نشریه زمین شناسی مهندسی ایران
سال چهاردهم شماره 3 (پاییز 1400)

Over time and production from the reservoir, the pore pressure of the production layer decreases if there is no source of pressure supply. This reduction in pressure directly alters the amount and direction of stresses. Changes in the amount of stresses can cause geomechanical changes in the reservoir and production layers. If the reservoir layers are faulted, reducing the reservoir pressure can activate these faults and also change the tensile strength of the well bore for new drilling in the discharged layer. This research was conducted in one of the reservoirs of southwestern Iran. In this reservoir, three production layers with different thicknesses were examined and the probability of reactivation of faults and tensile strength in the initial state and after the pressure drop of 1800 psi was evaluated. In layer 1, the value of the stress path was 0.67, which due to the fact that it is tangent to the critical stress value, the faults will be reactivated by producing from the reservoir and reducing the reservoir pressure in this layer. Also in this layer, the maximum weight of the drilling mud allowed for non-failure of rock traction in the initial state is 17.81- 25.13 PPG and after a reduction of 1800 psi of layer pressure, it is in the range of 15.07- 23.42 PPG. . In addition, the most resistant state of the well bore is drilling with an angle of 60 degrees and in the direction of minimum horizontal stress.

Besides stone perishing, generated vibrations during stone cutting process can lead to bending, deflection and finally breakage of cutter disks. Therefore, study and predicting vibrations, is unavoidable in stone cutting process. In this research, by means of laboratory and statistically analysis, a study is carried out to predicting vibration of stone cutting process. For this purpose, a stone cutting machine in laboratory scale which equipped with vibration measurement tools, was provided. On a carbonate rock specimen, the study is carried out under different circumstance such as different practical cut depth (15, 22, 30, 35 mm), different cut advance rate (100, 200, 300, 350, 400 cm/min), different cutter disk rotation speed (1540, 1770, 2550 rpm). Results indicate that increasing in cut depth and cut advance rate, lead to increase in vibration intensity. Vibration intensity quantity even increased 6 times, when cut advance rate varies from 100 to 400 cm/min. Using SPSS software, after laboratory result investigation and statistically data analysis, vibration signal predicting statistical models are presented. Results of statistical tests indicates that the best fitting models enable predicting vibration quantity accurately and precisely with correlation coefficient range of 0.92 - 0.87, confidence level of 90% and error less than 10%.

In this study, the effects of four grinding aids with three different levels on the three important characteristics of the cement, namely the specific surface area, the compressive strength of the concrete and the grinding efficiency (energy saving), have been evaluated in the clinker grinding process. In the first step, by kinetic grinding tests, the required grinding time to reach to the Blaine value of Ordinary Portland Cement (OPC) of the Urmia Cement Plant (3636 cm2/g) was obtained, which was 78.24 minute by 2.19% deviation. Then, 13 laboratory grinding tests were performed by using of Urmia cement and four grinding aids (in 3 different doses of 0.02, 0.05 and 0.08%) and the results were compared. The results showed that the combination of Triisopropylamine 0.08% (TIPA-0.08) with a Blaine number of 4032 cm2/g and a grinding efficiency of 31.57% had the greatest effect on the fineness and grinding efficiency. On the other hand, the prepared samples of the all combinations were used to test the compressive strength of 2, 7 and 28 days. The results showed that the highest increase of compressive strength for all ages was obtained by TIPA-0.08 which was 36.92%, 31.23% and 21.85% for 2, 7 and 28 days, respectively.

Losses are among the collapsible soils that, if saturated, their volume will rapidly drop. Iran is one of the countries where Loess soils are spread in different parts of it. The purpose of this study is to improve the strength parameters of loess Gorgan (North of Iran) using different ratios of geopolymer (a combination of loess and metakaolin). For this purpose, in this study, in addition to conducting index tests, a series of uniaxial compressive strength, Brazilian tensile strength, compressive wave velocity and modified compaction tests have been done. Furthermore, SEM, EDX and XRD tests have been conducted to investigate micro-structural features of non-stabilized and stabilized soils. In the samples stabilized with geopolymer, with increasing ratio of loess to metakaolin and the curing time (with fix alkaline activator solution), uniaxial compressive strength, tensile strength and compressive wave speed decreases. So that, with increasing curing time, the uniaxial compressive strength of the specimens decreased to 0.83 and the rate of this decrease was greater in the first 7 days. The results of XRD analysis and SEM images show that the disperse structure of loess soil is altered by the addition of geopolymer and by the production of alumina-silicate gel which results in increasing strength, decreasing porosity and homogeneity of loess soil structure.

In the present research, a probabilistic neural network based on the Bayesian probabilistic ‎algorithm was employed to classify the grade of Ali-Abad copper deposit in Yazd. For this ‎purpose, induced polarization (IP) and resistivity (Rs) geophysical data and rock type of ‎exploration borehole cores as geological information corresponding to four geophysical ‎profiles, DD-1, PD-2, PD-3 and PD-4 were used as input parameters as well as the copper ‎grade of the boreholes as target parameter. To achieve the goal, 488, 528, 188, and 456 data ‎were randomly collected from the sections related to DD-1, PD-2, PD-3 and PD-4 geophysical ‎profiles so that 75% of total data were selected for training and 25% to test the probabilistic ‎neural network. The performance of the proposed approach was evaluated by confusion ‎matrix through the ratio of summation of data on the main diameter to the total test data, as ‎well as determination of Commission and Omission errors. The results of the research show ‎that the probabilistic neural network could estimate the test data for DD-1, PD-2, PD-3 and ‎PD-4 profiles with accuracy of 60, 74, 60 and 83.3%, respectively which are reasonable ‎considering the type of available data. In addition, the results were qualitatively evaluated ‎through plotting isograde maps of four exploratory cross-sections over the geophysical ‎profiles. This process was carried out using the assay data of exploration boreholes, gridding ‎and the grid interpolation with the high accurate kriging estimation method, which was leaded ‎to favorite results.‎

Underbalanced drilling is in fact the best drilling method for oil reservoirs that their pressure has been reduced. This study aimed at obtaining a criterion for estimating the minimum and maximum underbalanced presUnderbalanced drilling is an advanced technology and a drilling operation in which the drilling fluid pressure inside the well is less than the pore pressure of sures of the drilling mud for enhancing oil recovery and preventing damages to the formations in the Iranian carbonate reservoirs. To this end, data on 13 wells in various Iranian oil fields were first collected. The oil wells were simulated at different drilling mud pressures with the help of the finite difference method (FDM)-FLAC2D. The elastoplastic normalized yielded zone area (NYZA) method was used for stability analysis and estimation of the minimum and maximum underbalanced pressures of the drilling mud. The NYZA diagram was plotted separately for each well. Considering the drilling mud pressures on the NYZA diagram in the range of NYZA=1 to the pore pressure, a minimum and maximum drilling mud pressure of NYZA=1 and NYZA=0.2 was calculated, respectively. Eventually, a correlation was proposed as a fraction of the pore pressure to estimate the minimum and maximum underbalanced pressures. This correlation is expressed as a factor or fraction of the pore pressure. The minimum and maximum underbalanced pressures of the drilling mud to enhance oil recovery and prevent damage to the formation can be estimated solely by inserting the pore pressure of the formation in this correlation.

In nature, sandy soils are rarely clean and often contain some clay and silt. These fines grain have a significant effect on the resistance and dilation behavior of sandy soils. Therefore, in this study, resistance and dilation behavior of sand mixture with fine grains such as silt and clay using a small scale direct shear test have been studied. Tests are conducted on specimens of sand with various fine content ranging from 0 to 40%, density of 30, 60 and 90 percent and the samples are subjected to three normal stresses 0.5, 1.0 and 1.5 kg/cm2 with two percent of optimum and saturation moisture. The test results show with increase in percentage of fine grains, the shear strength of sandy soil decrease and with increase in percentage of clay the shear strength decreases further. Also, dilation angle and angle of friction decreases with increase fine grains content and cohesion parameter increases with increase fine grains, Of course, it more increases with increase clay content and the rate of change of the cohesion parameter increases with increasing fine-grained percentage.