Saturated Limestone Research Articles

Acoustic velocity properties of Danian limestone section exposed at the Curfs quarry, Southeastern Netherlands

In order to establish the relationship existing between the seismic velocity and petrophysical properties of limestone, ultrasonic pulse transmission technique under simulated pressure of 2.5 to 10 Mpa and at a frequency of 300 to 800 kHz was used in the determination of both compressional-wave and shear- wave velocities. The measurements were carried out for both dry and fluid saturated limestone obtained from the Curfs quarry in Limburg, Southeastern Netherlands. Compressional wave velocities values range from 2218.2 to 3280 ms-1 for dry samples and 2448 to 3730 ms-1 for fluid saturated samples. While those for shear-wave velocities values range from 2024 to 2982 ms-1 for dry samples and 1568.2 to 2024 for fluid saturated samples.These velocities values were used to constrained limestone into two lithogic units- the compacted limestone units, also know as the hardgrounds (high velocity values) and undercompacted limestone units (low velocity values). The compressional wave velocities of fluid saturated limestone samples are relatively higher than those obtained for equivalent dry ones, while the shear wave velocities of the same fluid saturated limestone samples were lower than the dry ones. The degree of diagnesis in the weakly cement limestone is responsible for the high value of both compressional- wave and shear wave velocities obtained from the acoustic velocity measurement. The velocity obtained from the time average equation is much more than the velocity obtained from the laboratory measurement of velocity for the curfs quarry. Key words: Acoustic, compressional and shear-wave velocity, cement, fluid saturation.

Estimating Elastic Parameters of Framework and Pore Fluid from CLYJ Saturated Limestone Samples

AbstractIn this paper, numerical method which is dominated by inversion is used to analyze CLYJ saturated limestone samples. Elastic parameters of rock framework and pore fluid are estimated from the overall measured density and velocity data in different porosities based on the effective inversion method. A critical porosity model is used, and elastic parameters are calculated after grouping. The estimating process includes grouping, calculating, counting and evaluating. Firstly, three samples are chosen as a group and there are N different ways to group. The samples are grouped in both integral way and individual way. Secondly, for each group the component elastic parameters are calculated based on the critical porosity model and N groups of results are obtained. Third, the results are analyzed to estimate the elastic parameters of samples. At last, the results are evaluated through comparisons of statistic parameters between the estimated values and measured ones, such as maximum, minimum, mean, and standard deviation. The results indicate that the method to estimate the elastic parameters of rock framework and pore fluid is effective and reliable. The component elastic parameters reflect the elastic properties of CLYJ limestone samples, and enrich the contents of these samples.

Application of Non-Destructive Technology in Evaluating Concrete to Sulfate Attack

The deterioration on sulfate attack was investigated both in physical crystallization and the chemical erosion. Specimens that suffered long-term immersion and dry-wet cycles in saturated sodium sulfate solution are compared to trace the physical attack. And the chemical erosion was conducted by comparing specimens which have been suffered long-term immersion in saturated sodium sulfate solution and saturated limestone solution. In the investigation, the non-destructive detecting indexes, such as the ultrasonic velocity, and the dynamic modulus of elasticity were measured. The permeability, the porosity and mechanical strength at 28-day age were measured. The flexural/compressive strength was measured after 90 wet-dry cycles. And then all the specimens were cut into cubes to take the measure of compressive strength. Based on the experiments, feasibility of various parameters, such permeability, relative dynamic modulus of elasticity, ultrasonic velocity and relative flexural/compressive strength, were investigated to evaluate the concrete deterioration. The results indicate that there is a close relationship between the deterioration by sulfate attack and concrete permeability, so the reduction of permeability is effective in promoting the resistance. The index of the resistance expressed by the dynamic modulus of elasticity ratio is comparable to that expressed by the relative flexural strength. A novel method was suggested in evaluating concrete by sulfate attack, namely, combined with some mechanical tests, the parameter of relative dynamic modulus of elasticity can be used to evaluate the deterioration; the permeability denoted as the amount of transporting charges within 6 hours can be used to evaluate the properties to sulfate attack.

Experimental Study on Influences of Chemical Solutions on Mechanical Properties of Brittle Limestone Under Triaxial Compression

A series of triaxial compression tests on dry and saturated limestone (soaked in water solutions of Na2SO4 and CaCl2 at 0.1 mol / L ionic strengths with varying pH, and distilled water for 240 days) have been carried out. The corresponding complete stress-strain curves are obtained. The influences of chemical solution on rock mechanical behaviors are studied. Results from these tests indicate that: 1) Dry limestone samples have obvious brittle feature. Even if the confining pressure reaching 20MPa, the sample is still ruptured suddenly. After soaked in chemical solutions for 240 days, the deformation and failure behaviours were changed from brittle manner to more ductile. 2) Chemical corrosion is an important reason for the strength deterioration. With the same saturated time and confining pressure, the strength degradation level depends on ionic components and pH value of chemical solutions. Acidic solutions have the most significant influence on samples’ mechanical properties. The study has a good reference to researches of deep rock mechanics, and water-rock interaction.

Noncondensable gas steam-assisted gravity drainage

To investigate steam-assisted gravity drainage (SAGD) mechanisms, experiments with and without carbon dioxide or n-butane mixed with steam were conducted in a scaled physical model. It is packed with crushed limestone premixed with a 12.4° API heavy-oil. Temperature, pressure, production data, and the asphaltene content of the produced oil were monitored continuously during the experiments. For small well separations, the steam condensation temperature and the steam–oil ratio decreased as the amount of carbon dioxide increased. The heavy oil became less mobile in the steam chamber due to lower temperatures and more viscous oil. Thus, the heating period was prolonged and the cumulative oil recovery as well as the recovery rate decreased. Less oil recovery was obtained as the fraction of carbon dioxide injected increased. Little or no change in oil recovery, and the rate of oil recovery, was observed for greater well separations regardless of the fraction of carbon dioxide in the injection gas. Similar behavior was observed when n-butane was injected along with steam instead of carbon dioxide. Cumulative oil recovery, rate of oil recovery, and steam–oil ratio decreased independent of well separation compared to a reservoir with no initial noncondensable gas. These experimental results add to the state of the art understanding of thermal gravity drainage processes. The addition of noncondensable gases during steam-assisted gravity drainage was not beneficial to oil recovery. Nevertheless, experiments do teach that steam injection is effective for producing heavy-oil saturated limestone.

Using NMR to Measure Fractal Dimensions

A comment is made on the recent PFG NMR measurements by Stallmach, et al. on water-saturated sands [Phys. Rev. Lett. 88, 105505 (2002)]. It is pointed out that the usual law for the time-dependent diffusion coefficient D(t) used by these authors is not valid for a fractal surface. It is shown that (1-D(t)/D0) \~ t^[(3-Ds)/2] at short times for a surface of fractal dimension Ds, where D0 is the bulk diffusion coefficient. Preliminary PFG NMR data on water saturated limestone and plastic beads are presented to illustrate this analysis.

Electrical Resistivity Investigation for Subsurface Exploration along the Right of Way of the Sewage Flow Conveyance System in Alexandria, Egypt

Abstract By using the electrical resistivity Wenner configuration, 22 sounding points were used to study the shallow subsurface geology along a proposed pass for construction of a flow convergence system in a part of Alexandria, Egypt. The study indicated that no abnormal hidden subsurface objects are present to prevent completion of the project. Lateral inhomogeneities are detected by differences in resistivity values. Some saturated limestone layers also are detected. The associated water may hinder the drilling activities. The geophysical data correlate with the results obtained from nearby boreholes.

Sensitivity and Reliability of Two Fracture Detection Techniques For Borehole Application

Kleinberg, R.L., Schlumberger-Doll Research Chow, E.Y., Schlumberger-Doll Research Plona, T.J., Schlumberger-Doll Plona, T.J., Schlumberger-Doll Research Orton, M., Schlumberger-Doll Research Canady, W.J., Schlumberger-Doll Research Summary Currently deployed devices for detecting fractures in borehole environments often fail to detect fractures, give an indication of a fracture when none is present, or both. This work describes a systematic laboratory and signal-processing study of the effects of unfavorable formation and borehole conditions on the effectiveness of two circumferential acoustic fracture detection techniques. The conditions investigated include lithological variation, surface roughness, shallow cracks, transducer standoff, blind spots, nonradial fractures, variable fracture closure, and variations in acoustic path length. Introduction Various techniques have been used to search for fractures intersecting boreholes. These include analysis of amplitudes in the sonic log, the fracture identification log (FIL), which relies on electrical measurements, and a borehole televiewer. Devices using sound waves propagating circumferentially around the borehole include the circumferential microsonic tool (CMS/CMT) and the circumferential acoustic device (CAD). A number of studies have indicated that a very careful analysis of some of these logs can be useful in locating fractures. However, others have found currently available tools to be lacking in reliability. In this paper we present the results of an investigation of the sensitivity and reliability of two fracture detection methods based on measurements of acoustic waves propagating circumferentially in a borehole. A series of laboratory experiments that simulated measurements in various borehole environments was conducted. The analysis of the measurements provided insights into the performance of these fracture detection provided insights into the performance of these fracture detection techniques. Under Experiments we describe the general experimental conditions under which measurements were made. Then the acoustic fracture-detection techniques under study are described. We then discuss sensitivity of the fracture detection methods to effects such as depth of fracture, lithology changes, and surface roughness. Experiments The majority of measurements were made in an Indiana limestone formation of 16% porosity. The geometry of the block is shown in Fig. 1. The formation has a smooth borehole 20 cm [8 in.] in diameter and can be separated into two pieces by means of the radial sawcuts that intersect the center of the borehole along a diameter. These radial sawcuts act as smooth fractures. The two nonradial sawcuts extend only halfway through the block. A radially intersecting, "natural" vertical fracture is also shown in Fig. 1. The entire formation was submerged in a tank of water. Measurements were made with the blocks connected to form a complete borehole. The bulk slowness in the limestone measured 216 mu sec/m [66 mu sec/ft] for the compressional wave, 383 mu sec/m [117 mu sec/ft] for the shearwave, and 410 mu sec/m [125 mu sec/ft] for the planar pseudo-Rayleigh wave. The density of the saturated limestone was 2.5 g/cm3 pseudo-Rayleigh wave. The density of the saturated limestone was 2.5 g/cm3 [156 lbm/cu ft], and the fluid speed measured 666 mu sec/m [203 mu sec/ft]. The transducers used in this study were commercially available ultrasonic hydrophones with radially symmetric radiation patterns. Direct sonic paths between transmitter and receiver were blocked by fitting the transducers with reflective baffles. The typical measurement involved moving a source and receiver pair around the borehole while keeping the angle between them constant. The waveforms transmitted from the source to the receiver were recorded for analysis. The transducers could be adjusted in height such that in a complete rotation around the borehole, they would cross either three or five vertical fractures. The three fractures included the two sawcuts and the "natural" fracture. The extra two fractures were the nonradial sawcuts. Center frequencies varied between 50 kHz and 130 kHz [50,000 and 130,000 cycles/sec]. For ease of interpretation the graphs of fracture response vs. angle are coded (with wavy lines) to indicate sectors in which fracture detection would be anticipated. The marked sectors differ from graph to graph because of variations in the transducer spacing, the path along which the transducers were moved, and the waveform analysis, either single (energy) or double (semblance). JPT p. 657

Effect of Pressure on Rock Drillability

Published in Petroleum Transactions, AIME, Volume 213, 1958, pages 1–6. Abstract A laboratory drilling rig has been devised and placed in operation which permits the application of hydrostatic, terrastatic, and formation pore pressures to a rock sample for drilling under controlled conditions. Calibrated tests of this equipment indicate qualitative agreement with field results oil the effect of weight on bit, rotary speed, and rate of circulation on drilling rate. Tests under pressure, using water and air as the drilling fluids, indicate that when drilling saturated limestone samples, a pressure differential between hydrostatic and formation pressure is the only pressure which affects drilling rate. A differential in either direction causes a reduction in rate, but the same differential from the wellbore into the formation causes the greater reduction. Also, in limestone, air favorably affected drilling rate only when compared to water at high hydrostatic pressure, all other conditions remaining constant. Large increases in drilling rate with air could be obtained in the laboratory only while drilling a shale, which offered a limited permeability to nitrogen and which could be drilled with a differential from the formation into the wellbore. In general, the magnitude of the changes due to the pressure effect were small coin pared to changes in drilling rate obtainable by changing either bit weight or rotary speed. In the course of Humble's drilling research program, the desirability of investigating several factors which lend themselves to laboratory rather than field study became obvious. Principal reasons for this are the expense involved in field studies and the difficulty of exercising the required degree of control. Of primary importance are investigations of the effect of fluid properties on drilling rate, the effect of pressure on rock drillability, and a study of the fundamental mechanics of rock failure and chip generation. Several years ago some work in the laboratory on the effect of mud properties on drilling rate was reported to the API, but the completion of this work and the investigation of the other variables affecting drilling rate required equipment somewhat more elaborate than that used on these earlier tests. This equipment has been assembled to form Humble's Drilling Engineering laboratory.