Structural Uncertainty Modelling

The superior structural modelling tools in RMS have been further strengthened in RMS 2013 with the addition of new functionality for exploring uncertainty in fault and horizon representation in the reservoir model.

Traditionally, best-case estimates of both faults and horizons have been used throughout the reservoir modelling process, neglecting the inherent uncertainty in these interpretations, and thereby running the risk of severely underestimating the uncertainty in reservoir volumes.

With RMS 2013, new fault and horizon uncertainty tools tightly linked to structural modelling and 3D gridding have been added, making it fast and easy to build several geological scenarios to investigate the effect of structural uncertainty.

Fault Uncertainty Modelling

The fi gure below shows two realisations of possible fault throws where the upper row realisation has larger throw on the two leftmost faults than the lower realisation. Since the Fault Uncertainty tool is tightly integrated with structural modelling and 3D gridding in RMS, the user can now rapidly build these models in full, to investigate the scenarios corresponding to the uncertainty in the input data.

Changes in fault throw created through an automatic workfl ow.

Perturbing fault parameters like throw dip, strike and location in the new Fault Uncertainty Modelling job is also accessible from the RMS’ Uncertainty Management module, allowing fast investigations of multiple fault scenarios, where also the dependency between the faults are properly accounted for.

Horizon Uncertainty Modelling

The new Horizon Uncertainty tools adds the possibility to incorporate realistic uncertainties in the horizon models by specifying uncertainties in the form of standard deviations for all input data used in the horizon modelling process. These include isochore thicknesses, seismic interpretations in time with corresponding interval velocities, depth maps and well data in the form of both well picks and zone log information.

Allowing a user-specifi ed uncertainty on the well picks reduces bull’s eye effects in the resulting set of horizons, but importantly also provides the software a measure that is used to identify possible outliers and errors in the data, giving the users extremely valuable feedback that can be used to evaluate the data quality. The resulting horizons are all dependent on each other, such that an observation on one horizon also affects the neighbouring horizons ensuring a consistent, geologically valid result. Moreover, the set of horizons represents the most likely outcome based on the uncertainty in the input parameters whereby the user gets results that corresponds to the actual data uncertainty, traditionally neglected. In addition to the full set of horizons, the uncertainty in these can also be directly obtained: see the map view on the next page for an example illustrating how the uncertainty is low around well picks and along well trajectories.

IN SUMMARY

• Fault sensitivity studies made easy.

• Horizon sensitivity studies includes uncertainty of all data.

• Horizontal well data automatically accounted for.

• Realistic structural scenarios.

ROXAR AS, GAMLE FORUSVEI 17, PO BOX 112, 4065 STAVANGER, NORWAY TELEPHONE +47 51 81 8800 FAX +47 51 81 8801 WWW.ROXAR.COM

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2014

Structural Uncertainty Modelling

Estimated horizon depth uncertainty.

The ability to account for the zone log data in the wells have opened up a possibility to fi nally produce consistent structural scenarios that properly deal with long horizontal wells. Now an auditable, reproducible and fast tool provides the possibility to create a structural model where the well data corresponds to the model without the need for manual, time-consuming and non-reproducible workfl ows; this is illustrated in the fi gure below.

The upper intersection is extracted from a real model before a new well is drilled. In the middle intersection, a new well with non-corresponding data is added. The zone log is indicated by the colour of the well trajectory. The lower intersection shows the fi nal result after rerunning the setup, just adding the new well. The well picks honouring the transition between the zones are of course accounted for, but also the long part of the well trajectory being within one zone is automatically correct, without any manual editing. This proven technology has already been successfully applied on several real case reservoirs in many parts of the world.

Volumetric Sensitivity Studies

Moving faults or horizons can obviously change the volumes in place. With the new fault and horizon uncertainty tools, sensitivity studies in RMS are easy and straight forward to set up and run. By using the workfl ow concept in RMS, a range of different scenarios can be built and gridded by simply varying the input parameters and running the workfl ow.

Two regions of interest bounded by faults altered in the Uncertainty Management setup

for analysing their relative contribution to total oil in place.

The fi gure above shows an example where the positions of the four faults are allowed to move laterally within a pre-defi ned Fault Uncertainty Envelope. The volumes of interest are bounded by these faults, a top surface and two contacts being different in the two segments of interest, allowing output for the total fi eld or individual segments. The histogram shows the volume distribution for the fault segments. RMS provides, for example, Tornado charts demonstrating the impact of the different uncertain parameters, and can be used as a decision support tool which accounts for the fault uncertainties so commonly neglected.

Volume distribution in 100 simulations of fault location sensitivities.

To learn more please visit www.roxarsoftware.com or emailus on rss.marketing@emerson.com.

Upper fi gure: intersection with original structural model.

Middle fi gure: a new well is drilled. Observations of zone in well shows original model was too deep.

Lower fi gure: structural model automatically up-dated to obtain correct zonation