Organic-rich mudrocks (ORM) from the Brushy Canyon Formation in west Texas were deposited in the Middle Permian during the Guadalupian epoch in the Delaware Basin. Brushy Canyon ORM were examined for Re-Os isotope systematics with a goal of constraining their depositional age, the 187Os/188Os value of seawater at their time of deposition, and to examine how Re and Os partition into organic material in ORM. For these samples, Rock-Eval pyrolysis data (HI: 228-393 mg/g; OI: 16-51 mg/g) indicates predominantly Type II marine kerogen with minor contributions of Type III terrestrial organic matter. Rhenium and osmium abundances correlate positively with HI, and negatively with OI, which are proxies for organic matter type and degree of preservation. These data are consistent with previous work that indicates Re and Os abundances are controlled by the availability of chelating sites in the kerogen. Brushy Canyon Formation samples have (total organic carbon) TOC values between 0.97 and 4.04% and show a strong positive correlation with both Re and Os abundances, consistent with correlations between these parameters in other ORM suites. The positive slopes in these correlations are distinct between marine (higher slopes) and non-marine (lower slopes) lacustrine environments of deposition. The Brushy Canyon’s steep slopes are consistent with marine deposition of its organic matter and an open-ocean non-restricted setting. The relationship to other Re-Os and TOC data sets appears to be a function of the restrictivity of marine conditions, and associated variations in reducing conditions during ORM accumulation of the Delaware Basin compared with more restricted lacustrine basins with local drawdown of Re and Os.
The Re-Os isotope systematics of ORM from the Brushy Canyon Formation yields a Model 1 age of 261.3 ± 5.3 Ma (2.0% age uncertainty; MSWD = 0.82). Within the uncertainty, this agrees with the expected Guadalupian age for this formation. This Re-Os age represents the first direct, absolute age for Guadalupian organic matter in the Delaware Basin. The initial (187Os/188Os)i = 0.50 ± 0.06 obtained by isochron regression represents the 187Os/188Os of seawater at this time. This value is significantly less radiogenic than modern day seawater (~1.06). The lower 187Os/188Os of Guadalupian seawater recorded is likely caused by a decrease in the relative flux of radiogenic Os from continental weathering due to a number of local and global climatic and tectonic changes that were occurring during this time.
The purpose of the study was to quantify and evaluate the impact of geological heterogeneities on connectivity in channelized turbidite reservoirs. The main technical objectives of the project were: the identification of the architectural elements of the deep-water system under analysis, the development of different geological models, the quantification of reservoir heterogeneity and the evaluation of reservoir connectivity and the outline of an early appraisal strategy.
An integrated approach was applied, using different frameworks, to two eni's deep-water assets: the first, an exploration asset in the Mediterranean, and the second, a West African field in development. This methodology was based on an earth models construction phase (reservoir characterization and reservoir modeling) and on a dynamic simulations phase (streamline simulations and well test simulations).
Reservoir characterization was performed by interpreting 3D seismic data using a high precision 3D seismic interpretation software. Key surfaces were interpreted in the reservoir interval. Furthermore, deep-water elements and architectures, mainly stacked channels and distal lobes, were duly identified through the interpretation of seismic sections and amplitude maps.
Reservoir modeling consisted of Object-Based and Multi-Point Facies Simulation (MPFS) approaches. A sensitivity analysis was carried out to define critical parameters and their ranges in order to fully capture geological uncertainties and realize different static models. The selected parameters were: seismic conditioning in the MPFS (amalgamation), facies volume fraction, channels shape and shale drapes content.
To quantify heterogeneity and analyze connectivity, streamline simulations were carried out using a Streamline Simulator. For each geological model, a Dynamic Lorenz plot (storage capacity vs. flow capacity) and its related coefficient (standard measure of heterogeneity) were determined using an in house code. It resulted that all the selected parameters, except channels shape, impacted considerably on connectivity.
To outline an early appraisal strategy, well test simulations were performed using an hypothetical exploration well and a standard Dynamic Simulator. Well test simulation was found to be an interesting qualitative tool to identify heterogeneities, especially shale drapes content, and condition further appraisal decisions.
Considering the promising results, this approach will be further developed to effectively reduce the range of uncertainties, mitigate the associated risks and guide appraisal strategies in future deep-water prospects.
A new geostatistics-based seismic inversion method is introduced in this paper for determining reservoir models consistent with base seismic information. The proposed methodology entails two steps, the second one only being examined in this paper. First, cubes of acoustic velocities or impedances are derived from seismic inversion. Second, these data are incorporated into a matching process to identify reservoir models leading to acoustic responses close to the reference acoustic data. The parameterization of the facies and petrophysical properties populating the reservoir models is based upon the gradual deformation method (GDM), which relies on geostatistical concepts. This particular feature makes it possible to change the spatial distribution of the property of interest from a few parameters while preserving its spatial variability. The matching process is driven from a global optimization algorithm known as the particle swarm optimization (PSO). Such a global approach is reasonable for the problem considered as the forward modeling is very fast. A variant of the PSO algorithm is implemented to take advantage of the gradual deformation method properties. This approach yields reservoir models which honor the seismic data better than those derived from stochastic simulation only with seismic used as a secondary variable. A numerical experiment is then presented to stress the applicability of the proposed matching methodology: the GDM-based PSO approach is used to identify facies reservoir models and water-oil contact consistent with some reference acoustic P-wave impedances.
The utility and evaluation of cutoff values for net pay or net-to-gross determination have been hotly debated topics since the 1950s. There are numerous subtleties to cutoffs, but exactly how the values are calculated has largely been overlooked. Most cutoff users have been content to use a regression line to calculate the cutoff value.
We show that cutoffs obtained using a regression line are likely to be inferior to estimates produced by other methods. When four methods were applied to two field datasets and compared, regression-based porosity cutoffs were between 1 and 2 pu different than the values that give the smallest number of errors. Monte Carlo simulations broadly support the results obtained from the datasets. One method, the "trial-and-error?? method, performed well through most of the tests, reducing errors by 40% from those obtained using the regression line-based cutoff.
All cutoff estimation methods have errors, caused by the imperfect relationships we have between variables, such as porosity and permeability. This study shows we have a choice of methods. Because the better method can be easily applied in spreadsheet software, this should be a valuable addition to the petrophysicist's toolbox.