Lecture 1 Petrophysics PDF

# PETROPHYSICS - Petrophysics: is the study of the physical properties of rocks and their contained fluids. - Aim of Petrophysics: The purpose of the petrophysical calculations is to use all available data (logs and cores) to arrive the most accurate values of the petrophysical parameters (i.e., l...

# PETROPHYSICS - Petrophysics: is the study of the physical properties of rocks and their contained fluids. - Aim of Petrophysics: The purpose of the petrophysical calculations is to use all available data (logs and cores) to arrive the most accurate values of the petrophysical parameters (i.e., lithology, net pay, porosity, water saturation, and permeability, ... etc). - Petrophysics emphasizes: - the integration of core data with log data; - the adjustment of core data to reservoir conditions; - the calibration and regression line-fitting of log data to core data. - Petrophysics is mainly used in petroleum exploitation, but also in defining mining and ground water resources. # What is Petrophysical Analysis? - Petrophysics is the evaluation of the physical properties of rocks and their included fluids. - Petrophysical data can be obtained from well logs and from laboratory data on rock samples and cores. - Petrophysical data can be interpreted both qualitatively and quantitatively. # Petrophysical Properties - Petrophysical analysis can be used for the following: - Lithology determination - Net-pay (or pay/non-pay) determination - Porosity determination - Fluid-contacts identification - Water-saturation determination - Permeability determination # Table 3A.1 - Tool choices for a particular reservoir property* | Reservoir Property | Primary Tool | Secondary Tool | |---|---|---| | Thickness (bed boundaries) | Gamma ray log (borehole image log when available) | Electric log with SP log | | Lithology/rock type | Core and core analysis | Mud log | | Porosity | Density log (given rock type and fluid identification) | Neutron log (given rock type and fluid ID) | | Saturations (oil, gas, water) | Electric log (given porosity, rock type, and fluid ID) calibrated with a capillary pressure model | Carbon-oxygen log (given favorable borehole/formation environment) | | Fluid ID/characterization | Wireline formation tester | Mud log| | Permeability (absolute) | Core and core analysis | Wireline formation tester | | Fractional flow (oil, gas, water) | Core and core analysis | Wireline tester | *The choices in this table are subjective and can change depending on the investment risk a particular client company can tolerate and the geographical circumstances involved. # Petrophysical Evaluation: - **Drilling Data** - Mudlogs-Lithology, ROP, Gas shows - Formation pressure - LWD-CAL, GR, DENS, RES - Stratigraphy - **Core Data** - Sedimentology, Petrography - Routine Core Analysis - Electrical Measurements - Special Core Analysis - **Wireline Data** - CAL, GR, DENS, NEU, RES - Formation pressures and fluids - NMR, BHI, SWC, - Rock physics - **Well Test Data** - Reservoir pressure and fluids - Production rates and producibility These all lead to: **Petrophysical Evaluation** Petrophysical Evaluation leads to: - Lithology - Porosity - Water Saturation - Permeability - Reservoir Pressure Which leads to: - Layer Average Properties - Geocellular Model - Volumetrics - Reservoir Simulation # Scales of Petrophysical Analysis - **Pore Modelling** - SEM - Cores - Logs - **Tool Modelling** - Logs - **Borehole Geophysics** - New Well - Existing Well - Seismic - Logs - Seismic - **Seismic** These are scaled for: - μ - cm - m - 10-100m - >100m # Petrophysical Properties Most petrophysicists are employed to compute what are commonly called conventional (or reservoir) petrophysical properties. These are: - **Lithology**: A description of the rock's physical characteristics, such as grain size, composition and texture. Geoscientists can use a combination of log measurements, such as natural Gamma, neutron, density and resistivity, to determine the lithology down the well. - **Porosity**: The percentage of a given volume of rock that is pore space and can therefore contain fluids. This is typically calculated using data from density and neutron logs, but can also be derived from sonic and NMR logging. - **Permeability**: The quantity of fluid (usually water or hydrocarbon) that can flow through a rock as a function of time and pressure, related to how interconnected the pores are. Formation testing is so far the only tool that can directly measure a rock formation's permeability down a well. In case of its absence, which is common in most cases, an estimate for permeability can be derived from empirical relationships with other measurements such as porosity, NMR and logging. - **Water Saturation**: The fraction of the pore space occupied by water. This is typically calculated using data from measuring the resistivity of the rock (in laboratory and/or by logs). - **Net Reservoir Rock**: Thickness of rock with enough permeability to deliver fluids to a well bore. In the oil and gas industry, another quantity "Net Pay" is computed which is the thickness of rock that can deliver hydrocarbons to the well bore at a profitable rate. - **Reservoir Models**: are built upon their measured and derived properties to estimate the amount of hydrocarbon present in the reservoir, the rate at which that hydrocarbon can be produced to the Earth's surface through wellbores and the fluid flow in rocks. # Diagram of a rock 1. Framework 2. Matrix 3. Cement 4. Pores - **PORE** - **CEMENT** - **FRAMEWORK (QUARTZ)** - **FRAMEWORK (FELDSPAR)** - **MATRIX** # Rock volumetric model for shaly sand formation - **Sand:** 1 - Фe - Vsh - **Shale:** Vsh - **Shale Bnd Water** - **Effective Ф:** Фe - **Sand Irreducible Water** - **Key Equations:** - (1 – Фe - Vsh) + Vsh + Фe * Swe + Фe * (1-Swe) = 1 - Sandstone matrix volume + shale volume + water volume in sand + hydrocarbon volume in sand = total rock volume - Фe = ФТ – Vsh *Osh - **ФТ:** Total porosity. - **Sw:** Total water saturation. - **Фe:** Effective porosity (shale corrected). - **Swe:** Effective water saturation (shale corrected). - **Vsh:** Volumetric fraction of shale. - **Фsh:** Shale porosity. - **Bound water:** water in the pore space that does not flow. - **Irreducible water, Swi:** the lowest water saturation that can be achieved in by displacing the water by oil or gas # Schematic of a pore system relating mineralogy, water content, and porosity assessment. - **Quartz** - **Clay Layers** - **Clay Surfaces & Interlayers** - **Small Pores** - **Large Pores** - **Isolated Pores** - **Structural (OH) Water** - **Capillary Water** - **Hydration or Bound Water** - **Hydrocarbon Pore Volume** - **"Irreducible or Immobile Water** - **Matrix** - **VShale** - **Total Porosity Neutron Log** - **Total Porosity Density Log** - **Absolute of Total Porosity** - **Oven Dried Core Analysis Porosity** - **Humidity Dried Core Analysis Porosity** # ROCK volumetric model for shaly sand formation - **ENV CALC MODEL** - **Sand:** 1 - Φe - Vsh - **Shale:** Vsh - **Shale Bnd Water** - **Effective Ф:** Фe - **Key Equations:** - (1-Φe-Vsh) + Vsh + De*Swe + Фе*(1-Swe) = 1 - Sandstone matrix volume + shale volume + water volume in sand + hydrocarbon volume in sand = total rock volume - Фе = ФТ - Vsh *Osh - **Definitions:** - **ФТ:** Total porosity (PHIT), which includes the pore space in sand and shale. - **Фe:** Effective (shale corrected) porosity which includes only the pore space in sand. The pore space in shale which is filled with bounded water is excluded. - **Sw:** Total water saturation, the fraction of the pore space occupied by water. - **Swe:** Effective (shale corrected) water saturation. The volumetric fraction of De which is occupied by water. - **Vsh:** Volumetric fraction of shale. This includes medium to very fine silt plus clay and the shale bound water. - **Фsh:** Shale porosity. Volumetric fraction of pore space in shale. These pore space is filled with bounded water by definition.