Deterministic modeling method

In fact, the process of establishing geological model begins with the study of the original data of oil and gas reservoirs, and all kinds of available information are integrated to form a three-dimensional system of profile, plane and stereo with scattered well point data, and finally the required geological model is formed. Among them, the prediction of cross-well geological parameters is the core of modeling.

Reservoir modeling methods are generally divided into deterministic modeling and stochastic modeling.

The deterministic modeling method holds that the core and its analysis data obtained by drilling are first-hand real data, and the change between wells, that is, between data control points, is continuous. Therefore, interpolation between data control points is the only solution, and it is also deterministic.

Interpolation diagram of traditional geological work methods, mathematical geological methods such as Kriging, reservoir interpretation results of development earthquakes and data or logging interpretation results directly obtained along horizontal wells are all important basis for deterministic modeling.

Deterministic reservoir modeling generally goes through three steps [2]:

Step one, establish a well model;

Step 2, establish a hierarchical model;

The third step is to establish a parametric model.

The fourth step should be carried out in practical work, that is, coarsening the grid of geological model. Because the logging resolution can reach 0.2m, the grid size of geological model can be as fine as this size, but it is actually impossible to calculate the numerical simulation with the grid size of decimeter. Therefore, it is generally necessary to combine the grid sizes of geological models according to the needs and possibilities of numerical simulation, which is called coarsening. At present, this step is generally handled by conventional methods such as arithmetic average or geometric average.

(1) Establish well model.

1) converts all kinds of information obtained in the wellbore into development geological characteristic parameters, and establishes a one-dimensional columnar section showing various development geological characteristics of each well.

2) The key point is to establish an interpretation model that transforms all kinds of reservoir information into development geological characteristic parameters. At present, logging is the main means to obtain reservoir information.

3) Nine basic parameters in one-dimensional profile of wellbore are: permeable (sandstone) layer, effective layer and interlayer; Oil-bearing layer, gas-bearing layer and aquifer; Porosity, permeability and saturation.

4) Input the continuous columnar profile of basic parameters of wellbore reservoir, together with well location data such as well location coordinates and elevation, and complete the establishment of well model.

5) Because logging interpretation of well string parameters is an independent operation process, this step is generally not included in the existing geological model software, but linked with logging processing results in the form of database.

(2) Establish a hierarchical model

1) connects all geological units in each well through cross-well isochronous correlation, that is, the one-dimensional columnar section of the wellbore becomes a three-dimensional geological body, and the spatial framework of the reservoir is constructed.

2) The key point is to compare small units correctly. The smaller the correlation unit, the finer the reservoir skeleton.

3) At present, popular modeling software generally relies on geologists to manually compare a unit (such as a single sand layer or sand group) and input it into a computer. The further subdivision layers in the unit are given instructions according to certain geological laws, and are divided by computer machinery, such as longitudinal accretion, transverse accretion, overlapping, equal thickness contrast, uniform thickening and thinning contrast, etc.

Sequence stratigraphy and seismic lateral tracking are important foundations for establishing stratigraphic model with large well spacing.

(3) establish a parameterized model

1) gives various reservoir attribute parameters of each point in the reservoir internal space quantitatively.

2) The key point is to interpolate (extrapolate) various attribute parameters of the reservoir in the undrilled area between wells layer by layer according to the above-mentioned layer model and the parameter values of known well points (control points); The smaller the interpolation error, the higher the accuracy of the geological model.

3) At present, due to the immaturity of geophysical methods to directly explain permeability, the porosity model is generally established first, and then the porosity-permeability relationship measured by core analysis is converted from porosity model to permeability model.

4) Some deterministic modeling methods and corresponding software for establishing continuous parameter fields have been developed, which geologists should choose carefully. Different sedimentary types of sand bodies should adopt methods suitable for this kind of sand bodies and carry out corresponding tests.