Abstract
The shale volume is one of the most important properties that can be computed depending on gamma ray log. The shale volume of Mishrif Formation (carbonate formation from middle Cenomanian- early Turonian) was studied for the regional area of the middle and southern parts of Iraq. The gamma ray log data from seventeen wells ( Kf-3,Kf-4, Ad-1,Ad -2,Dh-1, Bu-47, Ns-2, Ns-4, Am-1,Am-2,Hf-2,Hf-115,Mj-3,Mj-15, Su-7,Wq-15 and Lu-7) distributed in the study area were used to compute the shale volume of Mishrif Formation. From the available data of the considered wells, a regional isopach map of Mishrif Formation was obtained. The isopach map indicates that the maximum thickness of Mishrif Formation is located at the eastern part of the study area. The results of the CPI and the shale volume map, which were computed using the Techlog and surfer software, show that the maximum value of shale volume is located at the southern part of the study area (Su-7 well), while the minimum value is at the eastern part (Hf-2well). According to the classification of Kamel and Mabrouk (2003), Mishrif Formation seems to be a Shaly Formation in the study area, except Halfaya oil field at the eastern part of the study area, which seems as a Clear Formation. The top map of the shale marker bed, which appears in most studied wells, shows a regional trend of the formation toward the northeast. According to the variation of the thickness of the shale marker bed, the study area is divided into four zones.
Highlights
The well log method is an important geophysical exploration method, which is used to explore the subsurface parameters depending on spatial physical properties [1]
Isopach map Mishrif is one of the formations of the Cretaceous period sequence found in most of the wells drilled in the study area; it varies in thickness and depth from one field to another
Information on the thickness and depth of Mishrif Formation was collected from 17 wells distributed in the middle and south Iraq from more than 11 oil fields, as shown in the Table 1
Summary
The well log method is an important geophysical exploration method, which is used to explore the subsurface parameters depending on spatial physical properties [1]. Abbas and Mahdi (2019) studied Mishrif Formation reservoir units in Majnoon oil field They used the well log data (gamma ray, porosity, and resistivity), along with core and cutting samples, to obtain the lithologic facies units. AL-Baldawi and Nasser (2019) studied the petrophysical characteristics of Mishrif Formation in Ahdab oil field They divided the formation into 5 units according to reservoir properties. Studied Mishrif Formation in selected wells of Tuba oil field depending on well log data They divided the Mishrif Formation into five units. Formation in a comparison study between Kumait and Dujailla oil fields using the seismic inversion method and petrophysical properties analysis They concluded that the lithology and porosity are the main factors affecting the acoustic impedance values [14]. After determining the shale volume, contour maps of shale volume distribution were plotted using the Surfer software
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