Changes In Geomechanical Properties Research Articles

EXPRESS 3D GEOMECHANICAL MODELING FOR INPUT TO HYDRAULIC FRACTURING ON CARBONATE OILFIELDS OF BASHKORTOSTAN REPUBLIC

The work describes a method of real-time 3D modeling of mechanical properties over the entire field area for the purposes of hydraulic fracturing. The uniqueness of this modeling approach is associated with the prompt acquisition of mechanical properties along the well paths of the field, which is especially important in conditions of insufficient geomechanics data.
 Traditional three-dimensional geomechanical modeling is a time-consuming and resource-intensive process. The data often describe the mechanical properties and stress-strain state of the rocks within the current drilling or development sector of the field and do not take into account the interwell space, especially in poorly drilled areas of the field. The method of real-time 3D geomechanical modeling makes it possible to quantify values of minimum horizontal stress used in hydraulic fracturing simulators, as well as static and dynamic Young's modulus and Poisson's ratio over the entire field area using the optimal amount of resources and in a shorter time.
 Based on the built three-dimensional cubes of elastic properties and stresses, correct data were obtained in the inter-well space, their vertical and lateral changes were analyzed, and frac design data were obtained at any well drilled through the simulated targets of the field.
 This paper covers the Arlanskoye, Znamenskoye and Yugomashevskoye fields (Bashneft PJSC). The target targets are carbonate deposits: Kashira and Podolsk strata of the Arlanskoye field, Tournaisian strata of the Znamensky field and Bashkir-Vereisky strata of the Yugomashevsky field.
 For the carbonate rocks of the target targets, laboratory core studies were carried out to determine elastic properties, and stable regional core-core relationships were obtained in the intervals of lower and middle Carboniferous carbonate deposits.
 1D geomechanical models were built in RN-SIGMA software 84 wells at the intervals of the study targets. In current 3D geological models are introduced and distributed values of Young's modulus, Poisson's coefficient and minimum horizontal stress gradient is calculated. Analysis of changes in geomechanical properties by area, for each study object was carried out and data were obtained to create frac designs for 15,000 wells.

Investigation of changes in geomechanical properties of sandstones under different saturation and anisotropy conditions: Example from Gümüşhane (NE Türkiye)

In this study, the changes in various geomechanical properties were studied for sandstones cropped out at the Mescitli region of the Gümüşhane city under different saturation and anisotropy conditions. For this purpose, 225 specimens were prepared considering the lamination planes of those were chosen to have orientation of 0, 30, 45, 60 and 90° relative to loading direction. Index properties of the sandstones such as dry unit weight (dry), saturated unit weight (sat), water absorption by weight (Aw) and water absorption by volume (Av) were assigned. In accordance with the objective of study P wave velocity, uniaxial compressive strength and indirect tensile strength values were determined based on different saturation and anisotropy conditions. It was noted as a result of the observations carried out that specimens parallel to lamination have higher wave velocities in general when compared with specimens that are perpendicular to lamination planes. While uniaxial compressive strength values for sandstones are high for specimens which are parallel and perpendicular to lamination, the lowest strength value was observed in specimens with an anisotropy angle of 30°. In addition, it was also observed that the strength values decrease at a significant level with increasing saturation conditions. Strength anisotropy ratio (RUCS) for sandstones varies between 1.28–1.49 based on different saturation conditions. Similarly, while indirect tensile strength values were higher in specimens that were parallel and perpendicular to lamination, they were lower for other anisotropy orientations. Indirect tensile strength values also decreased with increasing degree of saturation.

Study of CO2 injection in a depleted oil reservoir using geomechanically coupled and non-coupled simulation models

This study seeks to understand CO2 injection into a depleted reservoir through multiphase fluid flow and geomechanical modeling simulations using field data. A comparison of the one-way geomechanically coupled and non-coupled models is presented. Results suggest that computed fluid pressure response and CO2 distribution in the reservoir are significantly influenced by reservoir geomechanical properties. The non-coupled model shows <50% of CO2 penetration distance and laterally shallower reservoir pressure changes compared to the coupled model after 53 days of injection. However, in the non-coupled model, CO2 concentration is significantly higher at short distances from the injection well compared to the coupled model. This reservoir behavior was attributed to the alteration in relative permeabilities caused by changes in geomechanical properties in the coupled model. Therefore, upon the availability of computing resources, one should use more computationally intensive but accurate models involving two-way-coupling. Finally, accurate determination of engineering properties and proper geological characterization is desirable for meaningful prediction models.

Perforation location optimization through 1-D mechanical earth model for high-pressure deep formations

Optimum perforation location selection is an important study to improve well production and hence in the reservoir development process, especially for unconventional high-pressure formations such as the formations under study. Reservoir geomechanics is one of the key factors to find optimal perforation location. This study aims to detect optimum perforation location by investigating the changes in geomechanical properties and wellbore stress for high-pressure formations and studying the difference in different stress type behaviors between normal and abnormal formations. The calculations are achieved by building one-dimensional mechanical earth model using the data of four deep abnormal wells located in Southern Iraqi oil fields. The magnitude of different stress types and geomechanical properties was estimated from well-log data using the Techlog software. The directions of the horizontal stresses are determined in the current wells utilizing image-log formation micro-imager (FMI) and caliper logs. The results in terms of rock mechanical properties showed a reduction in Poisson’s ratio, Young modulus, and bulk modulus near the high-pressure zones as compared to normal pressure zones because of the presence of anhydrite, salt cycles, and shales. Low maximum and minimum horizontal stress values are also observed in high-pressure zones as compared to normal pressure zones indicating the effects of geomechanical properties on horizontal stress estimation. Around the wellbore of the studied wells, formation breakouts are the most expected situation according to the results of the wellbore stress state (effective vertical stress (σzz) > effective tangential stress (σθθ) > effective radial stress (σrr)).

Quantifying Rock Weakening Due to Decreasing Calcite Mineral Content by Numerical Simulations.

The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution.

The impact of the mineral composition of Carboniferous claystones on the water-induced changes of their geomechanical properties

In this article, the authors describe the characteristics and changes of geomechanical properties of Carbonifeorus claystones as related to their mineral composition and the time of soaking in water. Geomechanical properties, including bulk density, Young modulus, Poisson ratio, unconfined compressive strength, durability index, and swelling index were examined in dry rock samples, and in water-soaked samples after 3 hours of soaking, and 6 hours of soaking respectively. Changes in the geomechanical properties of rocks were also examined as a function of their mineralogical composition. In particular, the properties of rocks were examined in relation to present aluminosilicates and layered aluminosilicates, respectively. Changes in the geomechanical properties were also examined relative to the presence of minerals anatase and siderite. Correlation coefficients between physical parameters and mineral composition were examined. It was determined that the total quantity of aluminosilcates is a better predictor of geomechanical properties after soaking, than only the content of layered aluminosilicates. Calculated correlation coefficients were generally higher for most samples after 6 hours of soaking than after 3 hours of soaking. It was also determined that the increase of bulk density correlates much better with the mineral anatase content, than with the siderite content.

Modelling stress and strain in coal seams during CO2 injection incorporating the rock–fluid interactions

To reduce the adverse effects of global warming, geological sequestration has been suggested, which includes capturing and pumping anthropogenic CO2 into deep underground formations, such as coalbeds. Despite the advantages of coalbed sequestration, its geomechanical aspects are not well studied. In particular, the coupling between geomechanical and reservoir/adsorption behaviours of coal seam has been largely neglected. This paper aims to address this shortcoming by developing a coupled chemo-poro-mechanical model that predicts the geomechanical performance of a coal seam in which CO2 is being injected. Recent studies have shown that the interaction of CO2 and coal results in changes in geomechanical properties of coal, namely elastic modulus and peak strength. In order to investigate the significance of these changes in the geomechanical response of the storage site, an analytical solution was found to predict the distribution of stress within an axisymmetric reservoir, considering the effect of sorption-induced changes on mechanical behaviour. The analytical model was then coupled with a simplified dual porous reservoir simulation tool to study the effect of CO2 injection on reservoir and geomechanical performance of the coal seam. The results of the simulation showed that the changes in geomechanical properties of coal can significantly influence the stress and strain distributions within the formation, and therefore, the permeability distribution. Also, it was found that for the example simulated in this paper the adsorption induced reduction in strength did not influence the extent of the mechanical failure zone of the reservoir.

The Influence of the Salt Mist on the Deterioration of Rock Materials

Abstract The paper is focused on changes of geomechanical properties with regard to loss of long-term resistance in studies on the influence of salt spray on the structure of selected rocks from Poland. The investigation has shown that the analyzed rock material shows variable susceptibility to this corrosive factor. The most susceptible to ageing by salt mist were Śmiłów sandstones, whose progressive deterioration was observed in subsequent cycles. Analysis of resistance parameters has shown decreased resistance to uniaxial compression exceeding 30% also in the case of the Józefów limestones. Limestones from Raciszyn have revealed high resistance to ageing by salt mist.

Biocalcification of Sand through Ureolysis

Biological processes may provide great and previously unexplored opportunities for cost-effective, in situ improvement of the engineering properties of soil. A laboratory study was conducted to evaluate the changes in geomechanical properties of sand attributable to the formation of calcium precipitates induced through ureolysis catalyzed by Sporosarcina pasteurii (S. pasteurii). Specifically, direct shear and California Bearing Ratio (CBR) tests were conducted on sand specimens subjected to treatment by growing, resting, and dead S. pasteurii cells in completely stirred tank reactors and completely mixed biofilm reactors, respectively. Scanning electron microscopy analyses were also conducted to evaluate microbially induced precipitation. The results of the study show that the bacterial cells effectively improved the geomechanical properties of the sand. Growing cells improved the sand properties owing to microbially induced precipitation and related pore volume changes, whereas dead and resting cells ge...

Fluid–solid interactions related to subsurface storage of CO2 Experimental tests of well cement

Abstract An on-going Norwegian research project focus on the geochemical interaction of CO 2 with cap-rocks as well as engineered material in wells, and corresponding changes in geomechanical properties. The aim is to establish the nature and extent of induced changes in petrophysics and geomechanical rock/material properties caused by geochemical reactions during long-term exposure to CO 2 and CO 2 -water mixtures. Furthermore, it is an aim to experimentally simulate a leakage situation, where improved understanding of transport and reaction mechanisms and qualification of monitoring techniques are important. Abandoned wells have been identified as one of the most probable leakage pathways for underground CO 2 storage. A comprehensive understanding of the fluid-solid interaction processes in the well and in the near-well area and methods for evaluation of long-term well integrity is necessary. This paper presents preliminary experimental results on the chemical interactions of well cement and brine- CO 2 at conditions relevant for subsurface storage of CO 2 in aquifers (100 bar, 50 ∘ C). Two different scenarios have been tested; the impacts of CO 2 on well cement in a static environment, and secondly, the effects of carbonated brine transport on well cement surfaces. Thus, cement cores have been the subject to a series of static batch experiments with variable duration and water content, as well as steady state flow-through experiments where a CO 2 saturated brine is forced through a channel in the cement. The batch experiments, resembling the long term storage situation, show extensive cement carbonation and near full conversion of Portlandite (Ca(OH) 2 ) to calcite and aragonite on the outer layers of the specimens. The flow experiments reveal a different behaviour due to the advective transport of reactants and reaction products. Cement decalcification to yield a layer of amorphous silica, was found to be rapid and quantitative in the immediate vicinity of the convective flow. Complete cement dissolution and consequent widening of the flow channel was also observed. Results on the propagation rate of reaction fronts are reported. Further work will include geomechanical experiments.

Gas hydrate growth, methane transport, and chloride enrichment at the southern summit of Hydrate Ridge, Cascadia margin off Oregon

At the summit of Hydrate Ridge (ODP Sites 1249 and 1250), pore fluids are highly enriched in dissolved chloride (up to 1370 mM) in a zone that extends from near the sediment surface (∼1 mbsf) to depths of 25±5 mbsf. Below this depth, brines give way to chloride values approaching seawater concentrations with lower chloride anomalies superimposed on baseline values. We developed a one dimensional, non-steady state, transport reaction model to simulate the observed chloride enrichment at Site 1249. Our model shows that in order to reach the observed high chloride values, methane must be transported in the gas phase from the depth of the BSR to the seafloor. Methane transport exclusively in the dissolved phase is not enough to form methane hydrate at the rates needed to generate the observed chloride enrichment. Methane transport in the gas phase is consistent with geophysical and logging data, estimates of gas pressure beneath the BSR, and observations of bubble plumes at the seafloor.In order to reproduce the observed chloride and gas hydrate distributions, the model requires an enhanced rate of hydrate formation in near surface sediments, which we implement through depth-dependent kinetic constants. We argue that this is justified by changes in geomechanical properties of the sediment. At depths shallower than 25 mbsf the force of crystallization can overcome effective overburden stress, and hydrate growth proceeds by particle displacement, thus minimizing capillary inhibition effects.Our calculations indicate the hydrates in the upper sediments of the ridge summit are probably younger than 1500 years, although the age is difficult to constrain. Independent estimates based on seafloor observations at this site yield gas hydrate formation rates at the ridge crest on the order of 102 mol m−2 year−1. These rates are several orders of magnitude higher than those estimated for Site 997 on the Blake Ridge.

Influence of physical and diagenetic processes on fault geomechanics and reactivation

Geomechanical and capillary properties of cataclastic and phyllosilicate framework fault rocks are related to physical anddiagenetic processes occurring syn- and post-deformation. Clay content influences mechanical properties both pre- and post diagenesis, although in different ways. Pre-diagenesis, clay-rich sandstones are often weak with lowered friction coefficients and cohesive strengths. Quartz cementation is influenced by temperature and enhanced by the presence of clays up to a certain volume and can strengthen fault rocks considerably. Changes in geomechanical properties of fault rocks resulting from these processes have implications for geomechanical predictive methods that are used to assess fault reactivation risk.

99/03647 Recovery and use of methane from coal beds: Lebedev, A. N. Ugol', 1998, (7), 56–58 (In Russian)

To reduce the adverse effects of global warming, geological sequestration has been suggested, which includes capturing and pumping anthropogenic CO2 into deep underground formations, such as coalbeds. Despite the advantages of coalbed sequestration, its geomechanical aspects are not well studied. In particular, the coupling between geomechanical and reservoir/adsorption behaviours of coal seam has been largely neglected. This paper aims to address this shortcoming by developing a coupled chemo-poro-mechanical model that predicts the geomechanical performance of a coal seam in which CO2 is being injected. Recent studies have shown that the interaction of CO2 and coal results in changes in geomechanical properties of coal, namely elastic modulus and peak strength. In order to investigate the significance of these changes in the geomechanical response of the storage site, an analytical solution was found to predict the distribution of stress within an axisymmetric reservoir, considering the effect of sorption-induced changes on mechanical behaviour. The analytical model was then coupled with a simplified dual porous reservoir simulation tool to study the effect of CO2 injection on reservoir and geomechanical performance of the coal seam. The results of the simulation showed that the changes in geomechanical properties of coal can significantly influence the stress and strain distributions within the formation, and therefore, the permeability distribution. Also, it was found that for the example simulated in this paper the adsorption induced reduction in strength did not influence the extent of the mechanical failure zone of the reservoir.