RESERVOIR PETROPHYSICS PETE 311

PETROPHYSICS Petrophysics is the study of rock properties and rock interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions). Modified from Tiab and Donaldson, 1996, p. 1

PETE 311 RESERVOIR PETROPHYSICS COURSE DESCRIPTION Systematic theoretical and laboratory study of physical properties of petroleum reservoir rocks Lithology Porosity Compressibility Permeability Fluid saturations Capillary characteristics Rock stress Fluid-rock interaction

RESERVOIR PETROPHYSICS Course Objectives By the last day of class, the student should be able to: Define porosity; discuss the factors which effect porosity and describe the methods of determining values of porosity; Define the coefficient of isothermal compressibility of reservoir rock and describe methods for determining values of formation compressibility; Reproduce the Darcy equation in differential form, explain its meaning, integrate the equation for typical reservoir systems, discuss and calculate the effect of fractures and channels, and describe methods for determining values of absolute permeability;  

RESERVOIR PETROPHYSICS Course Objectives Explain boundary tension and wettability and their effect on capillary pressure, describe methods of determining values of capillary pressure, and convert laboratory capillary pressure values to reservoir conditions; Describe methods of determining fluid saturations in reservoir rock and show relationship between fluid saturation and capillary pressure; Define resistivity, electrical formation resistivity factor, resistivity index, saturation exponent, and cementation factor and show their relationship and uses; discuss laboratory measurement of electrical properties of reservoir rocks; and demonstrate the calculations necessary in analyzing laboratory measurements;

RESERVOIR PETROPHYSICS Course Objectives Define effective permeability, relative permeability, permeability ratio; reproduce typical relative permeability curves and show effect of saturation history on relative permeability; illustrate the measurement of relative permeability; and demonstrate some uses of relative permeability data. Describe three-phase flow in reservoir rock and explain methods of displaying three-phase effective permeabilities. Demonstrate the techniques of averaging porosity, permeability, and reservoir pressure data. Demonstrate capability to perform calculations relating to all concepts above. (These are minimum skills to be achieved/demonstrated)

PETROPHYSICS Why do we study petrophysics?

Cross Section Of A Petroleum System (Foreland Basin Example) Overburden Rock Seal Rock Reservoir Rock Source Rock Underburden Rock Basement Rock Top Oil Window Top Gas Window Geographic Extent of Petroleum System Petroleum Reservoir (O) Fold-and-Thrust Belt (arrows indicate relative fault motion) Essential Elements of Petroleum System (modified from Magoon and Dow, 1994) O Sedimentary Basin Fill Stratigraphic Extent of Pod of Active Extent of Prospect/Field Extent of Play

PETROLEUM SYSTEM From Schlumberger Oilfield Glossary Timing of formation of the major elements of a petroleum system, Maracaibo basin, Venezuela.

DEFINITIONS - SEDIMENTARY ROCK Clastic Sedimentary Rocks (Such as Shale, Siltstone, and Sandstone) Consist of Broken Fragments of Pre-Existing Rock (cf. Detrital) Carbonate Sedimentary Rocks (and Evaporites) May Form by Chemical Precipitation or Organic Activity Rock Formed from the Weathered Products of Pre-Existing Rocks and Transported by Water, Wind, and Glaciers

CLASTIC AND CARBONATE ROCKS Clastic Rocks Consist Primarily of Silicate Minerals Are Classified on the Basis of: - Grain Size - Mineral Composition Carbonate Rocks Consist Primarily of Carbonate Minerals (i.e. Minerals With a CO Anion Group) - Predominately Calcite (Limestone) - Predominately Dolomite (Dolomite or Dolostone) 3 -2 Classified by Grain Size and Texture

SEDIMENTARY ROCK TYPES Relative Abundances Mudstone (Siltstone and shale; clastic) ~75% Sandstone and conglomerate (clastic) ~11% Limestone and Dolomite (carbonate) ~14% This slide shows the relative abundance of the major sedimentary rock types. These rocks comprise approximately 99% of all sedimentary rocks, including hydrocarbon source rocks and traps. Sedimentary rock can be divided into two major classes. CLASTICS - Sandstone, conglomerate, siltstone, and shale - Comprised mainly of silicate minerals - Classified on the basis of grain size and mineral composition CARBONATES - limestone and dolomite - consist mainly of the carbonate minerals calcite (limestone) or dolomite (dolostone)

Grain-Size Classification for Clastic Sediments Name Millimeters Micrometers Boulder Cobble Pebble Granule Very Coarse Sand Coarse Sand Medium Sand Fine Sand Very Fine Sand Coarse Silt Medium Silt Fine Silt Very Fine Silt Clay 4,096 256 64 4 2 1 0.5 0.25 0.125 0.062 0.031 0.016 0.008 0.004 500 250 125 62 31 16 8 (modified from Blatt, 1982) Commonly, phi-sizes are used for sediment analysis

DUNHAM’S CLASSIFICATION - CARBONATES Carbonate rocks can be classified according to the texture and grain size. From Schlumberger Oilfield Glossary

GENERATION, MIGRATION, AND TRAPPING OF HYDROCARBONS Seal Seal Fault (impermeable) Oil/water contact (OWC) Hydrocarbon accumulation in the reservoir rock Migration route Seal Several conditions must be satisfied for an economic hydrocarbon accumulation to exist. First, there must be sedimentary rocks that have good source rock characteristics and have reached thermal maturity. Second, the hydrocarbons must have migrated from the source rock to a potential reservoir, which must have adequate porosity and permeability. Finally, there must be a trap to arrest the hydrocarbon migration and hold sufficient quantities to make the prospect economic. Hydrocarbon traps usually consist of an impervious layer (seal), such as shale, above the reservoir and barrier such as a fault or facies pinch that terminates the reservoir. Reservoir rock Top of maturity Source rock

DESCRIBING A RESERVOIR Structural Characterization Since petroleum reservoirs are generally located many thousands of feet below the surface, it is necessary to use sophisticated tools, such as wireline logs, to gather important information about the reservoirs. This information is then interpreted by highly trained industry professionals, using various mathematical and empirical models, to determine fundamental reservoir properties, such as porosity and permeability.

STRUCTURAL HYDROCARBON TRAP This structural trap is formed by an anticline and a normal fault. From Schlumberger Oilfield Glossary

DOMAL TRAP Are hydrocarbons in this field oil or gas? What is the volume of hydrocarbons In this trap? What are the reserves? Closure. In map view (top), closure is the area within the deepest structural contour that forms a trapping geometry, in this case 1300 ft [390 m]. In cross section A-A', closure is the vertical distance from the top of the structure to the lowest closing contour, in this case about 350 ft [105 m]. The point beyond which hydrocarbons could leak from or migrate beyond the trap is the spill point. From Schlumberger Oilfield Glossary

WATER DRIVE What is the Drive Mechanism? A reservoir-drive mechanism whereby the oil is driven through the reservoir by an active aquifer. As the reservoir depletes, the water moving in from the aquifer below displaces the oil until the aquifer energy is expended or the well eventually produces too much water to be viable. From Schlumberger Oilfield Glossary

GAS EXPANSION DRIVE What is the Drive Mechanism? A gas-drive system utilizes the energy of the reservoir gas, identifiable as either as free or solution gas, to produce reservoir liquids. Are there other drive mechanisms? From Schlumberger Oilfield Glossary

TYPES OF HYDROCARBONS Composition Molecular structure Physical properties

PHYSICAL PROPERTIES OF HYDROCARBONS Color Refractive Index Odor Density (Specific Gravity) Boiling Point Freezing Point Flash Point Viscosity

FLUID DENSITY ˚ API = 141.5 - 131.5 ٧ ˚ API = API gravity  = specific gravity - 131.5 ˚ API = API gravity What are the standard reporting conditions? 

FLUID VISCOSITY Importance Units – centipoises (μ, cp) Strongly temperature dependent Standard reporting conditions

DRILLING RIGS Drillship Semisubmersible Jackup Submersible Land Rig From Schlumberger Oilfield Glossary

ROTARY DRILL BIT, WORN From Schlumberger Oilfield Glossary

Next Class: RESERVOIR POROSITY Definition: Porosity is the fraction of a rock that is occupied by voids (pores). Origins and descriptions Factors that effect porosity Methods of determination