Fractures and faults have worldwide importance because of their influence on successful extraction of resources. Many faults and fractures are difficult or impossible to characterize adequately using currently available technology. Consequently, reservoirs that contain fractures have been intractable to describe and interpret effectively, posing serious challenges for exploration, development, and accurate reservoir simulation and reservoir management. Characterization and accurate prediction of reservoir fractures hold great potential for improving production by increasing the efficiency of exploration and recovery processes.

The Fracture Research and Application Consortium seeks fundamental understanding of fractures and fracture processes with the aim of improved prediction and diagnosis of fracture attributes in the subsurface.

 

Accurate, Site-Specific Fracture Analysis

New methods to obtain accurate, site-specific information on fracture attributes are extremely important because inadequate fracture sampling is a problem in virtually all reservoirs.

Consortium research resulted in a breakthrough in the diagnosis of fracture attributes. We showed that microstructures in core samples can be used to infer attributes of large fractures.

A key advantage of this approach is that it provides site-specific fracture information reliably and at any user-specified level of completeness. Therefore, our methods can work even without measuring elusive, difficult-to-sample large fractures, as demonstrated in figures 1 and 2.

Our current research is exploiting this breakthrough in several ways:

This research involves case studies in a wide range of formations worldwide.

The following sections on scaling and fracture quality illustrate practical results of recent case studies.

 

Scaling

Large open fractures and interconnected fracture networks have the greatest effect on fluid flow quality in fractured reservoirs. Consistent scaling patterns of fracture apertures, illustrated in figure 1, suggest that large and small fractures are commonly merely different size fractions of the same fracture population.

In this example from West Texas, because the spatial frequency of fractures having apertures smaller than 1 µm to nearly 1 cm follows a single relation, the microfractures provide an accurate means of predicting the abundance of large fractures. Note that the regression line in this example is only fit to the microfractures, yet the large fractures are accurately predicted.

Used with care, rigorous scaling analysis is a potentially powerful tool for reservoir management (for example, by specifying optimal horizontal well length) and a link to fractured reservoir simulation.

 

Fracture Quality

Figure 2 shows one way we can distinguish fractures that contribute to production from those that do not, without directly sampling the large fractures. In this case, microstructural proxies for the large fractures were measured in sidewall cores and have successfully identified the well having open, conductive natural fractures (the producer) from the well having closed, mineral-filled fractures (the dry hole).

Among other applications, this is a powerful approach for mapping fracture quality and identifying fracture "sweetspots," for calibrating well logs and seismic data, and for testing models that predict fracture attributes.

 

Scope of the Project

The scope of this project includes measurement, interpretation, prediction, and simulation of reservoir fractures. The general goals of the project are to

The aims of this study are intensely practical—to improve prediction and diagnosis of natural-fracture attributes in hydrocarbon reservoirs and accurately simulate their influence on production.

New analytical methods will lead to more realistic characterization of fractured and faulted reservoir rocks. These methods will produce data that can enhance well-test and seismic interpretations and that can readily be used in reservoir simulators.

Testing diagnostic and predictive approaches is an integral part of the research. Our requirement is that new methods must ultimately be cost effective.

Testing of diagnostic and predictive approaches developed from outcrop, core, and well-test studies is generally carried out on samples loaned by member companies.

Our results are applicable to fractured hydrocarbon-bearing carbonate, siliciclastic, and crystalline basement rocks. Research on fundamental fracture and rock properties and simulation methods is the basis for creating methods of obtaining and using information about subsurface fractures and faults. Testing these methods involves outcrop, core, image log, and well-test studies.

The research program is designed to accomplish project goals that include (1) geologically realistic descriptions of fractured and faulted reservoir rocks, (2) new techniques that enhance well-test and seismic interpretations, and (3) reservoir fracture improved simulation.

 

Current Studies

Among the issues being addressed in specific studies are currently the following:

Research Team

Our research team of petroleum engineers, geophysicists, and geologists applies a wide range of techniques, including novel use of geomechanical modeling, rigorous scaling, and microstructural and structural diagenetic analysis.

Project staff include geoscientists and engineers of the Bureau of Economic Geology and the Departments of Petroleum and Geosystems Engineering and Geological Sciences, The University of Texas at Austin.

 

Opportunities for Corporate Sponsorship

Companies can participate in this Industrial Associates program through a subscription of $35,000 per year. Research results are shared equally among supporting companies at annual review meetings and through our project Web site (a part of which is reserved for industry members only), technical reports, and technical research papers. Research support from the consortium of Industrial Associates is leveraged by grants from State and National funding agencies.

 

Contacts