A Comparative Modeling Study of Thermal Mitigation Strategies in Irreversible Electroporation Treatments

Irreversible electroporation (IRE), otherwise known as non-thermal pulsed field ablation (PFA), is an attractive focal ablation modality due to its ability to destroy aberrant cells with limited disruption of extracellular tissue architecture. Despite its non-thermal cell death mechanism, application of electrical energy results in Joule heating that, if ignored, can cause undesired thermal injury. Engineered thermal mitigation (TM) technologies including phase change materials (PCMs) and active cooling (AC) have been reported and tested in isolated preliminary studies to limit the risk of thermal damage, but their performance compared to one another is relatively unknown. Further, the effects of pulsing paradigm, electrode geometry, PCM composition, and chosen active cooling parameters have not been examined. Here, we develop a computational model of conventional bipolar and monopolar probes with solid, PCM-filled, or actively cooled cores and simulate clinical IRE treatments in pancreatic tissue. We find that probes with integrated PCM cores can be tuned to drastically limit thermal damage compared to traditional solid probes. Actively cooled probes, on the other hand, provide even more control over thermal effects within the probe vicinity and can altogether eliminate thermal damage. In practice, these differences in performance are tempered by the increased time, expense, and effort necessary to use actively cooled probes compared to traditional solid probes or those containing a PCM core.

Implementation of HPHT RSS for Performance Improvement in Deep Shale Gas Drilling

Sichuan shale gas development will move to reservoirs deeper than 3,500m TVD in the future after a production milestone breakthrough of 10 billion m3 per year from Southern Sichuan basin was achieved. 80% of Sichuan shale gas total resources will come from deep reserves compared to reservoirs at a shallower depth. Improvements in drilling efficiency are the key success factor of deep shale gas development to enhance production and cost control with the increasing activity. Due to complex engineering and geological conditions, drilling deep shale gas horizontal wells in the Southern Sichuan basin is more challenging than traditional shallower wells. The High Pressure and High Temperature (HPHT) harsh drilling environment has caused the frequent failure of the standard Rotary Steerable System (RSS), Measurement While Drilling (MWD), and Logging While Drilling (LWD) tools during recent drilling operations. The surface cooling system, combined with thermal mitigation practices, positively impacted the increasing trend of bottom hole circulating temperature (BHCT) and extended equipment life in short horizontal sections. However, thermal mitigation reduced in effectiveness with the increase in the length of the horizontal section as frictional heating increased. BHCT reached above 150degC while drilling and exceeded the operating limits of standard tools. The challenge of managing the circulating temperatures resulted in approximately 50% of the total runs in 2020 being tripped before the run objectives were met, creating non-production time (NPT) and significantly decreasing drilling efficiency. To overcome this challenge and reduce NPT, two options were evaluated. A high-temperature Motor bottom hole assembly (BHA) brought risks of poor well trajectory control, resulting in well placement issues during geosteering, and lower potential reservoir exposure. For the first time in China Shale gas, an HPHT RSS with near-bit gamma-ray imaging was selected to maximize drilling efficiency and reservoir exposure. In addition to the tool selection, an HT optimization process was created that included horizontal well BHCT modeling and prediction and deep shale gas RSS drilling best practices. The near-bit gamma imaging quality was enhanced to improve steering. These changes delivered record runs in deep shale gas long horizontal wells and significantly decreased NPT. Reducing the reliance on surface cooling systems also increased overall operating efficiency. This paper reviews the choice of equipment, implementation of HPHT RSS, and development of HT optimization process that improved the drilling efficiency, reduced well time and enhanced long horizontal well placement in this complex drilling environment.

River temperature dynamics downstream of a shallow reservoir: process-based modelling to evaluate thermal mitigation strategies

<p>This study focused on Alouette River, located in south coastal British Columbia. During summer, water is released from shallow reservoir at a near-constant rate from an outlet about 6-10 m below the water  surface. Outlet temperatures in summer 2013 were initially cool hypolimnetic water, followed by alternating cool and warm water associated with an internal seiche, and finally dominated by warm epilimnetic water during the period of highest water temperature. An energy-balance model was used to evaluate potential strategies to ameliorate thermal habitat conditions for Pacific salmon downstream of the dam. Restoration of deforested banks that represented 4% of the reach length reduced daily maximum temperatures by only about 0.5 °C , while releasing more flow exacerbated temperatures during the warmest week of the year. The only effective strategy for thermal amelioration would be to release water from deeper in the reservoir.</p>