Doug Patterson

Unconventional Reservoir Fracture Evaluation Utilizing Deep Shear-Wave Imaging

Unconventional shale reservoir evaluation and development are extremely challenging. One of the most dominating aspects is permeability, which is measured in the nano-darcy range. Although these wells are stimulated to enhance production, the presence or absence of natural fractures can have a large impact on the production results. In addition, the fracture variation across a reservoir can be substantial, leading to large production variations, even in adjacent wells. Gaining insight about the natural fracture system, both intersecting and around the borehole, is crucial and can often help determine the economic success of a well and/or reservoir. The standard means of fracture evaluation, such as borehole imaging, Stoneley permeability analysis, and azimuthal shearwave anisotropy evaluation from cross-dipole, provide valuable information when evaluating fractures. These standard methods, however, can only investigate a limited area around the borehole—imaging looks at the borehole wall and the other borehole acoustic methods rely on refracted and guided modes that respond to an area as large as 2 to 4 ft out into the formation. The flexural wave from the dipole is one of the guided modes that generally reads the deepest and is used in the standard cross-dipole analysis. In addition to flexural mode, the dipole source creates shear body waves that radiate away from the borehole and into the formation. When these shear waves impinge on a fracture their energy reflects back to the borehole, enabling the facture to be imaged. The reflection strength is a function of the shear-wave polarization and the nature of the fracture, with the strongest response occurring from the shear waves intersecting a fluid/gas-filled fracture and polarizing in the fracture’s strike direction. Another important aspect is that these shear waves have azimuthal sensitivity, providing a means to determine the fracture direction. These features enable the evaluation of fractures over a much larger area around the well, often in excess of 60 ft from the borehole, and even detecting major fractures that do not intersect the well. We will look at the application of this deep shear-wave imaging technology in several unconventional reservoirs across North America. Our review includes conventional methods and the deep shear-wave imaging analysis, showing its value in gaining important insight about the natural fracture system around the borehole, especially non-intersecting fractures. In addition, we will look at its application in mapping geologic structures in horizontal wells, demonstrating the ability to detect sub-seismic faults.

Ultrasonic signal noise reduction processing in borehole imaging application

Ultrasonic imaging instruments are routinely used for formation fracture, stratigraphie dip, and borehole shape determination. Pulse-echo transducers measure the properties of the echoes reflected from the formation, and the signal amplitude and travel time are typically displayed as a circumferential image of the borehole wall. However, a significant interference pattern can be generated when the electroacoustic ringdown of the transducer interferes with low amplitude echoes. In this paper, an image signal processing technique based on borehole fluid/eccentricity correction and median filtering is applied to extract the interference pattern. The proposed processing provides a good noise reduction, preserving formation features.

Obtaining anisotropic velocity data for proper depth seismic imaging

The paper deals with the problem of obtaining anisotropic velocity data due to continuous acoustic impedance-based measurements while scanning in the axial direction along the walls of the borehole. Diagrams of full conductivity of the piezoceramic transducer were used to derive anisotropy parameters of the rock sample. The measurements are aimed to support accurate depth imaging of seismic data. Understanding these common anisotropy effects is important when interpreting data where it is present.

Advanced Dipole Borehole Acoustic Processing – Rock Physics And Geomechanics Applications

Today’s advanced borehole acoustic analysis not only enhances the rock physic characteristics of shale gas plays but it also provides new insights in geomechanics applications and fracture identification. Current borehole acoustic tools can detect the azimuthal and transverse shear wave intrinsic rock anisotropy. They also help identify stress-sensitive formations and help in the evaluation of natural fractures, those that intersect the borehole as well as those that do not.

Using Radon Transform For Efficient Acoustic Wave Separation By Velocities In Wireline And Lwd Acoustic Logging

Different acoustic wave components in the borehole acoustic logging differ by frequencies, amplitudes, travel times, and velocities. Depending on the application, some of these components are considered to be informative, and others are detrimental. In some cases, wave propagation conditions and certain tool design limitations do not allow distinct separation of these components without destructive interference between them. Simple time-frequency filtering does not always solve these problems. For example, in case of poor quality of casing cementing job the casing “rings”, and this ringing dominates the informative signal of interest that propagates through the formation. The frequency separation is inefficient in this case, due to the overlapping of the signal frequencies. We propose adding “time-velocity” signal representation to the traditional “time-frequency” consideration. We demonstrate incremental improvement in the data quality when progressing from the traditional Semblance method to the improved non-windowed Hilbert Semblance, and finally to a special case of the Radon transform. We believe the proposed approach can be adapted and efficiently used for different borehole acoustic or seismic applications.