PARADIGM CUSTOMER STORY
PETROINDEPENDENCIA
Combining Geostatistics with Seismic
Attributes to Improve Reservoir
Management Strategies: A Case Study
from the Orinoco Petroleum Belt
The Challenge
The Orinoco Petroleum Belt is a vast area rich in heavy and extraheavy oil located north of the Orinoco River in Venezuela. This
reservoir is believed to hold the largest heavy oil accumulation in
the world. One of the most strategic challenges faced by PDVSA
today is turning the Orinoco Belt into a driver for economic, social,
industrial and technological development for the country. For this
reason, it is essential to integrate all available data for the Orinoco
Belt’s main reservoirs, and create subsurface images that accurately
represent their structural and stratigraphic complexity.
The construction of such geologic models will help delineate potential
prospects, thus optimizing the location of future drilling locations and
minimizing the risk associated with new horizontal wells.
The most important production formation comes from nonconsolidated, fluvio-transitional sands, where we observe a complex
pattern of stacked crossing channels. This increases the difficulty of
representing the distribution of sedimentary facies in a static 3D model.
The Solution
The aim of the PDVSA and Paradigm teams was to model the
reservoir’s properties in order to perform an efficient analysis and
provide a reliable prognosis. For this purpose, Paradigm used its
SKUA-GOCAD™ and Stratimagic®/SeisFacies® software to create
an accurate subsurface 3D model representing the lateral and
vertical facies. The following workflow was followed:
Structural map obtained after structural modeling (generation of
contours and textures associated with fault breaks)
1. From the available 2D/3D seismic interpretation, a structural
and stratigraphic model was built using the pillarless technology
embedded in SKUA-GOCAD. This shortened the process while
honoring both the stratigraphic and structural deformation.
2. To map the facies distribution, a seismic facies volume was
generated from several poststack seismic attributes, such
as signal envelope, amplitude and RMS frequency. The
interpretation of the channels was facilitated by the use of this
information rather than calculating each attribute separately.
3. A fine 3D geologic grid was built. With SKUA-GOCAD, faults
are discontinuities and not pillars: Cells are cut by faults,
keeping the same indexes on both sides of the fault.
4. Facies logs were blocked and the seismic facies volume was
transferred onto the geologic grid. This method allows analysis of
the relationship between sedimentary and seismic logs, and the
derivation of probability volumes associated with each sedimentary
facies described, showing the most probable facies distribution.
The seismic information acts as soft data in the process.
5. As the distribution of the facies corresponds to what is observed
in the seismic data and calibrated at the wells, reservoir properties
can be propagated accurately. Quality control of distributed
properties was performed by creating a probability index cube.
6. The geologic grid was upscaled for dynamic simulation. The
reservoir properties were upscaled in the simulation grid, in
Final geological grid
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such a way that they represented what was observed in the
geologic grid. Various grids were built for each horizontal well
to evaluate the volume of oil per block.
7.
To estimate OOIP, a probabilistic-based methodology was performed, using Paradigm Jacta® to generate optimistic, most probable and pessimistic scenarios of the 3D geological model. This was made possible by using a LatinHypercube approach with 1000 realizations. The analysis provided a better understanding of uncertainties about resource distribution, setting a basis for estimating project economics on various cases.
The Results
The model built using the Paradigm platform honored the medium
heterogeneities, matched the production capacity of the reservoirs,
and enabled PDVSA to measure the associated uncertainties in
the results. It was possible to generate several realizations through
combining geostatistical methods with propagation trends in order
to estimate the risk associated with drilling in the new locations.
The combination of the efficient solutions supplied by Paradigm
and its ongoing support contributed to outstanding results:
95% correlation with the wells that are currently being drilled.
Support and Training
The Benefit
The Paradigm team provided specialized training and mentoring in
the main workflows needed to successfully complete the project.
These workflows included SKUA-GOCAD modules for Structure
& Stratigraphy, Reservoir Data Analysis, Reservoir Properties, and
Reservoir Risk Assessment, as well as Seismic Facies Classification
using Stratimagic/SeisFacies.
Efficient workflows, robust numerical methods, a user-friendly
interface, probabilistic calculations, and compatibility with other
vendors’ software all contributed to the successful use of SKUAGOCAD as a tool for generating a quantitative basis of PDVSA’s
exploitation plan.
Ongoing support was provided, both onsite and by email and
phone. Advanced methods were introduced for constructing
geostatistical–structural models, and integrating well data and 3D
seismic data (seismic facies blocks), to obtain a better definition of
stratigraphic geobodies.
“While we had a lot of good input data, we did not have a
robust software or hardware platform with which to successfully
create models that would represent the real stratigraphic and
structural configuration of the subsurface. SKUA-GOCAD
allowed us to efficiently integrate all the available data in simple
and convenient workflows, and generate key tools to identify,
characterize and produce in the zones of interest.”
Paradigm and PDVSA worked in close collaboration, with the
PDVSA team collecting seismic data, logs, markers and well data,
and performing quality control of the data used in the project.
Kenia Salazar, Simulation Engineer - Geomodeling at PDVSA
Calibration of seismic facies vs. sedimentary facies
Facies propagation: result of integrating well data and maps - seismic
facies block, showing the trend of crossed channels
Workflow for facies propagation
Results after simulation
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