Accuracy and precision of the CSLT measurement system: An experiment to defect diagnoses in bored piles

A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on the size, shape, and orientation of defects in a bored pile. The CSLT measurement system has not (yet) been accredited in Hong Kong for foundation testing. Bored piles in Hong Kong are generally wide and deep. Existing measurement accuracy studies do not consider this large type of bored piles. The objective of this research is to quantify the measurement accuracy and precision of the CSLT method for large diameter bored piles (the most common pile type for public housing projects in Hong Kong). A test pile was constructed with known defects and perform experiments with a CSLT measurement system to quantify its accuracy and precision. CSLT is found to be accurate in detecting shape, size, and location of large defects but small defects close to the tube are difficult to detect. Generally speaking, CSLT has satisfactory accuracy and precision for practical use. The use of CSLT can be considered as a feasible method in defect diagnosis of bore piles in Hong Kong.

Potential and prospects of photocatalytic disinfection: using sustainable solarenergy- driven photocatalysts

A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on the size, shape, and orientation of defects in a bored pile. The CSLT measurement system has not (yet) been accredited in Hong Kong for foundation testing. Bored piles in Hong Kong are generally wide and deep. Existing measurement accuracy studies do not consider this large type of bored piles. The objective of this research is to quantify the measurement accuracy and precision of the CSLT method for large diameter bored piles (the most common pile type for public housing projects in Hong Kong). A test pile was constructed with known defects and perform experiments with a CSLT measurement system to quantify its accuracy and precision. CSLT is found to be accurate in detecting shape, size, and location of large defects but small defects close to the tube are difficult to detect. Generally speaking, CSLT has satisfactory accuracy and precision for practical use. The use of CSLT can be considered as a feasible method in defect diagnosis of bore piles in Hong Kong.

Successful Unconventional Fracturing Tight and Highly Laminated Silicilyte Reservoir Leading to Economic Field Development

South Oman contains several tight silicilyte reservoirs with significant locked hydrocarbon volumes. Successful hydraulic fracturing is key for unlocking commercial production. Low production rates coupled with fast declines have remained a challenge and a new economically attractive development scheme was required. Through integrated re-evaluation of the geology and reservoir, a modified frac approach was designed to create more connectivity to the reservoir height, using an unconventional frac design and frac fluids plus over-flush. Poor well productivity in tight silicilyte reservoir can be explained by low permeability of 0.001-0.1 mD and laminated texture with almost zero vertical permeability. Fit for purpose modelling was performed to assess the forecasting range for sub-surface uncertainties and frac parameters. One of the key changes for a successful development strategy was to place a higher number of fracs to overcome the extreme lamination. [1] It was observed that the "conventional" fracturing approach inaccurately assumed higher vertical fracture coverage of the reservoir and that the guar fluid used was much more damaging due to low recovery after frac clean-up. Fifteen unconventional fracs were pumped successfully with over-flush pumping technique. To understand if this new unconventional approach was effective in overcoming the extreme lamination required additional understanding of fractures geometry and orientation. To confirm fracture dimensions and flowing heights; a set of radioactive, chemical tracers and logging activities were completed. Flowback results showed that the unconventional frac [3] fluid used, was relatively easy to recover from formation and better cleaning-up of fractures can be achieved. This led to successful well clean-up compared to previous wells in the same field and confirmed better fracs clean up. Initial production results confirmed at least double well initial productivity, which should lead to better stable oil production from the field. Radioactive tracers logging, Sonic logging and Spectrum Noise Logging (SNL) confirmed mechanical and conductive fracture heights. Sonic logging also confirmed frac orientation. Oil and water dissolvable tracers confirmed fractures clean up from water and oil production intervals. Full geological and reservoir understanding, out of box thinking in frac technology allowed the asset team to come up with an unconventional development approach to improve commercial production from tight silicilyte reservoirs. The new frac approach included unconventional frac design and fluids, and execution using over flush and resulted into unlocking significant reserves. A more economic full field development is being planned and replication of the new frac approach is already ongoing in other fields.

Modeling of acoustoelastic borehole waves subjected to tectonic stress with formation anisotropy and borehole deviation

Sonic logging is a promising technique to estimate tectonic stress around a borehole. The key to successful evaluation of tectonic stress is having a thorough understanding of forward model which implies responses of borehole waves to tectonic stress. We propose a generic model to simulate responses of borehole waves to tectonic stress based on semi-analytical finite element method and acoustoelasticity. This model can compute distribution of tectonic stress around an inclined borehole with arbitrary anisotropic formation and simulate acoustoelasticities of borehole waves under this complicated stress. To avoid tedious and time consuming code development, we also provide an easy access to the model by reformulating and implementing the governing equations in a commercial software package. We validate the model by using three case studies where analytical/numerical solutions are available, showing good agreements between the results from our model and solutions in the literature. We then apply the model to some important applications in boreholes, demonstrating that this model can provide a powerful tool for understanding of responses of borehole waves to tectonic stress.

Non-destructive testing of bored piles

Quality control of bored piles is a complex operation aimed at determining possible defects in the pile shaft and the strength of the pile material made by different technologies. The presence of pile shaft defects and a decrease in the strength characteristics of the pile shaft material lead to the development of negative processes at the stage of subsequent operation of the building and structure. It is known that the bearing capacity of the pile material should not be less than the bearing capacity of the ground. Consequently, it is necessary to strictly observe the quality of the concrete of the design strength values to ensure the reliability of the designed building concerning the service life. Nowadays different methods of nondestructive testing such as pile integrity test, cross-hole sonic logging. The paper presents a discussion of the advantages and disadvantages of each of them, experimental data also are given

A Novel Method to Detect Cement through Direct Measurement – Case Histories

Cement quality is typically determined through the use of sonic logging tools, more commonly known as cement bond logs (CBLs), or more recently ultrasonic imaging tools (USITs). In general, these tools have served the industry well over time, but with the advent of new and exotic cement blends, as well as multistage cement jobs in today's unconventional horizontal wells, the quality and even location of the cement has become more problematic for basic CBL/USIT tools to detect. In addition, these tools are ineffective through multiple uncemented casing strings. A novel method to detect cement was developed as an offshoot of a technology used for detecting proppant in hydraulically fractured wells. This technique uses a non-radioactive tracer which exhibits a high thermal neutron capture cross section that is then incorporated into the proppant grains during manufacture. The proppant can then be detected using standard neutron-logging tools, at any time during the well's life. By incorporating small volumes of this detectible proppant into the cement slurry, the cement can then be detected using the same logging tools. This leads to identification of the top of cement, as well as the cement quality. If desired, the taggant can be staged such that the top and bottom of a cement stage can be detected. This paper will first review the industry concerns with cement detection. It will then discuss the principles and theory behind how the taggant works, both for basic proppant detection, as well as the novel application as a vehicle for cement detection. This will also include lab testing showing no impact of the tagged proppant on cement performance. The authors will conclude by presenting several case histories of cement detection, including two horizontal well applications, one each in the Permian and Canada. A third case history will also be presented in which the cement was detected through multiple strings of uncemented casing, to verify success of a cement squeeze in a surface casing remediation. This new technique allows for cement detection in wells in which conventional CBL/USITs are difficult to interpret, including detection of exotic cement blends, and through multiple strings of casing. This allows for more confidence in cement isolation, particularly in today's unconventional wells, where isolation of uphole formations is critical. This paper will be useful for drilling and completion engineers who are concerned with their ability to confirm cement quality, as well as production engineers who must perform remedial cementing operations.