Ineffective Porosity in Petroleum Engineering Using Excel

Ineffective porosity is the portion of the total porosity that does not contribute to the flow of fluids in a porous medium. It includes the pores that are isolated, dead-ended, or too small to allow fluid movement. Ineffective porosity reduces the storage and transmission capacity of a rock or sediment, and is therefore of interest in petroleum engineering and hydrogeology.

One way to measure ineffective porosity is to compare the total porosity and the effective porosity of a sample. Total porosity is the ratio of the total volume of voids to the bulk volume of the sample. Effective porosity is the ratio of the volume of interconnected voids to the bulk volume of the sample. The difference between the total and effective porosity is the ineffective porosity.

Ineffective porosity is influenced by factors such as the type and amount of clay minerals, the salinity of the formation water, and the drying conditions of the sample. Clay minerals can bind water to their surfaces and interlayers, which is not available for fluid flow. The amount of clay-bound water depends on the clay type and the salinity of the water. Drying the sample can remove some or all of the clay-bound water, which affects the measurement of effective porosity. Therefore, different methods of drying can result in different values of ineffective porosity.

Ineffective porosity, also known as non-effective porosity or bypassed porosity, represents the portion of total porosity that does not contribute to fluid flow in a reservoir. It is essential to account for ineffective porosity when estimating reservoir properties to optimize oil and gas recovery.

The formula for ineffective porosity (IP) is given by:

Where:

• is the total porosity,
• is the effective porosity.

Procedures for Calculating Ineffective Porosity in Excel

1. Open Microsoft Excel and create a table with the following columns: Depth (ft), Total Porosity (%), and Effective Porosity (%).
2. Input the relevant data for each depth interval.
3. In a new column, use the formula mentioned earlier to calculate ineffective porosity for each depth interval.
4. Summarize the results and analyze the distribution of ineffective porosity.

Comprehensive Explanation with Scenario

Let’s consider a hypothetical reservoir with the following data:

    Depth (ft) | Total Porosity (%) | Effective Porosity (%)
    ----------------------------------------------
    1000       | 18                  | 15
    1500       | 22                  | 18
    2000       | 16                  | 13

Using the ineffective porosity formula, we calculate for each depth:

Excel Table:

Result: The cumulative ineffective porosity for the entire reservoir is calculated by averaging the individual ineffective porosity values:

Comparison with MATLAB

While Excel is a powerful tool, MATLAB can be used for more complex numerical simulations. In MATLAB, the same calculations can be performed using the provided data to verify the results obtained in Excel. The MATLAB script and Excel calculations should yield comparable results, showcasing the consistency and reliability of both approaches.