CHAPTER 02 CHAPTER 02 RESERVOIR RESERVOIR INTRODUCTION INTRODUCTION CONDITION FOR AN ACCUMULATION OF CONDITION FOR AN ACCUMULATION OF OIL AND GAS OIL AND GAS ° A mature source rock ° A reservoir rock ° A migration route (betw. Source & Res.) ° An impermeable seal ° A trap RESERVOIR RESERVOIR ° A single continuous deposit of gas and/or oil in the pores of a reservoir rock. A reservoir has a single pressure system and don’t communicate with other reservoirs. ° The portion of the trap that contains petroleum, including the reservoir rock, pores, and fluids. ° A pond, lake or environment that is used store liquids. Exp: RESERVOIR Exp: RESERVOIR OF CUU LONG OF CUU LONG AND SOUTHERN AND SOUTHERN CONSON BASINS CONSON BASINS Figure 1 RESERVOIR (cont.) RESERVOIR (cont.) ° There are two fundamental physical properties that a good reservoir must have: + Porosity or sufficient void space contain significant petroleum. + Permeability, the ability of petroleum to flow into, or out of these voids. ° The only common rock type that have favorable combination of porosity and permeability to be reservoirs are sandstones and carbonates. POROSITY POROSITY ° Porosity is the percentage of volume of voids to the total volume of rock. It has the symbol : 0 ≤  ≤ 1 ° Effective porosity: the amount of internal space or voids that is interconnected, and so able to transmit fluids. ° Non-effective porosity: isolated pores and pores volume occupied by adsorbed water. Figure 2: Figure 2: The frequency of oil and gas reservoirs plotted against porosity The frequency of oil and gas reservoirs plotted against porosity . . Almost all Almost all reservoirs have reservoirs have porosities in a porosities in a range of five to range of five to thirty percent thirty percent with the majority with the majority falling between falling between ten and twenty ten and twenty percent. percent. POROSITY (cont.) POROSITY (cont.) ° There are three main types of porosity: + Interconnected porosity has multiple pore throat passages to connect neighboring pore. + Connected porosity has only one pore throat passages connecting with another pore space. + Isolated porosity has no connection between pore. ° Interconnected and connected pore contribute effective porosity because hydrocarbon can move out from them. Interconnected porosity Interconnected porosity Connected porosity [...]... passages (pore throats or capillaries) between pores It is measured in darcies or millidarcies Figure 4 k * ( P1  P 2 ) * A Q   * L Where: • Q: rate of flow K: Permeability ° (P1-P 2) : Pressure drop across ° A: Cross-section area of sample ° : Viscosity of fluid ° L: Length of the sample Due to flow rate depends on the Ratio of K to , so in term of commercial rates: Gas… ° PERMEABILITY (cont .) ° °... Vuggy (range, dimension)  Fracture (range, dimension)  Determine collection capacity PRIMARY FACTORS CONTROLLING POROSITY ° GRAIN SIZE ° THE SHAPES OF THE GRAIN ° GRAIN SORTING ° ROCK FABRIC ° EFFECTS OF COMPOSITION DURING OR AFTER DEPOSITION RANGE OF POROSITY VALUES QUALITATIVE EVALUATION OF RESERVOIRS  (percent) Qualitative evaluation 0–5 Negligible 5 – 10 poor 10 – 15 fair 15 – 20 good > 20 very... occurs within the sediment grains themselves  Second porosity  Fenestral  Intercrystalline  Solution (moldic and vuggy)  Fracture Primary Porosity • Primary porosity is divisible into two types: intergranular or interparticle porosity, which occurs between the grains of a sediment ( Figure 1 ) and intragranular or intraparticle porosity, Intergranular porosity intragranular porosity Secondary Porosity... intragranular porosity Secondary Porosity Secondary porosity is porosity formed within a reservoir after deposition The major types of secondary porosity are: • Fenestral; • Intercrystalline; • Solution (moldic and vuggy); • Fracture Fenestral porosity is developed where there is a gap in the rock framework larger than the normal grainsupported pore spaces Fenestral porosity is characteristic of lagoonal pelmicrites... process whereby a pre-existing calcium carbonate deposit is replaced by dolomite Figure 1: A sketch of a thin section of a crystalline dolomite Several types of secondary porosity can be caused by solution Fracture porosity • Fractured reservoirs can occur in any brittle rock that breaks by fracturing rather than by plastic deformation Thus, there are fractured reservoirs in shales, hard-cemented quartzitic... fluid ° L: Length of the sample Due to flow rate depends on the Ratio of K to , so in term of commercial rates: Gas… ° PERMEABILITY (cont .) ° ° ° Absolute permeability is a measure of the ease (permeability) in which a single fluid can flow through the pores of the rock when it is 100% saturated with that fluid Effective permeability refer to the presence of two fluids in a rock, and is the ability... another fluid when the two fluids are immiscible Relative permeability is ratio Absolute permeability/Effective permeability RANGE OF PERMEABILITY VALUES QUALITATIVE EVALUATION OF RESERVOIRS K values (mD) 1,0 – 15 15 – 50 50 – 100 100 – 1000 > 1000 Qualitative evaluation Reservoir Poor to fair Moderate Good Very good Excellent Grain Size • Porosity is independent of grain size Permeability, however, . BASINS Figure 1 RESERVOIR (cont .) RESERVOIR (cont .) ° There are two fundamental physical properties that a good reservoir must have: + Porosity or sufficient void space contain significant petroleum. +. between falling between ten and twenty ten and twenty percent. percent. POROSITY (cont .) POROSITY (cont .) ° There are three main types of porosity: + Interconnected porosity has multiple pore. interconnected, and so able to transmit fluids. ° Non-effective porosity: isolated pores and pores volume occupied by adsorbed water. Figure 2: Figure 2: The frequency of oil and gas reservoirs plotted