• Energy Research

Most of the developing oil and gas fields in Russia are located in Arctic regions and constructed on permafrost, where recent environmental changes cause multiple hazards for their infrastructure. The blowing-up of pingos, resulting in the formation of gas emission craters, is one of the disastrous processes associated both with these external changes and, likely, with deep sources of hydrocarbons. We traced the channels of fluid migration which link a gas features reservoirs with periglacial phenomena associated with such craters with the set of geophysical methods, including common depth point and shallow transient electromagnetic methods, on an area of a prospected gas field. We found correlated vertical anomalies of acoustic coherence and electrical resistivity associated with gas chimneys in the upper 500–600 m of the section. The thickness of the ice-bonded permafrost acting as a seal for fluids decreased in the chimney zone, forming 25–50 m deep pockets in the permafrost base. Three pingos out of six were located above chimneys in the study area of 200 km2. Two lakes with parapets typical for craters were found. We conclude that the combination of applied methods is efficacious in terms of identifying this type of hazard and locating potentially hazardous objects in the given territory.

Transient electromagnetic (TEM) surveys constitute an important element in exploration projects and can be successfully used in the search for oil and gas. Different modifications of the method include shallow (sTEM), 2D, 3D, and 4D (time-lapse) soundings. TEM data allow for solving a large scope of problems for estimating resources and reserves of hydrocarbons, discriminating reservoir rocks, detecting tectonic features, and characterizing drilling conditions. TEM surveys are applicable at all stages, from initial prospecting to production, and are especially efficient when combined with seismic surveys. Each stage has its specific objectives: estimation of net pay thickness, porosity, and fluid type during prospecting, optimization of well placement and prediction of drilling conditions in exploration, and monitoring of flooding during production. Electromagnetic soundings resolve permafrost features well and thus have a high potentiality for exploration in the Arctic petroleum province. At the first reconnaissance stage of regional prospecting in East Siberia, electromagnetic and seismic data were used jointly to map the junction of the Aldan basin (part of the Aldan-Maya foredeep) with the eastern slope of the Aldan uplift and to constrain the limits of Neoproterozoic sediments. The TEM-based images revealed reservoir rocks in the Upper and Middle Neoproterozoic strata. TEM data have implications for the amount of in-place oil and gas resources in prospects, leads, and plays (Russian categories D1–3) at the prospecting and exploration stages and contingent recoverable reserves (C2) during exploration (latest stage). The contribution of the TEM survey to oil and gas evaluation is quantified via economic variables, such as the value of information (VOI) and expected monetary value (EMV).

The permafrost of Arctic West Siberia stores extremely rich resources of hydrocarbon fuels that remain a key energy source and an important element of the global economy. A large amount of natural gas in permafrost is bound in gas hydrates which may become an alternative fuel of the future. Shallow subsurface in the permafrost area of northern West Siberia has been studied by transient electromagnetic (TEM) soundings to estimate the permafrost thickness and to detect faults as channels for fluids and heaving features as possible indicators of gas hydrate accumulations. The shallow transient electromagnetic (sTEM) surveys were conducted in discontinuous and continuous permafrost at two sites in northern West Siberia (the northeastern Yamal Peninsula and the southern Gydan Peninsula), with a focus on the vicinities of lakes and cryogenic landforms (frost mounds). The sTEM method resolves well the heterogeneous permafrost structure, with faults, numerous unfrozen zones (taliks), and frost mounds marked by resistivity and seismic anomalies. Some lakes are located above faults, and their origin may be related to deformation, whereas the frost mounds may mark deep-seated fluid dynamic processes. Local thickening of permafrost may be associated with the presence of gas hydrates. The detected features may trace gas migration pathways and reveal possible sites of gas emission.