N255 An Integrated Approach to 3D Seismic Interpretation

Seismic interpretation is the process of integrating subsurface data and geologic knowledge to produce a suite of technical products and presentation materials that addresses specific objectives and informs specific decisions. This may involve developing a regional or basin-scale understanding of petroleum systems and play fairways, identifying specific leads and prospects, defining drilling locations for exploration, appraisal or development wells, estimating risk and calculating reserves.

While each project workflow must be unique and fit-for-purpose and often involves multiple iterations and refinements, the process can be broken down into a series of generic steps:

1. Assemble and understand the available data
2. Define subsurface geometries
3. Infer structure and stratigraphy (i.e. the geological context and meaning)
4. Assess and calculate potential hydrocarbon presence and volumes
5. Quantify risk and uncertainty
6. Communicate results to subsurface team and decision makers

Each step in this process may involve specialists, such as seismic processors, rock physicists, petrophysicists and sequence stratigraphers. However, it is typically the job of the interpreter to understand and incorporate the results of specialists, to drive the entire process towards coherent conclusions and to communicate the results and uncertainty effectively.

Introduction
The step-wise approach and its iteration. Defining objectives. Workflows to achieve objectives quickly and efficiently. Thinking creatively.

Seismic data volumes
Theory and definition of stack volumes and attributes in use in the industry. Angle-stacks, coherence, AVO attributes, AI and EI inversion. Time domain vs depth domain. Recognising and understanding the differences and value of each of these. How to load and use multiple volumes most effectively. Frequency, phase and time shifts. Use of gathers.

Workflows
Project objectives. Understanding client, manager and/or partner objectives. Appropriate pick density. When to pick and when to grid. Good work-habits: rigorous and meaningful naming conventions, capturing and recording work in real time.  Making maps suitable for your audience.  Use of 3D displays. Depth conversion procedures, quality control and error quantification.

Seismic “noise”
Acquisition noise: the acquisition footprint, sources of processing noise. Geological “noise”:  multiples, including water bottom multiples, the effects of shallow channels and seabed variability on amplitude and depth conversion. Gas effects, fault shadows, velocity push down and pull-up.

Recognising anomalies
Recognition and classification of seismic anomalies. Recognition and interpretation of phase changes. Developing and carrying alternative models. Techniques for highlighting models.  Pitfalls: surface/shallow effects, focusing, anisotropy, facies variation, high and low angle faulting.  Techniques for identifying anomalies quickly.  Physics-based risking.

Recognising geology
Interval maps; isopachs and amplitudes. Defining pinchouts. Recognising and mapping sedimentary features. Chronostratigraphy vs. lithostratigraphy. Differential compaction. The art of the well tie. Resolution, detection and tuning.

Data and interpretation display
Frequency analysis, filtering and noise reduction techniques. Colour bars suited to various seismic attributes (instantaneous amplitude, average energy etc). Scales and scaling. Contouring. Voxel picking techniques. Review of specialist software. Slicing datasets. Opacity displays. Surface drape. Shaded relief.