RESERVOIR ANALYSIS

Overview

analogue_1100x588

Outcrop and Well Interpretation

Diagense_neu

Diagenesis and Fluid Flow

seisseqstrat_550x294

Seismic Interpretation

palynostratigraphical_correlation

Palynostratigraphic Correlation and Integrated Sequence Stratigraphy

Outcrop and Well Interpretation

Focus
Facies, depositional geometries
Poroperm properties, reservoir potential
Structural analysis
Well log interpretation and correlation
Reservoir-outcrop analogue analysis

Well log interpretation and correlation
Vertical well log trends and their lateral changes within a seismic and biostratigraphic framework represent the most important data for basin-wide correlation. Well logs and GR spectroscopy from the outcrop provide two directly comparable data sets for outcrop-resrevoir studies.

Reservoir-outcrop analogue analysis
Lateral and vertical heterogeneities in facies, petrophysical properties and diagenetic overprint are critical parameters of targeted reservoirs. High-frequency, meter-scale vertical stacking patterns and their lateral variabilities within and across specific depositional environments exert a highly important control on fluid-flow behaviour in the subsurface.

High-resolution data sets of the reservoir architecture and the lateral/vertical distribution of key reservoir features allow improved reservoir models and therefore reduce exploration risk. In addition, such data sets are essential for forward numerical models of sedimentary systems and fluid-flow behaviour during basin development.

However, industry subsurface data sets bear inherent limitations in both vertical and lateral resolution imposed by the interpolation between wells and within 2D and 3D seismic data sets. These limitations can be redurced or overcome by outcrop-reservoir analogue studies.

Diagenesis and Fluid Flow

Focus
Field-studies, sampling
Thin section petrography
Cathodoluminescence
XRD, SEM
Poroperm properties
Major and minor element geochemistry
Stable and radiogenic isotopes
Fluid inclusion thermometry and Cryo-Raman spectroscopy
Crush-leach analyses

Field-studies, sampling
An essential prerequisite for a diagenetic study is the careful sampling in the field or from cores and cuttings. If possible, this should be undertaken by the responsible scientist. In the field, the areal distribution of certain diagenetic phases and of porosity types as well as eventual leaching episodes has to be established. In the case of dolomitization, precursor rock samples have to be collected as close as possible to the dolomitization front.

Thin section petrography and fabric analyses
Standard petrographic studies in transmitted and reflected light are a first step in outlining different diagenetic phases as well as macro-porosity. Also the horizontal or in the stratigraphy can be outlined. Selective dissolution of specific components or of parts of the rock is of special importance. Staining with different solutions, e.g. potassium ferricyanide, further helps in the analysis of the distribution of specific diagenetic phases.

Cathodoluminescence
Cathodoluminescence (CL) microscopy is a powerful tool for better outline of different diagenetic phases; it gives also the first hints to trace element contents of these phases. Cathodoluminescence can be applied to carbonate rocks as well as clastic sediments, but also to some ore types.

XRD, SEM
XRD analysis is crucial for the determination of different mineralogical phases; in the case of dolomitization, bulk mineralogy, stoichiometry and ordering of dolomites can be investigated, which are of importance to understand the type of dolomitization.
SEM is of special importance for the distribution of minute mineralogical phases as well as of microporosity and obstructing mineral phases, e.g. kaolinite, illite.

Poroperm properties
The poroperm properties and their regional and stratigraphic distribution are of special importance for applied studies, especially when cross-checked with other analytical results, e.g. with the distribution of pores observable in thin sections.

Major and minor element geochemistry
Geochemistry is an essential tool for most applied studies, especially when very small and areawise strictly defined samples can be taken and analyzed. Sr, Na, Fe and Mn are important tracers. Diagenetic overprint can often be well established with these analyses.

Stable and radiogenic isotopes
Stable isotopes (C, O) are a standard tool in diagenetic and fluid flow studies. They allow, for instance, to decipher if a rock contains the original sea-water values or has been strongly modified and recrystallized. It is also important to compare the values of less diagenetically altered rocks with those of altered ones. Negative or positive excursions, especially of carbon isotopes, can often be used for isotope stratigraphy, even in dolomitized rocks.
Sr isotopes are an important tracer for the amount of recrystallization and the rock-water interactions in a closed or open diagenetic system, but also for contact of more radiogenic fluids derived from specific lithologies.

Fluid inclusion thermometry and Cryo-Raman spectroscopy
Fluid inclusion studies provide information on the relative salinity of the fluids, from which the different diagenetic phases precipitated, as well as on their temperature, if pressure corrections are applied. Salinity calculated only from microthermometry may lead to an underestimation of true salinities, because not only Na ions may be present and complex mixtures are difficult to calculate.

Cryo-Raman spectroscopy, i.e. a combination of Raman spectroscopy and low-temperature microthermometry reveals in much greater accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions. This improved analytical method of fluid inclusions analysis is a valuable contribution for the interpretation of fluid history and fluid flow.

Crush-leach analyses
In the crush-leach method, the single diagenetic phases are crushed and the fluids entrapped in fluid inclusions are washed out with deionized water and/or methanol. Often Cl, Br, Na, K, Ca, Mg and Li are analyzed and their ratios calculated. This allows, for instance, to draw conclusions on the relationship between a diagenetic fluid and sea-water. From the salinity determined by microthermometry and the Cl concentration in the crush-leach solution, the values can be recalculated to estimate their concentration in the fluid inclusions. Halogen ratios, specifically Cl/Br, are useful indicators of the source of salinity, especially if seawater is supposed to be involved. In contrast to Cl and Br, elements such as Na, K and Li are easily changed from their original concentration by fluid-rock interactions.

Selected services are carried out in cooperation with other laboratories.

Seismic Interpretation

Focus
seismostratigraphic interpretation;
structural interpretation
basin architecture & development
structural balancing & subsidence/uplift modeling
lithofacies & petrophysical modeling

Palynostratigraphic Correlation and Integrated Sequence Stratigraphy

Focus
Palynostratigraphy – correlation at basin & reservoir scale
Palynofacies – depositional environment analysis & additional correlation
Integrated sequence stratigraphy – multidisciplinary cross-calibrated sequence stratigraphic analysis

Palynostratigraphy
provides high resolution stratigraphic frameworks throughout earth history. Palynomorphs cover a wide range of depositional settings – deep marine to near-shore and terrestrial – and can be used in surface and sub-surface samples. The focus of palynostratigraphic analysis in GeoResources is in the Palaeozoic, especially Devonian and Carboniferous. Palynostratigraphic analysis is based on the most recent global to regional correlation schemes.

palynostratigraphical_correlation

Palynofacies
quantifies the different groups of organic matter (palynomorphs and non-palynomorphs), giving detailed data about the depositional setting, to improve the basin analysis based on sedimentological and geochemical data. It provides different proxies to be used as additional stratigraphic tools (event stratigraphy). This increases significantly the resolution of well or basin correlation based on palynostratigraphy, especially in underexplored areas. Palynofacies data are part of the integrated sequence stratigraphic interpretation and the the final integrated basin modeling.

Integrated Sequence Stratigraphy
is a multidisciplinary cross-calibrated approach on sequence stratigraphic analysis. It is based on the combination of organic matter based proxies from extended palynofacies analysis and lithological analysis from wireline logs, mud logs and seismic data, which strongly improves the reliability of the sequence stratigraphic scheme. It also enables high-resolution correlation far beyond biostratigraphic resolutions, from basin down to reservoir scale, providing well corrrelation transects and interpreted seismic lines with high-resolution sequence stratigraphic units. It also can significantly improve the assessment of lateral continuities and vertical connectivities for flow and reservoir units. This workflow is developed and successfully applied by GeoResources on Devonian-Carboniferous basin fills of the northern Gondwana margin.