fence diagram, Oil & Gas Glossary

What Is a Fence Diagram?

Fence diagram (also called a fence section or panel diagram) is a three-dimensional geological cross-section display consisting of multiple intersecting vertical cross-sections arranged in a fence-like pattern across a field or basin. Each panel represents a line of section drawn between wells, and where two lines intersect, the panels meet at a right angle, creating the visual appearance of fence posts and rails. The result is a three-dimensional framework that allows geologists and reservoir engineers to visualize the lateral continuity and correlation of stratigraphic horizons, reservoir units, and facies changes between widely spaced wells simultaneously.

Key Takeaways

A fence diagram combines multiple intersecting vertical cross-sections to create a 3D visual of subsurface stratigraphy across a field or basin.
Well log data (gamma ray, resistivity, sonic) is correlated along each line of section and projected onto vertical panels.
Fence diagrams reveal lateral facies changes, formation thickness trends, and reservoir continuity that a single cross-section cannot show.
They are a foundational tool in reservoir characterization, unitization studies, and field development planning.
Modern fence diagrams integrate with 3D seismic data, allowing direct comparison of log-derived stratigraphy with seismic reflectors.

How a Fence Diagram Is Constructed

Construction begins by selecting a set of wells distributed across the study area and defining lines of section that connect them. These lines are typically chosen to cross structural or stratigraphic gradients, so that the panels capture the most geologically meaningful changes. Each line becomes one panel of the fence, oriented vertically with depth on the vertical axis and horizontal distance along the line on the horizontal axis. The panels are then assembled into a three-dimensional perspective view, with intersecting panels joined at their shared well locations.

Once the framework is established, well logs are posted on each panel at their true well locations. Gamma ray curves, resistivity logs, and sonic logs are the most commonly displayed data because they provide lithologic and porosity information that enables stratigraphic correlation. Formation tops picked by the geologist are marked at each well and connected by correlation lines across the panel. Where two panels share a well at their intersection, the formation tops and log character must be consistent on both panels, providing a geometric check on the correlations. Color-coded facies fills between correlation lines complete the diagram, making stratigraphic units visually distinct.

In practice, the construction process is iterative. If a correlation picked on one panel creates an inconsistency at the junction with a crossing panel, the geologist must revise until all panels are mutually consistent. This discipline makes fence diagrams more rigorous than isolated cross-sections, because every pick is tested against at least one independent line of section.

Fast Facts: Fence Diagram

Data displayed: Gamma ray, resistivity, sonic logs; formation tops; facies fills; fluid contacts
Typical panel count: 2 to 6 intersecting panels for a field-scale study
Vertical axis: Depth (true vertical depth or measured depth) or two-way travel time
Horizontal axis: Distance along line of section (in metres or feet)
Common software: Petrel, Kingdom, IHS Harmony, LogPlot
Primary use: Inter-well stratigraphic correlation and reservoir characterization
Integration: 3D seismic volumes, structure maps, isopach maps
Regulatory use: Unitization studies, field development plan submissions

Field Tip:

When building a fence diagram, always choose at least one panel that runs roughly parallel to the depositional dip direction and one that runs along strike. The dip-oriented panel captures thickness and facies changes in the direction of sediment transport, while the strike-oriented panel reveals lateral pinch-outs and facies belts. The two together give a much more complete picture of reservoir geometry than either direction alone.

Types of Data Displayed on Fence Diagrams

The most informative fence diagrams layer multiple data types onto each panel. Wireline logs form the primary data backbone: the gamma ray log distinguishes shales from sands or carbonates, the resistivity log identifies hydrocarbon-bearing intervals, and the sonic or density log provides porosity and lithology discrimination. Formation tops derived from log interpretation define the boundaries of each stratigraphic unit and are correlated well to well across the panel. In carbonate reservoirs, image logs and core descriptions may be added to characterize fracture intensity and pore type.

Beyond log data, fence diagrams can incorporate seismic-derived information. When 3D seismic is available, interpreted horizons extracted from the seismic volume can be draped onto the fence panels, allowing direct comparison of well-log picks with seismic reflectors. Discrepancies between log picks and seismic events flag potential correlation errors or lateral velocity changes. Fluid contacts from formation tests or production data can also be posted on the diagram, helping engineers understand the areal extent of hydrocarbon columns and the location of oil-water or gas-oil contacts.

Fence Diagrams in Reservoir Characterization and Field Development

Reservoir characterization relies on fence diagrams to answer fundamental questions about reservoir geometry: Are the sands laterally continuous between wells, or do they pinch out? Does reservoir quality deteriorate in a particular direction? Are multiple sand bodies connected or isolated by shale barriers? These questions directly affect decisions about well spacing, completion design, and recovery strategy. A fence diagram that reveals a shale barrier separating two reservoir intervals, for example, may prompt a decision to perforate both intervals independently rather than commingling production.

In unitization studies, fence diagrams provide the geological evidence needed to define the boundaries of a producing unit and allocate production among working interest owners. Regulatory bodies in Canada, the United States, and the North Sea typically require cross-sections and fence diagrams as part of unitization applications to demonstrate that the reservoir is a single connected body extending across multiple lease blocks. The intersection discipline inherent in fence diagram construction makes them more defensible in regulatory and legal proceedings than collections of isolated cross-sections.

Fence diagram is also referred to as:

fence section — common informal synonym used in exploration and production geology
panel diagram — emphasizes the individual panel elements that make up the display
3D cross-section display — descriptive term used in technical reports and regulatory submissions

Frequently Asked Questions About Fence Diagrams

How does a fence diagram differ from a standard cross-section?

A standard cross-section is a single vertical panel drawn along one line of section between wells. A fence diagram combines two or more intersecting cross-sections into a three-dimensional display. The key advantage of the fence diagram is that correlation picks must be geometrically consistent at every intersection point, providing a self-checking quality control mechanism that isolated cross-sections lack. Fence diagrams also reveal spatial trends in reservoir properties that a single 2D panel cannot capture.

Can fence diagrams be built without 3D seismic data?

Yes. Fence diagrams are constructed primarily from well log data and require no seismic input. They were a standard geological tool long before 3D seismic became widely available. However, integrating 3D seismic improves the diagram significantly: seismic-derived horizons can be extracted and draped onto the panels, and the seismic can help interpolate stratigraphy in inter-well regions where log data does not exist. In mature fields with dense well control, log-based fence diagrams alone can provide detailed and reliable reservoir geometry.

What software is commonly used to build fence diagrams?

Schlumberger Petrel and IHS Kingdom are the most widely used commercial platforms for building fence diagrams in 3D environments. Both allow geologists to post logs on panels, pick and correlate formation tops, apply facies color fills, and view the panels in perspective. LogPlot and Neuralog are common tools for preparing individual log strips before importing into the fence framework. Some operators build fence diagrams in specialized geological drafting software or even in CAD packages for high-quality publication figures.

Why Fence Diagrams Matter in Oil and Gas

Fence diagrams remain one of the most effective tools for communicating subsurface geology to multidisciplinary teams, investors, and regulators. They translate the abstract language of well logs and seismic data into an intuitive three-dimensional picture that non-specialists can interpret. For reservoir engineers building simulation models, the fence diagram defines the stratigraphic layering and lateral connectivity that the model must honor. For drilling engineers planning infill or stepout wells, the diagram identifies which stratigraphic targets remain undrilled and where reservoir quality is expected to be highest. In an industry where a single development well can cost tens of millions of dollars, the investment in a well-constructed fence diagram pays returns in reduced geological risk and better-informed decisions.