Case Histories

In this paper we show that a single aspect ratio applied to the total porosity of a sand-clay mixture can accurately model both P- and S-sonic data. We also show that the variation of this optimal aspect ratio can be predicted from the petrophysical properties of the rocks, whilst keeping the effective elastic properties of the minerals constant of large geological intervals.

This paper demonstrates the use of deterministic vs. geostatistical inversion, and illustrates the benefits of using geostatistical seismic inversion for reservoir characterization of two oil reservoirs in Kuwait: 1) the Ratawi Limestone carbonate reservoir and 2) the Wara sandstone clastic reservoir. Geostatistical inversion methods integrate the well log data, geological constraints, geostatistical parameters and seismic data to produce a highly detailed reservoir description. The examples in this paper are from the Umm Gudair and Burgan fields in southern Kuwait.

In quantitative reservoir characterisation we try to extract absolute inforamtion about reservoir rocks from the seismic data. One method is to invert the seismic data to elastic rock properties and then interpret these rock properties in terms of reservoir properties. Here we present a solution based on deterministic inversion that results in a low resolution image of the porosity within a channel sand reservoir, yet permits an understanding of the general variations in the distribution useful for well planning and field development.

In this paper we show that a single aspect ratio applied to the total porosity of a sand-clay mixture can accurately model both P- and S-sonic data. We also show that the variation of this optimal aspect ratio can be predicted from the petrophysical properties of the rocks, whilst keeping the effective elastic properties of the minerals constant of large geological intervals.

В данной работе рассмотрены общие принципы детерминистических и геостатистических инверсий волнового поля: какие данные необходимы для их применения и как выбрать оптимальную методологию для решения актуальных геологических задач. Анализ проведен на примере одного их месторождений Тимано-Печорской провинции.

Acoustic and shear impedance images, obtained from deterministic simultaneous inversion of a high-resolution crosswell seismic survey, were used to obtain the internal structure of Niagaran reef in Michigan. The crosswell seismic survey was conducted using two monitor wells external to the reef. These wells had depths that extended beyond the depth of the reef, and imaging used reflections from above and beneath the reef, resulting in the best seismic images of any Niagaran pinnacle reef obtained to date.

Geology, rock physics and geophysics are combined quantitatively in a geostatistical inversion to produce reservoir models of a tidally influenced shoreline to deltaic environment. The impact of the geological facies probability volumes versus the seismic influence on the results can be estimated by comparing models with those produced using probabilities alone and with those using seismic inversion alone.

A Seismic to Simulation study was undertaken on the Aboozar field with the goal of optimizing and quantifying ultimate production from the field. The resulting simulation model achieved a 95% match against well data with minimal permeability modifiers and NO porosity modifiers.

An AVA seismic forward modeling study was carried out with the objective of understanding the key contributors to amplitude response prior to further advanced processing such as Simultaneous Inversion work.

Acoustic impedance inversion (AI) and simultaneous angle-dependent inversion (SADI) of a 3D seismic data set to characterize reservoirs of Mississippian Morrowan age in the triangle zone of the frontal Ouachita Mountains, Oklahoma.

A multi-disciplinary and interactive approach, guided by seismic inversion techniques and real-time petrophysical data, resulted in the successful planning and execution of the Longtom-3 and subsequently the Longtom-4 drilling and evaluation program.

This study demonstrates how geostatistical AVA-inversion workflow was used to obtain reservoir properties and risk assessment of the Lekharyaga prospect area.

The result shows that lateral varying wavelets can compensate for the shallow gas effect in the seismic data, and reduce the uncertainty of the seismic inversion modeling for reservoir characterization.

In order to reduce the risk for the future drilling plan, and to get a better understanding of the lateral facies distribution of reservoirs in the field, a constrained sparse spike inversion was applied to convert the 2D full-stack seismic data recorded in the area into 2D acoustic impedance lines, calibrated to the existing wells.

Full band-width simultaneous inversion was performed on a base and two monitor surveys over the Girassol field, offshore Angola. Careful calibration of the low frequency models of the elastic properties for the base survey was performed to identify the reservoir away from well control.

In this paper, we discuss how we arrived at a seismically constrained petrophysical interpretation in the Scarborough gas field in the Exmouth Sub Basin, offshore North West Australia.

This paper describes the application of a novel AVA stochastic inversion algorithm to quantitatively integrate pre-stack seismic data and well logs. The stochastic inversion algorithm is used to characterize flow units of a deep-water Miocene reservoir located in the central Gulf of Mexico.

The high-resolution geostatistical simulation results of Kotabatak have provided an effective interpretation framework that assists detailed sequence stratigraphic mapping and information on reservoir quality. Recent new well log information confirms the results.

This paper describes a novel methodology to integrate well logs and 3D pre-stack seismic data. The objective is to assess lateral continuity and spatial extent of lithology and fluid units penetrated by a well.

The 4D seismic data acquired on Girassol one year after the start of production have been used to update the reservoir flow model. First, the time-lapse seismic data and the reservoir flow model output have been transformed into directly comparable quantities (impedance) at the same spatial resolution. Then a comparison and analysis of discrepancies were performed. In a first qualitative step, these observations have been used to modify the reservoir model via manual adjiustments to the rock properties and reservoir boundaries. The next step will be quantitative use in a history matching procedure. NOTE - This is an update to the 2004 Girassol study incorporating a second monitor survey.

Simultaneous angle dependent inversion (SADI) was performed on three angle stacks from the Alpine Field. Additionally, post-stack inversion was carried out on the near angle stack (using P-impedance log data) and on the far angle stack (using elastic impedance). The results of the work helped interpreters better characterize the distribution of the reservoir in the field and was used to facilitate well planning and reserves estimation.

This paper presents a combined reservoir characterization and modeling workflow for a producing field in the southern Persian Gulf. A cornerstone of the process is tight integration of geostatistical inversion with the upscaling and geocellular model construction.

We discuss how geostatistical inversion results allowed new methods of computing seismic net pay and net-to gross into our toolkit, delivered a better match to geologic models through higher resolution and added value by providing the flexibility of evaluating different probabilistic scenarios.

This paper focuses on the inclusion of the finely laminated sands through the integration of high resolution petrophysical data with seismic data. This integration of data with very different vertical resolutions was achieved through rock physics modeling.

This paper reports on the experience gained with a pilot project aimed at quantifying the value of geostatistical inversion for the detection and delineation of thinly bedded hydrocarbon reservoirs.

To investigate and characterize fluid movement, a novel workflow involving joint simultaneous inversion of baseline and monitor seismic AVO data was applied. The results from the time lapse AVO inversion confirm the hypothesis based on production history analysis that aquifer support comes from the southeast.

One of the main difficulties of the interpretation in this field was to distinguish the porous sandstones from the low velocity shales. Log analysis indicated separating the two lithologies would be possible. Volumes of P and S wave impedances were generated and elastic parameters derived alowed better quality reservoir characterization.

This article reports on a seismic inverse modeling study from an oil-producing field in the Suphan Buri basin, Thailand.

The limitations of using low-frequency 3-D seismic data for detailed reservoir characterization are well recognized. Nonetheless, these data are very well suited for quantitative estimates of the net-to-gross, which is a reservoir scale property critical in deepwater turbidite reservoir characterization and development projects.

This paper presents an applied workflow and the results of an integrated team effort to define the commercially recoverable reserves associated with the Buah fractured carbonate reservoir of the Makarem sour-gas accumulation in the Sultanate of Oman.

A case study from a maturing oil field shows how integrating data within a common sequence stratigraphic framework approach can lead to the improved understanding of the distribution of fluids and reservoir properties.

Amplitude inversion is widely used to enhance seismic resolution and discriminate reservoir from non-reservoir by applying a cut-off on the computed impedance.

In this paper, we first overview the data, techniques, and studies used to justify the 3-D OBC survey. Next, we present images of the new OBC and reprocessed streamer seismic data that show 4-D, AVO, and converted-wave results. Finally, we suggest a new, preliminary interpretation of the Alba reservoir that is supported by two recently drilled wells.

It was determined that the Simultaneous Inversion methodology extracts a more dynamic range of information from offset seismic stacks, and results in an improved response to reservoir identification and mapping over that of traditional seismic AVO analysis.

In the lower cretaceous glauconitic and regional incised valleys of southern Alberta, Canada, valleys can be filled with sands and/or shales of similar acoustic impedance. Angle-dependent inversion assists in discriminating facies types and compensates for angle-dependent tuning, scaling, and phase in the seismic data.

With the first well being drilled less than a year after seismic acquisition started, the new data arrived in time to make a significant commercial impact on the field’s development. We hope our results at Alba will cause further development and more widespread use of this exciting new technology.

Modern seismic inversion methods model both wavelet amplitude and phase effects and offer the opportunity for improved resolution and presentation of data in a form immediately recognizable to both geophysicists and geologists. This has re-focused our attention to the problem of non-uniqueness. Since the bandwidth of the seismic data is finite, there can be more than one mathematical solution to the seismic inversion problem. It has therefore become our task to differentiate between similar mathematical solutions on the basis of their geophysical and geological viability.

The impedance values of the non-reservoir lithologies significantly overlap those of the reservoir sands, causing problems in the use of impedance to predict reservoir sands. Jason Geosystem (with support from Statoil, Norsk Hydro, and Saga Petroleum) created a new inversion scheme (InverMod) to overcome this challenge.