Reservoir modeling extends field life

With average global oil and gas recovery rates in the low 20% range, the smallest improvements can have a huge impact on both future oil and gas production and the bottom line.

Toward this end, the last few years have seen a renewed technology focus on squeezing more from less and in extending the life of oil and gas reservoirs through a plethora of EOR and artificial lift techniques. And the stakes and benefits are huge. There are predictions that an increase of just 1% in recovery rates would replace three years of global oil consumption.

The default platform for predicting behavior

One often overlooked means of extending reservoir life and increasing recovery rates is reservoir modeling. Three-D reservoir modeling today is the standard platform for mapping, understanding, and predicting reservoir behavior. A robust, reliable, and accurate reservoir model that captures all the field's complexities can provide operators with the crucial information they need when developing their assets and extending the reservoir's life.

Such models provide operators with a spatially accurate analysis of the field, tools to explore reservoir management possibilities, and crucial information on oil in place and how the oil can be produced.

One of the key ways in which today's reservoir modeling packages can achieve this is in their ability to deal with whatever structural or modeling complexities are thrown at them while generating predictive reservoir models that realistically represent the underlying seismic data.

Making full use of seismic

Any reservoir model that oversimplifies geological complexities is not going to deliver the vital information operators require and will lead to reduced field productivity and lower recovery rates. This is particularly important when it comes to incorporating 3-D and 4-D seismic into the reservoir model.

RMS 2012 incorporates new inversion and attribute tools. (Images courtesy of Emerson Process Management)

It is with this in mind that Emerson's Roxar RMS enables 4-D seismic data to be incorporated into the reservoir model alongside existing data types such as geological, geophysical, and simulation data. Facies modeling tools also enable the user to rapidly improve the quality of interpretations, structural and property models, simulation models, and well plans.

The latest version also comes with new seismic inversion and seismic attribute tools. The inversion tool and increased automation, for example, allows geoscientists to use seismic data to create a rock property model quickly and accurately. This is achieved through combining high-frequency information from well logs with band-limited frequency information from the seismic data. Users also can create attributes that more clearly define reservoir structures and guide them through the facies modeling process.

A new object-based, facies modeling tool combines data extracted from seismic with geostatistical tools such as guidelines and trends to generate well-constrained sedimentary bodies. This ability to access both deterministic and statistical techniques gives the modeler access to the gray area between seismic resolution and data-con- strained statistical modeling. The net result is a realistic property model conditioned to well observations and with accurate volume calculations – all vital information when looking to extend the life of the reservoir.

These are just a few of the features provided by today's reservoir modeling solutions. Other tools include field planning to design multiple targets, optimize pad and target locations, and automatically generate well paths; fracture modeling and well correlation tools; and improved integration and usability features. The result is a seamless route from seismic to simulation – absolutely central to efforts to improve oil and gas recovery and extend reservoir life.

North American case studies

One example of where this reservoir modeling software helped reservoir management and well productivity was in Pemex's Kutz offshore field, which is part of the Cantarell asset, one of the world's largest oil and gas fields. Production peaked at 2.1 MMbbl/d in 2003. The field was placed on nitrogen injection in 2000. Production has declined since 2003, however, falling to 464,000 b/d by year-end 2010.

A stochastic 3-D model of the Kutz field in Mexico will help Pemex plan for future EOR activities.

Pemex wished to create a more detailed 3-D reservoir model of the Kutz field – a field that comes with significant reservoir heterogeneities, including a symmetrical anticline, complex compressional faulting, and a diversity of sedimentary environments.

There was a need for a 3-D model that tackles the field's geological complexities, leads to a greater understanding of the asset and its reserves, and helps support updated field development plans based around its 12 existing wells. The reservoir model also will provide input to further simulations and decisions around the adoption of future EOR techniques.

With its ability to enable direct reference between the model and the 3-D seismic; its fault, fracture, and object-based facies modeling capabilities; and its simulation-friendly grids, this software was the ideal solution for Pemex and helped generate a robust and accurate model of the Kutz field addressing all geological complexities as well as honoring reservoir heterogeneity. The model will be used for the further development of the field, in future simulation processes, and in maximizing oil recovery through water, gas, CO, and nitrogen injection processes.

North Sea case study

The North Sea is another region where operators are investing in and using reservoir models as a means of extending reservoir life and increasing recovery rates. One of the leading operators in the region, Statoil, has a target recovery factor of 65% for platform-operated fields and 55% for subsea-operated fields and is starting to make good on these goals.

Today the North Sea is delivering recovery factors of approximately 46%, with the highest recovery ratios on the Norwegian Continental Shelf.

Many of these fields – including 92% of all Norwegian fields – are employing Roxar RMS. One example is Statoil's Statfjord field, which in 1987 posted the record (still going to this day) of the highest daily production ever recorded for a European oil field outside Russia of 850,204 bbl. Today Statfjord is one of Statoil's late-life fields, delivering recovery rates of up to 66% and currently scheduled to remain active until 2019.

Here, according to INTSOK, a joint partnership between the Norwegian oil and gas industry and Norwegian government, reservoir modeling software has played a crucial role generating predictive models for the field and providing input to well intervention, 4-D seismic, and water management decisions. Any IOR efforts for the field such as water injection also are very dependent on the predictive model developed.

No more focus on the short term

Too often oil and gas production strategies have been guided by short-term decision-making – predominantly by fluctuating oil and gas prices – and a knowledge that once the easy oil has been found and a recovery rate of 30% has been achieved, easier oil can be found elsewhere.

However, as oil and gas become harder to find and as energy demand continues to rise, the industry no longer has this luxury.

It is encouraging to see that reservoir modeling today is playing such a crucial role in extending reservoir life and delivering high oil and gas recovery rates.