Fifth EAGE/AAPG Tight Reservoirs Workshop

This paper introduces a completely new protocol (DMX) for three Dimensional DFFN (Discrete Fault and Fracture Network) modelling which combines for the first time realistic 3d discontinuity distribution and interaction following both established geological models and observed assemblages and statistical and probabilistic drivers.

Examples of the principles of the protocol, modeling results, flowcharts, and calibration to real data are presented.

Daniudi gas field is one of the seven tight largest sources of gas in non-conventional deposits of China. This field has been exploited since 2002, but to 2008 the production has decreased considerably as a result of the strong heterogeneities of the reservoirs. For this reason, the field needs a new 3D facies modelling that allows identifying the facies where the sweet spots will be recognized, in order to drill new horizontal wells, and thus increase the production of gas in commercial quantities. Consequently, the surface-based method is applied to the facies modelling of the Xiashihezi formation. Due to this method considers the architectural elements and depositional process of the facies into a 3D structural framework. Therefore, the modelling allows establishing the area which will be used as a border for the next modelling of lithological, flow units and petrophysical. The 3D facies modelling honours the geological model into the grid cells, and attempt to replicate the spatial variations, honour the data set, and the sedimentary model. And it incorporates the hierarchies of the surfaces and the sandbodies interaction in order to represent the spatial organization of the facies into the reservoir.

Enzymes

DIF

Filter Cake

Filtration

Formation Damage

Corrosion Inhibitor

The fracture characterization-based borehole image provides information about the fracture morphology (Open, cemented, induced, …) and in case of water-based mud, fracture aperture can be estimated using electrical image (FMI*). Fracture apertures processing based on the measured excess current as the tool crossed the fracture. The aperture calculation follows an equation published by Luthi and Souhaite, 1990.

The Acoustic measurement (Sonic Scanner) determine anisotropy which can be classified as stress induced fractures, intrinsic anisotropy (Natural open Fracture, Layers) using dispersion plots.

The ability of Sonic Scanner to distinguish between open and close fractures, refine the fracture identification from borehole image and provides accurate open fracture sets that can be used for fracture aperture estimation.

This approach was applied in Algeria (for Tight gas sandstones reservoirs and the highest dry gas potential in the Sahara region) having as objective to provide client estimated value of fracture aperture to update their DFN model.

In this work, we concept-proved a core-to-log methodology that provides a fast calibration method for log-based elasticity. We measured rebound hardness in parallel to dynamic measurements of ultrasonic surface wave velocities (P and S) at the milimetric scale, then calibrated the results with discrete triaxial tests performed on plugs, representing all relevant lithological facies, and finally compared the results against log-based parameters. Our work shows that such integration helps at developing robust core-tolog elasticity relationships in the entire core length, eventually providing a proper foundation for better stiffness model prediction, at a fraction of the cost and time of traditional core acquisition programs. We have shown that calibrated high-resolution measurements at the core scale may be used to create accurate dynamic to static correlations, to identify and characterize potential barriers to fracture growth, and to characterize lithological facies for predicting their elastic properties at new wells when core data is not available.

Cleat characterization using two independent log measurements, acoustic logs and micro-resistivity image logs is a direct indication of possible flow path within a CBM reservoir. Cleat orientation and its relationship with the present day stresses is carried out to define the completion criteria of different coal seams.

Array sonic logs are used to carry out fracture analysis to calculate reflection coefficient and transmission coefficient. Using the different correlation among the slowness, reflection and transmission coefficients in different coal seams, coal seams with higher cleat density can be identified. Combining the acoustically determined cleat density of each coal seam with the fracture and dip analysis of the high resolution image data, the coal seams are characterized in terms of cleat density and cleat orientation. Cleat density in a coal seam is the distinct indicator of the reservoir flow capacity and permeability. The present day and pre-existing stress direction is calculated using sonic-image data to assess the primary flow and reservoir permeability in CBM wells. This exposition of cleat system along with its correlation with near well bore stresses is important input for selection of completion criteria, which in turns affect the producibility of different coal seams.