Wilcox cross section after the fault offset operation has been applied. Note general conformance of all surfaces and their projection into the faults. (b) Wilcox structure maps (for purple surface in section view) after the fault offset 3-D modeling operation has been applied. Fault polygons are automatically generated as the up- and down-thrown intersections of offset structure surfaces with the faults. Purple line of section shows position of section view relative to map.

Next-generation well log interpretation technologies are integrating the latest geo-modeling techniques into exploration-focused interpretation tools. These applications allow mainstream prospectors to build reliable 3-D framework models from well log data alone — providing unprecedented insight into previously overlooked reservoirs and unlocking a new wave of drilling opportunities in mature oil and gas provinces.

The easy oil is nearly gone, and energy demand is skyrocketing, sending oil and gas operators back to mature fields in search of deeper reservoirs and overlooked traps. While these prospects have potential, their remaining reserves are often out of reach for seismic interpretation tools either because they are below seismic resolution or occur in poor shooting areas. In this landscape, exploration geologists are finding themselves faced with economically viable plays that can be incredibly difficult to map, model, and accurately interpret.

What many older assets do have readily available are considerable amounts of well log data, at least for shallow, previously explored reservoirs. Leading software companies are now empowering exploration geologists with next-generation technology that leverages widely available well log data to create 3-D framework models of the deep traps left in mature fields. This new approach integrates an established geologic principle, conformance mapping, with the latest geomodeling technology to provide geologists with improved understanding of complex subsurface formations — resulting in more informed drilling decisions, less non-productive time, and greater return on investment.

3-D geomodeling in exploration

Despite advances in reservoir modeling in recent years, 3-D geomodeling technology has yet to substantially impact exploration geologists’ work. Most conventional well log interpretation applications cannot build 3-D models at all. They still require geologists to interpret, grid, and map one structural surface at a time, and they make little or no reference to adjacent surfaces. This makes creating even a 2-D holistic view of a potential reservoir prohibitively difficult.

Two key issues have limited the ability of conventional well log interpretation applications to create accurate framework models of the subtle plays remaining in mature fields. First, the amount of available well log data decreases with depth, making most maps of deeper structures unreliable. Second, with applications that examine only one surface at a time, discontinuities such as faults and unconformities that truncate or trim structural surfaces are extremely challenging to integrate into a comprehensive set of maps.

The new approach taken by industry leaders integrates 3-D geomodeling technology into exploration-focused interpretation tools. The software offers exploration geologists a multi-surface interpretation system that leverages existing well log data to accurately build sophisticated, topologically correct 3-D framework models of deep traps. These models provide exploration geologists with a new level of insight into previously explored fields, leading to the identification of traps overlooked by conventional interpretation applications.

Landmark has incorporated this innovation into its next-generation GeoGraphix SmartSection and FrameBuilder applications, where
early commercial applications have produced impressive results. One independent operator working in Eastern Europe reported saving hundreds of hours during field evaluation by using this new technology to map deeper structures.

Reliable prospect maps at depth

Powering this new well log interpretation software is conformance mapping, a robust and intuitive technology that can accurately model multiple surfaces even when equal numbers of well-top data are not available for all surfaces. This occurs often in mature fields, where shallower reservoirs have been more extensively explored than deeper structures.

However, in most structural settings it is safe to assume that multiple adjacent surfaces are roughly parallel — that they conform to each other. Next-generation software exploits this principle by first creating isochore (surface-to-surface thickness) maps of all adjacent surfaces sampled from the deepest well penetrations. The software then progressively adds these isochore maps to shallow, well-imaged surfaces in a down-building process to rapidly estimate the structure of deeper targets with precision and confidence (Figure 1).

In effect, conformance technology enforces thickness relationships between each modeled surface and ensures a fully integrated, internally consistent 3-D framework model. This robust model does a much better job projecting multiple surface geometries between and below the total depth of wells to enable superior inter-well interpretations. Because the models are dynamically updated as data are added, the model continues to evolve and improve.

Conformance mapping isn’t a new idea. In the past, geologists drawing structure maps on paper would overlay maps on a light table to make the contours of adjacent horizons parallel. Some existing software applications do allow geologists to combine isochore and structure maps to create new maps of adjacent surfaces. However, these processes often require special scripts, technical knowledge, and time that most geologists simply don’t have. The new approach being taken by today’s technology companies has automated conformance mapping’s tedious steps to allow exploration geologists to apply this technology with a click of a button.

Workflows simplify mapping

Building on the capabilities of the conformance mapping technology, new well log interpretation applications also leverage an advanced topology engine to allow geologists to accurately account for faults and unconformities. With the ability to create reliable maps of deep, complex plays, exploration geologists can interpret exploration areas quickly and accurately, lending critical insight to an operator’s costly drilling decisions.

The accurate interpretation of faults that intersect just a single surface has been difficult in most current exploration mapping software applications. These traditional applications lack the capability to detect 3-D surface-to-fault intersections and to properly accommodate surface truncation and offset relationships. The next-generation exploration technologies now hitting the market integrate fault gapping, offsetting, and networking tools into their applications. This automates previously painful workflows and empowers exploration geologists to create more accurate subsurface maps of complex structures.

The latest software applications provide a number of tools for integrating fault and structural surfaces in the framework-building process. These integrated framework-building workflows result in robust three-dimensional structural frameworks which honor multiple-surface thickness relationships (using conformance mapping) and
vertical separation data and which properly integrate fault-surface intersections in map and section views. These tools include log and fault correlation tools that support fault gapping (used to map vertical separation) and missing top picking in the gaps.

In addition to assisting geologists in their ability to create accurate structure maps, next-generation well log interpretation software also speeds and simplifies prospect identification in areas where unconformities are an issue. Exploration geologists can identify missing sections by gapping unconformities and picking missing tops to ultimately model stratigraphic discontinuities such as onlap, toplap, downlap, and erosional truncation to generate vital unconformity subcrop maps. Again, conformance mapping can be added downward in unconformity scenarios or upward to better model or project formations through unconformities prior to trimming.

More informed drilling decisions

By taking a new approach to well log interpretation, leading industry software companies have enabled exploration geologists to generate more accurate, reliable 3-D subsurface maps than ever before — from widely available well log data. With these applications, exploration geologists are gaining unprecedented insight to the industry’s mature fields and guiding oil and gas operators to brand-new classes of oil and gas opportunities. Ultimately, these new technologies will help to replace reserves and meet future demand.