Geophysical and Seismic Studies to Determine Regional Stresses at Various Objects of the Romashkinskoye Field

Abstract

The purpose of this work is to build maps of regional stresses in the Romashkinskoye oilfield formations.The use of the obtained data in the design of field development allows subsequently to keep the system at the maximum production rate for a long time (A.V. Ulybin, 2017) and to fully develop hydrocarbons from the subsoil, predict the direction of fracture formation and increase the efficiency of field development. The novelty of the work is due to insufficient knowledge of the influence of rock stresses on the development of the analyzed objects. For the first time for the analyzed territories, a map of regional stresses was obtained to assess natural and induced fracturing due to hydraulic fracturing. Cross-dipole sonic logging is based on the use of at least one monopole source with a carrier frequency of the order of 8-12 kHz and a bandwidth of 0-20 kHz, to create longitudinal and transverse waves, as well as Stoneley waves. Registration occurs at probe distances that correspond to the far zone of the wave field (S.V. Dobrynin, access date 2020). Microseismic imager (MCI) logs primarily display resistivity measurements of formations near the borehole wall. As a result of using this method, it is possible to obtain information on changes in porosity, lithological composition and structure of layers, the presence of fractures and caverns. Passive seismic monitoring consists in continuous recording of microseismic noises by permanently installed or periodically installed seismological sensors in order to localize sources of underground microseisms of a natural and man-made nature (O. V. Kizim, date of access 2020). In the process of studies carried out at the wells of the Romashkinskoye field, it was noticed that the calculation of anisotropy in the interval of the Verean layer is complicated by the presence of decompacted rocks and high cavernosity. From the analysis results, conclusions can be drawn about the depth of the hydraulic fracture propagation. As a result of the analysis of the MCI logging results, performed at the wells of the Romashkinskoye field, the boundaries of the stratum, the dip angles, the dip azimuth for the Kashirian, Bashkirian, Aleksinian, Upino-Malevian beds were identified. Angular unconformity between some strata is revealed. In the analyzed wells, "healed" fractures were identified in the Verean layer, the Bashkirian stage, the Aleksinian and Tulian layers, and in the Upper Turnaisian substage, and their dip angles and azimuths were established. The purpose of the passive ground microseismic monitoring of hydraulic fracturing carried out at the wells of the Romashkinskoye field was to determine the azimuths, extent, developmental character of fracture zones and to assess the zones of probable proppant penetration in the formation during hydraulic fracturing in the vertical wellbore. As a result of the research, the azimuth of the center line, the length of the center line, the length of the proppant penetration zones, and the predicted fracture height were determined for the wells. Based on the results of geophysical and seismic studies the Romashkinskoye oilfield formations,a map of regional stresses was built, which allows the correct selection of wells for hydraulic fracturing.