Merlin can provide geological expertise to support clients' work-programmes across the complete spectrum of their Exploration and Production evaluation activity, including Operations Geology. Members of the Merlin team have diverse backgrounds with skills and experience gained in major operating companies, small independents and specialist consultancies. These in-house skills, married to those within Belltree, enable Merlin to provide high-quality geological services in both conventional and unconventional spheres of petroleum geology. As with all Merlin services, the focus is on generating results which help our clients achieve commercial success: the thoughtful application of petroleum geoscience in an appropriate business context.
At Merlin, stratigraphy provides the underpinning framework for much of the geoscience work that is carried out within the company. The stratigraphic expertise is provided by Philip Copestake and Tony Loy. It is essential that all aspects of subsurface interpretations are based on a consistent stratigraphic framework, including lithostratigraphy, chronostratigraphy and sequence stratigraphy. This consistent framework is developed by interpretation of all available well data and is then provided to the seismic interpreter working on the particular project in question. In addition, the same framework is then used for other evaluations including reservoir evaluations (reservoir zonation), petrophysics (to constrain the petrophysical zones), geochemistry (for example the chronostratigraphy is used in basin modelling, and the framework is used to place source rock intervals into their correct stratigraphic position).
Sequence stratigraphy is used as a standard technique, whereby well successions are subdivided into depositional sequences, defined between unconformities recognised by stratigraphically defined breaks in succession. This is aided by biostratigraphic interpretations of all available data. These sequences then are tied to the mapped seismic sequences interpreted by the seismic interpreters in the company.
Figure 1 shows a typical detailed well correlation of the type produced within Merlin, in this case using Oilfield Data Manager software. This example, from the Outer Moray Firth Basin, UK North Sea, shows the typical complexity of the North Sea Upper Jurassic, whereby intra Kimmeridge Clay sandstones (allocated to the Claymore and Galley Sandstone Members) can be correlated between two wells only two kilometres apart. The 15/24a-9 well was drilled as an appraisal to the 15/24a-4 well, which discovered hydrocarbons in the Galley and Claymore Sandstones. The seismic interpretation suggested that at the 9 well location, that both sandstone units would thicken and improve both in quality and net reservoir thickness. This was the case, although the reservoir quality was poorer than expected and the block was ultimately relinquished without further drilling (refer to JX Nippon relinquishment report for licence P1465).
Aspects of reservoir geology contribute to many of the project delivery workflows carried out by Merlin. At basin analysis and acreage evaluation stages, mapping of reservoir distributions, palaeo-facies mapping and gross properties (e.g. gross thickness, Net:Gross, average porosity) is typically carried out based on a rigorously defined stratigraphic framework developed in-house. While geological mapping is supported by software products such as the Kingdom® Suite, Petrel®, TerraStation™ and Surfer®, often map construction by experienced hand rather than by algorithm is preferred. However, mapping is captured to digital form and is now regularly incorporated into ArcGIS® projects for visualisation against other project data and for Common Risk Segment map production.
At field, prospect and well scales, Merlin can provide a series of reservoir characterisation services, many covered in sections on this page. Merlin's in-house expertise is complemented by a range of external specialists with whom the company has worked for many years. In this way, clients can be assured of accessing class-leading experts, but in a way that retains an integrated approach to delivering the project goals.
In-house petrophysical reviews are an important part of the integrated services that Merlin can provide. Frequently, regional mapping and reservoir characterisation work-flows are hampered by inconsistent, inappropriate or missing petrophysical analyses. In such situations, the Merlin approach is to carry out multiwall reanalyses within the sequence stratigraphic framework developed for the project. In some cases, this needs to be an iterative process, as the petrophysical analyses may suggest that the sequence stratigraphy should be modified. The benefit of Merlin's integrated approach is that such iterations are fast and efficient, occurring within the workflow and not just being recognised as necessary when individual reports land on the client's desk (or inbox!).
Merlin also undertakes standalone single or multi-well petrophysical analyses, including providing operations petrophysical support for client's wells. Frequently, Merlin is asked to review wells where reservoir analyses yield ambiguous hydrocarbon saturations or where some aspect of the initial evaluation is questionable. In these circumstances, a clear picture of the uncertainties is developed and all additional pertinent data are incorporated into any evaluation. While Merlin specialises in incorporating and aligning core, petrographic, pressure, fluid property and mudlog data into petrophysical interpretations, it remains the case that there may never be a definitive petrophysical answer within the data available.
Terrasciences Inc. petrophysical, correlation and mapping package TerraStation™ II is the primary tool used within Merlin. The toolset within Terrastation™ is robust for both single and multiwall evaluations and is particularly well matched to the iterative revision of petrophysical analyses as stratigraphic frameworks are refined.
Where projects require specialist petrophysical approaches (e.g. NMR, Sonic waveform analysis), Merlin can draw on a number of class-leading petrophysical specialists to complement the in-house skillset: we know our in-house limitations.
Merlin offers an Image log interpretation service, either as a standalone product or as part of an integrated services package. Interpretation of both wireline and LWD image log data is carried out in-house utilising the Image Log extensions to TerraStation™ II. Close co-ordination with clients ensures that the project scope for Image data interpretation is focused on need and that the results are easily incorporated into the forward evaluation workflows. In outline, the image log interpretation workflow is generally:
- Careful data processing and rigorous quality control
- Manual dip picking and drilling/acquisition artefact recognition
- In-situ stress and borehole stability analyses
- Structural interpretation including fault and fracture analysis and the identification of unconformable or condensed sequences
- Sedimentological interpretation including structural dip removal, sand body analysis, thin sand analysis and net-pay calculations
Single or multi-well studies can be undertaken, within both clastic and carbonate successions. Near real-time LWD image data interpretation is available to supplement the operational capabilities that Merlin offers.
Image log analysis as a standalone product can be very useful: interpretations result in some great displays and reams of data. However, a standalone interpretation alone is of limited impact. Where real value can be realised is by taking a fully integrated approach to bridge the resolution gap between seismic, log and core data. What Merlin offers is the ability to unlock this extra value by utilising the integrated, cross-disciplinary skills of the whole geoscience team. For instance, dip swing patterns in the tadpole plots, changes in azimuth on walkout plots and the like can all be set against other data in order to reveal deeper geological truths and better to test existing interpretations of seismic or well stratigraphy data.
Within the Merlin in-house team we have experienced Ph.D. level structural geologists who are highly skilled at structural analysis at multiple scales, from outcrop to basin. Merlin also has the capability to perform structural interpretations from Image Logs. We aim to extract the maximum value from your seismic database by using conventional seismic interpretation combined with the application of Incoherence volumes, Dip volumes and horizon attributes. When integrated with the results Image Log interpretation, it provides a powerful integrated tool kit for detailed structural analysis. The Merlin team is acutely aware of the importance of building a strong structural framework for all interpretation work, whether be an exploration evaluation or for development planning. We aim to use a range of software tools and our combined experience to ensure features of interest are captured at a range of scales representing the fractal character of faults and folds.
Structural interpretation relies on the recognition and deep understanding of features, from granulation seams to prospect-scale structures. Our team is highly skilled in the analysis of structural geology in the field, and has broad experience of many tectonic regimes from numerous studies around the globe.
Merlin frequently conducts exploration-scale structural studies, which may include: the understanding of tectonic phases and styles, the identification of robust trap types, an assessment of fault and top seal risk, as well as an understanding of hydraulic top seal integrity. Structural analysis also feeds into petroleum systems modelling, where an understanding of the tectonic history, and potential migration conduits, is vital to the identification of play sweet-spots. Appraisal and Development interpretations are more usually focused on the identification and understanding of small scale structure, which may have both positive and negative economic impact. Indeed, the subtle details of fault linkage and fold geometry can often separate successful wells from failures.
If specialist studies are required, the Merlin team is ideally placed to propose and manage third party providers. These may include fault seal analyses, structural restoration, strain analysis or fluid flow modelling.
Before building a static model, the prime question to ask is "what is the model for?". Unfortunately, this question rarely has an easy answer as the understanding of what a static geomodel is expected to deliver often varies dramatically across a client's asset team. Merlin seeks to ensure that the expectations of all "interested parties" are reconciled before recommending a work flow for any geomodelling project. During model builds, retaining the team's "feel" and understanding of a field is essential, particularly when capturing uncertainty. Consequently, Merlin does not undertake standalone model builds which are expected to be carried out at arms-length from the relevant asset team.
Merlin's preferred tool for reservoir modelling is Baker Hughes JewelSuite® which allows geologically meaningful modelling of fault surfaces and structural surfaces, robust property modelling and strong quality control functionality. Upscaling and connectivity with industry standard dynamic simulators (e.g. CMG IMEX, Schlumberger ECLIPSE®) is fully supported within the JewelSuite® environment, as is visualisation of the resulting simulation results.
Schlumberger's Petrel® software has also been licensed by Merlin.
Through Merlin's partner, Belltree Reservoir Development and Management Ltd, a fully integrated "seismic to simulator" workflow can be delivered to clients. In association with Belltree, Merlin also offers a peer review service for both static and reservoir models.
Since inception, Merlin has provided operations geological support for over 40 exploration, appraisal and development wells, most of which have been operated wells drilled by our clients. As a consequence, Merlin has good working relationships with many well management companies, wellsite geological contractors and well services companies. We have placed operations geologists in clients' offices or, more often, provided a full 24/7 operations geology service from the Merlin facilities.
Operational geology should not be considered as a stand-alone service: at the sharp end, operational decisions need to be taken quickly, with safety always in mind and with full awareness of the implications of any decisions on the wider project beyond the well. Contracting operational support from a company that understands the regional picture, delivers the prospects and is aligned with the business drivers ensures clients have the best chance that operations will be a properly integrated facet of an overall programme.
The Merlin team is able to provide on the ground support for exploration activities. This may include geological mapping, planning seismic surveys, selecting well sites and collecting samples for third party lab based geochemical or biostratigraphic analysis. Fieldwork undertaken by Merlin staff and associates has had a direct impact on improving exploration success. Merlin staff are fully insured and have experience working as individuals or in small groups in a range of global settings including Europe, Middle East and the Americas.
- Identified faults at surface which were mapped into the sub surface across a planned well-bore. Casing shoes were positioned to avoid the faults resulting in fast safe drilling.
- Identified stable ground for well pad in an area prone to land slips and salt at surface
- Discovered outcrops of early-mature high-TOC source rocks in an area where source presence was considered to be a high risk factor in the petroleum system.
- Surface hunt and sampling of seeps.
- Discovered outcrops of previously unknown clean high quality sandstone which significantly reduced reservoir risk in a complex compressional petroleum system.
- Developed palaeogeographic reconstructions of petroleum systems based on evidence of depositional settings (e.g. Hummocky Cross Stratification is characteristic of shallow water storm deposits). This kind of analysis can be fed into seismic interpretation and static geological models.
Folded shales identified in a rare storm washed outcrop in a remote stream were found to contain TOC >20%. Maturity levels indicated good potential for discovering oil and gas in the area.
Spectacular basalt outcrops in Iceland, a potential field analogue for deposits mapped in offshore seismic datasets, West of Shetland.