This article reviews the results of measurement of optical properties of oil, such as polarimetry, refractometric, luminescent-bituminological research, IR-spectrometry and UV-visible-NIR spectrometry used to solve geo-bituminology development of hydrocarbon deposits. The authors pay special attention to optical research in the field of UV-visible-NIR electromagnetic radiation, the results of which allow us to estimate the residual oil reserves, separate production for each formation during the operation of multi-layer objects, determine the producing gas-oil ratio, density and content of hydrocarbons, efficiency of hydraulic fracturing, flow-reducing technologies, and injection of solvents of heavy oil sediments, etc. The published approaches to methods of optical research, which are carried out by laboratories or in-well devices, have been analyzed. This article analyzes the main advantages and disadvantages of current technologies for determining the optical properties of oil. The authors propose wellhead devices for determining the optical properties of oil in UV-visible-NIR radiation (190–1100 nm) and their functional schemes, with a description of the operating principle.

Long-term phased development of a multi-layer field, including tens and hundreds of oil-bearing horizons and local deposits, combined with their vertical and horizontal separation, creates conditions for the formation of residual oil reserves. For the purpose of identifying and spatial localization of residual reserves, an algorithm for retrospective analysis was developed and applied on the example of the Upper and Lower Devonian terrigenous deposits of the Romashkinskoe oil field, which have been developed since 1952. The long history of geological study and development of oil-bearing formations of the Pashiysky D1 (layers g and e), Mullinsky D2, Ardatovsky D3, Vorobyevsky D4 and Biysky D5 horizons is analyzed according to the data of 2605 wells. It is proposed to single out 6 categories of formations and the reserves contained in them. Previously undeveloped formations composed of conditioned reservoirs are classified as category 1. Formations composed of more clayey and less permeable reservoirs are awarded with category 2. Category 3 includes previously developed formations, but left before reaching the limit of water cut, and category 4 – currently being developed intervals. The least promising are those that are stopped after reaching the maximum water cut (category 5), as well as wedged out, replaced by non-reservoirs or considered water-bearing (category 6) formations. Categories were mapped to identify, visualize and describe the main patterns in the distribution of residual reserves, which are established both in single wells and in bypassed oil that include a group of wells. The algorithm was tested on the corporate information base of historical data on geological exploration, research and development of the Abdrakhmanovskaya area of ​​the Romashkinskoe oil field. Examples of experimental workover operations to include the identified residual reserves in the development are given.

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The structure and composition of oil reserves deteriorate in the course of a mature oil field development due to geological and technological factors. The geological factors include vertical and lateral macro-and micro-heterogeneity of the reservoirs under development. At the same time, macro-heterogeneity leads to the formation of bypassed residual oil in low- permeability and stagnant layers, zones and lenses that are not exposed to stimulation, while micro-heterogeneity contributes to the formation of residual reserves of capillary oil and oil films. Technological factors include impossibility to fully account for reservoir heterogeneity when substantiating well spacing, pressure gradient, or flooding technology. The key problem here is the lack of clear understanding of the distribution pattern, quantity and deterioration of the quality of residual oil in water-flooded reservoirs, which makes it challenging to reasonably select a technology for effective oil extraction. Despite the improvements constantly made to the production logging, hydrodynamic and interpretive, seismic, lithofacies and other methods of exploration and residual reserves modeling, it is often impossible to obtain timely reliable information about the percentage of reserves depletion and their coverage with the development activities. This paper proposes another method — optical — that, in combination with well logging and hydrodynamic surveys as well as geological and hydrodynamic simulation, has been tested to assess the quantity and spatial pattern of residual oil reserves of the Kynovian (Do) and Pashian (D1) horizons at the experimental site of the Romashkinskoye oil field (Devonian formation). From the theoretical and methodological standpoint, this method is underlain by the results of in vitro studies of core columns and involves the selection and research of optical properties of oil wellhead samples, mathematical processing and correlation of the obtained optical and field data. The obtained estimate of residual reserves is compared with data derived from geological simulation, the most promising automated method for identifying, geometrizing and calculating residual recoverable oil reserves (RROR). The proposed method offers such advantages as ease of use, promptness, reliability, functionality and cost-effectiveness. It uses actual data on cumulative well production and takes into account the current reservoir and fluid porosity and permeability (P&P), which provides the possibility to obtain more precise estimates of the RROR quantity and spatial pattern.