How to use well spacing rules to estimate which leases can still be drilled

Well spacing is one of the quickest ways to screen a shale lease for future drilling potential. By comparing the number of wells a spacing unit may legally or technically support with the wells already drilled, you can form an initial view of whether a lease contains remaining locations. The result is an estimate rather than a reserve statement, but it can help prioritise due diligence.

For Australian investors and professionals, the method is especially useful when reviewing United States opportunities from Brisbane, Perth, Sydney or regional offices. Shale Navigator brings together map layers for shale plays, permits, lease offers, pipelines, mineral rights and property information, making it easier to compare a lease with nearby development activity without relying on disconnected spreadsheets.

The key is to treat spacing as a framework, not a guarantee. State rules, field orders, operator plans, geology, surface access, infrastructure and title restrictions can all reduce the number of economically drillable locations. A lease that appears underdeveloped on a map may have little practical upside if its acreage is stranded, faulted, already dedicated to another unit or difficult to reach.

Understand what a spacing unit represents

A spacing unit is the area assigned to one well or a group of wells under a regulator’s rules or an approved field development plan. In a horizontal shale play, the relevant measurement is often the length of horizontal wellbore within the productive formation rather than the size of the surface parcel. Several surface locations may serve wells that extend into the same unit.

Spacing rules can be expressed as acres per well, minimum distances between wells, lateral-length assumptions or a combination of these. For example, a 640-acre unit with an eight-well density assumption may support eight well locations in a simple screening model. That does not mean eight wells can be drilled from one pad, nor that every location will have identical value.

Check whether the rule applies to the entire lease, a pooled unit, a drilling and spacing unit or a specific field. A lease may cover 1,200 acres, while only part of it falls within an approved unit. Conversely, a horizontal well may cross multiple tracts, meaning the lease’s value depends on pooling, allocation and participation arrangements.

Gather the inputs before counting locations

Start with the lease boundary, the relevant shale formation and the applicable spacing rule. Then collect producing wells, permitted wells, cancelled permits, plugged wells, unit boundaries, operator acreage positions and any announced development plans. Shale Navigator’s map layers can help place these items in the same geographic view, while public regulator records should be used to verify legal status.

The well count must be formation-specific. A lease may contain producing wells in one bench while another target interval remains undeveloped. In stacked plays, such as formations with multiple prospective zones, a single surface footprint does not necessarily exhaust the lease. Review the well’s target formation, lateral path, completion status and ownership before treating it as a used location.

Dates also matter. A permit from several years ago may have expired, while a recently drilled well may not yet appear as producing. A lease acquisition or farm-in may have changed the operator’s development schedule. Keep separate columns for producing, drilling, permitted, expired, cancelled and proposed wells rather than placing all of them in one total.

Read the map beyond the lease outline

A lease boundary rarely tells the full commercial story. Examine nearby unit lines, roads, rivers, towns, pipelines, compressor stations, processing facilities and property parcels. A theoretical location near a residential area or a protected feature may require a longer lateral, a different pad or an exception to ordinary setback requirements.

Look at the direction of existing laterals. If surrounding operators consistently drill north-south wells, that pattern may reflect geology, lease boundaries or surface access. It may also reveal that the apparent open acreage cannot be drained efficiently in the direction suggested by a basic grid. Pad placement and lateral orientation can materially change the number of practical locations.

Australian users will recognise the importance of separating cadastral boundaries from operational boundaries. A rural property near Toowoomba or the Surat Basin may look like one holding on a property map, while petroleum tenure, easements and land access arrangements divide it into different commercial interests. In the United States, county roads, townships and private mineral ownership create similar complications.

Calculate the theoretical remaining inventory

A simple screening formula is:

Theoretical remaining locations = permitted or allowable locations − used locations

To estimate allowable locations, divide the relevant net acreage by the applicable acres-per-well assumption, then apply any rounding and unit rules. If a lease includes 320 net mineral acres in a 640-acre spacing unit, an eight-well density assumption might produce four gross locations before other adjustments. The lease’s net revenue interest and working interest are separate calculations and should not be confused with location count.

For horizontal development, a more useful approach may be to estimate lateral slots. Divide the productive boundary by the expected well spacing, then test whether each proposed lateral can fit within lease and unit lines. A 330-foot or 660-foot spacing assumption can produce very different results, particularly on narrow or irregular tracts. Use actual nearby development patterns as a reality check rather than relying solely on a generic rule.

Count existing wells by the acreage or target interval they drain, then subtract wells that are genuinely capable of holding the relevant rights. A vertical well may not consume a horizontal location in another bench. An injection well, abandoned well or well completed outside the target formation may need separate treatment. Document every assumption so another analyst can reproduce the estimate.

Apply legal and commercial adjustments

Spacing rules establish what may be allowed, but they do not establish what will be drilled. Setbacks from dwellings, roads, rivers, municipal boundaries and environmentally sensitive areas can remove surface pad sites or force longer laterals. State regulators may permit exceptions, yet an exception should be treated as an upside possibility rather than included in the base case.

Pooling and unitisation are equally important. A lease may contain an undrilled portion that cannot support a standalone lateral but could contribute acreage to a larger unit. Conversely, a unit may include acreage from several owners, creating consent, allocation and development-timing issues. Review lease clauses covering pooling, depth limitations, continuous-development obligations, shut-in periods and retained acreage.

The Australian comparison is useful here. Petroleum and gas regulation is divided among states and territories, with Queensland’s framework affecting Surat and Bowen Basin projects, Western Australian rules applying around the Perth Basin, and separate arrangements relevant to the Beetaloo in the Northern Territory. Native title, land access, groundwater concerns and environmental approvals can influence project timing in ways that have no direct equivalent in a US spacing calculation.

Economic constraints deserve their own adjustment. A lease may have technically available locations but weak economics because gathering infrastructure is distant, gas prices are low or water handling is expensive. In Australia, market access around Brisbane, Gladstone or Perth can shape the value of a project differently from a US basin connected to an established pipeline network. Never present an undrilled count as a forecast of revenue without modelling costs and timing.

Build a repeatable screening workflow

Use a consistent process for every lease, whether reviewing an individual mineral interest or a larger portfolio. Start with the gross and net acreage, identify the applicable formation and spacing regime, map existing and planned wells, then classify each apparent location by confidence. High-confidence locations satisfy the acreage, formation and access tests; medium-confidence locations need pooling, permitting or engineering work; low-confidence locations depend on speculative assumptions.

A paid data package may be worthwhile when the analysis requires broader permit coverage, more detailed property information or repeated screening across multiple plays. Shale Navigator provides subscription access for users who need more than the initial free account period, although regulator filings and title documents should still be checked independently.

Use the following recommendations when estimating remaining drilling potential:

• Confirm the current spacing order or field rule rather than relying on a nearby operator’s pattern.
• Separate gross acreage, net mineral acres, working interest and net revenue interest.
• Count wells by target formation, lateral path and legal status.
• Map setbacks, unit boundaries, roads, pipelines and surface constraints before assigning locations.
• Maintain low, base and high cases for spacing density, pooling and future development.
• Record the source and date of every assumption so the estimate can be updated when permits or unit plans change.

A practical report should show the lease map, the spacing basis, existing well inventory, remaining theoretical locations and the adjustments that reduce that count. Include a confidence rating and identify the documents needed for verification, such as title records, lease amendments, pooling orders, permits and operator presentations.

For Australian decision-makers, this format makes remote review more efficient. A Perth-based investor can screen a US lease before instructing counsel, while a Brisbane land professional can compare acreage and infrastructure without confusing US regulatory concepts with Queensland tenure rules. The analysis becomes a prioritisation tool rather than a substitute for legal, geological or engineering advice.

Apply the method to one lease first, save the assumptions, and compare the result with nearby drilling activity. Then use the same framework across the wider portfolio to identify acreage that deserves title review, operator contact or a more detailed development model.