Optimizing hematite filter cake treatment using reducing agents.

In drilling operations, the formation of a filter cake is crucial for well stability, but its removal post-drilling is essential to restore rock formation productivity. This study focuses on hematite-based filter cakes and investigates factors influencing their solubility and removal, addressing a significant knowledge gap in the field. The research methodology involves examining the effects of various factors, including types and concentrations of reducing agents, temperature, particle size, and treatment duration, on the dissolution process. Notably, Nuclear Magnetic Resonance (NMR) tests are employed to assess the treatment's impact on core porosity. Among the diverse reducing agents examined, ferrous chloride emerges as the optimal choice for effectively enhancing hematite solubility. Particularly, a composite solution of ferrous chloride (10 wt.%) and hydrochloric acid (6 wt.%), was highly efficient demonstrated by exhibiting rapid solubilization of hematite filter cakes. A removal efficiency of approximately 99%, with a parallel enhancement in core permeability was achieved. NMR tests reveal the treatment's success in reinstating the porosity system, which had undergone reduction due to drilling fluid particles. Crucially, the solution exhibits a considerably lower corrosion rate than concentrated hydrochloric acid, highlighting its potential to mitigate environmental concerns while ensuring efficient filter cake removal. The findings of this research provide valuable insights into optimizing post-drilling operations, balancing environmental sustainability and operational efficiency. The identified composite solution offers a promising approach to efficient filter cake removal while mitigating environmental concerns associated with corrosion. Overall, this study contributes to advancing the understanding and practice of well productivity enhancement in the oil and gas industry.

H2, CO2, and CH4 Adsorption Potential of Kerogen as a Function of Pressure, Temperature, and Maturity.

We performed molecular dynamics simulation to elucidate the adsorption behavior of hydrogen (H2), carbon dioxide (CO2), and methane (CH4) on four sub-models of type II kerogens (organic matter) of varying thermal maturities over a wide range of pressures (2.75 to 20 MPa) and temperatures (323 to 423 K). The adsorption capacity was directly correlated with pressure but indirectly correlated with temperature, regardless of the kerogen or gas type. The maximum adsorption capacity was 10.6 mmol/g for the CO2, 7.5 mmol/g for CH4, and 3.7 mmol/g for the H2 in overmature kerogen at 20 MPa and 323 K. In all kerogens, adsorption followed the trend CO2 > CH4 > H2 attributed to the larger molecular size of CO2, which increased its affinity toward the kerogen. In addition, the adsorption capacity was directly associated with maturity and carbon content. This behavior can be attributed to a specific functional group, i.e., H, O, N, or S, and an increase in the effective pore volume, as both are correlated with organic matter maturity, which is directly proportional to the adsorption capacity. With the increase in carbon content from 40% to 80%, the adsorption capacity increased from 2.4 to 3.0 mmol/g for H2, 7.7 to 9.5 mmol/g for CO2, and 4.7 to 6.3 mmol/g for CH4 at 15 MPa and 323 K. With the increase in micropores, the porosity increased, and thus II-D offered the maximum adsorption capacity and the minimum II-A kerogen. For example, at a fixed pressure (20 MPa) and temperature (373 K), the CO2 adsorption capacity for type II-A kerogen was 7.3 mmol/g, while type II-D adsorbed 8.9 mmol/g at the same conditions. Kerogen porosity and the respective adsorption capacities of all gases followed the order II-D > II-C > II-B > II-A, suggesting a direct correlation between the adsorption capacity and kerogen porosity. These findings thus serve as a preliminary dataset on the gas adsorption affinity of the organic-rich shale reservoirs and have potential implications for CO2 and H2 storage in organic-rich formations.

Review of Kerogen's Geomechanical Properties: Experiments and Molecular Simulation.

Measuring the mechanical properties of kerogen, the predominant constituent of organic matter in shale is exceedingly difficult as it constitutes small-scale aggregates interspersed in rocks. Kerogen is characterized by significantly lower stiffness compared to inorganic minerals, thereby the kerogen regions are potential areas for study during, for example, drilling or macroscopic fracture propagation in the course of hydraulic fracturing. For instance, the elastic modulus of kerogen-rich spots is around 10 GPa, while it is about 70 GPa for quartz. Failure of the kerogen nanocantilever beam shows an elastic strain-hardening behavior, indicating a higher energy requirement to propagate a crack. Studies illustrated that the kerogen's mechanical properties are controlled by maceral composition and are positively correlated to the maturity level. This paper provides a comprehensive review of how the mechanical properties of kerogen are elucidated experimentally and contrast the results with the properties delineated from molecular simulation. In addition, we relate kerogen innate attributes, such as maturity and type, to the physical qualities measured and substantiate why accurate knowledge of the mechanical characteristics is pivotal from a hydraulic fracturing perspective.

Geomechanics of Organic Matters Contained in Shales: A Molecular-Level Investigation.

Petrophysical and mechanical properties of kerogen are difficult to obtain through conventional techniques due to length scale limitations. Characterization of kerogen requires the isolation of organic materials from the rock matrix, which is associated with a high probability of mechanical damage or chemical alteration of the properties. Alternatively, computational modeling and molecular representation of kerogens can be used to simulate the outcomes of the experimental work. Volumetric and thermodynamics modeling of kerogens has provided the means for recreating nanoscale structures virtually. This research implements existing three-dimensional (3D) kerogen macromolecules to form kerogen structures that can be analyzed for the mechanical behavior of type II organic matters, mainly found in shales, at different maturity levels. Additionally, the underlying factors that could control the mechanical behavior, such as the density and porosity, were investigated. The results are compared against those reported following a similar methodology or other advanced fine-scale experimental work. The results revealed an elastomer-like mechanical behavior of kerogen with comparable elastic moduli regardless of maturity level. Moreover, the mechanical behavior of kerogen was sensitive to the type of fluid contained within the structure. Such observations can help shed more light on the macroscopic mechanical properties of shales, especially for formations with high organic contents.

Study of the Mechanical Behavior of Organic Matters Contained in Source Rocks: New Insights into the Role of Bitumen.

Assessment of mechanical properties of organic matters contained in unconventional formations is needed to understand the geomechanics of source rocks. The organic matters are part of the source rock matrix, and they are made of kerogen and bitumen. Although the literature has some studies addressing the properties of kerogen and bitumen, no apparent attempts were made to address the mechanical behavior of organic matters as a combination of both. Isolation of organic matters from the rocks for experimental assessments has some risks of altering the original properties because of their delicate nature and their existence as micro- and nanoconstituents. Some computational approaches such as molecular simulation can serve as an alternative platform for the purpose of delineating organic matter properties including the mechanical ones. This work implements available 3D molecular modeling of kerogen and bitumen with different ratios to mimic organic matters that can be investigated for the mechanical properties. Upon the recreation of different configurations of organic matters molecularly, mechanical parameters such Young's, bulk, and shear constants, as well as the stress-strain relationship for the elastic and plastic deformations were extracted. The mechanical behavior was closely monitored before and after saturation with a number of gases that are commonly found in subsurface formations such as methane, carbon dioxide, and nitrogen. The results revealed that the organic matters had a mechanical behavior envelope similar to what were reported for organic-based materials such as polymers. Moreover, the structures containing bitumen exhibited larger values of Poisson's ratio, indicating less likelihood of them to degrade upon applied stresses. The presented data substantiate the importance of accounting for both bitumen and kerogen in modeling the petrophysics and the mechanical behavior of the organic matters.

Petrophysics of Kerogens Based on Realistic Structures.

Combining hydraulic fracturing with lateral drilling has allowed for economical hydrocarbon production from unconventional formations. Nevertheless, beyond hydraulic fracturing, our understanding of how hydrocarbons are stored and transported from the stimulated volume of a reservoir is still limited. Source rocks consist of organic materials finely dispersed within an inorganic matrix. Despite their small size, these organic pockets are capable of storing significant amounts of hydrocarbon due to their large surface area. The extent of the source rock's storage capacity is determined by several factors, including the natural fracture abundancy, organic material content, type, and level of maturity. The petrophysical properties of organic materials, also known as kerogens, are subject to a high degree of uncertainty. Kerogens are difficult to isolate experimentally, which hinders accurate petrophysical analysis. The objective of this research was to use a molecular modeling approach to explore the petrophysical characteristics of kerogen. Kerogen macromolecules of different types and maturity levels were recreated via a computational platform. Then nanoporous structures representing these kerogens were obtained and characterized. Several elemental parameters, including porosity, density, pore size distribution, and adsorption capacity were closely delineated. The kerogen properties were found to correlate with the kerogen type and thermal maturity level. Kerogen type III showed the highest storage capacity, followed by types II and I, in a descending order. Moreover, in the same type of kerogen, a general trend of increasing storage capacity was observed as the maturity level increased. Methane adsorption capacity was modeled as a function of kerogen porosity. A transition flow regime was found to be the predominant mechanism. Such observations have significant implications for reservoir-scale modeling of unconventional resources.

Molecular Fractionation in the Organic Materials of Source Rocks.

Hydrocarbons that are transported in a hierarchal path from the nanoporous constituents of a shale matrix to natural and then hydraulic fractures are subject to continuous fractionation during the journey. The organic nanopores of a source rock matrix known as kerogen have pore sizes on the angstrom scale. At that degree of confinement, pores can act as a selective membrane, preferentially maintaining some components over the others in a continuous fractionation phenomenon that alters the adsorption/desorption isotherm. Several studies have considered the adsorption/desorption behavior of kerogen on the basis of a single component. In reality, methane is associated with other hydrocarbons, making that assumption questionable. The present work investigates the multicomponent gas sorption of kerogen structures via a molecular computational approach. The continuous fractionation results in the accumulation of heavier components. The compositional changes alter the phase behavior, enlarging the anticipated two-phase regime. Additionally, the ability of molecules to diffuse from kerogen was also found to be affected by the fractionation effect. These microscale effects provide some insights into the potential factors that influence the productivity at the reservoir scale.

Effect of Kerogen Thermal Maturity on Methane Adsorption Capacity: A Molecular Modeling Approach.

The presence of kerogen in source rocks gives rise to a plethora of potential gas storage mechanisms. Proper estimation of the gas reserve requires knowledge of the quantities of free and adsorbed gas in rock pores and kerogen. Traditional methods of reserve estimation such as the volumetric and material balance approaches are insufficient because they do not consider both the free and adsorbed gas compartments present in kerogens. Modified versions of these equations are based on adding terms to account for hydrocarbons stored in kerogen. None of the existing models considered the effect of kerogen maturing on methane gas adsorption. In this work, a molecular modeling was employed to explore how thermal maturity impacts gas adsorption in kerogen. Four different macromolecules of kerogen were included to mimic kerogens of different maturity levels; these were folded to more closely resemble the nanoporous kerogen structures of source rocks. These structures form the basis of the modeling necessary to assess the adsorption capacity as a function of the structure. The number of double bonds plus the number and type of heteroatoms (O, S, and N) were found to influence the final configuration of the kerogen structures, and hence their capacity to host methane molecules. The degree of aromaticity increased with the maturity level within the same kerogen type. The fraction of aromaticity gives rise to the polarity. We present an empirical mathematical relationship that makes possible the estimation of the adsorption capacity of kerogen based on the degree of polarity. Variations in kerogen adsorption capacity have significant implications on the reservoir scale. The general trend obtained from the molecular modeling was found to be consistent with experimental measurements done on actual kerogen samples. Shale samples with different kerogen content and with different maturity showed that shales with immature kerogen have small methane adsorption capacity compared to shales with mature kerogen. In this study, it is shown for the first time that the key factor to control natural gas adsorption is the kerogen maturity not the kerogen content.

Artificial Lift and Mobility Enhancement of Heavy Oil Reservoirs Utilizing a Renewable Energy-Powered Heating Element.

The improvement of heavy oil recovery by steam injection or electric heating has been investigated extensively. However, the potential benefit of placing a permanent heating element around the pay zone has not received significant attention. Previously, numerical models were mainly used to investigate improvements in reservoir fluid mobility but rarely when considering the impact of downhole heating on a wellbore's vertical lift performance. In this study, a coupled mass and heat transfer model was developed and applied to a reservoir/wellbore system to investigate the impact of a heating element on recovery improvement. The numerical simulations showed that heat propagation due to the heating element did not exceed 10-15 ft while the reservoir's fluids were being produced. However, much longer distances could be reached through heat conduction under shut-in conditions. It was determined that more than a 40% improvement in the productivity index could be achieved at low production rates. However, no productivity improvement was noticed under convection-dominated heat transfer, which occurs at relatively high production rates. A heating element could also reduce the flowing bottomhole pressure required in a wellbore by more than 200 psi, a result caused by a continuous temperature increase as the fluids flowed into the heated wellbore section.

Pore Network Modeling Study of Gas Transport Temperature Dependency in Tight Formations.

Temperature's effects on rock permeability are ambiguous; both positive and negative correlations have been reported in the literature. Temperature can affect the geomechanical behavior of porous media, as well as influence the mode of fluid transport. Rocks are subject to deformation, compaction, and chemical alteration at elevated temperatures. Conversely, confined fluids can undergo augmented non-Darcian mechanisms. In this research, a multiscale, multiphysical study of temperature's effects on gas permeability in tight formations is presented.