Abstract Under the conditions of Arctic, a number of hazardous natural phenomena was established: shallow gas («gas jets and pockets» in the upper part of the oil and gas field section), gas hydrates, porkmarks-craters, regressive depression of the seabed.
The fact of gas accumulations occurrence, as well as the degree of their influence on the final indices of the development of oil and gas field, should be considered both at the prospecting and exploration stage and at the hydrocarbon extraction stage. Moreover, the assessment of all possible risks in the Arctic climatic conditions is of a particular importance.
The analysis is given concerning engineering geological surveys on the Sakhalin shelf of the Okhotsk Sea, and risk assessment criteria were developed for drilling operations, ranking was performed related to the amplitudes of 2D seismic anomalies in the upper part of the cross-section of Kirinsky and South-Kirinsky gas condensate fields, indicating the degree of gas saturation of the sediments and level of hazard.
To ensure safe drilling of wells on the shelf in the areas with shallow gas, it is proposed to perform: identification and mapping of shallow gas accumulations at the objects of sea shelf based on the data of reprocessing and interpretation of the results of seismic exploration and engineering-geotechnical surveys; development of the well drilling technology and well design in gas accumulation conditions in the upper part of the cross-section of the offshore fields, including performance of the calculations of the exploration, wildcat and production well designs.
Several types of influence on the deposit are considered: local rounded deepening (porkmarks), regressive depression of the seabed surface of gas condensate fields that violate the natural equilibrium state of the subsoil resources, creating prerequisites for the occurrence of deformations of the rock massif and the seabed surface. The main and most dangerous forms of these consequences are: depressurization of the bore-hole annulus of wells, deformation of the underwater communications, possible failure of the production platform fixing anchors.
At present, the forecast of these negative phenomena and the reduction of the scope of their consequences are a current problem for the specialists.
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