Estimation of Static Young Modulus for the Third section in Zubair Oil Field :A Comparison Study

A detailed analysis for the mechanical properties of the rock is necessary to maintain a well bore and avoid problems with well bore instability. Static young's modulus is one of the most crucial rock mechanical properties utilized in the drilling process to assess wellbore integrity and setting-up geomechanical earth model. Static young’s modulus change with varies of formation lithology’s which arise the critical need for estimation. The current study, a static young modulus values of different formations in section 12.25“in Zubair oil field are determined by depending on correlation to indicate variations in units and layers. Data of Gamma ray (GR), density log, sonic compression log (DTCO), and sonic shear log (DTSM) logs of well ZA-2 are utilized to estimate this attribute. Four different correlations that are set-up in Techlog 2015 software are used to achieve the aim of this study. These outcomes are calibrated using the fundamental laboratory tests (Brazilin and Triaxle test). The results showed that the modified Morales correlation provides a good matching with Calibration data, while four key data points are poorly correlated with the results of John Fuller's analysis.Also, Morales correlation shows unconformity when porosity reduced by less than 10% at different intervals, and Plumb Bradford correlation produces incorrect findings of static young’s higher than the dynamic. The results declare inversely relationship between porosity and young’s modulus.


Introduction:
The assessment of wellbore stability, reserve compacted, and management of the layer's the rock mechanical characteristics and static young's modulus estimation for the reservoir formation is crucial, [1]. Young's modulus is an elastic mechanical rock characteristic that indicates a stone layer's resistance to an unaxial load, [2]. Estimating the static modulus is a critical step in the creation of geomechanical earth models, [3]. it is particularly vital in the static drilling of hydrocarbon wells since it helps to describe the formation and total stresses, which is utilized for manage wellbore instability, [4]. Static young's modulus changes greatly with the different of the lithology, [2,5]. For shale, the static Young's modulus varies from 0.1Mpsi to 0.99 Mpsi. It ranges from 8 and 12 Mpsi in limestone and 2 to 10 Mpsi in sandstone, [5]. These differences in young's modulus values emphasize that this characteristic changes with lithology, making it essential in prediction of the static young modulus along hydrocarbon wells.
Probability of failure rises with depth in deep wells deeper than 1500 meters, it is crucial to determine the mechanical characteristics of the rock. One essential elastic rock mechanical property for wellbore stability study is static young's modulus. Also best indication for unconfined compressive strength is young's modulus, this is because young's modulus directly measures the load-bearing rock structure and has a relationship with geometry, [6,7,8]. The majority of drilling failure issues are brought on by unstable boreholes, whether they are brought on by stuck pipe or lost circulation as a result of wellbore instability. The capacity of a rock to fracture under a minimum amount of deformation or strain is characterized by the important mechanical feature of brittleness, [9].
A geomechanics distinguishes rocks mechanisms, such as young's modulus, uses solid mechanics and geological interpretations to includes the influences of anthropogenic agents.
The multidisciplinary branch of engineering known as engineering mechanics requires cooperation across the physical, mathematics, and geological sciences, as well as civil, petroleum, and geotechnical engineering, [10]. For reservoir development, management, and prospect appraisal in exploratory locations with very little to no borehole-based rock mechanical data, predictive methods for rock mechanical parameters are crucial. There are certain methods existing for measurement or evaluating the young modulus. Lab testing for plugs are the most direct method of obtaining the rock mechanical data. An indirect approach should be used because it is impossible to derive rock mechanical characteristics directly using logging tools. This study demonstrates an alternative method for calculating static Young's modulus, which is a frequently used dynamic Young's modulus that is obtain from sonic log by utilizing Techlog software in 2015.

Area of Study
One of Iraq's largest crude oil reserves was located in the Zubair oil field that was discovered in 1949 and the oil recovered in 1951. As depict in Figure (

Methodology
The most prevalent issue is the variety of required data. Data was gathered from ZA-2 production well in the Shuaiba dome of the Zubair oil field. Due to drilling difficulties such drilling mud loss and wellbore instability, Section 12.25" was considered for studying since its penetrated six formations (Sadi, Tanuma, Khasib, Mishrif, Rumulla, and Ahmadi).
The focus of elasticity theory is that there is a linear relationship between the applying force (stress) and the resulting deformation(strain). As seen in Figure (2), Hooke's law states that the Young's modulus E or the Modulus of Elasticity is represented by the stress-strain diagram's slope, [2,9,13]. dynamic Young's modulus is first determined from sonic log since static cannot be derived directly from it. The elastic characteristics were computed using the sonic log data under the assumption of a homogeneous, isotropic, and elastic formation as follows.

Dynamic Modulus
These mechanical rock characteristics can be calculated from logs with aid of (sonic shear, compression log, and density log). Equations (2) and (3) can be used to calculate dynamic shear and bulk modulus (Gdyn and Kdyn) at the first, then equation (4) can be used for calculate dynamic young's modulus. The dynamic young's modulus may be larger than the static young's modulus, according to various previous research, [14,15]. The dynamic Young's modulus may be 1.5 to 3 times higher than the static one [16] and other studies indicate that dynamic may be 10 times bigger than static, [17,18].
Where Gdyn is dynamic shear modulus, Kdyn dynamic bulk modulus, ρb is bulk density in gm/cm3 and t shear is sonic shear velocity while Edyn is dynamic young's modulus.

Static Young Modulus
In-situ stress state on the reserve was a consequence of the static and dynamic young modulus value, [19]. For calculation the static young modulus precisely, an expensive experimental test on an actual core sample was needed, [20]. linear regression analysis and then recovered using a variety of high-permeability materials.
Plumb Bradford correlation was developed in 1998 for sandstone rock. Dynamic young's modulus was used as the input data for this correlation as follows, [23].
The last correlation was Modified Morales correlation which is developed in 1997 by Tom Bratton using Morales data from 1993. The total porosity and dynamic young modulus served as the input data with this correlation as shown in equation (10). For sandstone and shale rock with porosity less than 35%, this correlation is recommended as follows, [24].

Results and Discussion
According to Figure ( Only dynamic Young's were used as the input data for John Fuller correlation, as seen in  The third and fourth tracks were used as input data for the Modified Morales correlation, as seen in Figure (7). The last track was estimating the static young modulus using this correlation, and as can see, the black circles containing the core data were an excellent fit.
According to the findings, minimum values of this characteristic make the formation would failure and collapse, as porosity increases the young's modulus decreased.
The Modified Morales correlation was the best method for estimating the static young modulus, according the findings of the four correlation. In comparison to previous