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Microseismic monitoring of reservoir processes can be performed using surface or near-surface arrays. We review the published technical basis for the use of the arrays and the historical development of the method, beginning with locating earthquakes through geothermal exploration to the growing field of hydraulic-fracture monitoring. Practical considerations for the array deployment and data processing are presented. The road ahead for the technology includes a move toward life-of-field buried arrays as well as opportunities for extended interpretation of the data, particularly inversion for source-mechanism estimation and measurement of anisotropy in the monitored subsurface.

Small Microseismic Surface Acquisition System for oilfield monitoring is presented. Algorithms for data processing are based on the mathematical theory of inverse problems and the using of the supercomputer calculations. A distinctive feature of the suggested system is high mobility, compactness and universality. The technology based on the this acquisition system is intended not only for hydraulic fracturing monitoring but also for long-duration passive monitoring of fluid injection, for hydrocarbon drainage area estimation and for oilfield block structure mapping. Case Study has more than 50 examples.

Monitoring of induced microseismic events usually results in locations for these events and a geometrical interpretation of these 'dots in the box'. In this study we show how additional information obtained from observed microseismic events, namely the source mechanisms, were used to generate a discrete fracture network. Using the wide aperture of a surface star-like array (FracStar®) allows inversion for both shear and non-shear source mechanisms. Both volumetric and shear-only source mechanism inversion was carried out on microseismic events from the treatment of a shale gas reservoir in the continental US. During the same hydraulic fracture stimulation treatment, both dip-slip and reverse faulting sources were active in this reservoir. The source mechanisms revealed fracture orientations more accurately than could be inferred from microseismic event locations alone. The activity associated with different mechanisms is interpreted as indicating reactivation of existing fractures in the rock, as well as suggesting generation of new fractures. Failure analysis using source mechanisms on individual events allows an integrated understanding of the complex fracture interactions taking place in the reservoir, and also provides a more complete understanding of the stress conditions in the reservoir during the treatment. Fracture orientations, locations, and failure mechanisms are translated into discrete fracture network (DFN) models that can be used to verify the extent and character of the fractures created or reactivated during the fracture treatment, and may ultimately be used to generate fracture flow properties for reservoir simulation.

It has been noticed that the Testacea sent from Antigua with the Corals have been stated to belong to the present age. This is correct; but there are a few Shells and casts of Shells of an older date. A Helix , common as a fossil, is not now, according to Dr. Nugent, an inhabitant of the island; and the extinct Melaniæ are found in great abundance with silicified Woods. Both in Jamaica and in San Domingo there are late Tertiary Shells and Corals, but it is impossible to bring these facts in antagonism with those which give a more remote age to the strata whence the specimens described were obtained. So with regard to Antigua, Barbuda, and Barbadoes, it is not correct to give the whole Islands a Pliocene or Postpliocene age because recent and subfossil Shells are found in them. As yet, the Testacea have not assisted in determining the geologic age of the three coral-formations of Antigua; but Mr. C. Moore has given a Miocene age to the Mollusca from the San-Domingan shales, whence the Corals here described were derived. The Alabama Eocene Shells and Corals are distinct from those of the raised Coral-beds of the West Indian Islands; and it is worthy of remembrance that, although there are genera and species of Corals in Antigua, San Domingo, and Jamaica belonging to the great European Miocene Coralage, still there are a few European Miocene genera of Corals which are not as yet known to belong to the West Indian Miocene.