Marcelo Benabentos

Combining rock physics analysis, full waveform prestack inversion and high-resolution seismic interpretation to map lithology units in deep water: A Gulf of Mexico case study

A successful seismic-based reservoir properties estimation effort has three steps: accurate seismic inversion in 3D to obtain relevant reservoir parameters, rock physics transformation to relate reservoir parameters to the seismic parameters, and mapping these parameters in 3D. This problem is nonunique and thus any available information—specifically geologic interpretation—should be used to improve our ability to infer the reservoir properties of interest with confidence. Moreover, uncertainty associated with the different predicted values (i.e., confidence interval and estimate of misclassification probability) must be provided as well, so that proper decisions can be made. Thus, it is evident that this involves interdisciplinary effort that includes rock physics, geologic interpretation, and seismic inversion technology. However, for quantitative description of reservoir properties, one must derive a way to quantify the errors and uncertainties associated with the process.

Reservoir characterization in Burgos Basin using simultaneous inversion

This paper summarizes results obtained in the identification of sandy geobodies that have potential gas accumulations in an area of Burgos Basin.

Cascaded Sweeps- A Method to Improve Vibroseis Acquisition Efficiency: A Field Test

One of the techniques introduced in the last decade to address the improvement in productivity for vibroseis land acquisition was the cascaded sweep method (Andersen, 1995; Moerig et al., 2001). The potential to reduce the acquisition time by using this method comes from reducing the listening and system resetting time by concatenating the sweeps. In the summer of 2004 Repsol-YPF and WesternGeco conducted a field experiment in the Reynosa-Monterrey Block, Mexico, to determine if the use of the cascaded sweep method could be beneficial for the seismic exploration program planned for this block. In this article we present the results of this field experiment.

Density estimate from well log data using a diagenetic rock model

Summary A method to estimate density using other well logs, like sonic, gamma ray and resistivity logs, in a unified rock model is proposed. An empirically derived rock model is an efficient way to compute density information including pore pressure and diagenetic effects, such as cementation and dissolution. This method provides a direct correlation between changes in density due to changes in lithology and fluid content. One immediate benefit of estimating pore-fluid density using well-log data in very low porosity rocks is its value in verifying the integrity of the log data. Another benefit of this method is that performing fluid replacement in the rock model provides an effective means of predicting zones prone to gas accumulation, sometimes by-passed by incorrect values or absence of data in the density logs. The rock model is constructed as a mixture of two lithologies, sand and shale, with variable proportions of each mineral, and brine as the pore fluid. For very low porosity rocks, under certain temperature and pressure conditions, the mineral composition can be related to grain mineral velocities by bounding equations. Lithology and porosity is then empirically related to velocity by the timeaverage equation or Issler’s transform with An applied diagenesis factor. A diagenesis factor is estimated and applied to porosity. Once the relationship between density and velocity is established from the available well log data, the transform from velocity to density can be performed.

Seismic survey design, data acquisition and processing of complex Andean structures

Narrow offset seismic data has limitations in areas with structural complexity. Seismic acquisition cost makes prohibitive to acquire quality seismic data, therefore balancing acquisition cost and data quality is a challenge. Combining technologies such as recording Wide Offset seismic to be processed in the Shot-Receiver domains using Wave Equation Migration (WEM) algorithms is a rational approach. A reduced number of shots during acquisition results in lower operational costs. Forward WEM modeling is required during the survey design to estimate the correct shot decimation in the presence of noise, to avoid losing of structural information.

Fracture characterization in low porosity sands: a statistics rock physics feasibility analysis.

Acoustic logs from one well were used and s-wave velocity prediction was performed within the target zone that includes the reservoir and adjacent shale layers. Fluid substitution was carried out at the reservoir level to estimate the elastic response of the low porosity sand for 100% and 20% of brine saturation. Hydrocarbon was assumed dry gas and the acoustic properties were estimated at reservoir condition.