In fact, from the perspective of logging evaluation, reservoir description technology is to further develop single well (point) formation evaluation into surface (regional) multi-well comprehensive evaluation. According to its development process and the problems that can be solved, reservoir description can be divided into two stages: static description and dynamic description. Static description is the basis of reservoir description, while dynamic description is the further development and perfection of static description technology.
(I) Static description of oil reservoir
Static description mainly includes: the study of oilfield geological structure and reservoir geometry, the study of lithofacies and sedimentary environment, the spatial distribution of reservoir parameters and the calculation of oil and gas geological reserves.
1) comprehensively uses dip logging, seismic and geological information to study and determine oilfield geological structure (including fault analysis) and reservoir geometry.
2) Determine the lithofacies of well profile strata and study the sedimentary facies of oil fields and basins.
3) Accurately calculate the basic parameters of the reservoir, study its spatial distribution, and draw equal thickness map, equal porosity map, equal permeability map and equal oil and gas saturation map.
4) Calculate the geological reserves of oil and gas.
5) Study the mechanical properties of rocks, predict the gradient of formation pressure and fracture pressure, and study the direction of in-situ stress.
To accomplish the above tasks, it is necessary to take all accurate geological, logging, seismic, analysis and formation test data, standardize oilfield logging, establish a practical interpretation model and the conversion relationship between oilfield parameters, conduct fine formation evaluation, logging facies analysis and stratigraphic correlation of single wells and multiple wells, study the vertical and horizontal distribution law of reservoirs and the distribution law of oil, gas and water, and draw maps such as equivalent maps, three-dimensional maps and slice maps of various parameters with computer drawing technology.
(II) Description of reservoir performance
Dynamic description is the reservoir description in the development stage of oil and gas fields.
1) to study the change law of basic parameters of oil and gas reservoirs during oil and gas field development. Estimate the oil-gas pressure, relative permeability and oil-gas saturation, determine the liquid production profile of production wells and the water injection profile of water injection wells, monitor the movement of oil-water interface, and dynamically describe oil and gas fields.
2) The dynamic simulation of a single well or the whole reservoir is carried out, which provides a basis for making the best development plan and improving oil and gas recovery. The purpose of single well simulation is to make the parameters predicted by single well model match the measured values well. For example, by adjusting the permeability and skin factor of each production layer in oil well simulation, the predicted oil well flow profile, pressure drop and pressure recovery response are basically close to the measured values. In this way, improved, reliable and consistent reservoir dynamic description results can be obtained. This dynamic description not only integrates available information such as open hole logging, core analysis, repeated formation tester, well testing and production logging; But also make these different types of measurement data match each other and make full use of all the information of oil well performance.
Obviously, reservoir description can only be realized through the combination and infiltration of multiple disciplines. The main tasks of logging in reservoir description include: the selection and research of key wells, the standardization of logging information in the whole oilfield, the establishment of oilfield logging interpretation model and parameter conversion, the spatial distribution of oilfield parameters and the drawing of corresponding maps, and the dynamic simulation of single well. Obviously, these tasks must be completed through the close combination of logging with geology, core analysis and testing, formation testing and development information.
(3) Characteristics of logging interpretation in reservoir description technology.
1) emphasizes the consistency of logging and geological information in depth.
2) The logging data of the whole oilfield should be standardized to minimize various non-geological factors and errors.
3) Optimize the interpretation model, interpretation method and some parameters suitable for the whole oilfield.
4) Establish the conversion relationship between logging information and geological parameters in the whole oilfield, and solve the parameter calculation problem of incomplete wells in logging projects.
5) Using the latest technology, extract as many useful parameters reflecting geological characteristics as possible from the logging information, analyze the logging facies of the oil well profile, and identify the logging facies analysis results with cores.
6) The single well dynamic simulation results have been verified by production logging and oil well testing.
7) Widely adopt database technology.
8) Draw various equivalent drawings, three-dimensional structure drawings, slice drawings, etc. Using various drawing techniques, the reservoir is described in detail and objectively.
(IV) Basic achievements of reservoir description
1. Single well evaluation results
That is, the digital processing result chart and data table of single well, mainly including lithology and basic parameters (shale or clay content, porosity, water saturation, permeability, cumulative porosity and cumulative oil and gas volume, etc.) of single well reservoir. ). For key wells, it should also include the basic parameters of core analysis and various conversion relationships.
2. Comprehensive research results of the whole oilfield
Comprehensive data table of various parameters in the whole oilfield, and equivalent maps of various parameters (such as isothickness map, isoporosity map, isopermeability map, total porosity map, net porosity map, oil and gas saturation map, etc.). ), three-dimensional structural map (including three-dimensional map cut from different angles), calculation results of oil and gas reserves in the whole oilfield, etc.
(V) Reservoir description process
Figure 7-70 is the flow chart of reservoir description. It should be emphasized that the description of oil and gas reservoirs is a process of repeated practice and deepening understanding. The role of reservoir description in the exploration stage is to describe the oilfield statically. At the beginning of exploration, the reservoir structure, spatial distribution of reservoir parameters and reservoir boundary are preliminarily determined by using logging, geological, logging and seismic data of a few wells (such as 3-5 wells) through single well interpretation, key well research, multi-well evaluation and comprehensive research, and corresponding maps are drawn to guide the next oilfield exploration in time, especially rolling exploration.
Figure 7-70 Block Diagram of Reservoir Description in Niuzhuang Oilfield
With the development of oil field exploration and development and the increase of wells, more logging, logging, core, test production and seismic data are needed to describe and evaluate oil and gas reservoirs more accurately. The more wells, the richer the data, the more perfect and accurate the reservoir description, and the more real it is. It can be said that from the initial stage of oil field exploration and development to the later stage of oil field development, it is necessary to continuously describe the reservoir, so as to continuously improve the economic benefits of oil and gas field exploration and development and maximize the ultimate recovery rate of the oil field. Realize the exploration and development goal of less input and more output.