How can you avoid common errors in porosity measurement?

1 Sample preparation

The first step in porosity measurement is to prepare the rock samples for the laboratory analysis. This involves cleaning, drying, and trimming the samples to remove any impurities, excess fluids, and irregularities that might distort the measurement. However, sample preparation can also introduce errors if not done properly. For example, if the samples are not cleaned thoroughly, some residual fluids or clay minerals might remain in the pores and reduce the apparent porosity. If the samples are dried at too high a temperature, some pore fluids might evaporate and create artificial pores. If the samples are trimmed too much, some representative features of the rock might be lost. Therefore, you should follow the best practices and standards for sample preparation and minimize the alterations to the natural state of the rock.

3 Fluid saturation

The third step in porosity measurement is to consider the effect of fluid saturation on the porosity value. Fluid saturation refers to the amount and type of fluids that fill the pores in the rock sample. The most common fluids are water, oil, and gas. Fluid saturation can affect the porosity measurement in two ways: by changing the density and compressibility of the rock and by interfering with the measurement technique. For example, if the rock sample is saturated with gas, the apparent porosity will be higher than the true porosity because gas has a lower density and higher compressibility than water or oil. If the rock sample is saturated with oil, the apparent porosity will be lower than the true porosity because oil has a higher density and lower compressibility than water or gas. If the measurement technique involves the use of a fluid, such as helium or mercury, the fluid saturation can also affect the measurement by creating a pressure difference or a chemical reaction between the fluids. Therefore, you should measure the fluid saturation of your rock samples and correct the porosity value accordingly or use a measurement technique that is not affected by fluid saturation.

4 Rock heterogeneity

The fourth step in porosity measurement is to account for the rock heterogeneity in the porosity value. Rock heterogeneity refers to the variation in the properties and structure of the rock, such as mineral composition, grain size, pore shape, and spatial distribution. Rock heterogeneity can affect the porosity measurement in two ways: by creating a scale dependency and by introducing a sampling bias. For example, if the rock sample has a large-scale heterogeneity, such as layers or lenses of different minerals or pore types, the porosity value will depend on the scale of the measurement and the location of the sample. If the rock sample has a small-scale heterogeneity, such as variations in the grain size or pore shape within a layer or a lens, the porosity value will depend on the resolution and sensitivity of the measurement technique and the representativeness of the sample. Therefore, you should measure the porosity at different scales and locations and use a measurement technique that can capture the heterogeneity of your rock samples or use a statistical method to average or normalize the porosity values.

By following these four steps, you can avoid some common errors in porosity measurement and improve the quality and reliability of your core analysis results. Porosity measurement is a crucial step for understanding and optimizing the performance of oil and gas reservoirs, so you should always strive to achieve the highest accuracy and precision possible.