Differential Strain Analysis Research Articles

Study on the rock physical mechanical properties evaluation of tight oil reservoir in Chang 7 member, Longdong area, Ordos Basin, China

The study aims to investigate the rock mechanical properties of the Chang 7 member tight oil reservoir in the Longdong region of the Ordos Basin, China, with the goal of enhancing the efficiency of oilfield development. Despite numerous contributions in the field of rock mechanics, challenges persist in reconciling experimental results with actual geological conditions and achieving comprehensive understanding of rock mechanical properties in tight oil reservoirs. To address this, a variety of experimental methods were employed to systematically assess the mechanical properties of the target reservoir. Rock density was measured using volumetric methods, tensile strength was evaluated through the Brazilian test, uniaxial and triaxial compression tests were conducted to assess rock mechanics properties, and dynamic elastic modulus and Poisson’s ratio were obtained via sonic velocity measurements. Furthermore, differential strain analysis and imaging log analysis were employed to determine the magnitude and direction of geostress. The results revealed that fine-grained sandstone exhibited higher rock density and relatively higher tensile strength, while muddy siltstone exhibited comparatively lower values in these aspects. Analysis of the influence of confining pressure on rock mechanics properties demonstrated a strong positive correlation between compressive strength and Young’s modulus with confining pressure, while Poisson’s ratio exhibited more irregular variations. Additionally, a mathematical relationship between dynamic and static rock mechanical parameters was established. Lastly, based on the characteristics of geostress, reliable foundations for optimizing hydraulic fracturing and wellbore layout were provided. This study has enriched and complemented the investigation of rock mechanical properties in tight reservoirs, offering vital parameters and theoretical support for the development of tight oil reservoirs. This bears significant importance in enhancing petroleum extraction efficiency and optimizing engineering design.

A continuous and long-term in-situ stress measuring method based on fiber optic. Part I: Theory of inverse differential strain analysis

A method for in-situ stress measurement via fiber optics was proposed. The method utilizes the relationship between rock mass elastic parameters and in-situ stress. The approach offers the advantage of long-term stress measurements with high spatial resolution and frequency, significantly enhancing the ability to measure in-situ stress. The sensing casing, spirally wrapped with fiber optic, is cemented into the formation to establish a formation sensing nerve. Injecting fluid into the casing generates strain disturbance, establishing the relationship between rock mass properties and treatment pressure. Moreover, an optimization algorithm is established to invert the elastic parameters of formation via fiber optic strains. In the first part of this paper series, we established the theoretical basis for the inverse differential strain analysis method for in-situ stress measurement, which was subsequently verified using an analytical model. This paper is the fundamental basis for the inverse differential strain analysis method.

DEVELOPMENT OF A SUPPLEMENTARY TECHNIQUE FOR DETERMINING IN SITU STRESS MAGNITUDE USING ACOUSTIC WAVE PROPAGATION

In accordance with the increasing awareness of the importance of in situ stress information in the design of various geotechnical and other petroleum related subsurface engineering in Indonesia, a complete knowledge of the insitu stress is a fundamental requirement. Basically, complete information of the insitu state of stress means both the trends and magnitudes of the principal in situ stresses. Some stress determination techniques can provide a complete stress tensor (e.g. differential strain analysis, DSA, method), some provide an incomplete tensor (e.g. sleeve fracturing method), and some provide merely the directions of the principal stresses. The Shear wave (S-wave) splitting technique presented by Widarsono et al (1998), following the earlier works made by Yale and Sprunt (1989), obviously falls in the last category. In some cases, which usually do not require in situ stress information regarding the magnitudes as an input parameter, principal stress directions still provide useful information. Nevertheless, the expanding use of in situ stress information requires, as stated above, a complete information, which means the stress magnitudes as well as directions. Designs of hydraulic fracturing, wellbore stability, and prevention of sand problems are among examples for which information about in situ stresses is required. In relation to the requirement outlined above, the effort which results are presented in this paper was devoted to presenting efforts to predict in situ stress magnitude by using ultrasonic wave propagation. This paper mainly presents efforts to find relations between acoustic propagation and in situ stress magnitude with an ultimate goal to provide the S-wave splitting technique presented in Widarsono et al (1998) with a means for estimating stress magnitudes.

Development Of A Supplementary Technique For Determining In Situ Stress Magnitude Using Acoustic Wave Propagation

In accordance with the increasing awareness of the importance of in situ stress information in the design of various geotechnical and other petroleum related subsurface engineering in Indonesia, a complete knowledge of the insitu stress is a fundamental requirement. Basically, complete information of the insitu state of stress means both the trends and magnitudes of the principal in situ stresses. Some stress determination techniques can provide a complete stress tensor (e.g. differential strain analysis, DSA, method), some provide an incomplete tensor (e.g. sleeve fracturing method), and some provide merely the directions of the principal stresses. The Shear wave (S-wave) splitting technique presented by Widarsono et al (1998), following the earlier works made by Yale and Sprunt (1989), obviously falls in the last category. In some cases, which usually do not require in situ stress information regarding the magnitudes as an input parameter, principal stress directions still provide useful information. Nevertheless, the expanding use of in situ stress information requires, as stated above, a complete information, which means the stress magnitudes as well as directions. Designs of hydraulic fracturing, wellbore stability, and prevention of sand problems are among examples for which information about in situ stresses is required.In relation to the requirement outlined above, the effort which results are presented in this paper was devoted to presenting efforts to predict in situ stress magnitude by using ultrasonic wave propagation. This paper mainly presents efforts to find relations between acoustic propagation and in situ stress magnitude with an ultimate goal to provide the S-wave splitting technique presented in Widarsono et al (1998) with a means for estimating stress magnitudes.

Differential Strain Analysis: An Investigation Over Its Feasibility For Determining Coal’s Cleat Orientation

Gas production from coal bed methane (CBM) has been rising as supplement to conventional gas reservoirs. Effective CBM production is much determined by well placements with regards to orientation of the coal reservoir’s face cleat. This is true since this cleat type provides the main path of fluid migration from storage to wellbore. It is therefore imperative to understand and determine the general orientation of the cleats of concern. This information is usually obtained from visual description on core samples, and whenever available from analogy to outcrop data. This is considered as insufficient and a means for studying core sample’s interior is required in order to ensure consistency between external and internal appearances. This paper presents an investigative study over the possibility of differential strain analysis (DSA) technique to serve the purpose. The technique is normally used for measuring subsurface in situ stress field, and through the use of a similar basic concept it is proposed to be used for determining orientation of face cleats in coal samples. The study includes utilization of DSA data obtained from measurements on samples taken from great depths. Review and re-working over the data has shown that the technique can well indicate the orientation of face cleats. A general orientation over all tested samples is also indicated with reasonable degree of reliability. This leads into conclusion that the DSA technique can be well used to indicate cleat orientation and therefore help in better characterizing coal.

A stable strain gauge measurement method for monitoring in-situ stress

In-situ stress exists in all rock mass or structures, which is reflected in the deformation and failure of various underground or ground excavation in geotechnical engineering. In-situ widely used in the engineering practice, in-situ stress monitoring plays an important role in many aspects, such as mine development, slope support, and geological disaster prevention and control, etc. Strain gauge has been used to record rock deformation using Differential strain analysis (DSA), Hollow Inclusion Technique (CSIRO Cells), and other in-situ stress measurement techniques. Limited by the volume, cost, power, and connection scheme of the measuring instruments, the test data are always influenced by various immeasurable factors, such as bend of the measuring cable and change in the ambient temperature. Majority of the gauge measurement technologies are not suitable for in-situ stress monitoring because of the stability of strain gauge measurement is poor, limits the application range of the gauge measurement. A stable strain gauge measurement method can be used for medium to high-precision in-situ stress monitoring to serve various engineering developments. We made a new measurement scheme by using high-precision constant current with independent signal transmission channels to achieve a high stability and high-resolution strain gauge measurement circuit with low power consumption and space cost. The temperature drift is as low as 0.3 με/°C in 0°C–60°C temperature range at 8000 με strain input, which can achieve the measurement effect of the traditional desktop strain gauge in about 1/10th volume and very low cost. The error caused by the change of cable resistance is reduced to 1 ppm, and the error caused by the disconnection and reconnection is less than 1 με, which avoids the failures caused by various environmental factors in the monitoring process, and the installation distance of monitoring strain gauge can reach tens of meters. This creates conducive conditions for using traditional in-situ stress measurement technology with in-situ stress monitoring and establishes an efficient and low-cost in-situ stress monitoring system.

Variation in the orientation of the maximum horizontal stress in thick channel-fill sandstones with low-permeability: A case of the Bonan Oilfield in the Bohai Bay Basin, eastern China

Measurements of in situ stress in a single well from borehole breakouts, hydraulic fracturing, multipole acoustic logs and differential strain analysis of core indicate that the orientation of the maximum horizontal stress is northwest-southeast in thick channel-fill sandstones in the central-western Bonan Oilfield, while the orientation is northeast-southwest in the thin interbed siltstones and mudstones of the floodplain in the eastern Bonan Oilfield. This result shows that the orientation of the maximum horizontal stress in the thin interbed of siltstones and mudstones is in accordance with the regional stress orientation obtained by the focal mechanism of a natural earthquake, but has a 30°–40° variation with the thick channel-fill sandstones. Finite element simulation suggests that the main reason for the variation in the orientation of the maximum horizontal stress is the diversity of overall mechanical properties, especially modulus of elasticity, of the thick channel-fill sandstones and the interbedded thin layer of siltstones and mudstones. The average Young's modulus over the stratigraphic column governs stress rotations. The transformation of the orientation of the maximum horizontal stress from the central-western to the eastern locations is at the channel boundary. This research provides a case in which the variation in the orientation of the maximum horizontal stress is affected by thick channel-fill sandstones. It shows that lithological changes can cause variations in the direction of in-situ stress.

Study on distribution characteristics of cracks in aonan oilfield

In this paper, the combined method of laboratory experiment and theoretical analysis is applied to the research process of Characteristics of cracks. Through analyzing the dynamic response of the oil and water wells in the block, the characteristics of the fracture development are studied. The size and direction of ground stress are obtained through indoor experiments, such as sound velocity, differential strain analysis and Paleomagnetism, and combined with the experimental test of the outcrop. establishing the rock fracture criteria in Aonan oilfield, giving relative logic formula of the deduced stress and fracture parameters, so as to accurately describe the characteristics of crack distribution of different wells.

Differential displacement and strain analysis of transmission line cables

This paper presents a strain analysis in transmission line cables caused by mechanical vibrations induced mainly by the wind action that can cause the fatigue rupture of the cable. The tests were performed on a test bench that consists of two spans of 9 and 12 m, respectively, and it was built using elements of transmission lines (suspension clamps, insulators, anchoring towers, etc.). The vibrations were generated by an electrodynamics shaker. Strains were measured by means of micro-electric strain gauges set in 04 wires of the cross-section of the cable at the vicinity of the suspension clamp, which presents severe levels of dynamic stresses. The cable bending amplitude was measured with two laser transducers. The bending amplitude was converted in strain with the Poffenberger-Swart equation. The comparison between the measured strain and that predicted theoretically showed RMS errors of 31 and 48 % for axial load levels of 20 and 30 % UTS, respectively.

An Improved Differential Strain Analysis Method for Super Deep Wells

The deeper a reservoir is, the smaller diameter the drilled full diameter cores have. It is difficult to conduct in- situ stress experiments with conventional methods if the diameter of the full diameter cores is less than 6.0 cm, especially for cores abundant in natural fractures. In this paper, based on conventional Differential Strain Analysis (DSA) methods and wave velocity anisotropy methods, we developed an improved Differential Strain Analysis (DSA) method that is specially designed for small full diameter cores. The improved method, combined with the paleomagnetic core reorientation tests, can predict magnitude and orientation of in-situ stress. Results from the improved method are very close to those obtained from conventional Differential Strain Analysis. The improved method was applied to carbonate cores in Tahe Oilfield, which has a depth up to 6000 meters and has cores with a diameter from 5.5cm to 6.0 cm. The experimental results with the improved method show good consistence with the field-monitored ones, which shows that the improved method is reliable and practical.

Measurement of crack formation in concrete using embedded optical fibre sensors and differential strain analysis

Fibre Bragg grating sensors are embedded into concrete cylinders to monitor cracking deep within the specimens. Loading cycles and loading till failure tests are performed, with measurements from the sensors collected up to, and during, failure. Calibration of the off-axis angle of the optical fibre sensors is performed and the spread of this angle noted. The use of the bandwidth of the gratings to indirectly measure the differential strain across the grating, and thus the amount of internal cracking within the specimens, is proposed and tested. The results accord well with the theoretically predicted behaviour of bulk concrete.

In situ stress prediction using differential strain analysis and ultrasonic shear-wave splitting

Abstract Knowledge of the in situ states of stress in rock masses is of considerable importance to a number of subsurface engineering activities, including those involved in exploiting petroleum and geothermal energy reserves. In this paper, a comparison is made of two laboratory techniques, based upon stress-relief microcracks, for determining the in situ state of stress: differential strain analysis (DSA) and ultrasonic shear-wave splitting (USWS). Measurements on ten sandstone samples recovered from deep boreholes, made using the well-established technique of DSA, have been compared to those made by the comparatively new technique of USWS and to sleeve fracturing measurements of in situ stress made in the corresponding boreholes. The results obtained indicate that the USWS technique, with its ability to test a large number of samples quickly, provides a useful adjunct to DSA and sleeve fracturing in determining trends in in situ stresses. Used in combination, the two laboratory techniques have also proved useful for examining rock micro-structural features.

Permeability and porosity of the Illinois UPH 3 drillhole granite and a comparison with other deep drillhole rocks

Permeability, porosity, and volumetric strain measurements were conducted on granite cores obtained at depths of 0.7 to 1.6 km from the Illinois UPH 3 drillhole at effective confining pressures from 5 to 100 MPa. Initial permeabilities were in the range of 10−17 to 10−19 m2 and dropped rapidly with applied pressure to values between 10−20 and 10−24 m2 at 100 MPa, typical of other deep granite core samples. These values are several decades lower than equivalent weathered surface granites at comparable effective confining pressures, where weathering products in cracks and pores inhibit crack closure with applied pressure. Permeabilities of the Illinois cores were inversely related to sample depth, suggesting that stress relief and thermal microfractures induced during core retrieval dominated the fluid flow. Thus these samples provide an upper bound on in situ matrix permeability values. A comparison of core permeability from UPH 3 and other deep drillholes shows that stress relief damage can often dominate laboratory permeability measurements. We conclude that it may be difficult to make meaningful estimates of in situ permeability based on either borehole samples (possible damage during retrieval) or surface‐derived analogs (altered by weathering). Volumetric strain determined from porosity measurements was compared with differential strain analysis (DSA) data reported by other investigators on samples from the same depths in the drillhole. Our strain measurements (0.002 to 0.005 at 100 MPa) were nearly twice as large as the DSA values, probably because of the crack‐enhancing effects of fluids present in our samples that are absent in the dry DSA cores, as well as other time‐dependent deformation effects. This difference in observed strain magnitudes between the two measurement methods may be an important consideration if strain and/or porosity data from deep core samples are used in models of stress, fluid circulation, and excess fluid pressure generation in the midcrust.

In situ stress in the German KTB pilot hole deduced from differential strain analysis : Baumann, H Sci DrillingV3, N6, 1993, P263–270

In situ stress in the German KTB pilot hole deduced from differential strain analysis : Baumann, H Sci DrillingV3, N6, 1993, P263–270

Microcrack porosity and in situ stress in Illinois Borehole UPH 3

Differential strain analysis was used to study microcracks in granite core taken from 0.7 to 1.6 km depth from Illinois Deep Hole UPH 3. The majority of the microcracks are believed to have been generated by stress relief upon removal of the core from depth. Volumetric microcrack porosity was found to vary by an order of magnitude. Low values of microcrack porosity were found in highly fractured intervals, where large, open fractures have relaxed a portion of the in situ stress. Plotting microcrack porosity against mean in situ stress reveals a strong positive correlation over a range of 25 MPa. Large, subvertical fractures may locally influence the orientation of stress relief microcracks. The direction of maximum horizontal crack strain was found to be subparallel to the strike of the nearest large fracture in 7 of 8 fine‐grained samples.

The physical properties of a set of sandstones—Part II. Permanent and elastic strains during hydrostatic compression to 200 MPa

Permanent and elastic strains have been measured in 19 dry sandstones as a function of hydrostatic stress to 200 MPa. Differential Strain Analysis (DSA), a high precision strain measurement technique, was used to measure the total strain inthree orthogonal directions. Samples were cyclically loaded and unloaded from atmospheric to successively higher maximum pressures. The total strain is separated into elastic and permanent components. Permanent strains are the measured strains remaining after a loading cycle. The permanent strains are well behaved functions of maximum confining pressure yet they can be a significant fraction (30%) of the total strain and can be highly anisotropic. Permanent strains are compactive at low pressures but may become dilational at higher pressures. Permanent and elastic strains are related in a piecewise linear manner with slope Ψ. Ψ values range from 0.4 to – 1.0 and decrease as a function of increasing pressure. Negative values of Ψ are obtained when permanent strain increments are dilational. Elastic response depends on the maximum pressure to which a sample has been exposed previously. Permanent strains reflect permanent changes in the rock microstructure. These changes are important factors to consider when interpreting laboratory measurements of physical properties made under stress.

The physical properties of a set of sandstones—Part I. The samples

This paper and the succeeding ones contain new data on several physical properties of sandstones that are well characterized petrographically. PartI describes the samples on the basis of (1) backscattered electron imaging of polished sections and pore casts and (2) sieve analysis. Part II discusses the static elastic and inelastic properties as measured with a modification of Differential Strain Analysis. The samples are mostly clean quartz arenites, subarkoses and argillaceous quartz arenites. Kaolinite is the dominant pore-filling mineral. Total porosity is divided into intergranular (equidimensional, size comparable to grains), connective (tabular or tubular shaped), and micro (less than a few microns in size) porosity on the basis of point counting SEM images. The micropores occur within aggregates of clay. The ranges of porosity are: total porosity, 5–31% of whole sample; intergranular porosity, 24–76 of total porosity; connective porosity, 4–25% of total porosity; microporosity, 10–63% of total porosity. Comparison of porosity determined with an air pycnometer and porosity measured with the SEM indicates that microporosity and the volume of solid clay particles are approximately equal.

The influence of microcrack density on the elastic and fracture mechanical properties of Stripa granite

Microcracks can have a strong influence on the elastic and fracture mechanical properties of rocks if they are numerous, or if they are orientated in unfavourable directions in anisotropic rocks in particular. This paper presents results from a great number of mechanical tests on Stripa granite containing various amounts of microcracks. Variations in the microcrack density were obtained by shock-heating the rock at different temperatures in the range 100–600°C for 3 h. The results presented are obtained from sound velocity measurements, uniaxial compression tests, Brazilian tests and three-point bending tests. The density of microcracks in the heated rock is studied by means of optical microscopy, SEM and differential strain analysis (DSA). Some of the calculated parameters show a maximum value for specimens heat-treated at about 100°C. The tensile strength is, for instance, substantially higher for specimens shock-heated at 100°C than for non-heated ones. Another striking feature is the initial decrease of the diameter observed in specimens heat-treated at 600°C when loaded in uniaxial compression. Both optical microscopy and DSA experiments reveal a large increase in microcracking when the heat-treatment temperature exceeds 300°C.

Shock-induced microfractures in six terrestrial igneous rocks characterised with differential strain analysis : Siegfried, R W; McQueen, R G; Simmons, G J Geophys Res, V86, NB7, 10 July 1981, P6205–6218

Shock-induced microfractures in six terrestrial igneous rocks characterised with differential strain analysis : Siegfried, R W; McQueen, R G; Simmons, G J Geophys Res, V86, NB7, 10 July 1981, P6205–6218

Shock‐induced microfractures in six terrestrial igneous rocks characterized with differential strain analysis

Samples from a suite of 10 low porosity igneous rocks were shock loaded to low pressures (5 to 10 kbar). The specimens were recovered and analyzed with differential strain analysis (DSA) in order to characterize the microcracks and thus determine the influence of initial sample properties and shock pulse characteristics on shock‐induced microcracks. The DSA results reveal the following: The duration of a shock pulse is an important parameter; those samples that had been subjected to a shock of longer duration had a higher postshock crack porosity. If a sample initially contains a high concentration of cracks closing at a particular pressure, then such a concentration is also present in the postshock sample in addition to a concentration of cracks closing between 100 and 300 bars which is generally produced by the shock process. The shock‐induced cracks in samples with low initial crack porosity close over a wider range of pressures than those in samples with higher preshock crack porosity. Neither the grain size nor the high pressure (2 kbar) compressibility of the samples exerted any influence on the postshock crack distributions. Thus, the distribution of crack porosity with closure pressure of shock‐induced cracks reflects only the shock history and the initial crack distribution of a rock.