Large Block Test Research Articles

Improved Understanding of Acid Wormholing in Carbonate Reservoirs through Laboratory Experiments and Field Measurements

SummaryA comprehensive study on wormholing has been conducted to improve the understanding of matrix acidizing in carbonate reservoirs. This work is a continuation of the previous work by Furui et al. (2012a, 2012b). An analysis of additional experimental results, as well as field measurements, is provided to reinforce and extend the wormhole-penetration model and productivity benefits provided by Furui et al. (2012b).A series of small-block tests and one large-block test under geomechanical stresses have been conducted to characterize wormholing in outcrop-chalk samples. In addition, field data including acid-pumping data and post-stimulation pressure-falloff data have been collected and analyzed to evaluate stimulation effectiveness. Pressure-buildup data from stimulated wells have also been analyzed to evaluate the sustainability of the acid-induced skin benefits. Production-logging data have been used to investigate whether created wormhole networks have remained stable or have collapsed under production stresses. To statistically analyze the data more comprehensively, the new data were also compared to field data available in the literature.The following conclusions are drawn from an analysis of the laboratory data and field data: (1) A skin value of −4 is achievable in carbonate reservoirs by matrix acidizing; (2) the negative acid skin is relatively stable under production stresses; (3) the wormhole-penetration model is proved to successfully simulate matrix-acidizing processes in both laboratory-scale and field-scale work; (4) the small- and large-block laboratory tests reconfirmed wormholing efficiency, which was discussed as a scale effect in the previous studies; and (5) an understanding of the possible range of wormhole penetration has allowed us to improve field acid treatments and reduce the risk of connecting to water.This comprehensive study includes acid-linear-coreflooding tests, small-block tests, large-block tests, and field measurements to thoroughly analyze acid wormholing in carbonate rock. The database can be very useful information for understanding, benchmarking, and optimizing future completion/stimulation design.

Effects of dopaminergic medication on objective tasks of deftness, bradykinesia and force control

At least one small report has suggested the possibility that limb kinetic apraxia (a deficit in deftness) was not dopamine responsive and independent of bradykinesia and rigidity in PD. Quencer et al. (Neurology 68:150-151, 2007) observed that speed of finger tapping (bradykinesia) in optimally medicated persons with PD was largely comparable to healthy controls, yet their ability to manipulate and rotate a coin (deftness) was impaired. The authors concluded that deftness was independent of parkinsonian features. In this study, we measured tasks of deftness in a more objective way in both the ON and OFF dopaminergic state. Further, we evaluated whether finger-thumb force control was compromised in persons with PD. Eleven PD fluctuators (mean age 68 ± 9 years) and ten healthy age-matched controls (68 ± 8 years) were included. The bradykinesia items in the UPDRS and performance on the large box and block (LBB) tests were used to measure bradykinesia. A small box and block test (SBB), small coin rotation task (SCR) and small lock rotation task (SLR) were used as measures of deftness. Statistical analyses revealed a significant improvement in performance for the LBB, SBB, SLR and the bradykinesia items of the UPDRS following medication. Furthermore, our PD cohort's scores were comparable to controls on tests of bradykinesia and deftness (SLR, SBB and LBB) in the ON state, but they performed statistically worse than controls in the OFF state. On the other hand, analyses of the force control tasks revealed no significant difference between the groups. In summary, the improvement in deftness and bradykinesia in the ON state among our PD cohorts (and their comparable performance in the ON but not OFF state compared to healthy controls) suggests the possibility of a more uniform response of these motor features to dopaminergic therapy in PD.

Analysis of large block test data using three-dimensional discontinuous deformation analysis

Analysis of large block test data using three-dimensional discontinuous deformation analysis

Understanding the anomalous temperature data from the Large Block Test at Yucca Mountain, Nevada

The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is large enough to include a number of large fractures, while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized. Extensive mapping of the test block has established the presence of many small and large fractures. Preheat air injection testing has also revealed that the block is highly heterogeneous, with fracture permeability varying more than four orders of magnitude. We hypothesize that these large fractures and the resulting heterogeneity play a significant role in the development of coupled thermal‐hydrological (TH) processes in the LBT. A large volume of TH data, including temperature and saturation measurements, has been collected from the LBT. Some of these temperature data from the LBT, particularly those recorded by sensors TT1‐14 and TT2‐14, appear anomalous. We show that these anomalous temperature data can be understood only if heterogeneity is invoked. As an example, we show that the heat pipe signature, an indication of the extent of TH coupling, in TT2‐14 is significantly longer in duration than that in TT1‐14. We show that such a difference can be explained only if one includes a high‐permeability layer, the existence of which has been indicated by air injection testing, through the location of sensor TT2‐14. Similarly, the oscillating temperature pattern in all sensors of borehole TT2 during 4470–4500 hours of heating is shown to be the result of rainwater flowing down a high‐permeability fracture. The irregular temperature pattern in borehole TT1 happens because of rainwater reaching the source of heat quickly through a highly permeable, inclined fracture and vapor rising upwards through a less permeable vertical fracture. We also demonstrate that the anomalous temperature pattern recorded by TT1‐14 during 2500–3500 hours of heating can be explained in terms of continuous upward movement of vapor and the downward flow of condensate through the fractures. We conclude that the temperature data from the LBT are the results of coupled TH processes occurring in a heterogeneous environment.

Electrical imaging at the large block test—Yucca Mountain, Nevada

A monolithic block of densely welded tuff was excavated from a site on Fran Ridge near Yucca Mountain, Nevada so that coupled thermohydrological processes could be studied in a controlled, in situ experiment. A series of heaters were placed in a horizontal plane about 3 m from the top of the 3 m×3 m×4.5-m high block. Temperatures were measured at many points within and on the block surface and a suite of other measurements were taken to define the thermal and hydrologic response. Electrical resistance tomography (ERT) was used to map two-dimensional images of moisture content changes along four planes in the block. The ERT images clearly delineate the drying and wetting of the rockmass during the 13 months of heating and subsequent 6 months of cool down. The main feature is a prominent dry zone that forms around the heaters then gradually disappears as the rock cools down. Other features include linear anomalies of decreasing moisture content, which are fractures dehydrating as the block heats up. There are also examples of compact anomalies of wetting. Some of these appear to be water accumulation in fractures, which are draining condensate from the block. Others may be rainwater entering a fracture at the top of the block. During cool-down, a general rewetting is observed although this is less certain because of poor data quality during this stage of the experiment.

Investigation of Bacterial Transport in the Large-Block test, A Thermally Perturbed Block of Topopah Spring Tuff

AbstractTransport of bacteria is investigated as part of the Large-Block Test (LBT), a thermally perturbed block of Topopah Spring tuff. Two bacterial species,Bacillus subtilisandArthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and rifampicin, were selected from these species by laboratory procedures, cultured, and injected into the five heater boreholes of the large block hours before heating was initiated. The temperature, as measured 5 cm above one of the heater boreholes, rose slowly over a matter of months to a maximum of 142°C and to 60°C at the top and the bottom of the block. Samples were collected from boreholes located approximately 5 ft below the injection points. Double-drug-resistant bacteria were found in the collection boreholes nine months after injection. Biochemical tests support the identification ofB. subtilisin the collection boreholes. Double-drug-resistant microbes also appeared in the heater boreholes where the temperature had been sustainably high throughout the test. The number of double-drugresistant bacteria that were identified in the collection boreholes increased with time until the heater was deactivated. Negative indications in the collection holes after the heater was deactivated support the supposition that these bacteria were the species that were injected. An apparent homogeneous distribution among the collection boreholes suggests no pattern to the migration of bacteria through the block. The relationship between bacterial migration and the movement of water is not yet understood. These observations indicate the possibility of rapid bacterial transport in a thermally perturbed geologic setting. The implications for colloid transport need to be reviewed.

Rock mass deformational properties from a large scale Block Test : Cramer, M L; Cunningham, J P; Kim, K Proc 24th US Symposium on Rock Mechanics, College Station, Texas, 20–23 June 1983P267–270. Publ: AEG, 1983

Rock mass deformational properties from a large scale Block Test : Cramer, M L; Cunningham, J P; Kim, K Proc 24th US Symposium on Rock Mechanics, College Station, Texas, 20–23 June 1983P267–270. Publ: AEG, 1983

General characteristics of strain relaxation: A note on sample preparation for large‐scale tests

Overcoring and large block tests indicate that intact rocks are disturbed upon removal from outcrops so that their laboratory properties are not the same as their in situ properties. The disturbance occurs during strain relaxation for which there are general characteristics as listed in this note.