Geological field classification of reservoir rocks of Ardat horizon, Rodnikovsky field, Orenburg Oblast

Abstract

Major production zone on Rodnikovskoye field is Ardatov terrigenious deposit (D3 reservoir). At Brownfield stage when main reserves are recovered, more attention is paid to cross-section improvement. Typically, maximum oil is produced from reservoirs with good reservoir properties. Many researches describe the relationship between SP relative amplitude and silty and clay material in the reservoir. V.S.Muromtsev sufficiently describes reservoir classification method based on grain size and aSP (Nedra 1984). The feature of spontaneous polarization method (SP) in terrigenious rocks allows to identify shale volyme and grain size effect, i.e. define two main lithological parameters. They help to determine terrigenious rock deposition settings and evaluate rock properties. Table 1 shows rock type determined by authors vs. lithotype determined by V.S.Muromtsev. There is some discrepancy in prevailing sandy fraction. According to grain size analysis, the core samples are fine-grained sandstone which is due to insufficient quantity of samples taken in high aSP zones. Therefore, based on relative curve parameter aSP=0.75–1.0, coarse and fine-grained sandstone was associated with rock type I; based on V.S.Muromtsev classification, aSP=0.6–1.0 sandstone is divided into two types: coarse-grained and fine-grained. The range of aSP=0–0.25 corresponds to shales, aSP=0.25–0.5 corresponds to siltstone and argillaceous-silty rocks. Mixed rock type (sandy-siltyargillaceous) corresponds to average level of aSP=0.5–0.75. Thus, the grain size-typing study performed in TNNC does not contradict other investigators' data.