data Opportunities

Introduction: Why Cut a Core?

Calibrating core‐derived properties with log response is critical

That’s why !!!!

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)

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.

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

• Reduce exploration, sanction, and development risks • maximize field returns

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

The Coring Process and Types of Cores

Full Diameter Core Bit vs. Sidewall Coring

Sidewall Coring Types

Percussion• Explosive charges for

each hollow bullet• Best recovery in

unconsolidated lithologies

Rotary• Rotating head cuts

horizontal plug• Multiple samples per run

Sidewall Sample Gun

Sidewall Core Retrieval

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:• 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

Limitations:• Sample quality

– Tumbling– Partial penetration– Sample damage due to impact

• Large holes• Sample size• any others?

Rotary Sidewall Cutter and Plugs

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

Full Diameter or Whole Coring

Coring or Cuttings?

Core Bit and BarrelFormation Samples

Coring Bit

Full Diameter Core

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

Limitations:• Typically taken in 20 – 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?

Sidewall coring (SWC) • Depths more precise based on previous logging runs (open hole or

LWD)• Relatively inexpensive• Typically more fractured or compressed

Rotary SWC (RSWC)• Sample quality better, more expensive than percussion• Good in consolidated lithologies

Full diameter (FD)• 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!

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