Geology Reference
In-Depth Information
Quality Control
10.1
Introduction
This chapter focuses on the quality control of completed interpretations as expressed in
maps and cross sections. Quality control means locating and correcting errors in the data
and in the interpretation. Problems can arise from data transcription errors, incomplete
exposure in the field, interpolation uncertainties between wells and seismic profiles, and
missing or misleading information in seismic interpretations. The quality-control issues
discussed in this chapter can be broadly categorized as data errors and contouring arti-
facts, inconsistency of trends, bed thickness anomalies, and impossible fault shapes.
Additional techniques for detecting and correcting errors involving the restoration and
balancing of cross sections are covered in Chap. 11. Those topics are covered separately
because they also include related methods for extracting additional geological informa-
tion from the data and for making model-based predictions of the geometry. The single
best quality control for an interpretation is to build an internally consistent, 3-D model of
the entire structure. Many of the individual problems noted in the following sections would
be obvious in 3-D. The following sections discuss methods that are commonly applied in
2-D, that is, to geological outcrop maps, structure contour maps, and to cross sections.
10.2
Data Errors and Contouring Artifacts
Before a map is finalized, it should always be examined for data errors, edge effects,
and contouring artifacts. Some of these problems are nearly inevitable because of human
error in data input and the intrinsic behavior of computer contouring algorithms.
10.2.1
Data Errors
Data errors are a likely possibility where single points fall far from the average surface.
Problem points may be recognized by the presence of small closed highs or lows, usu-
ally defined by multiple contours that surround an individual point. Such errors com-
monly arise from mistakes in the interpretation of the unit boundaries or as transcription
errors in transferring data to the map. This type of error tends to produce very local
highs and lows on a preliminary structure contour map (Fig. 10.1a). Point 1 (Fig. 10.1a)
is almost certainly a bad data point as it forms a small, deep depression in the map
surface. Point 2 is a closure at an elevation consistent with other elevations on the map
