LEMIGAS Core Laboratory :: Sedimentology

Introduction

Routine
Core

Special
Core

Rock
Mechanic

SEDIMENTOLOGY
	One of the main objectives of reservoir geology evaluation is to examine the impact of reservoir heterogeneities on reservoir behavior. In other words, it is an investigation of the three dimensions continuity/discontinuity of porosity and permeability within reservoirs at all scales, and to obtaining a clear view of how this continuity will influence both static and dynamic fluid distributions.
	Cores provide the sedimentologists at LEMIGAS the opportunity to determine:
	» The origin of sedimentary deposit and the recognition of genetic units in the vertical and lateral sequence, which are achieved by detailed core description. » Rock/mineral composition, rock/grain texture, and diagenetic processes that are obtained from the integrated sedimentological laboratory analysis.
	Knowledge of the processes responsible for the described features in cores can be used to both predictive depositional models and pore structures for the sequence of interest. Therefore, by integrating the geological information with pore and fluid attributes determined from engineering analyses, a reservoir geometry with its constituent facies architecture can be delineated in order to optimize volume estimations and to asses reservoir connectivity and flow path tortuosity.
	Laboratory Services:	Sedimentology Studies:
	» Core Description » Sieve Analysis » Petrography » Petrographic Image Analysis » X-Ray Diffraction (XRD) » Scanning Electron Microscope (SEM) & EDAX » Cathodoluminescene » Fluid Inclusion	» Depositional Model » Diagenetic Model

	• Core Description:
	Core description is carried out in order to interpret the origin and geometry of reservoir rocks. Parameters such as depth, texture (color, grain size, sorting), lithology, primary/secondary sedimentary structure, bedding/contact features, vertical succession of the rock body, trace fossil, oil stains, and qualitative porosity are routinely observed, described, and illustrated. Porosity and permeability distributions determined from core analysis and both potential permeability barriers and conduits may be defined and physically characterized. In addition, the studied cores are used to calibrate the measurement of reservoir properties that performed using wireline logs, well tests and even a geophysical seismic.

	• Sieve Analysis:
	The purpose of sieve analysis is to determine grain size. The grain particles varying between 0.002 and 250 mm may be separated into regular size class interval by shaking a sieve nest. The sieve mesh sizes, raw weights, weight percentages and cumulative percentages are recorded. Statistical analysis is then carried out and the calculated data helps in interpreting the depositional environment of studied area.

	• Petrography:
	The main objective of sedimentary petrography is two folds: 1) Interpretation of depositional environment, and 2) Constuction of diagenetic regime. The analysis is performed on thin sections and the data collected includes mineralogic composition, grain and sediment provenance, fabric studies and determination of the sequence of diagenetic events. It is know become a routine procedure to collect the data quantitatively so that statistical analysis of facies associations and reservoir quality can be conducted.

	• Petrographic Image Analysis:
	Petrographic Image Analysis (PIA) can alleviate or eliminate the problems that may arise from standard petrographic analysis such as time consuming and synonymous observation and classification. PIA uses digital image acquisition to obtain quantitative information on sizes, shapes and numbers of pores exposed in thin sections. Quantitative variables derived from PIA can be correlated with petrophysical properties (Ehrlich, et al., 1991).

	• X-Ray Diffraction:
	Lemigas performs analysis of bulk rock, clay and swelling clay components using x-ray diffraction (XRD) analysis. XRD work is especially important for complete clay characterization that cannot be performed using thin section petrography or scanning electron microscopy alone. High quality XRD results are obtained by the use of rigorous sample and standard preparation technique. Lemigas technicians have minimized the effects of particle orientation and particle size in the preparation process. Quality results are enhanced further by the use of an automated XRD and advanced computer software.

	• Scanning Electron Microscope (SEM):
	Scanning Electron Microcope (SEM) combined with Energy Dispersive X-ray Spectrometry (EDAX) provides important microscopic information that needed on reservoir description. The following reservoir characteristics are a major contribution gained from SEM analysis:
	» Pore types identification » Architecture of the pore system » Clay minerals identification and morphology » Possible compatibility problems with well completion chemicals » Alteration of minerals

	• Cathodoluminescene:
	Cathodoluminescene (CL) works as an emission of light from crystalline materials by excitation with ‘catodhe ray’. CL petrography is now a routine technique that can provide essential information on:
	» provenance » growth fabrics » diagenetic textures » mineral zonation » Alteration of minerals » more precise quantification of constituents and fabrics
	In addition, CL readily enables distinction between detrital and authigenic components, and, with careful modal analysis, permits quantifications of porosity loss in sedimentary rocks due to pressure dissolution (Houseknecht, 1988). Burley, et al. (1989) believed that CL petrography is a pre-requisite to fluid inclusion studies in order to define the relationship between growth zones or healed fractures and multiple inclusion generations.

	• Fluid Inclusion:
	Most sedimentary diagenesis involves recrystallization or overgrowths on original minerals, or the growth of new phases. This new growth may trap fluids (waters, petroleum, gases) as inclusions that provide data not only on the nature, composition, pressure, and density of the fluids present during diagenesis, but particularly on the temperature at which the host crystals grew. The temperature and composition can be translated into three kinds of information of real value to petroleum exploration and development: » temperature, age and duration of mineral cement growth. » temperature and timing of episodes of fluid migration (including water, oil and gas). » temperature of fracture healing. Fluid inclusion geothermometry provides a means of timing modification of reservoir quality relative to oil or gas migration.