SPECIAL ISSUE
November 2009
AAPG-SPE-SEG HEDBERG RESEARCH CONFERENCE
The Geologic Occurrence and Hydraulic Significance of Fractures in Reservoir
AAPG-SPE-SEG Hedberg Research Conference on “The Geologic Occurrence and Hydraulic Significance of Fractures in Reservoirs”
Introduction
Natural fractures and their geomechanical framework often control the hydraulic behavior of reservoirs. These papers explore such questions as how to predict fracture occurrences and how to more effectively utilize geomechanics to predict, characterize, and model fractured reservoirs.
Mechanical and fracture stratigraphy
Not interchangeable terms
Mechanical stratigraphy is the byproduct of depositional composition and structure and chemical and mechanical changes superimposed on rock composition, texture, and interfaces after deposition. Fracture stratigraphy reflects a specific loading history and mechanical stratigraphy during failure.
Complex fracture development related to stratigraphic architecture: Challenges for structural deformation prediction, Tensleep Sandstone at the Alcova anticline, Wyoming
Don’t neglect stratigraphic architecture
In the absence of stratigraphic architectural controls, predictions of subsurface fracture character will always be limited in application. There is dramatic variability in fracture intensity owing to original depositional architecture, overall structural deformation, and diagenetic alteration of the host rock.
Impact of interlayer slip on fracture prediction from geomechanical models of fault-related folds
A geomechanical model
The application of finite-element-based geomechanical models has excellent potential for interpreting natural fractures in geologic structures. The basic premise of this approach is that geomechanical-model-derived permanent strains can be interpreted in terms of fracture characteristics.
Mechanical stratigraphy and faulting in Cretaceous carbonates
Small-displacement faults
Subseismic faults, or faults below a detection limit, can impart strong fluid transmissivity anisotropy to hydrocarbon reservoirs. This paper explores the factors that influence these small-displacement faults to discern any patterns that might be present in their distribution.
Crossing conjugate normal faults in field exposures and seismic data
Normal faults with opposite dips
Crossing conjugate normal faults, which thin and deform strata in the intersection region, occur in a variety of structural styles. Established conceptual models, such as normal faults that abut but do not cross one another, may lead to interpretations that miss these offset segments altogether.
Paleostress analysis from image logs using pinnate joints as slip indicators
Slip-sense and slip-direction
Paleostress analysis is the inference of orientations and magnitudes of ancient stress fields from deformation features. This analysis determines the deformation path and improves the quality of geological models as well as regional tectonic and seismic interpretations.
Fracture characterization at multiple scales using borehole images, sonic logs, and walkaround vertical seismic profile
Characterizing natural fractures
This paper presents a quantitative forward-modeling methodology to link and interpret measurements relevant to fracture mechanical properties. Two studies are conducted using the same fracture data to model fracture-induced anisotropy using data from a tight gas field.
Two-dimensional simulation of controls of fracture parameters on fracture connectivity
Controls on fracture connectivity
A theoretical study of fracture networks is conducted to investigate fracture connectivity with varying geometric properties. These include the number of fractures of the same set, the length of fracture increases, the orientation of fractures in a set, and the presence of fractures of multiple sets.
Natural fracture characterization in tight gas sandstones: Integrating mechanics and diagenesis
Predicting fracture network geometry
To understand the underlying mechanisms responsible for fracture, this paper presents a method of analysis that incorporates fracture mechanics and diagenetic processes to predict fracture network geometry and fracture aperture distribution and preservation.
Geomechanical wellbore imaging: Implications for reservoir fracture permeability
Reducing costs and increasing production
The utilization of image data to constrain geomechanical models in the study of fractured compartmentalized reservoirs is a promising improvement to existing flow models. This data allows characterization of fractures and faults, which control the performance of many low-permeability reservoirs.
Predicting the regional distribution of fracture networks using the distinct element numerical method
Modeling stress variations
Fractured rock correlates with areas of higher differential (>10 MPa) stress, as predicted by the distinct element method model, while areas of predicted low differential stress can be correlated with full-to-spill gas fields as shown in an example from the Penola Trough in South Australia.
Multivariate fracture intensity prediction: Application to Oil Mountain anticline, Wyoming
Predicting fracture geometry
Bayesian updating allows the integration of multiple variables that help reduce the uncertainty in predicted fracture geometry. These models better represent geological complexity and result in improved development decisions and production forecasting.
Quantifying and predicting naturally fractured reservoir behavior with continuous fracture models
A review of the CFM approach
Continuous fracture modeling can predict where naturally fractured intervals will be encountered in undrilled wells. New seismic processing and interpretation technologies will enhance the ability of this method to quantify the location and effects of fractures on well performance.
Assisted history-matching for the characterization of fractured reservoirs
Characterizing flow properties
Geologically realistic fractured reservoir flow models at reservoir scale are usually characterized from local dynamic tests. An inversion methodology facilitates the characterization of fracture properties from well test data with the aid of a genetic optimization algorithm.
Upscaling two-phase flow in naturally fractured reservoirs
An alternate simulation method
Discrete fracture simulation on unstructured grids is a simulation method to forecast production from naturally fractured reservoirs. A procedure is developed to compute multiphase flow properties from field data for use in conventional reservoir simulation where subseismic fractures cannot be represented explicitly.
Comparison of deterministic with stochastic fracture models in water-flooding numerical simulations
Understanding single and multiphase flow
Numerical simulations of water flooding on vein sets in fractured limestones are compared with values from stochastic models generated from outcrop data to determine the accuracy of effective permeability and water breakthrough time.