Mis-Tie

A mis-tie in seismic processing and interpretation is an inconsistency in amplitude, phase, or timing between seismic reflection events recorded at the same subsurface point from two different seismic lines or surveys that theoretically intersect — caused by differences in acquisition parameters, processing methods, static corrections, or normal moveout velocities between the two datasets, and representing a data quality problem that must be identified and corrected before the two datasets are merged or jointly interpreted for structural mapping or reservoir characterization.

Key Takeaways

Mis-ties are quantified as the time difference, amplitude difference, or phase difference between the same reflection event at the intersection point of two seismic lines, with an acceptable mis-tie typically being less than ± 4 milliseconds for time mis-tie and less than ± 15 percent for amplitude mis-tie in routine exploration surveys.
The primary causes of seismic mis-ties are: differences in near-surface static corrections between vintages; different NMO velocity models applied to different surveys; processing differences such as different bandpass filters or phase rotations; and acquisition differences including different receiver arrays, shot patterns, or recording geometries.
Mis-tie analysis is a mandatory quality control step when merging 3D seismic surveys from different vintages or different operators, as large mis-ties at survey boundaries can create false structural closures or hide genuine ones when the two datasets are placed on the same structural map without correction.
Well-seismic mis-tie refers to the discrepancy between the depth or time of a reflection event on the seismic section and the depth predicted by the synthetic seismogram from well logs, caused by velocity errors in the seismic, calibration errors in the well log, or depth reference differences between KB and the seismic datum.
Systematic mis-tie patterns across a survey area indicate a velocity error in the seismic processing (the mis-tie magnitude increases smoothly with depth or is correlated with structure), while random mis-ties suggest near-surface statics problems or acquisition noise issues.

Fast Facts

A well-seismic mis-tie of 20 milliseconds two-way time (TWT) at a target depth of 3,000 metres corresponds to a depth error of approximately 30 to 40 metres depending on interval velocity — enough to place a horizontal well outside the productive reservoir interval if the interpretation is not corrected. Seismic-seismic mis-ties at the boundaries of merged 3D surveys in the Gulf of Mexico have historically created phantom structural highs at line intersections that appeared in prospect inventories before careful quality control revealed them as data artifacts. The distinction between seismic time and well depth mis-tie is important: a time mis-tie in TWT at the well may be consistent with a specific velocity error in the seismic processing that can be modeled and corrected.

What Is a Mis-Tie?

In 2D seismic interpretation, every point in the subsurface that lies on two intersecting seismic lines should show the same reflection event at the same two-way time on both lines — the two lines record the same reflection from below the same point on the surface. If the event appears at different times on the two lines at their intersection, a mis-tie exists. The size of the mis-tie is the time difference between the two events at the crossover point and is measured in milliseconds of two-way time.

In 3D survey merging, a similar concept applies at the boundaries of two adjacent 3D surveys. If the same reflection horizon appears at different times on the two sides of the boundary — a step change in time — the two surveys have a time mis-tie at their junction. Structural maps that cross this boundary will show a false fault or step at the boundary if the mis-tie is not corrected.

Mis-ties are a quality measure for seismic data and processing: small, random mis-ties indicate good data quality with minor residual errors; large, systematic mis-ties indicate fundamental problems with velocity models, statics corrections, or processing phase that require investigation and correction before the data can be used for reliable structural interpretation.

Causes and Correction of Seismic Mis-Ties

Near-surface velocity variations that affect the seismic travel time from the shot to the reflector and back are the most common source of mis-ties between 2D lines. These near-surface statics errors can vary from line to line if the refraction statics were computed independently on each line without constraining the solution to a common datum. The correction is to reprocess the two lines together with a joint statics solution that ties the intersection point.

NMO velocity differences between two datasets acquired at different times or processed by different contractors are another major source of mis-ties. If one dataset uses a higher NMO velocity at a given depth, the NMO correction shifts the event to an earlier time, creating a positive time mis-tie relative to the other dataset. The correction is to reprocess one or both datasets to a consistent velocity model or to apply a time-variant shift to one dataset to flatten the mis-tie pattern.

Phase differences arise when two datasets have been processed with different minimum-phase, zero-phase, or mixed-phase wavelets, or when one dataset has undergone a phase rotation during de-signature processing that the other did not. These phase mis-ties produce amplitude and waveform differences at intersections even when time mis-ties are small, complicating joint amplitude interpretation. Phase harmonization through spectral matching filters is the standard correction.

Mis-Ties Across International Jurisdictions

Canada (AER / CGPA): The Canadian Society of Exploration Geophysicists (CSEG) and the Canadian Geoscience Standards Working Group have developed seismic data quality standards that include mis-tie analysis requirements for data submitted for AER regulatory purposes. AER exploration licence seismic submissions require that multi-vintage 2D line grids demonstrate acceptable mis-tie quality before being used as the technical basis for well licence applications in Foothills and deep basin exploration. WCSB seismic data archives held by Petrinex and provincial geological surveys contain multi-decade 2D grids where vintage differences create significant mis-tie challenges for modern reprocessing programs.

United States (BSEE / BOEM): BOEM requirements for exploration plans and development plans submitted for Gulf of Mexico lease blocks require that seismic interpretations underlying structural maps be based on adequately quality-controlled datasets. 3D survey merging is common in the GoM where adjacent lease blocks are developed by different operators at different times; BOEM's technical review of development plans assesses whether the seismic interpretation across survey boundaries is supported by adequate mis-tie analysis and correction. Deepwater operators routinely hire seismic contractors to perform comprehensive mis-tie analysis and cross-equalization when merging datasets from different vintages.

Norway (Sodir): Sodir's data quality requirements for NCS exploration seismic data, filed through the Diskos data management system, include documentation of mis-tie analysis for 2D line grids and merged 3D surveys. The Diskos archive contains one of the world's most comprehensive collections of offshore seismic data, spanning five decades of NCS exploration; mis-tie correction is essential when using multi-vintage data from this archive for modern regional studies and prospect evaluation. Equinor's geoscience quality standards specify maximum acceptable mis-tie values for seismic data used in resource estimates and development planning.

Middle East (Saudi Aramco): Saudi Aramco's extensive 2D seismic grid over the Arabian Shield and sedimentary basin areas includes vintage data from multiple decades of exploration. Aramco's exploration geoscience department conducts systematic mis-tie analysis on regional 2D grids before using them for structural mapping and prospect identification. Modern 3D surveys are acquired with careful datum control to minimize mis-ties with legacy 2D data, and residual mis-ties are corrected through bulk static shifts before integrating old and new data in regional interpretations.

Mis-tie is also written as mistie (one word) or mis tie (two words) in different publication conventions. Related terms include seismic statics, NMO correction, well tie, seismic interpretation, cross-equalization, and seismic processing. Well-seismic mis-tie is the related concept for depth discrepancies between well log synthetic seismograms and seismic reflection events at well locations.

Tip: When evaluating a seismic interpretation for a prospect, always ask to see the mis-tie map for the 2D grid or the mis-tie analysis at 3D survey boundaries before assessing the structural confidence. A prospect that straddles two seismic vintages with a 15-millisecond mis-tie at the boundary could have its closure defined entirely by the data artifact rather than by real geological structure — particularly if the "high" on the structural map correlates with the survey boundary rather than with the geological trend. Mis-tie correction should be a prerequisite for structural mapping that will be used for well placement decisions.

FAQ

How is a mis-tie corrected in seismic processing?
The standard correction for time mis-ties between two 2D seismic lines is to apply a bulk time shift (a constant time correction) to one line so that the event times match at the intersection. For systematic mis-ties across a grid of 2D lines (where different lines have consistent offsets from each other), a simultaneous mis-tie minimization algorithm adjusts shifts on all lines simultaneously to minimize the total mis-tie across all intersections. For 3D survey merges, a time-variant, spatially varying correction surface (derived from mis-tie measurements at numerous points along the survey boundary) is typically applied to one survey to match the other. Amplitude mis-ties require cross-equalization processing, where spectral matching filters are designed from the amplitude spectra of both datasets and applied to bring them to the same spectral character.

Can a well-seismic mis-tie indicate a problem with the well log rather than the seismic?
Yes. Well-seismic mis-ties can originate from errors in the well log data (cycle skips or depth shifts in sonic logs, incorrect density log calibration, KB datum errors, or casing shoe contamination of sonic readings near the bit) rather than from velocity errors in the seismic. Before attributing a well-seismic mis-tie to the seismic data, quality-check the sonic and density logs used to generate the synthetic seismogram: verify that cycle skips have been repaired, that the depth reference is correctly applied (KB elevation confirmed), and that the synthetic was computed using calibrated log values rather than raw measurements. A synthetic built from a carefully quality-controlled and depth-shifted log often reduces or eliminates mis-ties that were initially attributed to the seismic processing.

Why Mis-Ties Matter

Seismic mis-ties are a fundamental data quality issue with direct consequences for exploration risk and development well placement. An uncorrected time mis-tie of 10 to 20 milliseconds at a prospect boundary can translate to 15 to 30 metres of apparent structural relief — enough to make a subcommercial flat structure appear to have a closure large enough to justify a well, or to misplace a horizontal development well by a significant fraction of the net pay thickness. Systematic mis-tie analysis and correction is not a processing detail but a critical quality control step that determines whether the structural map and its uncertainty bounds correctly represent the subsurface or are contaminated by data artifacts that invalidate the interpretation.