Browsing by Subject "Well logging"
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Item A tri-axial electromagnetic induction tool for hydraulic fracture diagnostics(2019-02-11) Shiriyev, Javid; Sharma, Mukul M.; Sen, Mrinal K.; Foster, John T.; Nguyen, Quoc P.; Daigle, HughThe monitoring and diagnostics of induced fractures are important for the real-time performance evaluation of hydraulic fracturing operations. Previous electromagnetic (EM) based studies show that single backbone tri-axial induction logging tools are promising candidates for the real-time monitoring and diagnosis of fractures in uncased wells. To support the development of field deployable tools, the concept must be tested in experiments, in a controllable environment, before it is tested under field-like conditions. To this end, we have developed numerical tools which can simulate any wellbore environment while logging hydraulic fractures with the induction tool. We have designed and built a prototype induction tool and performed two sets of tests to compare with numerical simulation results. The computational and experimental setup consists of tri-axial transmitter and receiver coils in co-axial, co-planar and cross-polarized configurations. Both lab and shallow earth measurements are shown to be in good agreement with simulations for all examined cases. The average relative and maximum discrepancies of the measured signals from the simulated ones were lower than 3% and 10%, respectively. With the prototype tool, strong signals sensitive to the fracture’s surface area and dip-angle were measured in the co-axial coil configuration, while weaker signals sensitive to the fracture’s aspect ratio were observed in the co-planar configuration. Cross-polarized signals are also shown to be strong and sensitive to the fracture’s dip. Lastly, we resolved the detectable components of the measured signal tensor to obtain parameters for simplified fracture geometries. The inversion algorithm, a derivative free directional search model, uses an objective function defined as a combination of co-axial and cross-polarized signals from different tool spacing, and the function provides a well behaved global minimum. The robustness of the inversion algorithm is tested on synthetic data for single cluster fractures in a homogeneous and heterogeneous background electrical conductivity. All the effective model parameters for different cases, electrical conductivity, size and dip-angle, are shown to be recovered with good accuracy. We also evaluated the effect of neighboring fractures and suggested a multi-cluster inversion path which can recover the proppant distribution in a stage very accurately. Based on the numerical and experimental results we suggest a tool with specifications that can effectively recover far-field proppant distribution in the fractures.Item Estimation of static and dynamic petrophysical properties from well logs in multi-layer formations(2011-08) Heidari, Zoya; Torres-Verdín, Carlos; Sepehrnoori, Kamy; Peters, Ekwere J.; Preeg, William E.; Schneider, Erich A.Reliable assessment of static and dynamic petrophysical properties of hydrocarbon-bearing reservoirs is critical for estimating hydrocarbon reserves, identifying good production zones, and planning hydro-fracturing jobs. Conventional well-log interpretation methods are adequate to estimate static petrophysical properties (i.e., porosity and water saturation) in formations consisting of thick beds. However, they are not as reliable when estimating dynamic petrophysical properties such as absolute permeability, movable hydrocarbon saturation, and saturation-dependent capillary pressure and relative permeability. Additionally, conventional well-log interpretation methods do not take into account shoulder-bed effects, radial distribution of fluid saturations due to mud-filtrate invasion, and differences in the volume of investigation of the various measurements involved in the calculations. This dissertation introduces new quantitative methods for petrophysical and compositional evaluation of water- and hydrocarbon-bearing formations based on the combined numerical simulation and nonlinear joint inversion of conventional well logs. Specific interpretation problems considered are those associated with (a) complex mineral compositions, (b) mud-filtrate invasion, and (c) shoulder-bed effects. Conventional well logs considered in the study include density, photoelectric factor (PEF), neutron porosity, gamma-ray (GR), and electrical resistivity. Depending on the application, estimations yield static petrophysical properties, dynamic petrophysical properties, and volumetric/weight concentrations of mineral constituents. Assessment of total organic carbon (TOC) is also possible in the case of hydrocarbon-bearing shale. Interpretation methods introduced in this dissertation start with the detection of bed boundaries and population of multi-layer petrophysical properties with conventional petrophysical interpretation results or core/X-Ray Diffraction (XRD) data. Differences between well logs and their numerical simulations are minimized to estimate final layer-by-layer formation properties. In doing so, the interpretation explicitly takes into account (a) differences in the volume of investigation of the various well logs involved, (b) the process of mud-filtrate invasion, and (c) the assumed rock-physics model. Synthetic examples verify the accuracy and reliability of the introduced interpretation methods and quantify the uncertainty of estimated properties due to noisy data and incorrect bed boundaries. Several field examples describe the successful application of the methods on (a) the assessment of residual hydrocarbon saturation in a tight-gas sand formation invaded with water-base mud (WBM) and a hydrocarbon-bearing siliciclastic formation invaded with oil-base mud (OBM), (b) estimation of dynamic petrophysical properties of water-bearing sands invaded with OBM, (c) estimation of porosity and volumetric concentrations of mineral and fluid constituents in carbonate formations, and (d) estimation of TOC, total porosity, total water saturation, and volumetric concentrations of mineral constituents in the Haynesville shale-gas formation. Comparison of results against those obtained with conventional petrophysical interpretation methods, commercial multi-mineral solvers, and core/XRD data confirm the advantages and flexibility of the new interpretation techniques introduced in this dissertation for the quantification of petrophysical and compositional properties in a variety of rock formations.Item Mechanistic numerical simulation and interpretation of borehole measurements of spontaneous electrical potential acquired in complex petrophysical environments(2021-04-07) Bautista-Anguiano, Joshua Christopher; Torres-Verdín, Carlos; Prodanovic, Masa; Sepehrnoori, Kamy; Heidari, Zoya; Yilmaz, Ali; Katz, LynnBorehole measurements of spontaneous electrical potential (SP) are routinely acquired in wells drilled with water-based mud. However, to this day, the interpretation of borehole SP measurements is chiefly limited to imprecise calculations of formation water resistivity and qualitative assessments of volumetric concentration of shale and permeability. This dissertation develops new methods to numerically simulate borehole SP measurements and improve their quantitative interpretation. Interpretation products are water saturation, water resistivity, and radius of invasion of mud-filtrate invasion in permeable rocks, together with their uncertainty. The calculation of formation water resistivity from borehole SP measurements is commonly performed via Nernst’s equation under the assumptions of shallow mud-filtrate invasion, negligible streaming potentials, and water as the only rock-saturating fluid. To circumvent these limitations while honoring the governing physics of coupled mass transport associated with SP phenomena, a three-dimensional finite-difference algorithm is developed to incorporate electrochemical, membrane, and electrokinetic SP phenomena in the simulation of borehole SP measurements. The algorithm implements a mechanistic description of non-equilibrium thermodynamics, which is coupled to a fluid-flow simulator to quantify the effects of time-varying conditions within permeable formations due to mud-filtrate invasion. Simulations indicate that the best spatial resolution of rock properties possible with SP borehole measurements occurs when rock beds are perpendicular to the well; deviated wells or dipping beds give rise to extended and pronounced shoulder-bed effects on SP measurements. It is also found that the simplifying assumption of perpendicular beds relative to the borehole does not cause significant errors in the numerical simulation of borehole SP measurements acquired in well trajectories with a relative dip less than 30°, thereby reducing CPU time by a factor of at least 1.76. Furthermore, electrokinetic effects on SP measurements become negligible for commonly used pressure overbalance ranges. For the interpretation of borehole SP measurements acquired in hydrocarbon-bearing rocks, this dissertation explores whether the difference between borehole SP measurements and Nernst-equation predictions enables the estimation of in situ hydrocarbon saturation of porous rocks. A new petrophysical model is advanced and successfully verified to establish the limits of detectability of hydrocarbon saturation solely from borehole SP measurements. It is found that optimal conditions for the quantification of hydrocarbon saturation from borehole SP measurements take place when (1) capillary forces dominate the process of mud-filtrate invasion, (2) the matrix-pore interface region, known as the electrical double layer, has a relevant impact on the diffusion of counter-ions, and (3) the electrolyte concentration of drilling mud is greater than that of formation water. Three blind tests show that the developed petrophysical model and the mechanistic SP simulation algorithm enable the estimation of hydrocarbon saturation from SP borehole measurements without the need of electrical resistivity measurements or porosity calculations. The estimation is reliable when (a) the volumetric concentration of shale is negligible, (b) the pore network structure is constant throughout the reservoir, and (c) radial invasion profiles are similar to those observed in calibration key wells used to adjust the parameters of the new petrophysical model. Finally, this dissertation develops a new inversion-based method for the interpretation of borehole SP measurements, which concomitantly mitigates shoulder-bed and mud-filtrate invasion effects on SP logs via fast numerical simulations based on Green’s functions. The method delivers layer-by-layer estimates of (a) equivalent NaCl concentration, (b) radius of mud-filtrate invasion, and (c) sodium macroscopic transport number, together with their uncertainty, by progressively matching borehole SP measurements with their numerical simulations. Successful examples of implementation include noisy borehole SP measurements acquired in aquifers with various degrees of petrophysical complexity. Results confirm the possibility of accurately and reliably estimating the electrical resistivity of formation water resistivity solely from borehole SP measurements, i.e., without the need of porosity calculations or fitting parameters from independent core measurements (as is the case with borehole resistivity measurements). Inversion-based interpretation results (a) compare well to those obtained from resistivity and nuclear porosity logs, (b) provide estimates of uncertainty, and (c) can assimilate a priori knowledge of aquifer petrophysical properties in the estimation.Item Rock classification from conventional well logs in hydrocarbon-bearing shale(2011-12) Popielski, Andrew Christopher; Torres-Verdín, Carlos; Balhoff, MatthewThis thesis introduces a rock typing method for application in shale gas reservoirs using conventional well logs and core data. Shale gas reservoirs are known to be highly heterogeneous and often require new or modified petrophysical techniques for accurate reservoir evaluation. In the past, petrophysical description of shale gas reservoirs with well logs has been focused to quantifying rock composition and organic-matter concentration. These solutions often require many assumptions and ad-hoc correlations where the interpretation becomes a core matching exercise. Scale effects on measurements are typically neglected in core matching. Rock typing in shale gas provides an alternative description by segmenting the reservoir into petrophysically-similar groups with k-means cluster analysis which can then be used for ranking and detailed analysis of depth zones favorable for production. A synthetic example illustrates the rock typing method for an idealized sequence of beds penetrated by a vertical well. Results and analysis from the synthetic example show that rock types from inverted log properties correctly identify the most organic-rich model types better than rock types detected from well logs in thin beds. Also, estimated kerogen concentration is shown to be most reliable in an under-determined problem. Field cases in the Barnett and Haynesville shale gas plays show the importance of core data for supplementing well logs and identifying correlations for desirable reservoir properties (kerogen/TOC concentration, gas saturation, and porosity). Qualitative rock classes are formed and verified using inverted estimates of kerogen concentration as a rock-quality metric. Inverted log properties identify 40% more of a high-kerogen rock type over well-log based rock types in the Barnett formation. A case in the Haynesville formation suggests the possibility of identifying depositional environments as a result of rock attributes that produce distinct groupings from k-means cluster analysis with well logs. Core data and inversion results indicate homogeneity in the Haynesville formation case. However, the distributions of rock types show a 50% occurrence between two rock types over 90 ft vertical-extent of reservoir. Rock types suggest vertical distributions that exhibit similar rock attributes with characteristic properties (porosity, organic concentration and maturity, and gas saturation). This method does not directly quantify reservoir parameters and would not serve the purpose of quantifying gas-in-place. Rock typing in shale gas with conventional well logs forms qualitative rock classes which can be used to calculate net-to-gross, validate conventional interpretation methods, perform well-to-well correlations, and establish facies distributions for integrated reservoir modeling in hydrocarbon-bearing shale.Item Study on the feasibility of using electromagnetic methods for fracture diagnostics(2012-08) Saliés, Natália Gastão; Sharma, Mukul M.; Ling, HaoThis thesis explores two ways of developing a fracture diagnostics tool capable of estimating hydraulic fracture propped length and orientation. Both approaches make use of an electrically conductive proppant. The fabrication of an electrically conductive proppant is believed to be possible and an option currently on the market is calcined petroleum coke. The first approach for tool development was based on principles of antenna resonance whereas the second approach was based on low frequency magnetic induction. The former approach had limited success due to the lack of resonant features at the stipulated operating conditions. Low frequency induction is a more promising approach as electromagnetic fields showed measurable changes that were dependent on fracture length in simulations. The operation of a logging tool was simulated and the data showed differences in the magnetic field magnitude ranging from 2% to 107% between fracture sizes of 20m, 50m, 80m, and 100m. Continuing research of the topic should focus not only on simulating more diverse fracture scenarios but also on developing an inversion scheme necessary for interpreting field data.