Correlation of Mechanical Parameters in a Giant Carbonate Field, UAE

The rock properties in the reservoir rocks represent stiffness and strength properties, while the unexpected variation in the dense intervals varies with the fabric and other sedimentological and rock types. The purpose of this paper is to present the mechanical rock testing parameters of Lower Cretaceous reservoirs, including the tight intervals in a giant field of Abu Dhabi. In order to enable the evaluation of the mechanical parameters, there is a need to assess the reservoir rocks, as well as the stress configuration around and away from the wells. This paper introduces a workflow that integrates multidisciplinary data to develop a geomechanical model aiming to reduce drilling risks and optimizing reservoir appraisal. Cores, wireline logs, CT scans, SEM and thin sections were used to characterize the fracture systems and build the robust seismic driven geomechanical model. A conceptual model has been firstly developed, where reservoir heterogeneity has been quantitatively described in relation to tectonic deformation events, followed by incorporating a 1D-MEM's (Mechanical Earth Model), which used to calibrate the seismic based elastic properties. Results indicate good correlations developed between dynamic and static Young's Modulus, Biot's coefficient, Friction Angle and Unconfined Compressive Strength by incorporating the results of rock mechanics testing, leading to create a dynamic YME-driven correlation. Good correlations were also obtained between Effective Porosity, and Static Young's modulus, Biot's coefficient, Friction angle and Unconfined compressive strength, leading to create a Porosity-driven correlation. In addition, friction angle correlation increases if proper data is considered, making feasible to build a correlation in both dynamic YME and Effective Porosity. Finally, the presence of several partially conductive fracture sets within the reservoir, including both sub-vertical and moderately dipping conjugate sets, with gently dipping/bed-parallel fractures. They have been developed under a predominant strike-slip regime that swaps a normal faulting stress regime at depth. Fracture porosity is related to micro- and meso-scale fractures, and fracture permeability is more significant compared to the storage capacity of the matrix porosity. Rock fabrics are varied in different zones, which likely explains differences in the mechanical behaviour.

Geomechanical parameters of sedimentary rocks of Southern Sakhalin

The samples of terrigenous rocks of the Sakhalin were selected for geomechanical studies: the rocks of the Nevelskaya and Kholmskaya Formations from the Petropavlovsk quarry; ones of the Kholmskaya Formation on the west coast of the south of Sakhalin, rocks of the Junonskaya Formation on the east coast. The Kholmskaya Formation N1hl is represented by siltstones and interlayers of fine-grained sandstone. The Nevelskaya Formation N1nv is represented by siltstones with inclusions of tufogenic material. The Junonskaya Formation T2-Jun is represented by variegated greyish-green jaspers. Their static and dynamic parameters (strength limits, static Young’s modulus and Poisson’s ratio, cohesion and angle of internal friction) were determined. The obtained results are characterized by a significant spread of values, which is likely explained by the significant fracturing of the initial samples and the effect of anisotropy.

Estimation of Mechanical Rock Properties from Laboratory and Wireline Measurements for Sandstone Reservoirs

Mechanical rock properties are essential to minimize many well problems during drilling and production operations. While these properties are crucial in designing optimum mud weights during drilling operations, they are also necessary to reduce the sanding risk during production operations. This study has been conducted on the Zubair sandstone reservoir, located in the south of Iraq. The primary purpose of this study is to develop a set of empirical correlations that can be used to estimate the mechanical rock properties of sandstone reservoirs. The correlations are established using laboratory (static) measurements and well logging (dynamic) data. The results support the evidence that porosity and sonic travel time are consistent indexes in determining the mechanical rock properties. Four correlations have been developed in this study which are static Young’s modulus, uniaxial compressive strength, internal friction angle, and static Poisson’s ratio with high performance capacity (determination coefficient of 0.79, 0.91, 0.73, and 0.78, respectively). Compared with previous correlations, the current local correlations are well-matched in determining the actual rock mechanical properties. Continuous profiles of borehole-rock mechanical properties of the upper sand unit are then constructed to predict the sand production risk. The ratio of shear modulus to bulk compressibility (G/Cb) as well as rock strength are being used as the threshold criterion to determine the sanding risks. The results showed that sanding risk or rock failure occurs when the rock strength is less than 7250 psi (50 MPa) and the ratio of G/Cb is less than 0.8*1012 psi2. This study presents a set of empirical correlations which are fewer effective costs for applications related to reservoir geomechanics.

The Mechanical Stratigraphy of Kerendan Field in Upper Kutai Basin: Implication to Field Development with Massive Carbonate Tight Gas Reservoir

Understanding of field mechanical stratigraphy in terms of formation behavior due to coupled interaction between formation pressure depletion and state of stresses is crucial to achieving successful field development. These provide technical advantages of having a solid foundation for implementation in advanced well construction and completion strategy, especially in light of emerging and challenging plays related to unconventional reservoirs. This paper describes full-field interaction between formation behavior in 4D Geomechanical analysis of Kerendan Field located in Upper Kutai Basin, Central Kalimantan area on gas-condensate production from massive carbonate tight gas reservoir. Integrated 1D/3D/4D geomechanics study workflow result has enabled characterization of each mechanical stratigraphy unit, as follows: The overburden section is comprised of Miocene deltaic clastic succession which is characterized as “soft formation” with low stiffness (Static Young’s Modulus of 0.5 to 1.8 Mpsi) and low - medium rock strength (UCS of 800 to 2000 psi); Reservoir section comprised of Oligocene tight carbonates platform which characterized as “hard formation” with medium stiffness (Static Young’s Modulus of 3.0 to 4.5 Mpsi) and medium rock strength (UCS of 5000 to 6900 psi); Underburden section comprised of Eocene mixed-carbonate clastic succession and Pre-Tertiary metasediments which characterized as “very hard formation” with high stiffness (Static Young’s Modulus of 4.5 to 5.0 Mpsi) and medium rock strength (UCS of 6500 to 7900 psi). The Kerendan field would require implementation of special drilling and stimulation techniques in order to achieve optimum full field development potential owing to its reservoir characteristics. The field’s exhibit a large areal extent and massive tight limestone reservoir with relatively high Young’s Modulus, which is favorable for the utilization of extended reach drill (ERD) / horizontal wells followed with multi-stage acid fracturing stimulation. 3D/4D Geomechanical analysis is essential to assess the drillability and engineering limits of various development scenarios which will be strongly controlled by geomechanical fabric, pre-existing deformation/local discontinuities, prevailing principal stress tensor and stress changes during field production.

1-D MECHANICAL EARTH MODELING IN THE PERMIAN LUCAOGOU SHALE OF THE SANTANGHU BASIN, NORTHWEST CHINA FROM A COMPLETE SET OF LABORATORY DATA

Understanding various properties of unconventional shale plays is important for successful field operations and development. A total of 11 core plugs were collected from the productive unit of the Middle Permian Lucaogou Formation in the Santanghu Basin and were examined comprehensively with various experimental tools. Mineral assemblages were detected, and samples were found in the oil window with a combination of type I and II kerogens via XRD and Rock Eval analysis. Static and dynamic geomechanical methods provided us with a clear image of samples elastic properties and correlations were established between them through ultrasonic and geomechanical testing. Results showed that the samples have a brittle behavior with hydrostatic compressive strength ranging from 177.68 MPa to 419.63 MPa, and static Young’s modulus from 9.93 GPa to 53.24 GPa. In the next step, the measured data was used to calibrate the only-existing well log from where the samples were retrieved, and a 1-D MEM was built throughout the entire target formation. Ultimately, Partial Least Square Regression (PLS) analysis revealed that feldspar and calcite are the main stiff minerals that would affect mechanical properties positively, while clay minerals and organic matter could have a negative impact on the rock mechanics parameters.

Anisotropic strength and failure behaviors of transversely isotropic shales: An experimental investigation

The deformation and fracture of anisotropic shale rocks are of great interest to geoengineers concerned with assessing the stability of boreholes and underground excavations. However, some mechanic properties associated with anisotropic rock fracture remain ambiguous. We have purposely reported triaxial failure tests on two sets of transversely isotropic shale plugs (i.e., Marcellus and Eagle Ford shales) cutting parallel and perpendicular to the bedding planes. The experimental results suggest that the bedding planes give rise to considerable differences in the elastic properties, failure strength, and failure modes in the bedding-normal and bedding-parallel directions. In general, the static Young’s modulus is higher parallel to bedding than normal to bedding, whereas the static Poisson’s ratios measured from the vertical and horizontal shale plugs do not exhibit a certain relationship. The ratio between the bedding-parallel and bedding-normal failure strength is approximately 1.9 for Marcellus shales, whereas it is approximately 1.3 for Eagle Ford shales. At the failure point, the axial strains are appreciably larger than the radial strains. In contrast, the two orthogonal radial strains exhibit different characteristics in the bedding-normal and bedding-parallel directions, giving rise to complex failure modes. The extended cracks in the vertical plugs lead to fracturing in a shearing manner, with a single shear plane in the Eagle Ford shale and two conjugate shear planes in the Marcellus shale. In the horizontal plugs, the Eagle Ford shale exhibits shear banding in the bedding-normal direction and a combination of shear and extension in the bedding-normal direction. In contrast, the Marcellus shale exhibits three conjugated shear planes.

A comparative study of the stress-dependence of dynamic and static moduli for sandstones

Understanding the differences between the static and dynamic elastic moduli of reservoir rocks is essential for the successful exploration and production of hydrocarbon reservoirs. However, the controlling factors on the dynamic-static discrepancy for sandstones remain ambiguous. Consequently, we have purposely selected three outcrop sandstone samples with large porosity contrast to investigate the effects of the stress state, magnitude, and load-unload history on the dynamic and static moduli through laboratory measurements. The results suggest that the dynamic moduli are systematically larger than the static moduli at almost any hydrostatic or deviatoric stress magnitude. In contrast, the static moduli are much more sensitive to the stress variations than the dynamic ones, leading to the decreasing dynamic-static difference upon hydrostatic loading and the increasing dynamic-static difference upon deviatoric loading. When the maximum stress in a cycle is initially reversed, the dynamic-static ratio tends to approach one, whatever the bulk modulus under hydrostatic pressure condition or the Young’s modulus under triaxial stress condition. Under the subsequent unloading process, the static bulk modulus is always higher than that derived during loading. However, the unloading static Young’s modulus is larger than the loading Young’s modulus only at a relatively high deviatoric stress magnitude greater than 30 MPa, while showing an opposite trend at a low-stress condition of less than 25 MPa. From the microstructural viewpoint, it is believed that the static tests accumulate the elastic, viscoelastic, and nonelastic properties within a certain stress or strain range. In contrast to the dynamic modulus, the static modulus exhibits greater sensitivity to the pressure or stress changes under hydrostatic and deviatoric stress conditions. The strong stress dependence makes it important to consider the in situ stress conditions when establishing dynamic-static modulus relations.

Application of Machine Learning in Evaluation of the Static Young’s Modulus for Sandstone Formations

Prediction of the mechanical characteristics of the reservoir formations, such as static Young’s modulus (Estatic), is very important for the evaluation of the wellbore stability and development of the earth geomechanical model. Estatic considerably varies with the change in the lithology. Therefore, a robust model for Estatic prediction is needed. In this study, the predictability of Estatic for sandstone formation using four machine learning models was evaluated. The design parameters of the machine learning models were optimized to improve their predictability. The machine learning models were trained to estimate Estatic based on bulk formation density, compressional transit time, and shear transit time. The machine learning models were trained and tested using 592 well log data points and their corresponding core-derived Estatic values collected from one sandstone formation in well-A and then validated on 38 data points collected from a sandstone formation in well-B. Among the machine learning models developed in this work, Mamdani fuzzy interference system was the highly accurate model to predict Estatic for the validation data with an average absolute percentage error of only 1.56% and R of 0.999. The developed static Young’s modulus prediction models could help the new generation to characterize the formation rock with less cost and safe operation.