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Home / Issue Archive / 2006 / December #12 / Estimation of Technological Parameters of Filed Development with the Use of Calculations, Made on Sector Models

№ 12 (December 2006)

Estimation of Technological Parameters of Filed Development with the Use of Calculations, Made on Sector Models

Hydrodynamical calculations for some bed stimulation technologies (for example, steam or hot water injection, polymeric flooding, etc.) require significant computer resources and much time.

By А. Vinogradovа, I. Indrupskiy, K. Epishin, M. Budilin

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Usually, these types of treatment are tested using sector models - models of selected regions, characteristic of a deposit.

It is evident that when an area is being developed, formation zones with geological and physical characteristics different from the selected regions get included. This factor makes it difficult to apply calculations based on the sector models to the entire formation in the course of its gradual drilling out.

The work aimed at vindication of oil recovery factors for the N deposit in West Siberia resulted in devising a method for precise estimation of the development process' technological parameters for both a block and a region, and also for the entire deposit. The method is based on technological parameters obtained by calculations on sector models of characteristic regions.

The essence of this method is as follows:

The dynamics of annual parameters (such as oil, water and gas production, and agent injection) obtained as a result of calculations on sector models are multiplied by the quantity of wells put into production every year and by correction factors. These factors take account of changes in the annual parameters' dynamics depending on geological and physical characteristics, which are subject to change when advancing to new regions in the course of the formation's development. The parameters corrected in this manner are summed up, with application of a correction shift for the year in which each of the wells was put into production.

Vindication of the Method's Legitimacy

A full-scale model with a coarse grid was prepared for the N deposit's massive bottom-water-containing oil-and- gas formation. Within its limits, characteristic regions were selected, and separate sector models with fine grid were prepared for these regions.

Calculations made for all the models referred to the same basic technology of bed stimulation: cold flooding in vertical wells. However, on a full-scale model the wells were put into production gradually, to conform with the drilling rate preset on a yearly basis. The results of calculations on a full-scale model make it possible to suggest that when a specific region is brought into operation, its condition practically does not differ from the original condition (equilibrium). Otherwise, it may be presumed that a continued development of the neighboring regions brought into production earlier makes no significant impact on the process.

Next, the results obtained by means of calculations on a full-scale model and the results obtained by application of the considered method were compared with the results obtained by calculations on sector models (Fig. 2).

The divergence of development parameters obtained by two different calculation methods is insignificant. This may be explained by both the inexactitude of the considered method and, what's more important, by difference in dimensionality between the full-scale and the sector models' grids.

Method's Description

First of all, it is necessary to distinguish the main factors, which tend to change as a deposit is being drilled. According to these factors, characteristic regions for the construction of sector models can be selected. For the Russkoje deposit, the main factors were:

• the net oil-saturated thickness;

• the presence/absence of a gas cap.

The change of these characteristics during the development of the deposit's regions is determined by the wells' drilling rate. Hence, it is possible to make a table showing the amount of wells to be drilled every year (both in the sub-gas zone, and in the oil-water zone) and the average value of the net oil-saturated thickness being developed the same year.

Having calculations for at least two sector models, which differ in values of net oil-saturated thickness, but are located within the same zone of saturation (for example, in a sub-gas zone), it is possible to find that the rate of cumulative oil production for a defined period changes depending on thickness.

When selecting a suitable function in the course of work connected with the deposit discussed in this article, the polynomials with degrees from 1 to 3 were considered. The final choice was made in favor of the linear function. The choice was based on the comparison of technological parameters' dynamics obtained on the full-scale model with a coarse grid with dynamics of the same parameters obtained with the help of the given method using calculations of the same technology on sector models with a finer grid.

Thus, factors can be determined that enable us to modify the parameters calculated on a sector element with maximum thickness, for other thickness' values

The dynamics of annual figures calculated on a sector model are multiplied by the number of wells put into production in a given year and by the obtained factors. Then, the results are summed up and the correction shift for the year of putting into production is applied. By this method the final dynamics of annual parameters for a region or for the entire deposit are set up.

The given algorithm was used to create a program that allow to process simultaneously any number of parameters, and that helped to significantly facilitate the process of factors selection correctness control.

The application of the offered method is shown more clearly on Fig. 5 and 6. It demonstrates dynamics of the development parameters for one of the characteristic regions of a formation, as well as for the entireformation in case of application of an alternative stimulation method - a steam injection. It was impossible to make calculations for the given technology on a large-scale model due to computing limitations. That is why the given dynamics' curves for the deposit as a whole were constructed with the help of method discussed in this article.

Additional Possible Applications of this Method

Obviously, the method discussed in this article can be used to predict the development's technological parameters for cases with combined stimulation methods.

The obtained factors (Table 2) may be also used for a rapid assessment of the entire deposit's (reservoir's) oil recovery factor based on the oil recovery factor values calculated for characteristic regions.

КИНм= КИНу(sub-gas)5Qуб/Qмб5Jsub-gasKi5Ni + КИНу(oil-water zone)5Qуб/Qмб5Joil-water zoneKi5Ni,
where
КИНм - oil recovery factor of a deposit;
КИНу - oil recovery factor of a selected region;
Qмб - the deposit's initial in-place oil reserves;
Qуб - the selected region's initial in-place oil reserves;
Ki - factor for the first year of drilling;
Ni - the number of wells to be drilled in the first year.

Conclusions

1. A method allowing approximate determination of the dynamics of a deposit's development parameters was offered based on the results of calculations made for characteristic regions' sector models. It can be used to calculate bed stimulation processes, for which modeling based on a full-scale model is impossible due to computing limitations.

2. The offered method was used to validate oil recovery factors for one of the West Siberian deposits. The reliability of the obtained results has been proved by the comparison with results of calculations made on a full-scale model for a basic development method.

3. It is also possible to use this method for a rapid assessment of oil recovery facto r value for the entire deposit based on oil recovery factor values for characteristic regions.
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