THE ACCURACY OF GEOELECTRIC HORIZONS RESISTIVITY ESTIMATION USING ELECTROMAGNETIC DATA
V. S. EMEL’YANOV1, I. V. BUDDO2, M. V. SHARLOV1, N. V. MISYURKEEVA1, A. V. POSPEEV2, YU. A. AGAFONOV1
1JSC В«Irkutsk Electroprospecting Company» (IERP), 664011, Irkutsk, Rabochaya str., 2a, Premier Business-Center, Russia
evs@ierp.ru
2Irkutsk Scientific Center SB RAS, 664033, Irkutsk, Lermontova str., 134, Russia
biv@ierp.ru
Keywords: сигналы зондирования становлением поля в ближней зоне, удельное электрическое сопротивление, инверсия, коллектор, нефть и газ, TEM signals, electrical resistivity, inversion, reservoir, oil and gas
Abstract
In geological terms the section of the Kovykta gas condensate field and the surrounding areas is composed by three geo electric complexes-the post-salt terrigenous-carbonate; carbonate-halogen; and the pre-salt terrigenous-carbonate, lying at the basement. Within the two lower complexes reservoir horizons are spread regionally, with some of them bearing commercial hyd rocarbon deposits. Due to the presence of conductive saline pore solutions, the reservoirs are characterized by low electrical re sistivity. This leads to the geological effectiveness of the use of electromagnetic methods in the delineation of the zones of reservoir development. Transient electromagnetic soundings in the near field zone (TEM) is traditionally applied in Eastern Siberia in prospecting and exploration of hydrocarbon accumulations. Modern technologies of mathematical modeling and inversion of TEM signals allow to define geoelectric characteristics not only in the intervals whose thickness measures hundreds of meters, but also di rectly in thin reservoirs. Accordingly, the question arises on the accuracy of the electrical resistivity determination in each of the horizons. To solve this problem an original technique was developed consisting in synthesizing and noising of TEM signals and their inversion with estimation of resistivity recovery error of each horizon. Using the proposed method allows to evaluate the accu racy of the of reservoirs prediction in the sedimentary cover from TEM studies. To provide the inversion the automated minimi zation procedure based on the algorithm of the Monte Carlo method was used. The starting models based on the results of manual inversion and optimal scale of layers resistivity variations were used for reduction of the inversion time. The model of the longitudinal resistance of the layer comprising different conductivity horizons, evaluates the integrity of these geoelectric parameters considered. The use of the proposed method allowed us to estimate the accuracy of prediction of the presence of reservoirs in the sedimentary cover, depending on the resistivity contrast their properties and depth.
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