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The paper presents the methodology and results of coreflooding, taking into account the decrease in the permeability caused by the migration of natural colloids during fluid injection. As a porous medium, core samples of consolidated slightly clayey sandstone from one of the oil fields of the Komi Republic (Russia) were used. The coreflooding methodology implied a cyclic change in the injection rate and excluded the influence of other factors such as creep and chemical mobilisation of colloids on permeability. It has been established that a decrease in pore pressure leads to a more intense decrease in permeability during injection, which most likely indicates additional mobilisation of colloids. An analysis of the coreflooding results showed that porous media with lower permeability are more sensitive to colloid migration and pore-pressure changes.

In this paper, we present a mathematical model to predict the evolution of rock permeability depending on effective pressure during oil production. The model is based on the use of the results of well testing data from wells operating in the oil fields of the Perm–Solikamsk region in the north of the Volgo Ural oil and gas province. Dependences of the change in flow characteristics in the reservoir on the effective pressure were established. We performed a comparative assessment using permeability and effective pressure data that were normalized to dimensionless forms of k/ko and P/Po. The factors and their influence on the nature of the change in permeability from the reservoir pressure were determined. Depending on the type of rock, its composition, initial permeability, and bedding conditions, we determined the limits of variation of the constants in empirical equations describing the change in the permeability of rocks from the effective pressure. The mathematical model we developed enables the prediction of the change in permeability of rocks during oil production from reservoirs on the basis of reservoir properties such as initial permeability, initial reservoir pressure, average bedding depth, net-to-gross ratio, and initial effective rock pressure.

During the development of oil and gas fields, the permeability of the reservoirs decreases due to a decrease in reservoir pressure and an increase in effective pressure, as a result of which significant reserves of oil and gas remain in the reservoir. To predict the rate of decrease in oil production rates during field development and to respond quickly, it is necessary to know the law of permeability decrease with an increase in effective pressure. Existing methods for describing the change in the permeability of rocks were analyzed in the paper. Numerical analysis of the results of core studies from previously published papers and the results of field well testing on the examples of the north Perm region oil fields showed that in both cases, regardless of the type of rock and the type of reservoir, the change in permeability can be described by the same equations (exponential and power-law). Obtained equations can be used to predict changes in the permeability of terrigenous reservoirs of the north Perm region oil fields. At the same time, according to the results of well testing, an intensive decrease in permeability is observed with an increase in effective pressure. Analysis of the nature of permeability changes using the Two-Part Hooke’s Model showed that significant irreversible deformations are currently taking place in the formations of the oil fields under consideration. Predicting the change in permeability from effective pressure can allow to optimize the development of oil deposits.

This paper presents an experimental investigation on the nonlinear nature of the dynamic geomechanical characteristics of a clastic rock (sandstone). Rock samples of 7.5 mm in diameter and 15.6 mm in length were prepared. Rock properties were identified. Firstly, the limits of the rock linear elasticity zone were defined during quasistatic loading and uniaxial compressive strength determination at the Tinius Hounsfield rig. Secondly, the small experimental custom-built rig was designed to study the nonlinear nature of the Young’s modulus in the zone of linear elasticity. At the rig the sample was stationary preloaded. The dynamic load was generated by a piezoelectric actuator powered with a signal generator. The displacement of rock sample surfaces was recorded by a laser sensor and an eddy current probe. The dynamic experiments were conducted at the load amplitude ranging from 50 to 250 N for each of frequencies of 25 Hz and 40 Hz. It was found that the dynamic Young’s modulus increased with amplitude for all the frequencies studied. The newly developed experimental rig allows to investigate elastic moduli dispersion of rocks at the strain up to 10-3 under vibrations with frequency up to 40 Hz.

Summary The efficiency of oil production is influenced by various factors, the main of which are the reservoir properties of oil-bearing formations - porosity and permeability. Porosity determines the storage capacity and permeability determines the filtration ability. Reservoir properties generally depend on the type of reservoir, the particle size of the reservoir rock, the presence of clay particles, etc. However, the formation depth has the greatest influence on the reservoir properties. For all types of rocks, permeability and porosity decrease with the bedding depth increasing. The volume of the pore space and the permeability of rocks also depends on the effective pressure. In this work, on the example of the northern Perm Region oil fields, confined to layers of the same geological age, the influence of the layer’s geological characteristics on their reservoir properties is assessed. When analyzing the reservoir properties of 40 oil layers, equations that describe the influence of the depth and effective pressure on the reservoir properties of oil layers were obtained. Analytical dependences of the influence of porosity on the permeability of rocks are also obtained.

Summary During the development of hydrocarbon fields geomechanical characteristics of rocks change under the effect of nonlinear dynamic loads. Elasticity modulus is one of the most important characteristics of mechanical properties of rocks used in engineering. It is known that the elasticity modulus of dry rocks does not depend on the frequency of the applied load. However, dispersion of elastic moduli in dry sedimentary rocks still exists. The mechanism, in accordance with which dispersion of the dynamic component of elastic modulus occurs, remains not fully disclosed. Studies on the dispersion of the dynamic component of the elasticity modulus under the influence of uniaxial dynamic loads are conducted on dry sandstone samples in the zone of linear elasticity. Physically substantiated relations are proposed. The nonlinear nature of the dynamic elasticity modulus under the influence of dynamic loads of given frequency and amplitude was confirmed. The obtained relations allow taking into account the influence of nonlinear dynamic loads on the elasticity modulus of the rock in the calculations when designing the development of hydrocarbon fields.

The article presents the results of experimental studies of the influence of elastic oscillations on the structure of paraffin oil of a Perm region field. Oil samples are treated by elastic oscillations at a frequency of 22 kHz. As a result of cavitation and an increase in oil temperature, a decrease in the concentration and a decrease in the size of high-molecular paraffin compounds in oil is observed. With an increase in the time of ultrasonic treatment, the intensity of dissolution of paraffins in oil increases. A model of an experimental setup is proposed to study the effect of elastic oscillations on the permeability of a rock during the flow of paraffin oil. The impact of permeability deterioration around the production well on its flow rate is assessed.

The article presents a telemetry system for monitoring the bit trajectory during well drilling. Fiber-optic closed-loop gyroscopes are the main sensitive element in the telemetry system. The gyroscopes allow determining the azimuth and zenith angles of the well with a high accuracy exceeding most magnetometers. There is no need to use the expensive non-magnetic steels in the body of the telemetry system and non-magnetic drill pipes in the drill string. Fiber-optic closed-loop gyroscopes allow using the telemetry system when drilling near the casing of adjacent wells and magnetized rocks. An inertial navigation system is installed in the developed telemetry system as a measuring unit containing three angular velocity sensors and three accelerometers mounted rigidly. The sequence and results of simulation of a hydraulic link for data transmission from the bottom of the well to the top are described. Pilot tests of the telemetry system were carried out at well No. 450 of the Tatsuksinskoye field. The obtained values of the spatial intensity of the borehole curvature in depth are close in values to the directional survey data for the borehole. The trajectory obtained during the lift is close to the trajectory gathered from directional survey data.

This paper presents a mathematical model that reflects the nature of the dynamic Young’s modulus of a dry sedimentary rock during nonstationary uniaxial loading. The model is based on an idealized model of a system suggested by Jaeger J.C. A rock sample is considered as a spring with stiffness, the bottom point of which is fixed, while the upper point carries a mass. A sample experiences dynamic load and the rock matrix response. Displacement of the mass from the equilibrium state sets the variation of the sample’s length. Displacement of all the sample’s points goes according to the same law regardless of the point location. The response of a rock to a disturbing nonstationary load is selected based on the combination of conditions of each experiment, such as the load frequency and amplitude and the mass, length, and diameter of a sample. The mathematical model is consistent with experimental data, according to which an increase in load frequency leads to an increase in the dynamic Young’s modulus for each value of the load. The accuracy of the models is evaluated. The relations underlying the model can be used as a basis to describe the Young’s modulus dispersion of sedimentary rocks under the influence of nonstationary loads.

Under dynamic loading, the geomechanical properties of porous clastic rocks differ from those in quasistatic loading. A small experimental rig was built to directly assess the influence of vibrations on the uniaxial compressive strength (UCS), Young modulus, and Poisson&rsquo, s ratio. A piezoelectric actuator powered by a signal from an oscillator was used in the rig as a generator of vibrations. A laser sensor and eddy current probe measured the longitudinal and transverse deformation. Tinius Hounsfield and Instron Series 4483 installations were used to determine the geomechanical properties of new red sandstone in a quasistatic regime. The boundaries of elastic deformations determined in the quasistatic loading were implemented in the dynamic loading. To perform the experiments in the elastic zone (on the graph of stress (&sigma, )&ndash, strain (&epsilon, )), small samples with diameters ranging between 7.5 and 24.7 mm were manufactured. The investigation demonstrated that the Young&rsquo, s modulus of the sandstone increased with increasing values of the dynamic load and frequency.

The purpose of this paper is to present and analyze wax deposition mechanism on the inner oil pipe wall. It is shown that the factors such as pressure, temperature, wettability nature of washed surfaces, velocity of the oil during oil pipeline transportation, as well as resin asphaltene and hard paraffin concentration in the reservoir oil play key role in the wax matter deposition. The pigging tool which removes wax deposits is proposed. The advantages of this tool are compared with analogues. It is shown that tool increases operation reliability, oil pipeline life, high grade cleaning of oil pipeline in the curved areas and has low-cost production.

This paper shows and analyzes causes of oil reservoir properties deterioration. It describes changes in rock sate of stress during well drilling and perforation and analyzes existing technologies for oil well perforation. It is shown that abrasive jet perforation is the most efficient gentle method for well perforation. Upgraded abrasive jet perforation technology is proposed. That takes into account speed of wearing out of nozzles made of composite materials under abrasive jet influence of sand carrier based on mathematical simulation of well conditions. Due to qualitative well perforation proposed technology increases well productivity and decreases energy consumption.