Journal of Engineering Geology

---

The main objective of this research is to investigate the mechanism of cement-clay-heavy metal contaminant interaction from micro-structural point of view. To achieve this objective series of batch equilibrium and XRD experiments were performed. The results indicate that the addition of 10% cement not only stabilizes the soil, but also at 250 cmol/kg-soil of heavy metals causes 130% increase in heavy metal retention. Furthermore, the XRD analysis shows that in solidified samples with less than 10% cement, the main reason for reduction in peak intensity of clay fraction is due to the presence of heavy metals. However, as the percentage of cement increases, the clay solubility is the main reason for reduction in peak intensity of montmorillonite in XRD test

---

Free vibration of soil often occurs during earthquakes. Since the vibration caused by earthquake does not have (steady state harmonic vibration) continuity, the alluvium vibrates with its natural frequency between two natural seismic waves. This study evaluates the effect of piles on the period of free vibration of a soil layer using numerical method. In the first stage, using analytical equations for calculation of vibration period of a soil layer and a column with continuous mass, the results were analyzed by the software. In the second step, piles with the same dimensions and distance were added step by step, and the vibration period for the soil layer with piles was calculated. The friction or floating effects of the piles on alluvial soil vibration period was also examined. The results show that as the number of piles increases, the differences between the results of one dimensional analysis of alluvium soil and the results of the software become different, and this creates the need for specific arrangements for seismic analysis of this kind of alluvium (with inserted piles). The results also suggest that end-bearing piles have a greater effect on alluvial soil vibration period, and with increased amount of the floating of these piles, these effects decline.

 

---

Because of the diversity in petrography, peridotites have variable physical and mechanical properties. For this reason, knowledge of resistance properties and their deformation will help with the prediction of engineering behavior of these rocks. Due to the large spread of igneous rocks, especially peridotite, in Zagros, northeastern and central Iran, special attention has been paid to their petrographic, physical and mechanical characteristics. The construction of the structure within or on the peridotites and the choice for the purpose of the stone borrow depends on the recognition of its engineering geology characteristics. In this paper, in addition to the field and laboratory study, the geological characteristics of peridotite engineering has been investigated.                                    
Material and methods                    
In order to study the geological characteristics of the peridotites of Harsin region, 15 suitable blocks were selected and transferred to the laboratory. Accordingly, from collected rock samples, 150 cylindrical cores of diameter 54 mm were prepared and physical and mechanical tests were performed according to (ISRM, 2007) and (ASTM, 2001) guidelines. In this research, after sampling of the study area and preparing the core for the lithological characteristics of the samples by providing thin sections of them with polarizing microscopy was studied.
Results and discussion
By considering the results of laboratory tests and analysis from Harsin peridotites in Kermanshah province, we can acclaim that with increasing the percentage of minerals in olivine and pyroxene in rock, the strength was decreased and the levels weaknesses, which is due to the weak structure of the mineral-olivine and pyroxene. According to the physical properties test and Anon classification, the porosity percentage in porosity percentage is low and as a result the amount of water absorption index is low. Based on the Gamble classification, all peridotites are very resistant to durability and based on the Franklin and Chandra classification, all samples are extremely resistant. The results of this study showed that the single axial compressive strength, elasticity modulus, point load index and tensile strength were decreased with an increase in humidity content of peridotite samples. This is due to the fact that with the increase of humidity pore pressure of water increases. According to the Anon classification, the peridotites are very high in terms of the length of the longitudinal passage through the rock. The highest compliance between the Brazilian Tensile strength test (BTS) and Schmidt hammer (SHV) was achieved in the dry condition and the determination coefficient (R²) equals to 0.95 was obtained. Also there is an acceptable relation between the Brazilian Tensile Strength Test (BTS) and the dry volume unit weight (γ_d) with the determination coefficient (R²) of 0.93. In addition, there is an admissible relationship between durability test and single-axial compressive strength, with a coefficient determination (R²) of 0.94. Regarding the obtained regressions in this study, the physical and mechanical properties show good agreement and most of the equations have an acceptable coefficient determination.

---

Introduction
CO₂ injection in deep geological formations, such as depleted oil and gas reservoirs, in addition to the environmental benefits, is one of the effective method for enhanced oil recovery (EOR) as tertiary EOR. Presence of reservoirs with a pressure drop which require injection of gas in the southwest of Iran and having the technical and environmental effects of CO₂ injection have created a huge potential for CO₂ injection to EOR in this region. In the first step, to perform CO₂-EOR, the geomechanical assessment is needed to find out pore pressure, in-situ stress magnitudes and orientations and fractures and faults conditions. In this paper, the initial in-situ pore pressure is predicted using modified Eaton method for 47 wells in the length of the study field and calibrated using repeat formation test and mud pressure data. In-situ stress was obtained by the poroelastic method for 47 wells in the length of the study field and calibrated using leak off test and extended leak off test. Then, the orientation of in-situ stresses is obtained based on image logs. Hydraulical and mechanical activities of fractures and faults were performed by critically-stressed-fault hypothesis
Material and Methods
In this paper, the initial pore pressure is calculated using modified Eaton method and other corrections that are proposed by Azadpour et al. (2015). The estimated initial pore pressure is validated using mud weight pressure (Pmw) and repeat formation tester (RFT) data. In-situ stresses are composed of three orthogonal principal stresses, vertical stress (S_V), maximum horizontal stress (S_H), and minimum horizontal stress (S_h) with specific magnitude and orientations. The magnitude of S_V is calculated by integration of rock densities from the surface to the depth of interest. The poroelastic horizontal strain model is used to determine the magnitudes of the S_H and S_h. Then, the estimated minimum horizontal stress from poroelastic horizontal strain model is validated against direct measurements of LOT and XLOT tests. The orientation of breakouts was determined based on compressively stressed zones observed in the UBI log and using Caliper and Bit Size (BS) logs. The hole elongates perpendicular to the S_H and breakouts develop at the azimuth of S_h. Fractures and faults reactivation analyses are very important, they can potentially propagate upwards into the lower caprock and further through the upper caprock due to CO₂ injection. Fractures and faults identification were performed based on image logs. Based on performed seismic interpretations by NISOC (National Iranian South Oil Company), 15 faults have been detected in the field. Fractures and faults conductivity and activity in the current stress filed affect on fluid flow and mechanical stability or instability of the CO₂ injection site. Critically stressed fault hypothesis, introduced by Barton et al. (1995), states that in a formation with fractures and faults at different angles to the current stress field, the conductivity of fluids through their apertures are controlled by the interplay of principal stress orientations and fracture or fault directions. Hence, conductive and critically stressed fractures and faults in the current stress field were evaluated using critically stressed fault hypothesis. Fractures and faults are plotted in normalized 3D Mohr diagrams (normalized by the vertical stress), therefore conductive and critically stressed fractures and faults were determined.
Results and discussions
The maximum distribution of initial pore pressure was 20-25 MPa in the field and the average of initial pore pressure was 25 MPa in the field. Unlike the World Stress Map, the stress regime is normal in the reservoir. Because the Kazeroon fault and Dezful Embayment act as a strike-slip tensional basin, resulting in the subsidence of Dezful compared with other regions. The frequency distribution of calculated in-situ stress in 47 studied wells in the length of the field has been presented. The maximum frequency distribution of S_V, S_H and S_h were between 60-70, 50-60 and 30-40 MPa, respectively. A large amount of fracturing is observed in 20-25 m below the caprock. Based on the continuity of their low amplitude traces on the acoustic amplitude image of UBI, fractures are classified into 4 classes: discontinuous-open, continuous-open, possible-open and closed fractures. OBMI and UBI image logs processing were performed in 7 wells. As can be seen from the image log, and caliper analysis the most dominant strike of S_H around the well is 27^◦ and S_h strike is 117◦. These have two dominant orientation, some faults are along the strike of the Zagros fold-thrust belt (NW-SE) and the others are perpendicular to the Zagros fold-thrust belt strike (NE-SW).
Based on the normalized 3D Mohr diagrams it is clear that the fractures and faults that are oriented to the S_H will be the most permeable, because the faults and fractures experience the least amount of stresses in the direction of S_H and they have minimum resistance to flow in this direction, therefore will have relatively high permeability. Also, results showed the faults number 15, 6, 10 and 2 will be the most dangerous faults during CO₂ injection.
 
 

---

Chahar-Gonbad region of Kerman province is geologically located in the southern part of central Iran zone, dominantly in Uromieh-Dokhtar volcanic belt. In this region, many high potential prospects, specially Cu-Au mineralization, have been detected during large scale exploration and reconnaissance phases. In this paper, remote sensing and field geophysics were used for alteration mapping on the surface and ore body delineation on the subsurface, respectively. To this end, we used an ASTER satellite image and different maps were generated by spectral technics such as false color composites and spectral ratios. Results showed argillic (and phillic) alteration in Bab-Zangoeie area is surrounded by propylitic alteration, which could be a promising evidence for Cu mineralization. Integrating these results with previous exploration studies led to selecting target area selection for ground study and field geophysics. We used both induced polarization (IP) and resistivity (RS) methods as two powerful geoelectrical methods by a pole-dipole array along four profiles. After preprocessing analysis, forward and inverse models were constructed in 2D section and 3D overlay model of joint IP/RS anomalies were constructed. Based on the obtained results, the deposit in depth where we proposed drilling targets. Further drilling operation have proved the mineralization in our proposed targets../files/site1/files/152/%D9%86%D8%B8%D8%B1%DB%8C.pdf
 

---

---

---