How can you determine core sample porosity in petrophysics?

To determine core sample porosity in petrophysics, measure the volume of fluids (water and hydrocarbons) in the core and divide it by the total volume of the core. Porosity is calculated as the ratio of void space to total rock volume.

One common method involves the Grain Volume Method, where the volume of the rock's solid grains is measured and subtracted from the total volume of the core to calculate porosity. Other techniques include Fluid Saturation, where the sample's absorption of a known fluid indicates porosity, and Helium Porosimetry, which uses helium gas to measure pore volume due to its ability to penetrate small pores. Advanced methods include Nuclear Magnetic Resonance (NMR) Logging, and Computed Tomography (CT) Scans. Traditional approaches like applying Archimedes' Principle are also used. The choice of method depends on factors like rock type, equipment availability, and desired accuracy.

Porosity and how to measure it is an interesting challenge on core. Often broken down to either total or effective porosity. Total often referrs to all interconnected porosty where as effective refers to interconnected porosity with preserved clay structures. Most core analysis involves obtaining total porosity from which many of the other experiments hang off. Humidity drying was introduced to try and obtain a form of effective porosity which in my experience has yielded mixed results and requires careful supervision. It is often recommended to do total porosity on core with some humidity effective because total can be compared against well established total porosity petrophysical equations without the assumption of a Vclay term

Is a Laboratory study of a sample of geological formation, usually prospective rock, extracted during or after drilling a well. Economical and efficient production of oil and gas depends significantly on understanding key reservoir rock properties, such as porosity, permeability, and wettability. Core analysis is particularly important in shale reservoirs due to the vertical and lateral heterogeneity of the rocks and may include evaluation of rock properties and anisotropy; the content, maturity and type of organic matter; fluid content; fluid sensitivity; and geomechanical properties.????

In Chemical/Materials, we use bruneuer- emmet- teller (BET)?theory, which?aims to explain the physical adsorption?of?gas?molecules?on a solid surfaces?and serves as the basis for an important analysis technique for the measurement of the?specific surface of materials. Other method you can use is Scanning Electron Microscope (SEM) or Digital Microscope (which have digital images capabilty to the size of the poros structure on the surface, i.e. Keyence). There tons of methods but best way refer to ASTM standard

Through Water Saturation method.Saturation method--the pore volume of a rock sample may be determined from the difference between saturated-surface-dry and oven-dry masses.

Measuring the porosity of drill core samples is a crucial step in petroleum exploration, geological research, and related fields. Different methods are employed based on sample characteristics, precision requirements, the destructive or non-destructive nature of the measurement, and available equipment. Three commonly used methods are helium porosimetry, mercury injection, and water saturation.

1) Gravimetric methods The total volume is obtained by observing the weight loss of the sample when it is immersed in a liquid, or by the change in weight of a pycnometer when it is filled with mercury and when it is filled with mercury and the sample. The most used gravimetric methods are: – Covering the sample with paraffin and immersion in water. – Saturation of the sample and immersion in the saturating liquid. – Immersion of the dry sample in mercury. 2) Volumetric methods The methods used are the mercury pycnometer and the immersion of a saturated sample. ????

When it comes to comparing core porosity to log porosity, we should note the difference in the definition between reservoir engineers and petrophysicists. Based on reservoir engineering textbooks, The “total porosity” includes the porosity of both interconnected and isolated pore spaces, while the “effective porosity” includes only the interconnected pore spaces. In other words, “effective porosity” is “total porosity” excluding the isolated pores spaces which do not contribute to fluid flow in porous media and thus cannot be produced. However, petrophysicists define “effective porosity” as the “total porosity” excluding the clay-bound water.

The calibration and analysis of rock cores provide essential data for the exploration, evaluation and production of oil and gas reservoirs. In addition, they provide direct evidence of the presence, distribution and production capacity of hydrocarbons, cores provide ground truth data for calibration of well logs and allow the revelation of variations in reservoir properties that may not have been detected through measurements derived from downhole logs alone. Based on analysis of core-derived porosity, permeability, fluid saturation, grain density, lithology and texture, operators can better characterize rock pore systems and more accurately model the reservoir behavior to optimize production. ??

To determine core sample porosity in petrophysics, you can use different methods like lab measurements, well logging, or imaging techniques. Lab measurements analyze physical properties, while well logging and imaging provide valuable insights. These methods help assess reservoir quality and hydrocarbon potential.

In case, you have a bleeding core care must be taken to preserve it’s natural porosity. Core preservation is a very basic thing after core acquisition which must be supervised by onsite Well site geologist.

It is also important to take into account what the porosity of a rock can be determined through measurements of one, or a combination of several, of the following well logs: – Sonic record. – Density registration. – Neutron registry. Measurements from these logs not only depend on porosity, but also depend on the lithology of the formation, the fluids present in the pore space, and, in some cases, the geometry of the porous medium. When the lithology of the rock is known, porosity values can be obtained from measurements made with these logs, If the lithology is not known, or is a complex lithology formed by two or more minerals in unknown proportions, it is more difficult to obtain reliable porosity values from these logs. ??

By measuring the volume of fluids water & hydrocarbon in the core then divide it by the total volume of the core because the porosity calculated as the ratio of void space to total rock volume.

Core sample porosity in petrophysics is often determined using various methods, with one common approach being the use of the formula: \[ \text{Porosity} (\%) = \frac{\text{Volume of voids}}{\text{Total volume of the rock}} \times 100 \] This involves measuring the total volume of the core sample and the volume of the void spaces within it. The void spaces represent the pores where fluids such as oil or gas can reside. Techniques like helium or nitrogen gas displacement, mercury injection capillary pressure, or imaging methods may be employed to obtain these volume measurements. Different methods may have varying degrees of accuracy and precision.