Paper Example: Impact of Diagenesis on Reservoir Quality Evolution of Pre-Khuff Equivalent Sandstones

Introduction

Permian siliciclastic is a carbonate mixed succession from the West Khuff -1 well, southwest Karbala city, central Iraq. In Iraq, limestone and shale of the Upper Permian Chia Zairi Formation are equivalent to the Khuff Formation of the Gulf region and the Dalan Formation of southwest Iran. The formation, which reaches up to 810 m thickness in the area, has been drilled in only a handful of wells. Atshan-1 intersected 295 m of oolitic and argillaceous limestone, silty dolomite, shale, and sandstone. The formation was tight at this location (Abd Alwahab, and Al-Hamdani, 2013). The Chia Zairi Formation also penetrated at Jabal Kand-1 and Kifl West-1. The formation may be a prospect for gas, with the intraformational Satina Evaporite Member providing the seal.

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This research will highlight the cause of porosity reduction in sandstone reservoirs of the Chai Zairi formation during diagenesis processes that are deeply buried.

Sandstone Diagenesis

The main intention of the diagenetic processes is that they tend to alter some characteristics of the sandstones. These include the types of pores as well as their geometry. It alters porosity and permeability. The sedimentation compositions of the environments dictate the early patterns of Iraq (Mostafa et al., 2018; TamarAgha, 2009). At some point, the diagenetic patterns overlap too and cross the boundaries of the facies. Such effects come from the migrations experienced by the fluids movement patterns. The quality of sandstones heavily depends on their diagenetic histories (Tarling, 1999). All result in sedimentation, fluid migration, and other environmental depositions Iraq (Mostafa et al., 2018; TamarAgha, 2009). Three processes are describing the diagenetic processes. Amongst the methods are dissolution, which is also leaching, compaction, and cementation. Iraq is one of the zones prone to the diagenetic of Sandstones.

Causes of DiagenesisDiagenesis refers to the process that describes chemical and physical changes that occur in sediments as a result of increased pressure and temperature as they are buried under the surface of the Earth (Mohammed, 2019. In this regard, it is evident that temperature and pressure are the fundamental factors responsible for a diagenesis process. At its early stage the changing of sediments into sedimentary rocks (a process referred to as lithification) if faced with a reduced porosity, even though its components remain unchanged (Abd Alwahab, and Al-Hamdani, 2013).

Similarly, pressure also affects the diagenesis of sandstones. Ideally, more pressure increases compaction. Porosity decreases as the depth of burial increases (Tobia et al., 2019; Mohammed, 2019). While age also has effects on diagenesis. The porosity of sandstones diminishes with age. As time goes by, sandstones tend to lose their porosities. The processes of diagenesis include Cementation Compaction and Dissolution (Flugel, 2004).

Diagenesis fundamentally impacts the porosity and porousness of repositories and the arrangement of stores. After the affidavit, diagenesis in carbonates rapidly happens around the world's surface or gradually happens underground. The variables, which impact carbonate diagenesis, incorporate depositional condition, surface of dregs, mineral structure, entombment, temperature, weight, and pore-liquid properties (Mohammed, 2019). Under various diagenetic situations, the components noted already have various effects, hence indicating alternate diagenesis. The impact of diagenesis on store properties could be arranged into valuable and damaging.

Compaction and weight arrangement in Mesoproterozoic and Neoproterozoic developments could be characterized into three phases, in grouping, which are mechanical compaction, early weight disintegration, and later weight disintegration (Tobia et al., 2019). Mechanical compaction and early weight disintegration as a rule happen at shallow internments, appeared as a critical reduction of pores, unrelated contact transformed into concave-arched contact, even mutilated (Mostafa et al., 2018). Later weight disintegration happens during late diagenesis and the profound entombment time frame. The event of stylolite draws in insoluble issues, assembling around the stylolite. Grain mutilation and stylolite are the key highlights of weight disintegration and compaction

Deeply Buried Sandstone

Deeply buried Quartz usually undergo several chemical reactions and form carbonate cement to some extents. They have severe effects on the permeability of the sandstones since they result in calcite cement for the case of marine sandstones. Sedimentary processes control the volumes of the production of calcite cement (Tarling, 1999). Besides, it constitutes of the biogenetic carbonate cells. The result comprises of distribution of carbonated materials within the sediments. Shallow geological settings usually create deposits on the surface, thus causing continuous cementation of the affected zones. Uniform shell distributions for scattered carbonated concretes. Deep buried quarts, on the other hand, experience sedimentation through the compaction process. The compaction results from the pressure exerted from the elements above the minerals at the bottom. Similarly, the ages of the reservoirs also increase with time. Subsequently, porosity and permeability features will diminish. It, therefore, creates more room for compaction (Tarling, 1999). The result is a cemented sedimentary.

Diagenesis is a unique procedure including physical and concoction changes occurring in a residue or in a sedimentary stone after statement, during internment history and an improvement of a sedimentary bowl. Eo-and mesogenetic changes assume a significant job in postdepositional adjustment of supply parameters, for example, porosity and penetrability. Essential porosity might be diminished by mechanical compaction, concretes precipitation, mineral responses or weight arrangements, and additionally expanded (auxiliary porosity) during internment, because of grains and concrete disintegration, mineral responses or cracking. Penetrability is controlled for the most part by pore - throat size and its misfortune compares to the diminishing volume of essential porosity. Introduced work intends to research diagenetic changes inside profoundly covered tight Rotliegend sandstones from Polish Part of Southern Permian Basin and its effect on supply properties (Mostafa, Khadrah & Refaat, 2018). During advancement of sedimentary bowl, pore space of sandstones experience changes related todiagenetic stages. These procedures incorporate compaction, cementation, disintegration, substitution andrecrystalisation, and become increasingly more progressed with profundity. This connections changes primary porosity, prompting crumbling of supply properties (Mostafa, Khadrah & Refaat, 2018). The paper presents diagenetical changes occurred within profoundly covered tight Rotliegend sandstones from Polish piece of Southern Permian Basin and its impact on supply properties

Iraq Geological Setting

The geological setting of Iraq comprises of the lithostratigraphic unit blocks. The lithostratigraphic have lithologies within and are mappable. A new formation takes a geographical name, for instance, Tanjero Formation. The process deposits formations like Maastrichtian during the occurrence of tectonic activities.

Present Iraq Geological Structure

Iraq comprises of a wider anticlinorium. Anticlinorium consists of folds of the anticline in the NorthWest-SouthEast direction. The region around the Norther Eastern suffers much of the synclines and thrushes toward the Southwest direction of Iraq. Iraq's geology several tectonic divisions. The divisions occur as a result of the collisions from the Arabian and Iranian geological plates. The divisions comprise of the unfolded zone, which is Mesopotamia, the Desert found in the West, are known to be of high and low folds. Others are as a result of thrusts originating from the southwest creating the thrust zones and the imbricated areas. The figure shown represents the geological settings of Iraq. The Iraq geology experiences a time expansion of its stratigraphy columns. The columns indicate older to younger lithography as well as a bottom-top approach.

Permian succession in the Mesopotamian Basin represented by the permo-carboniferous Ga'raa and Middle-Late Permian Chia Zairi formations. According to Mostafa, Khadrah & Refaat (2018), the formations comprises of sandstone. The Chia Zairi Formation is composed of intercalation of shale, dolostone, sandstone, limestone, interbedded sandstone and dolostone and end with thick dolostone beds, deposited in homoclinic ramp, display shale - mudstone outer ramp, dolomitic skeletal ( fusulinids, bryozoans, and algal ) middle ramp and mudstone to wackestone, sandstone and locally evaporate of the inner slope facies associations ( Al-Hadidy, 2007 ). Pre-Chia Zairi unconformity separates between the syn-rift (AP5) and post-rift (AP6) phases of Neo-Tethys passive margin (Mostafa, Khadrah & Refaat, 2018; TamarAgha, 2009).

Types of Cementation in Sandstone Reservoirs

Quartz Cement: Quartz cement is one of the most abundant cement contained in sandstones. Factors that control the amounts of the cement in the sandstone include composition, the residence time in silica mobility window, fluid composition, flow volume, and the pathways (McBride, 2020). The cementation process in sandstones is controlled significantly by the sedimentary basin in which the sand deposits. Arkoses, which are sandstones in the rifts and litharenites, which are margin Collison basins, have little amounts of Quartz elements (McBride, 1989). The sandstones with a large concentration of Quartz include Quartzarenites, foreland and passive margin basins, and Quartzose sandstone of intracratonic. Clay and other minerals prevent the cementation by Quartz, while highly permeable sands sequestrate high amounts of Quartz cementation (McBride, 1989). In basins such as the Gulf Coast and North Sea basins, Quartz cement is precipitated by cooling, ascending formation water of depths of several kilometers where the temperature...