Browsing by Subject "Vertical wells"
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Item Analysis and interpretation of a hydraulic fracture treatment using offset vertical observation wells and a hydraulic fracture simulator(2015-08) Griffith, Christopher Adam; McClure, Mark W. (Mark William); Espinoza, NicolasAnalysis of hydraulic fracture treatments requires incorporating a wide range of data in order to make useful inferences about fracture properties. For example, microseismic monitoring and production decline analysis can be used to obtain the hydraulic fracture half-length, which is an important parameter for field development. The challenge in using these tools is that the methods used for analysis are open to interpretation and can make it difficult to rely on the results. This thesis integrates data from four horizontal wells that were hydraulically fractured in an unconventional shale play and results from a 2-dimensional hydraulic fracture simulator in order to make qualitative observations about fracture properties. The importance of the data set hinges on nine vertical observation wells that recorded pressure vs. time during the hydraulic fracture treatments. The observation wells were located at different distances and depths from the horizontal wells. This is important because it removes some of the ambiguity associated with making interpretations from microseismic data, production decline analysis, or other methods. Results from modeling and the data set indicated the following: (1) the networks of fractures created from these treatments were volumetric and complex, illustrated by the microseismic data and the pressure signals recorded at the observation wells, (2) microseismicity was generally successful in delineating where fluid progressed during pumping, (3) however, flow of fluid into fractures stimulated during previous stages was aseismic, a manifestation of the Kaiser effect, and (4) during long term production, fluid was not produced from the more distant parts of the reservoir that were pressurized and stimulated during the fracturing treatment. To explain these four observations, we hypothesize that proppant was not transported to the regions of the stimulated rock volume that were most distant from the stimulated wells. The stimulated, but unpropped, fractures in this region evidently lost much of their conductivity after closure that they did not contribute significantly to long term production.Item Numerical simulation and interpretation of sonic measurements in vertical and highly deviated wells(2016-05) Maalouf, Elsa; Torres-Verdín, Carlos; Daigle, HughBorehole sonic measurements are widely used to estimate formation elastic properties and to construct synthetic seismograms. However, presence of noise compromises the accuracy of sonic logs. Sonic logs are prone to errors originating from near wellbore damage or mud-filtrate invasion. Moreover, sonic logs are calculated from the numerical processing of waveforms over a wide range of receivers. Numerical processing induces errors in the sonic slowness because the slowness value is averaged over the length of the receiver array. I apply a fast modeling method using spatial sensitivity functions to calculate sonic logs. First, I define the spatial sensitivity function for the compressional and flexural modes. Then, I apply the fast modeling in a joint inversion of shear and compressional slowness logs to mitigate noise contaminating sonic logs. Joint inversion is performed in vertical and slightly-dipping wells, to estimate layer-by-layer formation elastic and mechanical properties for isotropic and anisotropic formations. Finally, I introduce a fast modeling procedure for compressional and flexural modes in deviated and horizontal wells. Results of the fast modeling are compared to finite-difference numerical simulations. The fast modeling of sonic borehole measurements in deviated wells can be applied in a joint inversion to estimate formation elastic and geometrical properties.Item Rapid modeling and inversion-based interpretation of borehole acoustic measurements acquired in isotropic and vertical transversely isotropic formations(2017-12-08) Maalouf, Elsa; Torres-Verdín, Carlos; Daigle, Hugh; Heidari, Zoya; Sepehrnoori, Kamy; Spikes, KyleBorehole acoustic measurements are often affected by instrument noise, motion and eccentricity, environmental conditions, and spatial averaging that can compromise the accuracy of elastic properties of rock formations calculated with conventional interpretation methods. Forward and inverse modeling can be used to improve the interpretation of acoustic logs acquired in the presence of spatially complex rock formations and adverse borehole conditions. However, forward modeling of acoustic modes often requires time-consuming numerical algorithms. The main objective of this dissertation is to develop fast-forward modeling and inversion-based interpretation procedures of borehole acoustic logs for isotropic and vertical transversely isotropic (VTI) formations. Fast-forward modeling is achieved with spatial sensitivity functions which are calculated from frequency-domain linear perturbation theory of borehole acoustic modes. Spatial sensitivity functions quantify both the dependence of measured slowness on elastic properties and the spatial averaging introduced by acoustic tools. Fast-forward modeling using spatial sensitivity functions is applied to synthetic examples that include thin layers, anisotropy, and dipping layers, and is successfully validated with numerical simulations performed with finite-difference and finite-element methods. Two inversion-based interpretation methods are then developed: (1) a physics-based inversion method to reduce noise and spatial averaging effects on acoustic logs acquired in horizontally layered formations penetrated by vertical wells, and (2) a sequential inversion method to estimate stiffness coefficients of VTI formations from multi-frequency flexural/quadrupole, Stoneley, and compressional logs. The physics-based inversion method is applied to mitigate measurement noise and spatial averaging effects of acoustic logs acquired in two hydrocarbon reservoirs. Results confirm the accuracy and reliability of the estimated layer-by-layer elastic properties compared to conventional numerical filters and are obtained in less than 14 CPU seconds for a 100 ft-depth log. In VTI formations penetrated by vertical wells, sequential inversion is applied to estimate layer-by-layer stiffness coefficients of synthetic formations from borehole acoustic logs. Results indicate that mitigating spatial averaging of frequency-dependent slowness logs prior to inversion improves the layer-by-layer estimation of slownesses by a factor of 2, and that sequential inversion yields accurate and reliable estimates of rock stiffness coefficients. Finally, in high-angle wells fast-forward modeling yields flexural slownesses measured with orthogonal dipoles with 2% relative errors and in 3 CPU minutes for a log consisting of 50 measured-depth samples, compared to 15 CPU hours when using finite-difference simulation methods. Analysis of field and synthetic examples confirms that inversion-based interpretation methods yield more accurate estimations of elastic properties than conventional sonic-log interpretation procedures. Spatial sensitivity functions constitute a fast, reliable, and efficient alternative for interpreting acoustic logs acquired in isotropic and VTI formations.