One oilfield service major leads the ranked field with 192 patent families, more than three times the fifth-place count of 62. That leader's filings are split across several corporate variants of the same group, which co-file frequently — the strongest co-assignee pairing shares 20 families. This concentration means the core sealing-pad and pretest-drawdown mechanics are heavily claimed by a small number of related entities, so a new entrant should expect to design around existing coverage rather than file into open space.

Filing peaked in 2018 at 28 records and has not returned to that level since. The leading assignee's own filings fell from 5 in 2021 to 2 in 2024, a 60% drop over that span, but 2025 and 2026 data are still incomplete because publication typically lags filing by about 18 months. The honest read is that the field has settled below its 2018 peak, not that it is accelerating or collapsing in real time.

E21B, the earth and rock drilling wells classification, covers 88.1% of the 571 records in scope, confirming this is primarily a drilling-hardware field. G01N (material analysis, 16.6%) and G01V (geophysics, 14.4%) show a meaningful secondary presence of analytical and geophysical claims. Smaller classes — G01R, B01L, G06F, G06V and F04B — each sit under 5% and mark cross-disciplinary claims in electronics, lab apparatus, data processing, imaging and pumps that sit outside the mechanical core.

The United States leads receiving offices with 199 filings, followed by the United Kingdom at 90 and WIPO/PCT filings at 63. Canada (47), Norway (40) and Australia (38) round out the leading receiving offices, consistent with major offshore and North Sea drilling regions. The sizeable PCT count suggests a real share of applicants are still routing toward multiple national phases rather than committing to a single jurisdiction.

US20240254877A1, filed by Halliburton and published in 2024, claims a downhole fluid sampling tool with a sample chamber, a pump, a filter on the flow-port inlet, and a removable filter cover that keeps fluid off the filter until sampling begins. It is a fairly specific mechanical arrangement rather than a broad method claim, so it constrains designs that use a removable filter cover in this configuration but leaves alternative contamination-protection approaches — different filter geometries, sensor-based contamination detection, or chemical barriers — open. Anyone building a similar tool should compare their filter-protection mechanism against this claim set specifically rather than assume the whole sampling concept is blocked.

The analytical and software layer around the mechanical core looks comparatively open: real-time mobility estimation, contamination sensing inside the sample chamber, and buildup-analysis software each sit in IPC classes with far lower record counts than the E21B drilling-hardware core. Image-based filtrate detection and miniaturised lab-on-chip sampling approaches also show thin coverage relative to their technical relevance. These are not guarantees of freedom to operate, but they are areas where filing density is low enough to warrant a first-claim search before assuming the space is occupied.