CLASI: coordinating innovative observations and modeling to improve coastal environmental prediction systems

The Coastal Land-Air-Sea-Interaction (CLASI) project aims to develop new “coast-aware” atmospheric boundary and surface layer parameterizations that represent the complex land-sea transition region through innovative observational and numerical modeling studies. The CLASI field effort will involve an extensive array of more than 40 land- and ocean-based moorings and towers deployed within varying coastal domains, including sandy, rocky, urban, and mountainous shorelines. Eight Air-Sea Interaction Spar (ASIS) buoys are positioned within the coastal and nearshore zone, the largest and most concentrated deployment of this unique, established measurement platform. Additionally, an array of novel nearshore buoys, and a network of land-based surface flux towers are complimented by spatial sampling from aircraft, shore-based radars, drones and satellites. CLASI also incorporates unique electromagnetic wave (EM) propagation measurements using coherent transmitter/receiver arrays to understand evaporation duct variability in the coastal zone. The goal of CLASI is to provide a rich dataset for validation of coupled, data assimilating large eddy simulations (LES) and the Navy’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®). CLASI observes four distinct coastal regimes within Monterey Bay, California (MB). By coordinating observations with COAMPS and LES simulations, the CLASI efforts will result in enhanced understanding of coastal physical processes and their representation in numerical weather prediction (NWP) models tailored to the coastal transition region. CLASI will also render a rich dataset for model evaluation and testing in support of future improvements to operational forecast models.

Corrosion Evaluation in Dual Completions Using a Multifrequency Electromagnetic Tool

Early detection of corrosion in well casings is of great importance to oil and gas well management. A typical well completion includes a production tubing inside a number of nested casings, which provide necessary well integrity and environmental protections. A multifrequency electromagnetic pipe inspection tool with multiple transmitter and receiver arrays was designed to accurately estimate the individual wall thicknesses of up to five nested pipes. The tool uses an axis-symmetric forward model to invert for wall thicknesses, among other pipe parameters. However, in cases where production occurs from two or more segregated zones, the well is generally equipped with more than one production tubing, which breaks the axial symmetry. In this paper, we show how the tool can further be employed to inspect the integrity of non-nested tubulars, such as dual completions. The performance of the tool is demonstrated using a full-scale yard mockup with known defects. A data-processing workflow, including multizone calibration and model-based inversion, is proposed to estimate the tubulars electrical conductivity, magnetic permeability, wall thickness, and eccentricity. An in-situ, multizone calibration method is applied to remove adjacent tubings influence, thus enabling accurate estimation of the thickness of outer casings without having to pull out the production tubing. In order to demonstrate the capabilities of the tool in wells with dual completions, a log was run in a 150 ft-long yard mockup with two strings of 2⅞ inch. tubing, two outer casing strings, and four different man-made defects on the casings. The tool is logged inside each of the tubing strings, and the two logs are inverted for the thickness and eccentricity of the tubing as well as the thickness of outer casings. Results from the yard test reveal that when the tool is logged in one tubing, it can accurately detect various kinds of defects on outer casings, even in the presence of a second tubing. The interference from the second tubing is shown to be minimal due to the employed calibration algorithm. A high degree of consistency is seen between the logs run in each tubing string. This suggests that if the goal is solely to monitor corrosion in the outer casings, it suffices to run the tool in only one of the tubing strings, further cutting nonproductive time. The techniques presented here enable pipe integrity monitoring without pulling the production tubings; tubings, therefore, minimizing inspection time and cost. The information provided by this tool can significantly improve the efficiency of well intervention operations, especially in areas with high corrosion rates.

Borehole Sonic Data Dispersion Analysis With a Modified Differential-Phase Semblance Method

Ruijia Wang, Richard Coates, and Jiajun Zhao The sonic wave fields produced by wireline and logging-while-drilling (LWD) monopole, dipole, and quadrupole tools often consist of multiple borehole modes. Classic frequency-slowness semblance-map methods used to process this data often detect only strongly excited modes and overlook weak ones, and erroneously detect some modes. Conventional dispersion processing methods can be separated into two groups: single-mode and multimode extraction algorithms. Single-mode methods are stable but only return one mode, the most energetic one, at each frequency. Single-mode methods include the differential-phase frequency-semblance (DPFS) method and the weighted spectral-semblance method. Multimode methods can return multiple modes at each frequency but may be unstable in some cases. Due to their assumptions about signal models, multimode methods are often sensitive to unbalanced receiver arrays, poor data quality, and formation heterogeneity. For example, in some extreme cases, such as a formation with strong heterogeneity, multimode methods may yield erroneous ghost modes or discontinuous dispersion curves for each mode. Borehole modes with different slowness have different arrival times. Converting the data to the frequency domain can obscure this critical information or encode these time differences into phase differences between adjacent frequencies. Conventional frequency-semblance approaches, which use only a single frequency independently from adjacent ones, ignore this phase information. In this paper, we propose employing the phase differences between adjacent frequencies to facilitate multimode dispersion analysis. We modify one conventional method to incorporate the arrival time of modes or the phase difference between adjacent frequencies. We validate the proposed approach with synthetic, laboratory, and field data. The results suggest the method can extract a much more comprehensive representation of modes present in the sonic data. Additionally, the method provides reliable estimates, even when the number of receivers is small. Unlike the Prony and matrix-pencil methods based on assumed signal models, the proposed approach, which we denote “Modified Differential-Phase Frequency Semblance” (MDPFS), is a modification of the single-mode differential phase approach. The MDPFS is still a semblance-based approach, and as with other semblance-based processing, it is expected to be less sensitive to unbalanced receiver arrays, poor data quality, and formation heterogeneity than other multimode algorithms.

Identifying reflector azimuth from borehole multicomponent cross-dipole acoustic measurement

The borehole dipole shear-wave reflection imaging method has a high potential in heterogeneous reservoir explorations because of its deep investigation depth and relatively large reflection amplitude. However, the generally used shear horizontal (SH) reflection approach can only indicate the reflector strike and has an inherent defect in azimuth ambiguity. We have developed a multicomponent cross-dipole array acoustic measurement with four azimuthally distributed receiver arrays and a method using reflected dipole P-waves to eliminate the azimuth ambiguity caused by the SH reflection. The recorded data includes cross-dipole waves with four components and two combined dipole-monopole waves that stack the data of the four azimuthally distributed receivers induced by each dipole source. A theoretical analysis indicates that the dipole compressional reflection is sensitive to the reflector azimuth. Therefore, the cross-dipole waves are first used to determine the reflective interface strike with the SH reflection. The compressional reflections obtained from both the cross-dipole data and the combined dipole-monopole data are then processed to identify the correct azimuth. The effectiveness and accuracy of the method are validated via both synthetic and field data examples in a soft formation. The proposed method may potentially solve the azimuth ambiguity problem in borehole acoustic reflection imaging and fully use cross-dipole acoustic measurements.

DAS/SOV: Rotary seismic sources with fiber-optic sensing facilitates autonomous permanent reservoir monitoring

With new developments of fiber-optics sensing and rotary sources, continuous active seismic monitoring for onshore applications has now the opportunity to be fully realized and applied to enhance utilization and resource extraction from the subsurface. To date, conventional seismic monitoring deployments consist primarily of receiver arrays, either fixed or not, with periodic data acquisition campaigns using temporarily deployed sources, resulting in time-lapse data with poor temporal resolution. Only a few niche efforts have demonstrated continuous acquisition using fixed source-receiver networks. Herein, we present initial results of a network of fixed rotary seismic sources, referred to as surface orbital vibrators (SOVs), coupled with a permanent distributed acoustic sensing (DAS) network at the CO2CRC Otway Field Site. While rotary seismic sources are not new, our development of the SOV focused on simplifying the cost and complexity of the source hardware while delivering broad frequency spectrum of the source signal. The upgraded hardware is aligned with a robust methodology for autonomous operation and data processing. At the Otway Site we deployed SOVs at nine locations, monitoring seismic response in seven DAS instrumented wells. Baseline operation of the DAS/SOV sensor array and source system demonstrates its capability with near offsets attaining a signal-to-noise ratio approaching 100 dB with an NRMS of 10%. Furthermore, analyses of travel-time repeatability indicate that the DAS/SOV system can deliver time resolution of +/- 500 µs.