Reservoir rocks and their Characters The diagram in the slide represents the ROCK CYCLE—a scheme that represents the processes of continuous changes that connect the three major groups of rocks: SEDIMENTARY IGNEOUS METAMORPHIC It also shows two other important parts of the “Rock Cycle” – SEDIMENTS and molten LAVA and MAGMA Department of Petroleum Technology , University of Karachi

Here is another version of the Rock Cycle Reservoir rocks and their Characters Here is another version of the Rock Cycle Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Wentworth Scale Size and name of the sediments Reservoir rocks and their Characters Wentworth Scale Size and name of the sediments Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Sphericity Roundness Sorting Department of Petroleum Technology , University of Karachi

Sphericity verses Roundness Chart Reservoir rocks and their Characters Sphericity verses Roundness Chart Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Sediments maturity Department of Petroleum Technology , University of Karachi

Graded Bedding and sediments settling Reservoir rocks and their Characters Graded Bedding and sediments settling Department of Petroleum Technology , University of Karachi

Sedimentary Rocks Reservoir rocks and their Characters Features of Sedimentary Rocks Bedding Mud Cracks Ripple Marks Cross Bedding Graded Bedding Fossils Composition of Sedimentary Rocks Clay Quartz Calcite Other Minerals….. Formation of Sedimentary Rocks Detrital (Clastic) Chemical Biochemical B. Process that leads to Lithificat 1) Weathering and Erosion 2) Transportation 3) Deposition 4) Lithification *cementation and compaction Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters How You Classify It Is How You Think About It Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Requirements of A Good Classification System Department of Petroleum Technology , University of Karachi

Nature is extremely complex: Reservoir rocks and their Characters Practical Problems With Rock Classification Nature is extremely complex: Rocks form in diverse and complex ways resulting in a very diverse and complex variety or rocks. The classification for clastics does not work for carbonates. Carbonates have their own classification. Rocks and the Earth evolve, making it a moving target. Department of Petroleum Technology , University of Karachi

Sandstone Shale Limestone Reservoir rocks and their Characters A Weathering Classification For Sedimentary Rocks Sandstone Based on the Simple Ideal Model Shale Limestone Department of Petroleum Technology , University of Karachi

Sedimentary Rock Classification Reservoir rocks and their Characters Sedimentary Rock Classification Clastics Carbonates Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Classification of Clastic Sedimentary Rocks Gravel, > 2mm Conglomerate Breccia Sand Dunes Sand, 1/16 – 2 mm Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Clastic Sedimentary Particles Sample of fine to medium grained quartz sand forming as beach sediments.  Note that these grains  have slightly rounded edges and are all about the same size. Large grains are about 0.3 mm  in largest diameter. Department of Petroleum Technology , University of Karachi

Cementation Reservoir rocks and their Characters Clastic particles ranging from silt-size to boulder-size may be deposited on the sea floor. As they are buried, ion-laden sea water may deposit minerals in the pore spaces between the grains, thus effectively cementing them together.  By this process the sediments become rocks such as siltstone, sandstone and conglomerate. Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Compaction Clastic particles smaller than silt, such as mud are deposited on the sea floor.  As they are buried, the weight of overlying sediments presses downward on the mud particles and compacts them, resulting in the formation of rocks such as claystone, mudstone or shale. Department of Petroleum Technology , University of Karachi

Non-Clastic Sedimentary Particles Reservoir rocks and their Characters Non-Clastic Sedimentary Particles Non-ClasticSedimentary Particles I Broken fragments of calcite,   mostly from algae.  Shallow  sub tidal sediments from the Yucatan, Holocene.   Largest fragments are about  1 mm in length. Non-Clastic Sedimentary Particles II Broken shell fragments of calcite frombivalve molluscs.  These shell fragments accumulated on a beach and are cemented together.  This rock  is almost 100 percent shell fragments, and is therefore called a coquina. Largest fragments about 2 cm in length. Department of Petroleum Technology , University of Karachi

Review Of Sedimentary Processes Reservoir rocks and their Characters Review Of  Sedimentary Processes This chart is a review of the various steps  involved in the formation of sedimentary rocks that have been discussed above.  Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters A reservoir rock A reservoir rock is one in which pore space exists for the accumulation of hydrocarbon, and the pore spaces are interconnected (permeability) so the hydrocarbon can move both into and out of the pore spaces. Understanding of diagenetic processes and predicting diagenetic histories within three dimensional reservoir facies is essential for optimal reservoir development strategies. Diagenesis of the reservoir rock, such as cement formation, can reduce the pore space volume and reduce the permeability so less hydrocarbon can flow through the rock. Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters During specific stages of drilling, a set of logging tools is lowered into the hole to measure various rock and fluid properties. This information, calibrated by rock cuttings and drill fluid analysis, helps identify the type of rocks and fluids encountered. Interpretation of the depositional environment of the rocks helps in predicting the distribution and quality of a reservoir or seal, and the porosity and permeability of the reservoir rock. Measurements of fluids provides information on the presence or absence of hydrocarbons. Department of Petroleum Technology , University of Karachi

Porosity and Permeability Reservoir rocks and their Characters Porosity and Permeability Porosity—amount of pore space in a material. Materials made of rounded particles have a lot of pore space. Materials like clay that are flat and angular have less pore space. The amount of pore space is greater if particles are the same size rather than if mixed sizes are present. Permeability—the ability of a material to transmit water. Well-sorted (same size and shape) materials are very permeable (GRAVEL and SAND). Impermeable—water does not pass through this material—clay packs are very flat, so even though there is pore space, the pores are not connected Department of Petroleum Technology , University of Karachi

Total Porosity Reservoir rocks and their Characters Definitions where Vv is the volume of voids (pores), VT is the total (bulk) volume, and VS is the volume of the solids. Note that porosity is a dimensionless quantity. Void Ratio (commonly used in engineering) (also dimensionless) Department of Petroleum Technology , University of Karachi

SANDSTONE HETEROGENEITY Reservoir rocks and their Characters SANDSTONE HETEROGENEITY Heterogeneity (essentially nonuniformity) in sandstone reservoirs is controlled by the following factors; The geometry of sandstone bodies (lens-shaped, tabular, etc.), Faulting and fracturing of the reservoir intervals; this influences oil trapping and retention, as well as influencing fluid flow at field and well scales, Mudstone and other low-permeability baffles that direct flow of fluids through the rocks, Vertical and lateral distribution of facies, and interbedding characteristics of the sandstone, mudstone, and other rock types, Sedimentary structures (cross-bedding, burrowing...), Laminae, (such as thin mudstone layers and calcite-cemented intervals), and Influence of diagenetic history on porosity/permeability preservation, destruction, and enhancement. Department of Petroleum Technology , University of Karachi

Porosity and Permeability Reservoir rocks and their Characters Porosity and Permeability Department of Petroleum Technology , University of Karachi

Porosity and Permeability Reservoir rocks and their Characters Porosity and Permeability Two separate characteristics of rocks control how effective they are as aquifers: Porosity is a measure of how much of a rock is open space. This space can be between grains or within cracks or cavities of the rock. Permeability is a measure of the ease with which a fluid (water in this case) can move through a porous rock. Microscopic structure of shale, sandstone, and limestone with water in pore spaces. Note differences in scale among views of each rock type Department of Petroleum Technology , University of Karachi

Porosity and Permeability in Sedimentary Rocks Reservoir rocks and their Characters Porosity and Permeability in Sedimentary Rocks Most oil and gas is produced from sandstones.  Both porosity and permeability are needed for production.  Porosity creates the spaces to hold the oil or gas.  Permeability allows the oil and gas to flow out of the rock. Porosity is normally expressed as a percentage of the total rock which is taken up by pore space.  For example, a sandstone may have 8% porosity.  8% is about the minimum porosity that is required to make a decent oil well.   Permeability in petroleum-producing rocks is usually expressed in units called millidarcys (one millidarcy is 1/1000 of darcy). A petroleum reservoir may have permeability in the range of a few millidarcys up to several darcys.  Most oil and gas reservoirs produce from rocks that have 10-100 millidarcys. Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters POROSITY The percentage of pore volume or void space, or that volume within rock that can contain fluids. Porosity can be a relic of deposition (primary porosity, such as space between grains that were not compacted together completely) or can develop through alteration of the rock (secondary porosity, such as when feldspar grains or fossils are preferentially dissolved from sandstones). Effective porosity is the interconnected pore volume in a rock that contributes to fluid flow in a reservoir. It excludes isolated pores. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Thus, effective porosity is typically less than total porosity. Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of Karachi

Reservoir rocks and their Characters Sedimentary rocks may be made of rock fragments—sediments—or by chemical reactions. The classification of sediments is shown below. Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Clastic rocks–made of cemented sediments—are classified by their grain sizes. Department of Petroleum Technology , University of karachi

Permeability and Porosity of Rock Structures Reservoir rocks and their Characters Permeability and Porosity of Rock Structures Petroleum deposits are called reservoirs. These are trapped layers of sandstone or limestone, or dolomite. Exploration and production companies are most interested in reservoirs that have good permeability and porosity. As we have seen, both oil and gas co-exist in their natural state with grains of sand, pebbles, rocks and boulders in a rock layer. Porosity is a measure of the spaces within the rock layer compared to the total volume of rock. Though both are porous, a sponge is much more porous than a brick. And though both can hold water in their pores, the sponge has a much higher capacity for holding liquids. Permeability is a measure of how well liquids and gases can move through the rock and thus is a function of how well the pores within the rock are connected to each other. In the formation below, porous areas are in blue. Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Generally, oil and gas are found in a geologic structure called a "trap" that prevents the oil and gas from escaping. Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Enhanced Oil Recovery Enhanced oil recovery once the natural flow of gas and oil ceases, the reservoir will have yielded only 10 to 25 percent of the total volume of the oil it contains. The rest is trapped in unconnected rock pockets or is thick enough to cling to the rock and refuses to migrate toward the well-bore. Department of Petroleum Technology , University of karachi

Reservoir rocks and their Characters Department of Petroleum Technology , University of karachi