Improving the accuracy of porosity calculation based on numerical methods for estimating fluid density from gamma-gamma density data

The main geophysical method to assess the porosity of the reservoir is gamma-gamma density logging. The equation of the relationship between density and porosity, among other constants, includes such a parameter as the density of the fluid in the pore space. When carrying out density logging after drilling, by the beginning of work, as a rule, a zone of penetration of drilling mud filtrate filling the pore space within the radius of the method study has time to form. However, at present, more and more geophysical studies are being carried out as part of the logging while drilling complex, which makes it possible to determine the properties of the reservoir that are not affected by filtrate. In the presence of a transition zone, the fluid density may vary depending on the ratio of the fractions of different phases, which will affect the results of porosity calculation, but in petrophysical equations, the fluid density is a constant.
Aim. To eliminate errors in the calculation of properties, it is necessary to find a way to determine the exact value of the density of the fluid mixture. The problem is complicated by the circumstance that to determine the fluid density, it is necessary to assess the reservoir water saturation, while to assess the water saturation, it is necessary to know the porosity. The interdependence of these quantities makes it difficult to construct petrophysical dependencies, and the type of functions excludes the possibility of an analytical solution of the system of these equations.
As an example, theoretical calculations illustrating the algorithm for determining properties, as well as the results of the implementation of this technique in the process of hydrodynamic modeling of one of the objects of the Vostochno-Messoyakhskoye field are given.
Materials and methods. The paper shows an algorithm for the numerical solution of such a system based on the method of simple iteration. This approach allows cyclical calculation of properties, increasing the accuracy of the estimate with each repetition.
Results. As an example, theoretical calculations illustrating the algorithm for determining properties, as well as the results of the implementation of this technique in the process of hydrodynamic modeling of one of the objects of the Vostochno-Messoyakhskoye field. The use of the algorithm made it possible to significantly improve the quality of adaptation of the hydrodynamic model without the need for local settings.
Conclusions. The only limitation of the method is the availability of density logging while drilling. The calculation algorithm does not use any complex mathematical models, which allows it to be implemented in any software product. The results obtained suggest that this method can be a reliable way to improve the quality of property assessment, and therefore improve the predictive ability of geological and hydrodynamic models.

1. Archie G.E. The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics // Trans, no. 146 (01), pp. 54–62.

2. Leverett M.C. Capillary Behavior in Porous Solids // Trans, no. 142 (01), pp. 152–169.

3. Verzhbitskiy V.M. Osnovy chislennih metodov [Fundamentals of numerical methods]. — Moscow: Vischaya shkola, 2022, 840 p. (In Russ.)

4. Priezzev I.I., Osipenko R.S., Borovkova E.E., Petrenko E.N. The example of neural Kolmogorov networks in reservoir properties forecast within West Siberia Pokur suite // Geofizika, 2022, no. (1), pp. 58–63. (In Russ.)