Geochemical Features of the Two Early Paleozoic Ophiolitic Zones and Volcanic Rocks in the Central-Southern Tianshan Region, Xinjiang

This paper deals with the geochemical features of the two Early Paleozoic ophiolite zones in the central\|southern Tianshan region and the central Tianshan igneous rock belt between them. Study results suggest that the central Tianshan belt was an Ordovician volcanic arc with an affinity of continental crust, and the Kumux\|Hongliuhe ophiolitic zone that is located on the southern margin of central Tianshan has a crustal affinity to back\|arc marginal sea. The Aqqikkudug\|Weiya ophiolitic zone is an accretionary boundary between the Tuha continental block and the central Tianshan volcanic arc during Late Silurian to Devonian; Ordovician ophiolitic blocks, Silurian flysch sequence and HP metamorphic rock relics are distributed along the Aqqikkudug\|Weiya zone. Geochemically, ophiolitic rocks in the Aqqikkudug\|Weiya zone have an affinity to oceanic crust, reflecting a tectonic setting of paleo\|trench or subduction zone. The Early Carboniferous red molasses were deposited unconformably on the pre\|Carboniferous metamorphosed and ductile sheared volcanic and flysch rocks, providing an upper limit age of the central and southern Tianshan belts.

Use of low-frequency signals to improve imaging quality under high-velocity basalt

Wave equation wave field numerical modeling technology is applied to the observation that deep layer imaging is difficult below a screening layer of high-velocity basalt. Three simple high-velocity basalt models are designed on the basis of basalt formation characteristics. The analysis of deep-layer reflection seismic signal energy shows that lowfrequency seismic signals are capable of both penetrating the thin high-velocity basalt layer and reducing the diffraction noise caused by the rough surfaces. The simulation experiment of a complete 2D basalt model confirms that the low-frequency signals can be used to boost the quality of deep-layer imaging under the high-velocity basalt layer and achieve good results in low-pass filter processing of actual data.

Real-Time Fracture Aperture Identification Using Mud Loss Data and Solution for LCM Combination

Managing server lost circulation is a major challenge of drilling operation in naturally fractured formations and it causes much nonproductive rig time. When encountered with loss, the fracture aperture intersecting the wellbore is not well-identified in time, which has a significant impact on the decision of drilling operation and the undesired result of loss curing. Therefore, the onset of fracture is identified in a timely manner and evaluated comprehensively to formulate an appropriate strategy over time. However, the mud loss date, which is the primary source of information retrieved from the drilling process, was not properly used in real-time prediction of fracture aperture. This article provides a detailed mathematical study to discuss the mechanism of mud invasion in the near-wellbore region and prediction of fracture aperture. The fracture aperture can be calculated from mud-loss data by solving a cubic equation with input parameters given by the well radius, the overpressure ratio, and the maximum mud-loss volume. It permits the proper selection of loss-circulation material (LCM) with respect to particle size distribution and fiber usage. The case study illustrates the applicability of this methodology with a discussion on LCM particle distribution in different scenarios and the result demonstrates the outcome of inappropriate LCM usage and the advantages of the novel fiber-based LCM treatment.