Page 188 - Petrophysics

PERMEABILITY-POROSITY R.ELATIONSHIPS 161

and compatibility between the measured parameters; (2) integrate
downhole measurements with data from pore studies, core analysis,
and geophysical surveys through interscale reconsolidation; (3) identify
lithofacies; (4) relate and integrate petrophysical interpretation with
geochemical, sedimentological, stratigraphic, and structural information;
and (5) contour different reservoir parameters such as porosity,
permeability, net thickness, tops and bottoms, fluid saturation, and fluid
contact.

Megascopic Heterogeneity
This scale of heterogeneity represents the flow units, usually
investigated through reservoir simulation. In fact, reservoirs are
engineered and managed at this scale of interwell spacing, which is
commonly inferred from transient pressure well test analysis, tracer
tests, well logs correlations, and high resolution seismic (3-D seismic,
conventional and reverse VSP, cross-well seismic, and 3D AVC).
Megascopic heterogeneity determines well-to-well recovery variation
and is the result of primary stratification and internal permeability trends
within reservoir units. It is at this scale that internal architecture and
heterogeneity become critical for identifying the spatial distribution of
reservoir flow units. Examples of megascopic heterogeneities include:
(1) lateral discontinuity of individual strata; (2) porosity pinch-outs;
(3) reservoir fluid contacts; (4) vertical and lateral permeability trends;
(5) shale and sand intercalation; and (6) reservoir compartmentalization;
(see Figure 3.44).

Gigascopic Heterogeneity
The whole field (depositional basin) is encompassed in this largest
scale of heterogeneities. Reservoirs are explored for, discovered, and
delineated at this level. This gigascopic field-wide scale, utilized to define
the reservoir outline, is the domain of structural and stratigraphic seismic
interpretation along with conventional subsurface mapping.
Hydrocarbon reservoirs are inferred from anomalies in the seismic
surveys. Characterization at this level begins from inter-well spacing and
extends up to the field dimensions. Field-wide regional variation in the
reservoir architecture is caused by either original depositional settings or
subsequent structural deformation and modification due to the tectonic
activity. Examples of types of information obtained from this megascopic
heterogeneity are: (1) division of reservoir into more than one producing
zone or reservoir; (2) position, size, shape, architecture and connectivity
of facies or reservoir units; (3) evaluation of the spatial distribution
or lithologic heterogeneity that comprises barriers, baffles, widespread