Integrated the Core Analysis Data, Image logs, and Conventional Logs to Understand the Reservoir Rock Type of the Mauddud Formation

Inner ramp carbonates with dolomitic limestone make up the Late Albian Mauddud reservoir in Arabian plate. The age of the Mauddud Formation is Albian–Early Cenomanian, and it overlies the Nahr-Umr Formation and the Ahmadi Formation. The depositional environments range from subtidal to lagoon and shoal environments. The main goal of this study is to integrate all the available information to recognize different rock types within Mauddud reservoir. Due to the limited core available in Mauddud reservoir, the rock types have been identified mainly based on the Full-bore formation micro imager tool. The formation micro imager readings were compared and calibrated by available core data and conventional well logs (Density Neutron). This study concludes that there are three rock types were recognized within Mauddud reservoir:

Gulf.In terms of regional dispersion and thickness, the Mauddud Formation is a significant geological formation in the Arabian basin.Moreover, since the 1940s, the formation has produced considerable amounts of oil in northwest Iraq and Bahrain, and it may include further oil in other potential locations.Henson reported the Mauddud Formation for the first time in an undocumented report from the Dukhan-1 well in Qatar in 1940 [8]."Limestone, light gray, grainy, mostly of rather moderate porosity excluding the bottom several feet, which are rather marly," explains the formation.The abundance of fine calcareous debris causes most of the limestone to appear silty.[8] published the first official description of the type section of the formation in Qatar, defining it as foraminiferal limestone ranging from lime mudstone at the bottom to wackestone, pellet and skeleton packstone, and wackestone at the top.In such horizons, the formation is dominated by Orbitolina and Trocholina tests [9].The Mauddud Formation consists of rudist grainstone and packstone with peloidal, Orbitolina-bearing limestone in northern offshore zones [3].The transition from the Nahr Umr's clastic rocks constitutes the Mauddud Formation, which lays conformably on the Nahr Umr Formation.The lower marly section of the Mauddud Formation comprises a transitional zone between the Nahr-Umr clastic sand the limestones appropriate to the so-called "Upper Mauddud" in the subsurface north region.The Ahmadi Formation is the overlying formation in the type locality, and its contact is similarly conformable and marked by a sharp gamma-ray peak [3].
In subsurface reservoirs, the core is usually taken because it provides a high-resolution database on which to collect sedimentological, diagenetic, and reservoir quality observations.As a result, it provides the essential building elements for creating a reservoir model.Core recovery from subterranean reservoirs is, however, exceedingly costly, and as a result, it is frequently limited in scope.In subsurface reservoirs, traditional wireline logs such as gamma ray, neutron, density, resistivity, and sonic logs are frequently collected with the goal of characterizing the reservoir rock (quantification of porosity, hydrocarbon saturation, etc.).This dataset includes the whole reservoir; however, it is especially useful at uncored intervals when data is limited.Conventional wireline logs frequently reveal lithological heterogeneity within a rock sequence, but texture variability is typically difficult to interpret accurately [1].This is especially problematic in limestone reservoirs, where the lithology is often consistent throughout and reservoir quality was determined by differences in carbonate textures and/or calcite cementation activity.
Borehole image logs are a type of digital log that represents the physical attribute (electronic resistivity or acoustic impedance) of borehole walls [7].Electrical borehole image measurement and interpretation give continuous oriented images with very high vertical resolution up to 5 mm of the borehole wall.Borehole imaging technologies add greatly to geological knowledge and interpretation of recorded intervals [7].Borehole imaging technologies might identify sedimentological and structural characteristics up to a few millimeters in resolution [10].Full-bore Formation Micro Imager (FMI), the advancement of the FMS tool, comprises four holding pads linked to two orthogonal arms, with each pad having an attached flap.As a consequence, the FMI could well be run in either 8-pad mode (using both the pads and flaps) or 4-pad (FMS) mode (using only the four pads).Each pad/flap has 24 buttons and is also in touch with the borehole wall.The 192 electrodes, which are arranged on four pads and four extendable flaps, yield 192 microresistivity curves that can be used to generate a computer-generated "image" of the wellbore wall.Borehole images are commonly utilized to complement core data in reservoirs where sedimentary features, which include cross-bedding, are prominent.Borehole images can offer not only a cheaper dataset with more stratigraphic coverage for sedimentological definition than the core, but they can also provide paleo currents orientation data, which is important for understanding the architecture of geo-bodies in the subsurface [4] [6].Sediment homogenization caused by bioturbation and other processes can result in a lack of sedimentary features in limestone reservoirs.There have been few studies on the sedimentological uses of borehole images in such reservoirs.It seems that you are referring to a study in the field of petroleum geology.The study suggests that hydrocarbon-producing zones are commonly found in clean carbonate lithologies located in the upper part of the Mauddud Formation.However, the wireline log signatures obtained from these carbonate reservoirs are not unique, making it difficult to determine their texture and reservoir quality accurately without core samples.To address this challenge, the study proposes using borehole images from one well in the Mauddud Formation to gain a better understanding of the reservoir's texture and quality.Borehole images provide high-resolution data that can help identify features such as fractures, vugs, and porosity, which are critical in evaluating the reservoir's productivity.By using borehole images, the study hopes to improve the accuracy of wireline log interpretation, which can help geologists and engineers make informed decisions regarding reservoir development and production.Overall, this study highlights the importance of using multiple data sources and techniques to fully understand subsurface reservoirs in the oil and gas industry.The appears that the study aims to characterize the sedimentological properties and reservoir quality of the carbonate deposits in the Mauddud Formation using FMI (Formation Micro-Imager) data.The FMI data is calibrated with core observations, which is a common practice in petroleum geology to ensure that the data obtained from well logging tools match the properties of the rocks sampled from the reservoir.
The ultimate goal of the study is to understand and predict the depositional and reservoir architecture of the Mauddud Formation using log-based datasets only.This means that the study aims to use wireline logs, which are commonly used in the oil and gas industry, to infer the depositional environment and the quality of the reservoir.
To achieve this goal, the study may use various techniques such as facies analysis, petrophysical analysis, and image analysis to interpret the FMI data and correlate it with the wireline logs.By doing so, the study may provide insights into the depositional history of the Mauddud Formation and identify the factors that control the reservoir quality.This information can be crucial for oil and gas exploration and production companies to optimize the development and production of the reservoir.

Geological settings
The Mauddud formation lays between two shale members; the lower contact is overlaying the upper Nahr Umr clastic formation shale member and the upper contact is underlaying the lower Ahmadi shale.The formation depositional environments progress from intertidal to foreshoal environments.Benthic foraminifera are a significant fauna group.The Orbitolina bearing limestone is a major lithology over the Arabian plate.The second common association is rudist grainstone in the upper part of the Mauddud formation figures 1&2.The other bioclastic fragments like echinoderms, algae, and mollusks are also described in the Mauddud formation.

Methodology
The core data.In the study well, 132m of core is available through the Mauddud Formation, which has a total thickness of 132m.All reservoir zones of the Mauddud Formation are covered by the cored interval.There are additionally 32 porosity and permeability core plug data available from the research well's cored interval.The sample density is higher in the carbonate lithologies, which are the focus of the investigation.These measurements cover the whole cored Mauddud stratigraphy.Logs of wirelines and borehole images (BHI).Throughout the Mauddud Formation, conventional wireline logs like as gamma ray, caliper, neutron, density, and resistivity are accessible.In the research well, FMI logs of commonly accepted quality are provided throughout the Mauddud Formation.This section outlines the method for determining the FMI predictability of the sedimentological make-up and reservoir quality.To comprehend the predictability, it is necessary to first characterize the Mauddud Formation's sedimentological make-up, diagenetic overprint, and reservoir quality properties.It should be noted, however, that this characterization is not the primary focus of this study and is only summarized here for predictive purposes.
Correction and quality control might be used to acquire and load the raw image data (dlis file).
(1) Inclinometer QC and correction are the primary processes in the workflow for processing the

Image facies reflection
The image facies of Mauddud Formation interpretation based on micro resistivity full-bore imager that reflect the rocks and fluid characterizes.The FMI patterns that show in the Mauddud Formation are: A-Resistive: When using traditional logging techniques, a resistive log response represents the high resistivity values from substances like hydrocarbons or low-porosity matrices (non-invaded and resistive substances like anhydrite).Typically, light hues, beginning with white, reflect off of resistive materials [5].Low resistivity measurements in marls, clays, and shales are recorded in conventional logs.
They are indicated by darker colors in image logs (often black).When saturated with drilling fluids, however, vugs or high-porosity zones are also reflected as conductive.

C-Mottled Image Facies:
Mottled: Mottles can be defined as the alternation of resistive and conductive patterns caused by different grain sizes.Irregularly formed mottles show grain sociations from moderate-tohigh-energy settings.Mottled-image facies are a kind of microfacies that includes bioclastic packstone, coral floatstone, rudstone, and breccias with variable-sized clasts or bioclasts.
Massive mottles reflect large benthic shells as resistive reflections on a high-porosity, conductive backdrop, whereas small mottles reflect small skeletal bioclasts.A conductive background with resistant grains, on the other hand, may suggest a high-porosity background with carbonate grains invaded by drilling fluids.Big mottles in the porous matrix often identify large bioclastic skeletal grains Table (1).

D-Laminated Image Facies:
This image pattern has thin, regularly layered conductive and resistive patterns of approximately consistent thickness.Laminated-image facies are generally found in lowenergy environments where mudstone and wackestone microfacies dominate.The argillaceous limestone deposits from the restricted environments represented by this pattern feature rare bioclast fragments Table (1).

E-Massive Image Facies:
Matrix and/or earlier calcite cements may be replaced with dolomite.Cements are made of late dolomite.Micritization, isopachous cements, dissolution, common blocky and neomorphism cements, and compaction are some of the terms used to describe these processes.The massive image reflection is resistive pattern due to low porosity and noninvasion by drilling fluid table1.