Three-Dimensional Organization of Low Angle Faults Planes and Fractures in Alberta — A View of Problems in Wells, Sweet-Spots and Migration Paths

Multidisciplinary 3-D integration can unravel structural elements not described before and can explain various types of unexplained anomalies. The present paper is essentially based on the large amount of public domain data available for the Western Canadian Sedimentary Basin; this includes drilling problems, production anomalies, abnormal gas occurrences as well as more typical geological data such as cuttings and core descriptions or wireline log data.

Commonly, anomalies aligned on a map are interpreted as linked to subvertical faults or fracture systems. On the other hand, apparently random anomalies remain unexplained as they cannot be linked to any other anomaly or structural feature. Three-dimensional exploration statistical tools can reveal the existence of planar relationships between these individual instances. Many low angle structural planes with less than one degree angle connect many interesting features that can be understood in the structural context of the areas involved.

A 3-D study of the southern part of the Peace River Area reveal two main planes connecting many large hydrocarbon producers, these two planes account for 56% of the hydrocarbon production covering a very large acreage (after filtering the very deep Devonian that were too rare and too scattered).

Drilling data is too commonly neglected in a structural analysis, it can be used with some caution because many problems can have been caused by operator mistakes or by consequences of previously solved problems (e.g. too high mud-weight following a gas kick inducing a loss circulation problem). The sheer amount of data available from drilling compensates for this kind of uncertainty. One example from West Central Alberta will show that some 40 planes connecting drilling problems coherently plot on a Schmidt diagram with great circles at 90 degrees from each other.

One example of abnormal porosity spikes delivers a near perfect low angle plane that is totally in line with today’s compressional stress regime orientation.

Other examples will show the use of gas composition anomalies such as H2S and a case of abnormal red stain in cuttings that shed new lights on the structural history of the Peace River Area. Combining data of different kind brings down the uncertainty linked to the proposed planar relationships.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California