Hussain, Maaruf (Baker Hughes, a GE Company) | Amao, Abduljamiu (King Fahd University of Petroleum and Minerals) | Muqtadir, Arqam (King Fahd University of Petroleum and Minerals) | Al-Ramadan, Khalid (King Fahd University of Petroleum and Minerals) | Babalola, Lamidi (King Fahd University of Petroleum and Minerals) | Jin, Guodong (Baker Hughes, a GE Company)
The knowledge of rocks elastic properties (REP) is crucial to geomechanical modeling throughout an asset life cycle. Reliable geomechanical models requires calibration of well log REP with core measurements. However, sample availability, representativeness, time, and cost are problems associated with core measurements. In this paper, we integrated REP derived from two laboratory techniques performed on several core covering over 800 ft interval samples from Paleozoic tight sands and shale reservoirs to obtain a continuous REP profile for better- upscaling of reservoir model parameters. For lithology delineation, intact core samples were scanned utilizing MicroXRF. While, REP was measured using Autoscan and AutoLab systems. The Autoscan employs non- destructive technique to characterize the variability of REP. The AutoLab uses the standard triaxial testing method to provide REP at reservoir conditions. The results were tabulated and statistically treated to establish significant empirical relationships. REP derived from triaxial tests on selected samples include, the P and S wave velocities (Vp and Vs), static moduli (Young’s modulus (Es) and Poisson’s ratio (vs)), as well as dynamic moduli (Young’s modulus (Ed) and Poisson’s ratio (vd)). While the reduced Young’s modulus (E*) was obtained from non- destructive method. Lithofacies were established from elemental data. The E* reveals details of several geomechanical heterogeneity and anisotropy which are not possible with traditional triaxial method. There is a significant correlation between E* and Es, Ed, Vs, and Vp. A continuous REP profile was developed using E* with geochemical data. Based on the characterized profile, fracture height growth barriers identified were toughness/modulus and interface barriers. These can significantly affect hydraulic fracture vertical growth within the studied Paleozoic tight sands and shale reservoirs units.
The approach, which uniquely considered scales of rock geochemical and mechanical properties and data analytics, demostrate the possibility of generating a continuous REP profile using laboratory aquired dataset. Thus, the difficulty associated with geomechanical characterization and model calibration of highly laminated unconventional reservoirs using actual laboratory data is resolved. This has a directly implication to both conventional and unconventional geomechanical modeling, where the determination of upscaled-reservoir model parameters matters.
The difficulty in obtaining a continuous rock elastic properties (REP) profile from triaxial test makes calibration of geomechanical characterization models subjective. The impulse hammer method however provides reliable, reproducible, and continuous proxy for REP dataset, allowing for rock profiling. The relationship between the REP from these two techniques is not well understood, this study employed multivariate data reduction analysis and modeling to extract relevant correlations between Impulse Hammer and Triaxial derived REP. We derived a Young's modulus proxy called reduced Young's modulus (E*) from core plug samples. The E* was acquired from each sample systematically with respect to rock heterogeneity, grain size, and macropore size. The E* was taken as an average of nine impulse hammer runs per sample on equally spaced gridded location on each sample surface. Dynamic Young's modulus (Ed) and static Young's modulus (Es) were derived from the conventional triaxial test. The geochemical analyses were carried out to capture the mineralogical variations in the selected samples. We used statistical analysis and modeling to establish empirical relationship between Impulse Hammer and Triaxial derived RMP.
The results showed that, E* reliably captures the variables within the rock elastic properties. A strong correlation between the Ed, Es, and E* were observed in the samples. We also observed that E*, reveals details of several geomechanical heterogeneity and anisotropy which are not possible with traditional triaxial method. The results show that the empirical relationship between E and E* can be established to generate a continuous REP profile.
Sample availability, representativeness, time, and cost are common challenges in traditional triaxial test. The Impulse Hammer method is a non-destructive technique that significantly saves time, and has a promising cost efficient workflow, which provides reliable, reproducible and continuous rock mechanical properties profile. A robust geomechanical characterization and model calibration can be performed by combining the outputs obtained from these two methods.
Muqtadir, Arqam (King Fahd University of Petroleum & Minerals) | Elkatatny, S. M. (King Fahd University of Petroleum & Minerals) | Mahmoud, M. A. (King Fahd University of Petroleum & Minerals) | Abdulraheem, A. (King Fahd University of Petroleum & Minerals) | Gomaa, A. (BP America)
ABSTRACT: The presence of pore fluid tends to affect the rock's physical and mechanical properties. It potentially causes drilling problems, casing failures and improper fracture propagation. It is vital to understand how much the strength of the rock is affected when saturated with fluids. Low porosity, permeability and complexities in pore structures can further thwart the effect. The effect of saturating fluid on the dynamic and static properties of low permeability Scioto sandstone outcrop samples was studied in this paper. It was seen that the Unconfined Compressive Strength (UCS) was decreased by 9% for oil saturated rocks and 25% for brine saturated rocks whereas the reduction in the tensile strength was 20% and 42% respectively. The UCS samples were monitored with acoustic emission (AE) and exhibited a series of events.
Geomechanical parameters of rocks are influenced when exposed to fluids. As the water saturation increases, a reduction in the Unconfined Compressive Strength (UCS) (Y agiz and Rostami, 2012) and Young's modulus is seen, while Poisson's ratios tends to increase (Widarsono et al., 2001). Usually sedimentary rocks are more affected by the water saturation than the igneous and metamorphic rock (Wong et al., 2016).
For carbonates, DeVilbiss (1984) partially saturated limestone rock with water and saw an attenuation in the acoustic velocities. Brignoli et al., (1995) performed UCS on fully saturated limestones and saw a 15 to 20% reduction in the Young's modulus. Fabricius & Eberli (2009) also saw a similar decrease.
Zhang et al., (2017) studied the effect of different water saturations on the geomechanical properties of siltstones. The highest reduction in strength was observed at 10% saturation. It was seen that as the water saturation decreased, the volumetric strain of the cracks and the sample decreased as a result from water easing crack initiation and propagation.
Mc Carter (2010) and Perera et al., (2011) performed UCS on coal and sandstones and saw a decrease in UCS and Young's modulus as water saturation increased. Labuz & Berger (1991) saw a decrease of 15 % in the Young's modulus as water saturation increased in granite while Vasarhelyi (2003) saw the same effect in Hungarian volcanic rocks. Henao et al., (2017) reported a significant decrease in strength in sandstone rocks when saturated with brine while a moderate decrease when saturated with dodecane.
Tariq, Zeeshan (King Fahd University of Petroleum & Minerals) | Abdulraheem, Abdulazeez (King Fahd University of Petroleum & Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum & Minerals) | Muqtadir, Arqam (King Fahd University of Petroleum & Minerals) | Murtaza, Mobeen (King Fahd University of Petroleum & Minerals)
In a quest to reduce the greenhouse gasses, geologic sequestration of carbon dioxide (CO2) in an underground hydrocarbon rock formation or aquifer is one of the most promising alternative to reduce the amount of CO2 release in an open environment. However, long-term storage of CO2 effects the geomechanical and geochemical properties of the host rock. In carbonate aquifers, water dissolves the injected CO2 gas forming carbonic acid which has the tendency to dissolve calcium compounds present in the formation. The dissolution of calcium is particularly worrying since it contributes to the matrix of the rock. Thus, the mechanical properties of the rock are altered, which left unattended could result and in compaction of the formation and surface subsidence.
This paper aims to study the degradation of the petrophysical and mechanical properties of two types of rocks namely limestone and sandstone due to the storage of supercritical CO2 for desired amount of time. Supercritical CO2 has low viscosity but high density and has ability to store in large amount within the same space and with the high pumping efficiency. Two different carbonate rocks and one sandstone rock were exposed to a CO2-brine solution at a pressure of 1200 psi and at 120 °C for durations ranging from 10 to 120 days. The mechanical properties were then examined by both static and dynamic mechanical tests along with the routine core analysis (RCA).
Results showed that long term CO2 storage affected the mechanical, acoustic and petrophysical parameters of rocks examined in this study, viz., Khuff limestone, Berea Sandstone, and ordinary limestone. The duration of solubility time brine-CO2-rock has a considerable impact on the petrophysical and mechanical parameters of the rock samples. Outcomes of this study also shows that the rock mechanical and petrophysical properties significantly affected when CO2 store for the longer period of time. CO2, rock, and brine interaction is dependent on time consequently the rock mechanical and petrophysical parameters changes are also time dependent. The potential candidate found for geological sequestration of CO2 studied is limestone because of its minimal rock properties altered.
Release of CO2 gas in the environment is one of the main concern and reason for the rise in the global warming because CO2 has the tendency to trap heat. Although about half of the greenhouse gasses are absorbed naturally (into deeper seas), the rest stays in the Earth's atmosphere for centuries.
Muqtadir, Arqam (King Fahd University of Petroleum & Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohammed (King Fahd University of Petroleum & Minerals) | Abdulraheem, Abdulazeez (King Fahd University of Petroleum & Minerals) | Gomaa, Ahmed (BP)
Hydraulic fracturing is performed to enhance production in reservoirs with low permeability. It's an effective technique but there are still several uncertainties associated in its implementation. One of the uncertainties is the dependence of breakdown pressure on the type of fracturing fluid used. The objective of this paper is to perform an experimental study to determine the role of fracturing fluid on the breakdown pressure of tight sandstone rocks.
The dimensions of the samples are 2 in. (diameter) by 2 in. (length). A hole of 0.25-in. in diameter and 0.75-in. length is drilled on one face of each core through which the fracturing fluid is pumped. A strong power relation between the viscosity of the fracturing fluid and breakdown pressure was seen. As the viscosity increased, the breakdown pressure increased significantly. Computed Tomography (CT) scan showed that the direction of fracture is along the bedding plane. As the viscosity increased, the fracture width and height increased. For most tests, the fractures created were bi-wing fractures. Some single wing fractures were created due to deformities in the borehole.
A Tight gas reservoir is commonly referred to as a low-permeability reservoir (Holditch, 2006). Saudi Aramco defines tight gas reservoir as the one having permeability less than 1 md, porosity less than 12% and requiring hydraulic fracturing to be commercially produced (Hayton et al., 2010). Production from such a reservoir is fairly challenging due to the amount of complexities in the reservoir. Geomechanics plays a key role in the extraction of hydrocarbon from tight gas reservoirs. Geomechanics deals with the study of how rocks deform when they are subjected to stress, temperature and other environmental factors. Most of the failures witnessed in the life of a well are due to geomechanics.
Hydraulic fracturing is an integral part of geomechanics and is used to improve the productivity from such reservoirs. Hydraulic fracturing technique is utilized to help in the economical production of hydrocarbons. The process involves inducing fractures in the rock formation to serve as highways for faster hydrocarbon travel. The process is carried out by injecting fracturing fluid containing water, proppant and other materials (Gandossi and Von Estorff, 2015). The importance of fully understanding the fracturing process is critical in properly developing an efficient hydraulic fracturing plan. The industry today still lacks the complete knowledge of the process and faces difficulties in designing the hydraulic fracturing job. As a result, improper designs have damaged many wells leading to uneconomical production rates (Syfan et al., 2013). Thus, effort must be placed to understand the fracturing technique. Therefore, this study aims to address some of the challenges for tight sandstone in the areas of geomechanics and hydraulic fracturing.
Jin, Guodong (Baker Hughes Incorporated) | Ali, Syed Shujath (Baker Hughes Incorporated) | Muqtadir, Arqam (King Fahd University of Petroleum and Minerals) | Hussaini, Syed Rizwanullah (King Fahd University of Petroleum and Minerals) | Nair, Asok (Baker Hughes Incorporated) | Alshanqaiti, Elham (Baker Hughes Incorporated) | Khodja, Mohammed R. (King Fahd University of Petroleum and Minerals) | Ali, Abdul Wahab Zaki (King Fahd University of Petroleum and Minerals)
This paper experimentally investigates the damage evolution (or the deformation process) induced by externally applied stress on unconventional shale samples. The focus is to understand the physics behind the complex failure process occurring at the micro-scale, and thus provide useful information on the macro-fracture mechanisms of unconventional shales. We perform the compression tests along with the acoustic emission (AE) measurement on cylindrical rock samples selected from Berea sandstone (BS), Eagle Ford (EF) and Marcellus formation. Tests are conducted under the same stress condition: uniaxial unconfined compression test and triaxial compression test with a confining pressure of 10 MPa. AEs are continuously collected to characterize the progressive damage process. The axial stress, axial and radial displacement are also recorded during experiments. Shale samples are drilled perpendicular or parallel to the beddings. The X-ray diffraction (XRD) analysis is used to measure the mineralogy and clay content. Prior to geomechanical testing, the high-resolution micro-CT imaging system is used for quality assessment of rock samples and characterization of microstructure and fracture presence.
All samples studied exhibit distinct characteristics of AE counts. In Berea sandstone, AE counts initially increase slowly with the axial strain, and then surge dramatically after reaching the yield stress point. This is consistent with the observed stress-strain behavior: a linear elastic part followed by the inelastic deformation till the rock fails. Compared to Berea sandstone, shale samples show a different characteristics of AE counts. AEs resulting from EF vertical sample monotonically increase until the sample fails, while three stages of AE activity are observed in the horizontal sample: initial increase followed by a stage of quiet period (no AE events), and increase again. Marcellus samples behave just the opposite: three stages of AE events are observed in the vertical sample, while monotonically increase in the horizontal sample. AEs are also observed to be affected by the test condition: different from the triaxial compression test, Marcellus vertical and horizontal samples have a similar trend in AE counts during the uniaxial compression test. Both initially increase in AE activity with the axial stress, and after a certain stress, a surge in AE activity is observed. The observed discrepancy of AEs can be due to the complexity of shale mineralogical compositions, pore geometry and thin layer structure. More detailed laboratory experiments are necessary to understand the physics behind the complex failure process and AEs occurring at the micro-scale in unconventional shales.