Figure 9 - uploaded by Govand H. Sherwani
Content may be subject to copyright.
Sequence identification based on the wireline log analysis only in Majnoon-5 Well (Mj-5) employing Vahrenkamp et al. (1993) methodology, which includes rescaling density (FDC) and sonic (BHC) wire line logs with narrower ranges (after Sherwani, 1998).
Source publication
The CenomanianÐEarly Turonian reservoirs of the Mishrif Formation of the Mesopotamian Basin hold more than one-third of the proven Iraqi oil reserves. Difficulty in predicting the presence of these mostly rudistic reservoir units is mainly due to the complex paleogeography of the Mishrif depositional basin, which has not been helped by numerous pre...
Contexts in source publication
Context 1
... the gamma-ray log is used as an additional marker for shaliness, which increases in protected lagoonal facies compared to the open-marine setting ( Vahrenkamp et al., 1993). Sherwani (1998) also used this methodology to differentiate protected lagoonal facies (PL) from the open-marine facies (OM) when studying the Mishrif as a part of a larger megasequence including the underlying Rumaila and Ahmadi formations (Figure 9). ...
Context 2
... shallow depositional conditions occur in Majnoon and Buzurgan fields where thick lagoonal successions were deposited (Figures 10 and 11). Keeping in mind the gradational contact between the Mishrif and Rumaila formations, and the deeper environmental conditions of the Rumaila and Ahmadi formations, Sequence I represents a regressive part of a sequence, which includes the Rumaila and Ahmadi formations (Figure 9), known as Sequence 2 of Sherwani (1998) or the early highstand above MFS K120 of Sharland et al. (2001). ...
Context 3
... of Sequence III varies around the Najaf Basin because the top of the Mishrif Formation (i.e. top of Sequence III) is frequently truncated by a sharp contact with the overlying basinal shales of the Khasib Formation (Figure 9). The Khasib-Mishrif unconformity is the most significant sequence boundary that can be clearly identified on the log signatures. ...
Citations
... Sedimentation had an important influence on the reservoir lithology, structure, and components [16,32,33]. As shown in Figure 10, the supratidal flat is dominated by dolomites. ...
The Early Cretaceous Yamama Formation of X oilfield, deposited in a semi-restricted setting, holds considerable oil reserves. However, the reservoir is extremely heterogeneous and is poorly studied. Integrating outcrops, cores, cast thin sections, regular or special core analysis, wireline logging data from six wells, and seismic data, this study provides an improved understanding of reservoir petrophysical characteristics and geological controlling factors including sedimentation, diagenesis, and sequence. The results showed that eight lithologies are developed in the Yamama Formation, of which packstone and wackstone are dominant. The physical properties span a wide range, with porosity mainly distributed between 10% and 25%, and the permeability mainly distributed between 0.1 mD and 1 mD. Nine types of pores are developed, with moldic pores, micropores, and skeletal pores being the most developed. The reservoir has six types of microstructures, of which the poorly sorted with mega-throat represent the best reservoir. The Yamama Formation was mainly deposited in a lagoon, along with five other facies, such as supratidal flat, patchy reef, back shoal, shoal, and open shelf. Six types of diageneses are developed, with dissolution during the penecontemporaneous stage being the most beneficial to the reservoir and cementation being the most destructive. Three sequences were recognized in the Yamama Formation. It concluded that the hydrodynamics in semi-restricted depositional setting is weak overall and does not have the potential to develop large-scale high-quality reservoirs. A wide range of bioclasts were selectively dissolved to form a large number of secondary pores. Sediments rich in Algae, Bacinella, and peloids tend to form moldic pores, skeletal pores, and intergranular pores, respectively, which are prone to be favorable reservoirs. Controlled by the coupling of sedimentation and diagenesis driven by sequence, the reservoir is extremely heterogenous.
... Consequently, the prevailing warm and humid tropical climatic conditions facilitated the proliferation of tropical carbonate platforms in southern and southwestern Iran (Rahimpour-Bonab et al. 2012, b;Taghavi et al 2006;Mehrabi 2023). The combined effects of fluctuating mean sea-level and tectonic activities resulted in several palaeoexposure surfaces within the Sarvak Formation and its equivalents in the Mesopotamian Basin (Mahdi et al 2013;Navidtalab et al. 2016, Wang et al 2021. The three most prominent discontinuities identified are the middle Cenomanian exposure surface (mC-ES), the late Cenomanian-early Turonian exposure surface (CT-ES), and the middle Turonian exposure surface (mT-ES; Navidtalab et al. 2016;Mehrabi et al. 2023). ...
This study investigates the diagenetic evolution and geochemical variations within the Sarvak Formation by integrating the core, thin-section, scanning electron microscopy, X-ray diffraction, trace elements, carbon-oxygen, and strontium isotopic data from three wells in the Abadan Plain. The formation displays diverse diagenetic processes, influenced by multiple exposure surface condition including the Cenomanian-Turonian boundary (CT-ES) and middle Turonian (mT-ES). Meteoric diagenesis, shaped by tectonic activities and eustatic sea level changes, played a pivotal role, leading to dissolution (karstification), brecciation, cementation, and palaeosol formation. Geochemical analysis revealed significant elemental variations across the studied wells. Magnesium (Mg) exhibited peaks at sequence boundaries, responding to facies changes, while iron (Fe) and manganese (Mn) concentrations increased below disconformities, reflecting changes in redox conditions and karstification. Sodium (Na) concentrations varied with facies changes, showing peaks at sequence boundaries, indicative of palaeoexposure events. Strontium (Sr) isotopes aided in delineating stratigraphic positions of palaeoexposure surfaces and absolute dating of sequences. Increases in87Sr/86Sr ratios below disconformities suggested subaerial exposure events, with shorter durations at CT-ES and longer durations at mT-ES, contributing to dissolution features development. The δ13Ccarb and δ18Ocarb values indicated severe meteoric diagenesis below sequence boundaries, characterized by dissolution and reprecipitation of calcium carbonate as low-magnesium calcite (LMC) cements. Cross plots of δ13Ccarb vs. δ18Ocarb displayed inverted-J patterns, indicative of meteoric diagenesis effects. Comparison with previous studies highlighted similar trends in geochemical variations, with notable differences in element concentrations between wells. This study enhances our understanding of diagenetic history of the Sarvak Formation in the Abadan Plain and, in a larger scale, provides insights into diagenetic evolution of palaeoexposure-related carbonate sequences.
... The reservoirs are characterized by high porosities and high permeability, such unique reservoir characteristics, which also have wide geographic extent, result in the Mishrif ranking as the number one reservoir in Iraq. So far the total proven reserves in the Mishrif reservoir exceeds 30% of the total Iraqi national reserves (Mahdi et al., 2013). ...
More and more attention has been paid to the waterflood development of carbonate reservoir in the Middle East with continuous expansion of the scale of carbonate reservoir development. Strong non-homogeneity of carbonate reservoirs results in serious conflicts between injection and production, causing low degree of water-driven control in the well network, and low degree of vertical mobilization. This article takes the main reservoir of an oil field in the Middle East region as an example, combining geological evaluation, dynamic analysis, and reservoir development strategies to study the effectiveness of water injection development in carbonate reservoirs. It shows that there is a correlation between pore type, oil-water relative permeability, and development method in the development of carbonate reservoirs. For reservoirs with matrix pores and micropores, water injection should be strengthened in the later stage of development; for reservoirs with dissolved pores and coarse pores, the iso-permeability point is relatively high, and the later development should focus on balanced water injection. Three different waterflooding models for formation development are designed to verify the feasibility of fine waterflooding schemes. The main differences are that one set of well patterns is combined injection and production, and three sets of well patterns are layered system waterflooding. The results show that the development effect in layered system waterflooding is the best. The daily production can be increased by about 16%, the cumulative oil production can be increased by about 8%, and the recovery factor can be increased by about 3%. Eventually, the stable oil and water control of carbonate reservoir can be realized.
... The Mishrif Formation of Iraq and the southern Arabian Gulf, and time-equivalents in Iran (Upper Sarvak) and Oman (Natih A-C), are prolific Middle Eastern reservoir formations. The Mishrif Formation is particularly important in the Mesopotamian Basin of central and southern Iraq where it holds over one-third of the country's oil reserves in giant oilfields such as Rumaila, West Qurna, Zubair, Majnoon, Nasiriyah and Halfaya (Aqrawi et al. 1998;Mahdi et al. 2013). The reservoir varies in thickness from 100 m to 400 m and forms part of a second order highstand (Sharland et al. 2001). ...
Middle Eastern carbonate petroleum reservoirs exhibit a range of heterogeneities which consist of variable combinations of primary stratigraphic and secondary diagenetic and structural characteristics. These produce diverse permeability architectures which can exert a profound influence on reservoir performance during secondary recovery. Of particular importance are laterally persistent discrete zones of elevated permeability (DZEP) that typically make up a volumetrically minor proportion of the reservoir yet show disproportionately high fluid inflow or outflow. The stratigraphic, diagenetic, and structural origins of elevated permeability in Middle Eastern carbonate reservoirs are considered here and the consequences of such features for reservoir performance are discussed.
The term DZEP denotes geological sources of elevated permeability at least an order of magnitude greater than background reservoir properties. Stratigraphically organised DZEP comprise coarse-grained layers, event beds or parasequence tops or bases in neritic or platform interior settings. Other origins include bioturbated layers, grainy clinothems, and bed-scale, grain-size variations in shoal deposits. Diagenetic DZEP are typically dissolution horizons with mouldic and touching-vug pore networks or dolomitized intervals which often overprint stratigraphic DZEP. Structural DZEP include individual faults, fracture corridors, and fracture concentrations related to mechanical stratigraphy.
During production through natural pressure depletion, DZEP may dominate well productivity. Under secondary recovery, the same intervals may dominate inter-well fluid flow, causing flood conformance issues, cross-zone fluid movement, bypassed pay, and earlier-than-expected water or gas breakthrough to production wells. Optimisation of production and ultimate recovery relies on collecting the correct kinds of data at a sufficiently early stage in the reservoir characterisation process to permit their inclusion in static and dynamic reservoir models.
... Uncontrolled instances of lost circulation pose serious pressure control risks and can potentially lead to the loss of the well itself [21]. [22]. ...
Loss of circulation while oil well drilling is a major problem and is regarded as the most challenging difficulty during drilling and well construction. A significant circulation loss can result in drilling risks such as sticking, blowout and well collapse. This research focused on Shiranish Formation downhole mud losses while drilling and stuck pipe in the saddle area of the Rumaila super giant oilfield, in southern Iraq. Over 1100 wells were drilled in the Rumaila oilfield and only a few wells within the saddle area experienced downhole formation losses/problems and stuck pipes. Seismic data, petrophysical data and drilling reports were used to investigate Shiranish Formation loss and stuck pipe issues. The seismic interpretation revealed small-scale faults and fractures within the examined area, most likely influenced by the strike-slip deep-seated Al-Hammar fault.
Correlation within three wells was performed to understand the effect of these faults within the Shiranish Formation, which demonstrated that the Shiranish Formation top is roughly 40 m different from the neighboring wells within 1.5 km and other formation tops are not affected within these faults. Identifying the location of faults and fractures will aid in avoiding drilling in these particular areas and choosing locations where there are no faults, or at the very least in mitigating and assisting the risk of drilling in such areas, such as controlling the rate of Penetration (ROP) while drilling and preparing extra mud and lost circulation materials (LCM).
... This study evaluates the Mishrif carbonate formation, a prolific oilproducing reservoir within the Majnoon oil and gas field, southern Iraq. The Majnoon Field under study is one of the largest oil and gas fields in the Mesopotamian Basin (Mahdi et al. 2013). It incorporates 13 oil-and gas-bearing formations from the Miocene to the late Cretaceous. ...
This study develops an innovative workflow to identify discrete lithofacies distributions with respect to the well-log records exploiting two tree-based ensemble learning algorithms: extreme gradient boosting (XGBoost) and adaptive boosting (AdaBoost). In the next step, the predicted discrete lithofacies distribution is further assessed with well-log data using an XGBoost regression to predict reservoir permeability. The input well logging records are gamma ray, neutron porosity, bulk density, compressional slowness and deep and shallow resistivity. These data originate in a carbonate reservoir at the Mishrif basin of southern Iraq's oil field. To achieve solid prediction of lithofacies permeability, random subsampling cross-validation was applied to the originated dataset to formulate two subsets, training for model tuning and testing for prediction of subsets that are not observed during model training. The values of total correct percentage (TCP) of lithofacies predictions for the entire dataset and testing subset were 98% and 93% by the XGBoost algorithm; and 97% and 89% using the AdaBoost classifier, respectively. The XGBoost predictive models led to attain the least uncertain lithofacies and permeability records of the cored data. For further validation, the predicted lithofacies and reservoir permeability were then compared with the porosity-permeability values derived from the Nuclear-Magnetic Resonance (NMR) log, the secondary porosity of the Full-bore Micro Imager (FMI) and the production contribution from the Production-Logging Tool (PLT). Therefore, it is believed that the XGBoost model is capable of making accurate predictions of lithofacies and permeability for the same well's non-cored intervals and other non-cored wells in the investigated reservoir.
... Seven facies, spanning from shallow open marine Tidal Flat, are recognized that correspond to palaeo-depositional environments. The paleo-geomorphy decreased toward the north when the formation as a whole was being deposited [29]. The paleo-geomorphical trend is controlling the decline in Mishrif's thickness especially around the carbonate ramp and the reef-rimmed carbonate platform. ...
Reservoir performance depends on many factors, and the most important one is permeability anisotropy. In addition, with high heterogeneity, it is essential to find unique relationships to predict permeability. Therefore, this study aims to predict vertical permeability based on horizontal permeability and porosity and to find new equations for carbonate reservoirs. This work relied on the 398 measured points of cores data collected from several wells in carbonate reservoirs. A new correlation for predicting vertical permeability for the whole data (369 samples) as a function of horizontal permeability and porosity has been developed. The results indicate that this new correlation can estimate the vertical permeability with correlation coefficients (RSQ) of 0.853. Then, the used data were divided into four groups depending on the Kv/Kh values: less than 0.1, 1–0.1, 1–10, and more than 10, and a new correlation for permeability prediction for each group has been developed with good RSQ values of 0.751, 0.947, 0.963, and 0.826, respectively. The previous studies lack the correlations to predict vertical permeability in carbonate reservoirs, so this study can be considered as a reference for similar cases.
... a-Traces and signs of the activity of organisms in the mud-dominated facies (soft sediments) which are known as Burrowing (Fig. 6: I, J). In seaward shoal facies, Burrowing is common in soft sediments (Mahdi et al., 2013;Wenju et al., 2020). ...
... A carbonate platform ramp may be seen in the Mishrif reservoir depositional environment [15]. Mishrif reservoir is comprised on Rudist, coral-reef, organic detrital limestone, shallow open-marine, and lagoonal facies [16] [17]. Mishrif reservoir had been classified into six layers (MA, MB11, MB12, MB21, MC1, and MC2) according to spatial variation of rock properties [14]. ...
The initial oil in place (IOIP) is an important factor that controls economic planning for production and field life. Therefore, this parameter must be determined precisely and carefully. The present paper is dealt with study the impact of adopting two different strategies of property modeling on IOIP value. 3D geological model constructed by using information likewise: contour map, oil formation volume factor, control processing interpretation (CPI) of well logs, and well heads and tops of twelve wells for selected field. The chosen oil field is feeding from Mishrif reservoir and located in southern Iraq. Mishrif reservoir is classified to six layers: MA, MB11, MB12, MB21, MC1, and MC2. Two strategies for distributing petrophysical properties: porosity, water saturation, and net to gross thickness of Mishrif reservoir are utilized. The two strategies are sequential Gaussian simulation and moving average. The volumetric method is used for estimating IOIP values. The impact of using the two strategies of property modeling was very clear where the values of IOIP had a significant difference. The IOIP value of 3D model whose petrophysical properties are distributed using moving average strategy is 5.145 billion barrels, while the 3D model distributed by Gaussian strategy had IOIP equal to 4.195 billion barrels. According to obtained results, the choice of distribution method is very important in estimation of IOIP. Selection of optimal property modeling strategy need to statistical comparison with selected oil field reports and input data, so finally, the closest representation of a protective reservoir and accurate value of IOIP.
... It mainly includes benthic foraminifera, non-fixed bivalves, rudist and echinoderms. Its unique external morphology, internal structure and particle size are the most important signs for identifying bioclastic types [27][28]. After the death and fragmentation of these organisms, they are elutriated and sorted by seawater to become carbonate particles, forming a large-scale bioclastic limestone of M Formation, which is in integrated contact with the underlying mudstone of R Formation and unconformity with the overlying K Formation (see Fig. 1). ...
In order to clarify the differential diagenesis of different sedimentary microfacies of bioclastic limestone in Cretaceous M Formation in the Middle East and systematically analyze the characteristics of reservoir pore evolution, the data of regional geology, well logging, core, cast thin section, scanning electron microscope, three-dimensional CT and conventional porosity and permeability test are comprehensively used, taking MB2-MC1 section in X oilfield as an example, starting from the diagenesis and pore evolution of bioclastic-arene shoal, the characteristics of diagenesis of each sedimentary microfacies in different environments are analyzed, and the differential diagenesis, pore evolution process and its influence on physical properties are studied. It is showed that the reservoirs of MB2-MC1 section are mainly developed in the ramp shoal and platform margin shoal. The shoal facies can be further subdivided according to the type of bioclastic debris. The sedimentary microfacies determine the original fabric and bioclastic type of M Formation, and then control the diagenetic sequence and strength. Each sedimentary microfacies mainly experiences different degrees of mud crystallization and burrows in seawater environment, dissolution and cementation in atmospheric freshwater environment, compaction, pressure solution and dolomitization in burial environment. High energy microfacies have the characteristics of non-selective dissolution, mainly developing intergranular pores and intergranular dissolved pores. Medium energy microfacies have the characteristics of selective dissolution, mainly developing mould pores and intragranular pores. The medium-low energy microfacies have the characteristics of moderate cementation, moderate compaction and moderate-weak dolomitization, mainly developing intragranular pores and visceral foramen pores. The low energy microfacies have the characteristics of strong cementation, strong compaction and moderate dolomitization, mainly developing micropores, intercrystalline pores and visceral foramen pores, which are non-reservoirs.
