Groundwater situation before production and after production stoppage in Al-Mishraq Sulfur field-1, northern Iraq

This study dealt with the reality of groundwater before Sulfur production in the Al-Mishraq field-1 and after production stopped in the field, by measuring the groundwater table for (44) wells in 2021, and comparing it to the groundwater table measured by the Polish company Centrozap in 1971, the groundwater table was a range between (187.71-205.8)m in 1971, but in 2021 it ranged was between (188.51-196.55)m. Maps of the groundwater movement and water table were created using these data. It turned out that there was little change in the direction of groundwater flow; in both cases, the flow is from the west and northwest towards the east with a slight slope toward the southeast and the Tigris River. As for hydraulic properties, it was analyzed in (29) wells, depending on pumping test data from the reports of Al-Mishraq, It was noted that the values of Transmissivity ranged between (1557.5-24.4) m 2 /day before production and (5020.6-39.4) m 2 /day after production, As for hydraulic conductivity, it ranged between (0.26-14.68) m/day before production, and after production, it was between (0.4-48.9) m/day.


Introduction
The groundwater aquifers in the Fatha formation are considered important aquifers and contain deposits of sulfur, which is extracted by the Farash method [ 1 ] .
Groundwater is considered one of the main factors controlling Sulfur extraction, as it posed a very great danger in the Sulfur extraction process because its levels are above the level of the producing layers, in addition to the flow of Sulfur towards the Tigris River when Sulfur is melted and transformed into a liquid forming Sulfur cones in the mid of the river reach opposite the Al-Mishraq Sulfur field-1, during production, as in Figure (1), to address the problems arising from the investment of Sulfur ore in the region and its impact on groundwater, the reality of groundwater in that region must be studied.
The current study aims to assess the reality of groundwater, determine the direction of groundwater movement and its natural discharge, and the hydraulic properties of groundwater aquifers before production and after production stops in the Mishraq field.

2-Study area description
Al-Mishraq field, one of three fields where sulfur extraction occurred, is situated in northern Iraq, approximately 45 km southeast of Mosul, between longitudes (′′59 ′17 43) and (′′24 ′20 43) east, and latitudes (′′55 ′00 36) and (′′04 ′05 36) north.The field's area is roughly 17 km 2 , as shown in Figure 2. Tectonically, the area of the study is located within the foothill zone of the unstable shelf, and due to its location at the intersection of the Tigris fault zone with the Hadhra-Bakhme fault system, Al-Mishraq zone is distinguished in its structural and sedimentary nature (Figure 3), [ 3 ] , It is the Anticline Mishraq fold whose direction is northwest-southeast is one of the sums of the contiguous folds whose direction is similar to that of the Mishraq fold [4], As well as the presence of several normal and strike-slip faults in two main directions, the first Northeast-Southwest perpendicular to the main fold axis, and the second northwest-southeast, as well as the presence of many thrust faults.In general, it can be said that some of these faults are oriented parallel to the axis of the main fold and others parallel to the direction of the Hadhra-Bakhme fault [5] .The rocks exposed in the study area are all rocks of sedimentary origin, as they are represented in the formations of the Fatha, Injana, and Quaternary sediments (Figure 4).The information on the stratigraphic sequence was obtained through the wells that were drilled by [1], as they penetrated the Euphrates formation.The age of this formation dates back to the Lower Miocene, consists of light to dark limestone that contains: Bituminous and fossils in some of its upper parts, As well as containing marly limestone, dark to light colored marl, and this corresponds to the lithological description of the same formation in Najaf Governorate [6], [7].There is no significant heterogeneity in the lithology formation between the upper part of the formation and the lower part of the Fatha formation above it.The surface separating them has been determined by microfossils and some types of well-logs.
While of the Injana formation (Upper Miocene).It unfolds in a narrow space, especially along the southwestern edge of the region, and consists of layers of clay, marl, and sandstone [8], [9].
The majority of the study area is covered by the Miocene Fatha formation, which is one of the most significant deposits in the area due to the presence of sulfur deposits formed as a result of the transformation and mineralization of layers of gypsum and anhydrite.The formation also appears in wells that have been drilled in the area and may be covered with Quaternary-age sediments [4].This formation consists of successive layers of gypsum, limestone, marl, mudstone, and silt [1].As for the sedimentary environment of this formation, it is a shallow marine environment [10], [11], and its rocks are characterized by weak resistance to erosion processes, which leads to form the erosional geomorphological forms such as karst and caves [12].
The Fatha formation in the study area was divided according to [13] into four sections from the bottom, namely: 1. Productive deposits series 2. Sulfate series 3. Carbonateterrigenous series 4. Sulfateterrigenous series While the Quaternary Sediments cover some narrow areas in the region and consist of gravel and sand of various sizes with clay lenses [3], the thickness of these sediments reaches (25) m in some places.

Methodology -3
1-The lithological sections of the wells available in the study area were drilled by [ 1 ] , the information of which was obtained from the Mishraq Sulfur State Company, which completely penetrates the Fatha formation.2-The reality of the groundwater before the production of Sulfur in the Al-Mishraq field was studied based on the data taken from the Mishraq Sulfur State Company, for the study carried out by Centrozab Company in 1971, which numbered (68) wells.After production stopped in the field, the researcher measured the depths of the groundwater in (44) wells in 2021 using the Groundwater depth detector.To ensure that the direction of water movement at any point is perpendicular to the equipotential lines, the spaces confined between the equipotential lines and the flow lines must be as close to squares as possible.The groundwater level map was drawn, which represents a contour map of lines equal to the height of the groundwater level from the surface of the sea (Equipotential Lines), for both cases, before production and after production stopped.The results of the experimental pumping were used for the production layers for (29) wells before producing Sulfur, The same wells were also used after the production process stopped.To obtain the hydraulic properties of the aquifers [14].Due to the importance of the productive layers aquifer in the production process and its impact on the drainage and consumption of industrial water in the production of Sulfur, which requires the study of hydraulic properties.

4-Results and discussion
aquifers in the study area The main Through the study of the lithological sections of the available wells in the study area excavated by the Polish company Centrozap, whose information was obtained from the Mishraq Sulfur State Company, and through previous studies, the aquifer carrying groundwater was identified and represented by the deposits of the Fatha formation, represents the main aquifer of the study area, and due to the lack of continuity in the rocky layers between the parts of the formation and the lack of similarity in groundwater levels.The deposition of Al-Mishraq was counted as a complex multiple aquifer, and it consists of three main aquifers separated by confining layers, these three aquifers consist of some secondary aquifers [15]Which: This aquifer consists of five secondary aquifers carrying groundwater representing the Quaternary in a narrow strip adjacent to the Tigris River, the Sulfate terrigenous series, upper part Carbonate terrigenous series, the Lower part Carbonate terrigenous series and the middle part of the sulfate series [1].Most of these aquifers are characterized by being discontinuous and poor flowing, as the water recharged for these aquifers places from the northwest side of the sedimentation area and along the direction of the main folds [15] .And because the depths of groundwater that were measured in the wells range between (51-81)m, this aquifer is considered a dry aquifer, or it may contain Perched aquifers.

Productive layers aquifer
This aquifer is the largest groundwater aquifer in the Al-Mishraq region, as it extends on both sides of the Tigris River, which includes the three sulfur layers of the lower part of the Fatah formation.The aquifer of productive layers of the Euphrates formation's upper part contains a marl layer, and the lower part of the overburden layers contains thick layers of gypsum and clay that serve as an aquitard for the aquifer from the bottom and the top [14].As for the hydraulic aspect, the aquifer occupies a large area and the movement of groundwater is from all sides, as the natural discharge of this water is towards the Tigris River due to the hydraulic connection with the river as a result of the erosion of the covering layers near the river and the presence of faults in the river area [16].The Productive layers aquifer is characterized as confined and continuous, as well as there is a hydraulic connection for this aquifer with the river in addition to the stable flow, as was proven during the pumping test operations.In general, the water is located within layers of sulfur cavernous limestone, and the average thickness of the water in the reservoir of productive layers based on the information available from hydrogeological wells is about (100 m) approximately [16].This aquifer was divided into three secondary aquifers according to [ 1 ] and separating the three productive layers of limestone with little porosity as well as the layers of compacted mudstone, which are the first productive layer, the second productive layer, and the third productive layer).

Euphrates aquifer
It is located at the top of the Euphrates formation and consists of a single layer of fossiliferous limestone with high secondary porosity.As shown in the stratigraphic sections of the two wells No. (XIX-11, XVIII-4) shown in Figures ( 6 and 7), as well as the cross-sectional stratigraphic section of the Southwest-Northeast shown in Figure 8.

flow 4-2 Groundwater
The depths of the groundwater before production ranged between 83.25-35.6 m, while after production stopped, it ranged between 81-47.37 m, Where it was found that the groundwater before production and after the cessation of production is deep in the axis of the fold and decreases in depth as we move away from the axis of the fold, as in Figures 9 and 10.Watertable is ranged between 205.8-187.71m in 1971, that is, before production.In 2021, after stopping production, it ranged between 196.19-187.67m,as shown in Table (1).The decrease in levels after stopping production is attributed to two reasons, the first is climatic, and the second may be due to the increase in hydraulic properties due to the production of Sulfur, which leads to an increase in effective porosity, which led to an increase in natural drainage towards the Tigris River and thus lower levels.To know the direction of groundwater movement and its natural discharge in the study area, a Groundwater Level Map was drawn, which represents a contour map of Equipotential lines to the height of the groundwater level above sea level, meaning that Equipotential Lines, for both cases, before and after production.Production stops so that the direction of water movement at any point is perpendicular to the Equipotential lines.Taking into account that the areas between Equipotential Lines and the lines of flow are in the form of squares as much as possible [17].From the observation of Figures (11 and 12), it was found that the direction of movement did not change much before production and after production stopped.In both instances, groundwater is moving in an eastward direction with a slight slope toward the southeast, indicating that the drainage area is east of the study area, which is represented by the Tigris River.The first layer contains less hydraulic pressure than the second and third layers, which helps in the rise of water from it to the first layer [14].It is in hydraulic contact with the river near the XV-9 well, as well as at the fault areas that represent the sites for the passage of groundwater to the drainage area.

4-3 Hydraulic Properties of the Aquifers
1-The values of Transmissivity (T) ranged between 1557.5-24.4m 2 /day before production, and between 5020.6-39.4m 2 /day after production stopped, while the hydraulic conductivity (K) ranged between 0.26-14.68m/day before production.But after production stopped, it was between 0.4-48.9m/day [14], as shown in Table 2.  2-We note that the values of Transmissivity and hydraulic conductivity before production increase east of the study area near the Tigris River and decrease towards the north and northwest of the study area as in the figures (17,18), The reason for the increase in these characteristics may be due to their influence on the tectonic activity resulting from the influence of the Hadhra -Bakhme fault, which causes the formation of faults and joints parallel to this main fault, which intersect with the joints resulting from the formation of folds and parallel to the axis of the main Mishraq fold, the point of intersection of both systems is considered the main leakage point.The hydraulic properties after production also increase linearly as shown in the figures (19, 20), it is due to the establishment of production sites (production stations) on and around the center of this increase, where large quantities of hot technological water were injected for the underground Sulfur smelting process in the second and third production layers, and that the withdrawal of this molten Sulfur has caused voids to occur There are many large cavities within the productive layers and the enclosing layers between them, where the effective porosity doubled, which was reflected on the hydrogeological behavior of the three secondary Aquifers, which led to an increase in the hydraulic properties of Transmissivity and hydraulic conductivity.

Figure 1 :
Figure 1: A. molten sulfur leakage in the Tigris River B-Sulfur cones in the Tigris River as a result.[2]

Figure 2 :
Figure 2: Location map of the study area

Figure 3 :
Figure 3: The tectonic map of Iraq from [4], showing the location of the study area concerning the Hadhra-Bakhme fault

Figure 4 :
Figure 4: Geological map of the study area[1]

Figure 12 :
Figure 12: Groundwater movement map in Al-Mishraq Sulfur field-1 after production

Figure 16 : 1 Figure 15 :
Figure 16: shows the relationship between hydraulic conductivity (K) before and after the production stop, in Al-Mishraq field-1 Figure 15: shows the relationship between Transmissivity (T) before and after production stops, in Al-Mishraq field-1

Figure 18 :
Figure18: A map representing the distribution of hydraulic conductivity (K) in the wells of the study area before production[14]

Figure 17 :
Figure 17: A map representing the distribution of Transmissivity (T) in the wells of the study area before production[14]

Figure 20 :
Figure 20: A map representing the distribution of hydraulic conductivity (K)in the wells of the study area after production[14]

Figure 19 :
Figure 19: A map representing the distribution of Transmissivity (T) in the wells of the study area after production[14]

Table 1 :
Depths and levels of groundwater In the study area