Excessive water production is an enduring problem in the oil industry that has always been an unbearable burden on the environment and a great damage to the ultimate oil recovery. Gel treatment has been routinely used for decreasing water production. Disproportionate permeability reduction (DPR) is a natural phenomenon in some polymer gels that can reduce the permeability to water more than to oil. The conformance improvement treatments with DPR can effectively reduce the water cut without substantially reducing the oil productivity in fractured reservoirs. At present, there are no widely accepted mechanisms of oil-phase permeability development and DPR. In this paper, nuclear magnetic resonance is applied to study the mechanisms of oil-phase permeability development, DPR, and permeability influence by scanning different core samples treated with Cr­(III)–acetate–hydrolyzed polyacrylamide polymer gels. Results show that the permeability difference leads to a certain alteration in NMR T2 curves, but final conclusions for the mechanisms are consistent. For the mechanism of oil-phase permeability development, initially, gel displacement in large pores accounts for the oil permeability development, after which the gel dehydration becomes the main mechanism. The mechanisms for DPR include the blocking of flow channels by gel rehydration and residual oil and the low permeability of gel relative to water. The results can be used to optimize the utility of polymer gels with a DPR property.

The Caribbean plate subducts beneath northwest South America at a shallow angle due to a large igneous province that added up to 12 km of buoyant crust. The overriding plate lacks volcanism and exhibits Laramide‐style uplifts over 500 km from the trench. Here, we illuminate the subduction structures through finite frequency teleseismic P‐wave tomography and connect those structures to the Laramide‐style deformation on the overriding plate. We use a new data set collected from the Caribbean‐Mérida Andes seismic experiment comprised of 65 temporary broadband stations integrated with permanent stations from the Colombian and Venezuelan national networks. We identify three segments of subducting Caribbean plate with one segment completely detached from the surface. The timing of the detachment aligns with other regional events, including the uplift of the Mérida Andes, about 10 Ma. Slab buoyancy post‐detachment likely resulted in recoupling with the overriding plate, reactivation of Jurassic‐aged rift structures and subsequent uplift of the Mérida Andes. Mantle counterflow over the broken segment induced by rollback of the attached slab likely contributed to the uplift of the Mérida Andes. We conclude that the northern limit of subduction lies south of the Oca‐Ancón fault, though the fault itself may be the surface expression of the boundary. The southern limit of subduction lies south of our study area.

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Both seismic and geodetic data suggested that the ∼120‐km long Weifang segment of the Tanlu fault zone, a large‐scale active strike‐slip system at east China, is a seismic gap with no obvious along‐strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P‐to‐S converted waves at the Moho (Pms) and core‐mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long‐lasting shear motion inside the fault zone.

Summary The accuracy of polar motion (PM) forecasting has been the focus of attention in the fields of satellite navigation and deep space exploration. However, the traditional or differential methods for forecasting X or Y series based on LS and AR models are straightforward and monolithic, and cannot reduce the range of forecast errors. Therefore, this study proposes a new method (called the between-within, B-W method) that combines the X, Y and Y-X series forecasts of the traditional and differential methods in pairs according to the mathematical relationship of Y-X. This approach is one way to obtain the minimum range of forecast errors by making full use of the advantages of each method in the combination. A total of 262-hindcast experiments were conducted during 2010–2020 with strictly simulated time delays. For forecasts of 1–180 days at the x-pole, the average improvement is 10.7 per cent over Bulletin-A. For the y-pole at 1–90 days an average improvement of 11.7 per cent over Bulletin-A is achieved. In addition, further incorporation of the last 1 day IGS (International Global Navigation Satellite System Service) Ultra-rapid (IGU) data can effectively improve the MAE at 1–10 days. The 2016–2018 performance of the B-W method at the x-pole may be related to the amplitude and phase of the Chandler wobble, and the 2013–2016 performance at the y-pole may be related to El Niño climate change events. In terms of overall stability, the B-W method is superior to the IERS Bulletin-A in the medium-short-term and has potential practical application.

<p>The Caribbean plate (CAR) collided with and initiated subduction beneath northwestern South America (SA) at about 60-55 Ma. Since the onset of subduction, it has formed the Lara nappes and subsequently the Laramide-style uplifts of the Merida Andes, Sierra de la Perija and Santa Marta ranges, with maximum elevations > 5km. The triangular Maracaibo block, bounded by the Santa Marta-Bucaramanga, Bocono and Oca-Ancon Faults, is currently escaping to the north relative to SA over both the subducting and nonsubducting elements of the CAR plate.</p><p>Although many petroleum related seismic studies have been done in this area, the details of the subduction geometry of the CAR plate beneath the Maracaibo block remain unclear. The few deeper seismic investigations are either very large scale, very local, or only peripheral to this area. Previous geodetic studies have suggested that this region has potential for a great (M~8+) earthquake (Bilham and Mencin, 2013). To investigate this complex region we fielded a 65 element broadband seismic array to complement the 48 existing stations of the Colombian and Venezuelan national seismic networks. The array is collectively referred to as the CARMArray.</p><p>In this study, we jointly inverted ambient noise Rayleigh wave Z/H ratios, phase velocities in the 8-30s band and ballistic Rayleigh wave phase velocities in 30-80s band to construct a 3D S-wave velocity model in the area from 75<sup>o</sup>-65<sup>o</sup> west and 5<sup>o</sup>-12<sup>o</sup> north. Rayleigh wave Z/H ratios are sensitive to the shallow sedimentary structure, while the phase velocity data have good resolution of the crust and upper mantle. The Vs model shows strong low-velocity anomalies beneath the Barinas-Apure and Maracaibo Basins, and the Paraguana Peninsula that are well correlated with surface geology. Sediment thickness beneath the Maracaibo basin reaches up to ~9 km depth, consistent with previous studies (Kellogg & Bonini, 1982). Crustal thickness beneath the Santa Marta uplift is 27-30 km, shallow for its nearly 4km elevation. From the trench to the southeast, Moho depth increases from 25-30 km near the coast to 40-45 km beneath the Maracaibo Basin, with the thickest crust, ~50 km, lying under the Merida Andes beneath the Bocono Fault. Crustal thickness decreases under the Venezeulan interior to ~45 km. From 50km to 150km depth, the CAR plate shows ~2% high Vs anomalies beneath the Santa Marta uplift and the Serrania de Perija range. Our slab image matches local slab seismicity very well (Cornthwaite et al., EGU 2021 GD7.1), and is consistent with and complements images from teleseismic P-wave tomography (Cornthwaite et al, 2021, submitted).</p>

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Users such as satellite navigation orbiting and deep space exploration are demanding more and more accuracy in polar motion (PM) forecasting, while the existing PM forecasting methods are limited in the single input data and forecasting strategy. To address the problem, this study proposes a new idea of PM forecasts by combining the differences between PM series and the sliding average within the PM series. We use the LS+AR models driven by IERS-14C04 series, to perform experiments with the traditional method and the sliding average method within the PMX, PMY and PM(Y-X) series, respectively. Among them, the prediction of PMX is obtained by subtracting the forecast of PMY of traditional method and the prediction of PM(Y-X) of the sliding average method, the forecast of PMY is obtained by adding the forecast of PMX of the sliding average method and the forecast of PM(Y-X) of the traditional method. The results of the 418-week hindcast experiment from 2012 to 2021 show that the proposed method has a greater improvement than the traditional method, and the corresponding 1-365-day forecasting accuracies are improved by 31.46% and 21.11% over the traditional method, respectively, on average. It has certain advantages over the IERS Bulletin-A in the medium-long term. This not only verifies that the stability and ability of the method have some competitive, but also provides a new idea for the research of PM prediction.