Maximising Reservoir Recovery - Formation evaluation and reservoir characterisation

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30 May 2017

Following a recent client event hosted by LR in Norway focussing on maximising reservoir recovery, Dr Iain Morrison, Head of Reservoir Services provides an overview on the presentations delivered and discussions generated. He also addresses innovative and traditional ways of interpreting the reservoir and the relevant data to optimise recovery and enhance value.

With estimates that only around 42 percent of the total expected resources on the Norwegian Continental Shelf have been produced, an enhanced understanding of the reservoir is essential in helping to unlock the potential of these fields, and assisting in optimising lifetime performance. The better we are able to predict the production potential of a well, through reservoir characterisation and formation evaluation, the more able we are to optimise the reservoir performance over the entire lifetime, maximising efficiency and value.

Future wells - Cost vs Value

Discussions started centred around the relationship between well design and recovery. Mike Byrne, Global Head, Rock Properties, LR, focused on the value rather than cost of the well, and bridging the gap between wells and reservoirs, improved well design and improved recovery. Wells are our only points of reservoir contact, through which we produce, inject and manage these reservoirs. However, well designs are often optimised on the cost of the well, rather than the value derived from it, as the latter is traditionally difficult to estimate. Using a fully-connected system to model the interaction between a well and the reservoir can allow us to quantify value and optimise design against that measure. A reservoir and well system is not a series of connected pressure drops, but a fully connected fluid system, therefore using an ‘advanced’ well modelling process, optimum well performance can be 'designed-in', resulting in better reservoir recovery and a recognition that the best well is not always the cheapest one.

Fractured Reservoirs

Dr Ali Gholipour, LR's Fractured Reservoir Expert, gave a detailed explanation of how fractures can be identified, predicted and characterised for better recovery, based on an integration of the rock mechanical properties and the strain caused by folding and faulting. The focus was on using this integrated approach, as fractures affect many aspects of field development such as well placement and design, drilling, productivity, ultimate recovery and success of any IOR and EOR processes. It was concluded that in fractured reservoirs the early identification and prediction of fractures distribution is essential for successful development. Ignoring or incorrectly characterising fractures may lead to irreparable reservoir damage, with associated loss of recovery, inefficient in-fill drilling programmes and poor economic outcomes.

Geomechanical modelling

Coupled reservoir-geomechanics modelling is the interaction between the reservoir simulator (fluid-flow) and the geomechanics simulator (stress-strain) with or without fracturing module. Phil McCurdy, Geomechanics Manager, LR, described how neglecting geomechanical aspects during reservoir modelling can lead to unexpected problems in development and missed opportunities. Examples from past projects illustrate how the insights provided by coupled reservoir models can highlight key risks and inform mitigation strategies. In one example, the appreciation of fracture growth during water injection allowed for modifying injection plans to minimise fracture growth into the cap rock and provided guidelines for monitoring likely fracture behaviour. In casing deformation the example showed an assessment of matching field-measured casing deformation to the model, showing the significant impact of sand production on casing strain. This also illustrated that, in the example shown, the deformation problem had stabilised and would not become worse over time. This allowed the operator to make an informed decision not to invest in expensive remedial measures.

Petrophysical approach to shallow geology

Moving towards the surface, we concentrated on a petrophysical approach to the investigation of shallow geology, using physical rock properties and their derivatives to constrain seismic data interpretation of lithology, fluid-fill and pressure. Francis Buckley, Principal Geoscientist, LR, discussed methods by which top-hole geohazard risk analysis can be considerably enhanced at minimal extra cost, the clarification of and refinement of complex risk scenarios, and how to carry out more rigorous analysis of High Resolution seismic data.

Maximising the value of all acquired data

To conclude, Ed Downer Head of Petrophysics, LR, shared the value of integrating gas log ratio analysis into a petrophysical interpretation, explaining that sometimes simplicity is still the most effective approach, especially when budgets are tight. When budgets and circumstances only allow for a reduced suite of data to be acquired, greater emphasis needs to be placed on maximising the value of all available data , such as gas logs, which are often underutilised. However, there is clear value in working the data up into an integrated interpretation and this presentation included a case study demonstrating how the interpretation of gas log ratios correctly predicted hydrocarbon type in a formation where wireline logs were inconclusive.

The event highlighted the huge technical benefits and value which can be realised by the integration of diverse data and how a ‘life of field’ approach can deliver far greater benefits than a focus on up-front cost savings alone.

For more information or to talk to one of our experts about maximising recovery from your reservoir, please click on their names in the above article.