Objective :
The objective of every coring operation is to gather information that leads to more efficient oil or gas production .
some specific tasks might include the :
Geological objectives :
- Geologic maps
- Fracture orientation
- Lithological information :
- Rock type
- Depositional environment
- Pore type
- Mineralogy/ Geochemistry
Petrophysical and reservoir engineering :
- Capillary pressure data
- Permeability information :
- Permeability / Porosity correlation
- Relative Permeability
- Data for refining log calculations :
- Electrical properties
- Grain density
- Core Gamma Log
- Mineralogy and cation exchange capacity
- Enhanced oil recovery studies
- Reserve estimate :
- Porosity
- Fluid saturations
Drilling and completions :
- Fluid/ formation compatibility studies
- Grain size data for gravel pack design
- Rock mechanics data
Why Core Analysis is important for Development Plan ?
Exploration :
- Exploration of structures and determination of their physical characteristics.
- Estimate of production possibilities for wildcats, extension wells and edge wells .
Well completion and workover operations :
- Selection of intervals for testing .
- Interpretation of tests during drilling -Comparison results -Explanation of test anomalies etc.
- Determination of the best combinations for order of completions when there are several horizons .
- Selection of intervals and choice of depths if plugs , packers , cement plugs etc. are installed to keep out water and gas influxes .
- Selection of intervals for perforations or acidizing .
- Estimation of completion efficiency .
- Selection of intervals for recompletion .
Field Development :
- Determination of optimal spacing .
- Determination of the location of new wells .
- Definition of field boundaries .
- Estimate of production for determination of field equipment .
- Definition of contact zones for the various fluids .
- Structural and stratigraphic correlations .
- Sampling and bases of interpretation for other well logging .
- Selection of intervals for optimum completion .
Well and reservoir evaluation :
- Determination of net pay zone .
- Estimate of initial productivity
- Estimate of water production rates and injection pressures .
- Estimate of decompression zones invaded bay water or gas , and simultaneous production of various zones .
- Estimate of probable recovery .
- Estimate of oil or gas reserves in place .
- Estimates for equitable shares in unitization operations .
- Reservoir engineering and programming for maintaining pressure or secondary recovery .
- Forecasts for optimum well completion and maximum future recovery .
Core Analysis Tests :
The experiments done on core sample are as following :
- Routine Test
- special test
- Geo-mechanics tests
- Formation damage tests
1. Routine Test :
- Porosity measurements
- Permeability measurements
- Saturation's measurements
- Grain density
These measurements are made to correct the well logs results and use this correction in non-cored intervals , as example :
- Tyne the Archie's equation constants (a, m ,n) until having matching to core saturation.
- Get a correlation between porosity and permeability .
- Rock Typing .
2. Special Test :
- Relative permeability : used for multiphase modelling in case of having saturation less than 100 % .
- Capillary pressure : used to determine the thickness of transition zone and the saturation distribution in this interval .
- Wettability : used a criteria in EOR applications screening .
- Rock compressibility : used especially for material balance calculations to estimate oil recovery and also in geomechanically applications .
- Acoustic properties : used to tune the Archie's equation constants to estimate the saturation and porosity from ell logs.
- Other tests like XRD and SEM .
3. Geomechanics Test :
Geomechanics has an important role to play in assessing formation integrity during well construction and completion and in the response of the reservoir to oil production , water injection and depletion .
The tests most commonly used to determine fundamental rock mechanics parameters are described including :
- Unconfined compressive strength
- Thick Wall Cylinder .
- Tensile Strength.
- Triaxial Tests .
- Pore Volume Compressibility .
- Elastic Moduli.
- Particle Size Analysis .
Application of Core Analysis Data:
- Permeability Modelling .
- Facies distribution modelling .
- Production prediction .
- Residual Oil Saturation targeted by EOR .
- STOIP calculation .
- Sand control .
