Sedimentologic Controls on Reservoir Quality - Essay Example

SENTIMENTOLOGIC CONTROLS ON RESERAVOIR QUALITY Student’s Name Subject Professor University/Institution Location Date Sedimentologic Controls on Reservoir Quality: An explanation of the different factors that influence reservoir quality in sedimentary rocks Introduction Many of the big grounds in the world produce hydrocarbons from carbonate reservoirs. Carbonate rocks have their own distinguishing and singular features in the fact that they are primarily “intra-basinal” by derivation, they are vulnerable to adaptation through post depositional means and that they are primarily depended on macrobiotic actions for their elements. The above three factors are very critical when it comes to differentiating the formation of sedimentary rocks which include carbonate rocks, shale and sandstone. Carbonate rocks specifically contain about 50% of the entire world’s Hydrocaron preserves. Living things play a key role in the determination of the quality of reservoir. Other developments such as lithification, compaction as well as other events that are related to diagenetic occurrences also determine or cause dissimilarities in reservoir quality and especially in carbonates (Ali et al 2010). Many carbonate sediments are especially very susceptible to changes in the environment and the sedimentation of carbonates is specifically one that can be hampered in a very easy way. Changes in temperature affect organic actions and lead to changes in the production of sediments. Therefore, the production of carbonate is extremely depended on intensity. When it comes to organic productivity, proficiency is always high when the conditions needed for carbonate sedimentation is high (Ali et al 2010). The opposite is true. This paper is aimed at establishing the different factors that affect the quality of sedimentary rocks. Discussion From the instant sediments are set down they are exposed to many chemical, physical and biological factors or forces which determine the kind of rocks they are going to develop into. The combination of bioturbation, compaction, chemical and burial that take place in between rocks, fluid and organic matter which are collectively known as diagenesis eventually lead to the feasibility of a reservoir (McKinley et al 2003). In the early days, the search for oil or gas reservoir was depended on the behavior of the tectonics in a particular region. Today, the search for the quality of a reservoir is one that is highly depended on diagenesis. Diagenesis generally refers to all natural changes that occur in sediments at the moment of deposition, continuing throughout compaction, and even during lithification and past these three, up to the point where metamorphism starts (Solano et al 2008). The only differentiating factor between the occurrence points of diagenesis and metamorphism cannot be established in a clear manner in terms of pressure force or heat, and there is not a clear difference between diagenesis and weathering. Diagenesis, which is the main factor upon which the quality of reservoir is almost entirely based, can be described as a process whose nebulous domain lies in between the not so well established borders of weathering and on its shallow end and low-grade metamorphism on its deep end. These post-authentication changes take place in conditions that are quite low in terms of pressure and temperature as well, which are also commonly known as the near surface conditions when it comes to the Earth’s lithosphere. Diagenesis encompasses every process that is capable of translating raw sediment into sedimentary rocks (Worden & Burley 2003). The process is usually a continually active one and it usually involves a reaction between the groupings of sandstone sedimentary in order to achieve symmetry in surroundings where pressure, chemistry and heat are not stabilized. These reactions are capable of leading to an improvement, modification or even the destruction of absorbency or sponginess. Before diagenesis, the control of absorbency and sponginess factors is usually a factor that is controlled by the composition of the sediment as well as any conditions that existed during deposition. It is worth noting that before a sedimentary element gets deposited, it goes through the changes that take place between its origin (whether erosion or a biological process) and its final deposition which are very crucial in determining the quality of reservoir (Worden et al 2006). It is also worth noting that diagenesis starts immediately after the sedimentary element settles down and that the character and swiftness of the period after depositional alterations are factors that are generally depended on the intermediary through which the deposition occurs as well as the kind of sediment that is being set down. Once the sediment is set down, it turns into a crossing point for the transportation of as well as any material that had been deposited before therefore, it becomes a factor through which the two conspicuously distinct physicochemical dominions (Needham et al 2005). At the point of its new depositing the sediment is usually deposited with various minerals in its composition which might or might not have a chemical stability with the neighboring surroundings as well as with the alterations in “interstitial composition of water” heat and pressure which in turn may result in changes in its chemic al and mineral modules. At the same level, or just below the new sediment layer, a local modification of the sediment may take place triggered by organisms that lair, swallow or footpath through it or in other words, organisms that sort out the whole sediment. This action sometimes subjects the sediment to bacterial changes and as the process of deposition continues, the shielding of the sedimentary process gets obscured low the depositional crossing point leading to a development of consecutively subterranean layers (Zviagina et al 2004). It is at this point that it comes across recurrently mounting pressures and heat that comes together with changes in chemical and biological circumstances. The new chemical and biological circumstances are the ones that encourage supplementary combinations and reinforcement of any wobbly sediment and in the end lead to the formation of lithified rock. Therefore the two main factors that determine the quality of reservoir are dependent on two factors which are the main factors of diagenesis namely: sedimentary and environmental factors. Sedimentary factors include the size of particle, the fluid content of the sediment, biologic al content and mineral content. Environmental factors include chemical, pressure and heat circumstances (Ali et al 2010). The process involves the following factors to which the particles are subjected: Compaction –This is a process through which the particles are kept in motion leading to a bombardment or contact with their neighboring particles through pressure. Cementation – This is a process through which particles get coated with impetuous substances Recrystallization - This is a process through which particles change in terms of shape and size without necessitating a change in their composition Replacement -This is the process through which particles change in terms of composition without necessarily changing in terms of shape and size Differential solution- This is the process through which some of the particles get dissolved either wholly or in part while other remain intact Authigenesis - This is a process through which chemical changes lead to changes in form, shape and composition Any other changes can lead to great changes when it comes to absorbency and sponginess and this greatly influences the dimensions and current rates in a reservoir. These special effects are therefore some of the most important factors that interest experts in petroleum especially geologists and engineers in their accomplishments when it comes to making maximum use of the processes that influence production and in achieving maximum productivity (Sachsenhofer 2001). Engineers that deal with productivity in the production of oil are required to deal with comparable circumstances in order to be in a position to offset the impacts of incompatibility of fluids, the activation of clay particles and reservoir condensation. The next part in this paper will look at diagenesis and the effects that it has on conventional reservoirs with its main focus being on the basic changes of absorbency and sponginess in carbonate and siliciclastic rocks. Initial stages The initial stages involve the control of absorbency and sponginess by sedimentary circumstances during the process of deposition but the conditions often get interferences from diagenesis. The surroundings of deposition are the ones that set out the conditions that lead to diagenetic processes that follow afterwards. The depositional surroundings for siliciclastic sediments which are the basis for the formation of sandstones differ in various ways from those of carbonates when it comes to how they act in response to their surroundings (Wagreich & Schmid 2002). Siliciclastics basically occur as a result of the erosion at the parent source, and their transportation takes place through water as a medium which could be sea or fresh water. It also takes place through other fluid mediums such as wind and ice. The deposition of sand is usually a factor that is controlled by the supply of sediments, but the supply of rough grains is usually determined by the force of the transportation medium (Needham et al 2005). When it comes to the transportation of materials by means of water, the force is usually depended on the function levels of the sea and therefore, it goes without saying that low sea levels or low levels of stand conditions, leads to the transportation of sediments past the continental shelf and these are usually deposited in the basinal marine surroundings or areas. On the other hand, when sea levels are high, or during periods of high stand in the sea, the retention of many clastics of rough grains occur and are retained in the fluvial structures and sometimes they could be deposited on the beach as opposed to being deposited in deep marine surroundings. The low leveled surroundings are the ones that lead to the formation and deposition of many course-grained Siliciclastics in petroleum basins that are found under water. By comparison, the deposition of carbonates is for the most part restricted to biological conditions in the sea which are in most cases restricted to a variety of conditions such as nutrient factors, heat, salinity and a contracted assortment of illumination as well as turbidity (De la Fuente et al 2000). These factors are the ones that tend to put a ceiling on most carbonates depositions and mainly restrict them to areas where the marine settings are superficial and steamy. Due to the fact that the deposition of carbonates is highly affected by deluge of superficial sea podiums, many of the carbonate deposits occur as a result of high stand sea levels and are abridged by low sea level conditions. These differences between the formation processes of siliciclastic and carbonate rocks in the process of sedimentation are some of the causes of reservoir quality. Sand that is deposited in times of high stands in sea levels is capable of being eroded and carried downstream in times of low stand levels in the sea (De la Fuente et al 2000). In comparison to Siliciclastics depositions carbonates that are deposited in times of high standing in the levels of the sea are capable of being exposed in times of low stands and this leaves the open to the elements meteoric fluids which expose them to chemical related changes, rework factors and absorbency changes such as karsting. There are many established projections and their diagenetic surroundings that have been premeditated and which have been portrayed comprehensively and this has led to the recognition by geologists of the resemblance an assortment of surroundings (Worden & Burley 2003). There are various structures therefore that gave been established with regard to the classification of diagenetic systems. Conclusion This paper has looked at some of the factors that influence the quality of reservoir and has found that getting to understand diagenetic processes is one of the ways through which the improvement of the ways of determining the quality of sandstone reservoir can be done. This paper has also found that diagenetics plays a key role in the determination of reservoir quality, and that one of the basic factors that influence the formation of new models of manifold reservoirs is highly depended on the levels if absorbency in a variety of conditions. Additionally, all the various conditions reservoir absorbency levels affect the depositional stages, th eerily stages of diagenetics and the late stages of diagenetics and in turn they also highly affect reservoir quality. The formation of grains and their assortment in terms of composition shape and size, early diagenetics, and burial conditions are highly affected by levels of absorbency and this in turn highly affects reservoir quality. List of References Ali, S, Clark, W, Moore, W, & Dribus, J, 2010, Diagenetics and Reservoir Quality, Oilfield Review Summer Vol 2 Issue 2 , 14-27. De la Fuente, S, Cuadros, J, & Linares, J, 2000, Quantification of mixed-layer illitesmectite in glass matrices by Fourier-transform infrared spectroscopy, Clay Clay Mineral Vol 48 , 299-303. McKinley, J, Worden, R, Ruffell, A, Worden, R, & Morad, S, 2003, Smectite in sandstones: a review of the controls on occurrence and behaviour during diagenesis, Clay Mineral Cement in Sandstones. International Association of Sedimentologists, Special Publication, vol. 34 , 109-128. Needham, S, Worden, R, & McIlroy, D, 2005, Experimental production of clay rims by macrobiotic sediment ingestion and excretion processes, Journal of Sedimentary Research 75 , 1028–1037. Sachsenhofer, R, 2001, Syn- and post-collisional heat flow in the Cenozoic Eastern Alps, International Journal of Earth Sciences Vol 90 , 579-592. Solano, W, Thomas, A, Lander, R, Reed, Ret al, 2008, Quartz cementation along cataclastic fault zones: Quantitative modeling and exploration implications for hydrocarbon recovery (abs.): AAPG Annual Convention Abstracts, New York: AAPG. Wagreich, M, & Schmid, H, 2002, Backstripping dip-slip fault histories: apparent slip rates for the Miocene of the Vienna Basin, Terra Nova Vol 14 , 163-168. Worden, R, & Burley, S, 2003, Sandstone diagenesis:The evolution of sand to stone, In S, Burley, & R, Worden, Sandstone Diagenesis: Recent and Ancient (pp. 3-44). Massachsetts: Wiley-Blackwell Publishing. Worden, R, Needham, S, & Cuadros, J, 2006, The worm gut: A natural clay factory and possible cause of diagenetic grain coats in sandstones, Journal of Geochemical Vol 89 , 428-431. Zviagina, B, McCarty, D, Srodon, J, & Drits, V, 2004, Interpretation of infrared spectra of dioctahedral smectites in the region of the OH-stretching vibrations, Clays and Clay Minerals Vol 52 , 399-410. Read More