Since inception in 1998, Merlin has continuously provided geophysical support and advice. Merlin's staff offer a wide range of experience previously gained at senior technical levels within operating oil companies and at research posts within various academic institutions. Merlin's core geophysical function is to provide seismic interpretations, preferably sequence-based and as part of Merlin's multi-disciplinary team including input from petrophysics, rock physics, geology and well stratigraphy. More recently, the integration and pragmatic evaluation of the various specialist seismic attributes has become another of our technical strengths. In addition to interpretation services, Merlin offers seismic acquisition and processing advice. Merlin also provides assistance in the wider fields of geophysics including potential field data and electromagnetic studies.
2D and 3D seismic interpretation is a core geophysical activity at Merlin and is undertaken using Kingdom® Suite (IHS), DUG Insight® (DUGeo), and more recently Petrel® (Schlumberger). Merlin prides itself in being receptive to clients' needs and tailoring any interpretation workflow to the project's specific requirements. This can range from a basic horizon structural interpretation, frequently completed within tight timeframes, to detailed integrated evaluations. Such detailed work often involves input from seismic attributes, rock physics, structural modelling and seismic stratigraphy coupled with detailed stratigraphic well correlation studies and all provided 'in house' as part of Merlin's integrated team. Merlin's interpretation team is especially strong in structural analysis, both at prospect and basin scales, and has a long track record of interpretation in many basin settings.
Well to seismic correlations are essential parts of any interpretation process. Consequently, Merlin provides correlations to different levels of detail. For simple, time constrained projects, synthetics created within the Kingdom® Suite are frequently adequate. Where a more thorough correlation is justified, synthetic gathers are derived using Rokdoc® (Ikon Science) software, usually following a petrophysical and/or rock physics evaluation of relevant well data. As well as undertaking a reliable well to seismic tie and undertaking an additional QC of the seismic data, this approach enables the prediction of offset sensitive seismic effects associated with specific geological intervals, thus allowing a comparison with any available processed attributes.
Rock physics analysis provides the link between seismic data and well logs. It explains why a reflector appears as it does and predicts how it might change if rock properties are varied. Away from well penetrations, a change in the character of a reflector can be related to a probable geological cause. In particular, the likely seismic signature of hydrocarbons can be identified by rock physics analysis, enabling the interpreter to recognize pay in seismic.
At Merlin, rock physics analysis is conducted using Ikon's Rokdoc® software suite. Our philosophy is to use rock physics analysis as part of an integrated approach to seismic interpretation, with continuous dialogue between the rock physics analyst and seismic interpreter. This workflow allows us to interrogate every piece of available data and ultimately map robust and defendable prospects.
Merlin also applies rock physics to make recommendations regarding how reservoir imaging might be improved. For example; new seismic acquisition, reprocessing to angle stacks or creation of inversion volumes optimised for distinguishing lithology and/or fluid fill.
Depth conversion is often critical to prospect definition and evaluation. Merlin has provided depth conversions within exploration, appraisal and detailed field evaluation studies. As required by the specific situation, Merlin offers depth conversion at differing levels of complexity. This can range from a simple time-depth polynomial, derived from regional well data, to a comprehensive layer cake velocity cube specified within Kingdom's VelPAK® module, offering rapid depth conversion sensitivity studies. VelPAK also allows the calibration of seismic processing velocity cubes, as required. Merlin also has significant experience in the iterative process of seismic depth imaging for both 2D and 3D onshore and offshore datasets and is well aware of the many pitfalls that this type of processing can offer!
Merlin offers pre and post stack attribute analysis and evaluation using the DUG Insight® software. The normal range of attributes are offered including incoherence, dip, instantaneous amplitude, frequency and phase, structurally oriented filtering and spectral decomposition. We can also use DUG Insight® Insight for full pre-stack evaluation of gather volumes. Merlin's strength lies within an integrated approach in which attributes are considered in terms of associated rock physics and petrophysical evaluations. The evaluation of attributes can sometimes be misleading but Merlin's wide experience, coupled with the closely integrated approach, goes a long way to a realistic and pragmatic interpretation of any seismic attribute dataset.
Merlin offers coloured inversion via the Kingdom® Suite (IHS). Coloured inversion is often used to define impedance intervals and boundaries in a relatively quick and simple way. One advantage to the method is that the results are not biased by interpreter input, such as a low frequency model. Impedance values generated are however relative, not absolute. Merlin use coloured inversion results as quick method to link between the seismic interpretation and any parallel petrophysical and/or rock physics studies. Following the workflow proposed by BP, the Merlin team has successfully used coloured inversion in field development situations to define variations in reservoir pay across a 3D dataset.
Merlin does not directly provide detailed acquisition and processing consultancy support. However, Merlin has associates with the necessary skills and experience to provide this support as and when required. Merlin's direct involvement with 2D and 3D acquisition design has frequently been to provide a link between the client and the acquisition parameter design specialist. This input can ensure that data are acquired to meet the client's specific target objectives and at an optimal price. Subsequently, Merlin's involvement with the data processing can also provide the necessary input to ensure that the client's data objectives are met by the use of applicable and cost efficient processing routines. Knowledge of the data's acquisition and processing history is frequently helpful in the eventual interpretation of the resultant dataset. This is particularly important if seismic attributes are to be evaluated in a multidisciplinary approach, as favoured by the Merlin team.
Although not offering detailed interpretation of potential field data, Merlin is keen to be involved and has often provided input and liaison with gravity and magnetic data interpretations. Too often, potential field data are interpreted in isolation, providing sub-optimal results. It is by the integration of the seismic structural interpretation together with the associated potential field data that the maximum information can be derived from combined datasets. Merlin often organises and oversees specialist gravity and magnetic processing, as part of a larger evaluation project. Merlin also has access to simple gravity and magnetic modelling software and frequently uses this to test the likely potential field responses to various concepts and ideas based upon, and suggested by, an interpretation of the associated seismic data.