Mechanical Properties Of Reservoir Rocks Research Articles

Laboratory experiments on the effects of corrosion inhibitor on the mechanical properties of reservoir rock

Geothermal energy production often involves use of corrosion inhibitors. We performed rock mechanical experiments (room temperature; confining pressure of 10/20/30 MPa) on typical reservoir rocks (Bentheim sandstone and Treuchtlinger limestone) in contact with two different inhibitor solutions or with demineralized water. The sandstone experiments show no discernible difference in rock strength between inhibitors or water, attributed to low quartz reactivity. The limestone experiments show a significant difference in rock strength (and Mohr–Coulomb envelope), dependent on inhibitor type, attributed to high carbonate reactivity. This implies that, depending on the reactivity of the rocks and local stress conditions, inhibitor leakage may lead to unpredicted reservoir failure.

Linking sedimentary properties to mechanical characteristics of carbonate reservoir rock: An example from central Persian Gulf

A comprehensive understanding of mechanical properties of reservoir rocks can help in all stages of hydrocarbon and geothermal exploration, field development, and Carbon Capture Storage (CCS). In this study, the sedimentological properties of a carbonate reservior have been studied and the effect these properties have on mechanical parameters such as Uniaxial Compressive Strength (UCS), Young's modulus (E), Cohesion (C) and Internal friction angle (φ) of the rock at ambient (20 °C) and reservoir (90 °C) temperature conditions. These carbonates were grouped in three units (A, B, and C) based on a statistical analysis of petrophysical logs and core analysis. The results show that changes in mechanical properties are mainly influenced by diagenetic processes. The two main influencing overprints in the studied samples are dolomitization and anhydrite cementation, which strongly affect porosity, the dominant pore type and mineralogy which in turn are the most important influencing factors on mechanical properties. Although samples with 25–35% anhydrite (Unit A) show the highest strength, this parameter strongly reduces under high temperature conditions. The effect of dolomitization on rock texture and on porosity as the main strength-controlling factor is also very apparent. Therefore, samples with crystalline carbonate texture (Unit C) show the lowest UCS, E, C and φ values.

Effects of Water and scCO2 Injection on the Mechanical Properties of Granite at High Temperatures

Geothermal energy is an important resource to substitute for traditional fossil fuels. The mechanical properties of reservoir rock under the conditions of water and scCO2 injection at different temperatures are crucial for the safety of Enhanced Geothermal Systems. However, the effects of working fluid on the mechanical properties of granite at in situ temperatures are still rarely reported. To reveal the impact mechanisms, conventional triaxial compression experiments were conducted on granite specimens with different confining pressures (2–20 MPa), different pore fluid (10 MPa water or CO2), and different temperatures (25–150°C) in the present study. SEM analyses were applied to the specimens to determine failure surface morphologies after the experiments. The experimental results show that the effective confining pressure, pore fluid, and temperature have significant effects on the strength of granite specimens. The strength of granite increases with the increase of effective confining pressure, with similar granite strength under the same effective confining pressure (dry, water, and CO2). Temperature strengthening of granite is limited by high confining pressure (∼15 MPa). Under the effective confining pressure of 5 MPa, temperature weakening occurs on granite specimens when temperature is higher than 90°C. There is fluid diffusion in the specimens during compression. The higher viscosity of water may cause a temporary decrease in effective confining pressure, which may increase the strength of granite. The growth or formation of cracks is mainly observed in quartz and feldspar grains without short-term chemical effects. More visible cracks are observed on the specimens and more volume of fluid is injected under CO2 injection conditions, which may be beneficial to increase the permeability of geothermal reservoir.

Classifying chalk microtextures: Sedimentary versus diagenetic origin (Cenomanian–Santonian, Paris Basin, France)

AbstractMicrotexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability.

Assessment of dynamic material properties of intact rocks using seismic wave attenuation: an experimental study.

The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1–1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient (α) and quality factor (Q) values for the five selected rock types for both primary (P) and secondary (S) waves, relative to the reference steel sample. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus (E), bulk modulus (K), shear modulus (µ) and Poisson's ratio (ν). The P and S wave velocities for the selected rock types varied in the ranges of 2.43–4.61 km s−1 and 1.43–2.41 km h−1, respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.

Numerical analysis of the effect of natural microcracks on the supercritical CO2 fracturing crack network of shale rock based on bonded particle models

SummaryThe problem of predicting the geometric structure of induced fractures is highly complex and significant in the fracturing stimulation of rock reservoirs. In the traditional continuous fracturing models, the mechanical properties of reservoir rock are input as macroscopic quantities. These models neglect the microcracks and discontinuous characteristics of rock, which are important factors influencing the geometric structure of the induced fractures. In this paper, we simulate supercritical CO2 fracturing based on the bonded particle model to investigate the effect of original natural microcracks on the induced‐fracture network distribution. The microcracks are simulated explicitly as broken bonds that form and coalesce into macroscopic fractures in the supercritical CO2 fracturing process. A calculation method for the distribution uniformity index (DUI) is proposed. The influence of the total number and DUI of initial microcracks on the mechanical properties of the rock sample is studied. The DUI of the induced fractures of supercritical CO2 fracturing and hydraulic fracturing for different DUIs of initial microcracks are compared, holding other conditions constant. The sensitivity of the DUI of the induced fractures to that of initial natural microcracks under different horizontal stress ratios is also probed. The numerical results indicate that the distribution of induced fractures of supercritical CO2 fracturing is more uniform than that of common hydraulic fracturing when the horizontal stress ratio is small.

Mechanical behaviour of Australian Strathbogie granite under in-situ stress and temperature conditions: An application to geothermal energy extraction

Geothermal heat has now been identified as an effective renewable energy source due to severe environmental impacts created by conventional fossil usage on global climatic change. However, its wide application has been limited due to the lack of knowledge, particularly of the geothermal conditions of reservoir rocks at elevated temperatures and pressures. Such high temperatures and pressures possibly alter the mechanical properties of reservoir rocks due to the associated micro-structural and mineralogical alterations of the rock mass, which are an important attribute for wellbore stability and stimulation of geothermal reservoirs for safe and effective geothermal energy extraction. This study therefore investigates the stress-strain behaviour under in-situ stress and temperature conditions by conducting a series of high-pressure, high-temperature tri-axial experiments on Australian Strathbogie granite under four different confining pressures (10, 30, 60, 90MPa) and four different temperatures (RT, 100, 200, 300°C). The effect of temperature on the mechanical behaviour of rock specimens was studied under tri-axial conditions and the corresponding fracture propagation behaviour was observed using an advanced acoustic emission (AE) system. The corresponding micro-structure alteration in granite was observed using SEM analysis. According to the findings, increasing temperature leads to an initial increment in reservoir rock strength and shear parameters followed by reduction, and the trend is aligned with the crack formation pattern of the rock mass. This was further confirmed by the SEM analysis, according to which the rock micro-structure is subject to only minor changes at relatively low temperatures and higher temperatures cause micro-cracks to develop along the rock mass grain boundaries. Furthermore, the conventional Mohr-Coulomb criteria failed to model the stress-strain response of rock under geothermal reservoir conditions, and was therefore modified for the corresponding in-situ conditions.

Estimating the Elastic Modulus of Reservoir Rock by Petrophysical Information Using the Geostatistical Method

Mechanical properties of reservoir rocks play an important role in drilling and production of a hydrocarbon reservoir. In addition, part of elastic modulus in determination of capability of drilling, wellbore stability analysis, sand production, as well as in determination of in situ stress field, is effective. To estimate these parameters, there are several methods, one of which is application of reservoir's petrophysical data. In this article, through using neutron and density logs and photoelectrical data, lithology of reservoir was first determined and at the next stage through applying petrophysical data, lithology, and also by means of empirical relations between travel time of shear wave and compression wave, travel time of shear wave was obtained. Then elastic modulus was calculated according to the relations existing. By using geostatistical method, such as kriging, rock's geomechanical property was evaluated vertical and continuously and with the least existing error. Furthermore, the amount of sensitivity to these data in relation to the selective variogram model and lags between points and the number of adjacency points will be examined and shown.

A Comparison of Various Statistical and Geostatistical Methods in Estimating the Geomechanical Properties of Reservoir Rocks

The mechanical properties of reservoir rocks play an important role in drilling and production of hydrocarbon reservoirs. In addition, part of the elastic modulus in determination of capability of drilling, wellbore stability analysis, sand production, as well as in situ stress fields is effective. There are several methods for estimation of these parameters, one of which is application of the reservoir's petrophysical data. This article compares a variety of statistical and geostatistical methods such as inverse distance weighted (IDW), normal distance weighted (NDW, and kriging in estimating the geomechanical properties of reservoir rocks. All three methods are suitable for estimating the elastic modulus of the rock to the side of the well and, among them, kriging has higher precision compared to IDW and NDW.

Salinity-dependent strength and stress–strain characteristics of reservoir rocks in deep saline aquifers: An experimental study

This paper presents an experimental study of the effects of salinity on the mechanical properties of reservoir rocks in deep saline aquifers. Nineteen sandstone specimens saturated in NaCl brines of varying salinity concentrations (0%, 10%, 20%, and 30% NaCl by weight) were tested in a uniaxial compression testing machine and the corresponding fracture propagation patterns were recorded using an advanced acoustic emission (AE) system. The stress–strain curves were analysed, with the simultaneous recording of the acoustic signals and the failure mode. In addition, a digital image correlation system, ARAMIS, was used to measure the lateral and axial strains during the loading period. Scanning electron microscopy (SEM) analysis was performed to understand the changes observed in the uniaxial compressive strength (UCS) and stress–strain behaviour of the rock specimens. According to the experimental results, the UCS and stress–strain behaviour of the rock specimens change with the increasing NaCl concentration of the host fluid. The SEM results show only minor changes in mineral structure during immersion. However, some depositions of NaCl crystals in the rock’s pore space were observed. Interestingly, the growth of the NaCl crystals depends on the brine concentration, the amount of growth increasing with increasing brine concentration. The observed changes in AE analysis are also explained by the crystallisation of NaCl in the pore space, which transfers more acoustic energy from the cracks to the AE sensors due to the crushing of NaCl crystals during the compression process.

Stochastic Simulation Study on Development of Reservoir Fracture - Taking the Third Segment of Wumishan Formation in Renqiu Buried Hill as an Example

The The mechanical properties of reservoir rock are more complicated and the various mechanical parameters of rock itself have a strong uncertainty. The mechanics characteristics of rock in the study area can not be well determined if only a limited number of experimental datas. Therefore, in this paper, the third segment of Wumishan formation in Renqiu oilfield is taken as an example, the probabilistic models are used to describe the uncertainty of the rock mechanical parameters based on ANSYS, in which predict and analyze the degree of fracture development at key wells in the target layer of the study area.

Petrophysical and geomechanical properties of rocks from the oilfields of the Krishna-Godavari and Cauvery Basins, India

The petrophysical and mechanical properties of reservoir rocks from two major basins on the east coast of India were studied using samples cored from 19 wells in the Krishna-Godavari and Cauvery basins. Several of these drill holes are located in the producing oilfields in these basins. The purpose of the study was to investigate the relationships between the properties of the rocks including dry density, effective porosity, uniaxial compressive strength, tensile strength and Young's modulus. Their relationships are further elucidated using regression analyses. The results indicated that the petrophysical and geomechanical properties vary widely for the different sedimentary rocks and basement samples related to their depth and geological age. It is emphasized that the work should be further extended to assess its full potential in reservoir studies of the oilfields in these basins.

Experimental investigation on the influence of temperature on the mechanical properties of reservoir rocks

Abstract This paper reports an investigation on mechanical properties of reservoir rocks obtained in laboratory at room temperature, and their pertinence to characterize the actual rock behavior under normal downhole or steam injection conditions. The investigation was based on triaxial tests performed by a servo-controlled system on samples of friable sandstones cored from a reservoir in the Potiguar Basin, Northeastern Brazil. The samples were tested at 24°C, 80°C and 150 °C, with confining pressure varying from 2.5 MPa to 20MPa. A finite element elastic-plastic analysis of wellbore stability was performed using mechanical properties obtained at these temperatures, showing quite different yielding zones. Although the results obtained so far are not sufficient to characterize completely these effects, they indicate that a more appropriate range of temperature must be used in laboratory to better represent real downhole and steam injection conditions.

Conduct and interpretation of gas permeability measurements in rock salt

This paper reports an investigation on mechanical properties of reservoir rocks obtained in laboratory at room temperature, and their pertinence to characterize the actual rock behavior under normal downhole or steam injection conditions. The investigation was based on triaxial tests performed by a servo-controlled system on samples of friable sandstones cored from a reservoir in the Potiguar Basin, Northeastern Brazil. The samples were tested at 24°C, 80°C and 150 °C, with confining pressure varying from 2.5 MPa to 20MPa. A finite element elastic-plastic analysis of wellbore stability was performed using mechanical properties obtained at these temperatures, showing quite different yielding zones. Although the results obtained so far are not sufficient to characterize completely these effects, they indicate that a more appropriate range of temperature must be used in laboratory to better represent real downhole and steam injection conditions.

Experimental investigation on the influence of temperature on the mechanical properties of reservoir rocks

This paper presents a numerical modelling approach for analyzing the coupled hydro-thermo-mechanical (HTM) behaviour of fractured hydrocarbon reservoirs. The coupled HTM approach is applied to generic models of five-spot reservoirs with different fracture patterns. The presence of fractures was shown to have important effects on cold water injectivity and sweep efficiency. Due to high fluid velocities along fractures, local areas particularly close to fracture intersections cannot be saturated with cold water. The volume of oil by-passed by the displacing water was found to be strongly dependent on fracture geometry, and was generally larger if the fracture conductivity enhancement due to fracture deformation is taken into consideration. The thermo-poro-elastic stress changes due to cold water injection were found to induce significant normal and shear displacements and conductivity changes along the fractures. Another important result of the numerical modelling is the possibility of creating secondary tensile fracturing close to existing fractures. The secondary fractures are generally oriented perpendicular to the natural fractures and are expected to help in draining the oil from the rock matrix towards the fractures.

Rock Mechanics of the Ekofisk Reservoir in the Evaluation of Subsidence

Mechanical properties have been determined for Ekofisk reservoir rock for use in subsidence simulation. Tests were to describe the mechanical properties of the Ekofisk chalk for reservoir conditions. The mechanisms and time dependence of chalk compaction and the effect of waterflooding on chalk strength were also examined.