Stratigraphic Trap Potential in the Lower Cretaceous Ratawi Interval, Partitioned Zone PZ, Saudi Arabia and Kuwait

The Lower Cretaceous Ratawi Oolite Formation is among the most prolific reservoirs in the PZ, having produced a significant amount of oil since the 1950's. The Ratawi is interpreted as a low angle carbonate ramp, with high-energy grainstone facies developing on structural highs. Production is focused on these structural highs, with very few well penetrations off structure. Recent work has identified potential Ratawi stratigraphic traps in prograding clinoforms along the flanks of the North Fuwaris structural high. Core data from Ratawi wells illustrate the interplay of depositional environment and diagenesis on reservoir quality. Gross depositional environment (GDE) maps created from the integration of seismic facies and core observations indicate the stratigraphic trap lies in the ramp slope. Reservoir quality variability of the ramp slope across the PZ is explained by the diagenetic history of the Ratawi. Early equant calcite cement develops from substantial meteoric runoff and lowers porosity, while later dissolution enhances reservoir quality. The area of interest is isolated from potential meteoric inputs; we do not expect equant calcite cement or the associated reduction in reservoir quality. Seismic interpretation was performed on recently acquired PZ 3D data to map the Ratawi section. Clinoforms (inclined geometry) were mapped along the western flank of the North Fuwaris high. These facies appear to have developed as a result of progradation to the NW and are indicative of good reservoir development. Leads were generated using the depth structure and GDE maps, supported by amplitude extraction and seismic inversion volumes. Amplitudes extracted from the clinoform shows that the strongest anomaly is along the structurally highest part of the horizon and the anomaly weakens downdip. High amplitudes could be a proxy for reservoir (porosity), and sharp turn-off in amplitude might indicate that lateral and updip facies changes to non-reservoir which is needed for an effective seal. Recent seismic inversion performed on the Ratawi interval shows a good match between the Acoustic Impedance (AI) from logs and the computed AI from the seismic. The Ratawi Oolite appears as a low impedance interval between overlying Ratawi Limestone and underlying Makhul. Porosity estimated from AI volumes appear to support possible Ratawi reservoir development along the flanks of North Fuwaris and Wafra highs.

Thrust Faults Promoted Hydrocarbon Leakage at the Compressional Zone of Fine-Grained Mass-Transport Deposits

Fine-grained mass-transport deposits (MTDs), especially their compressional toe zones, are traditionally considered as effective seal in constraining the vertical fluid migration underneath. However, this study documents thrust faults at the compressional toe zone of fine-grained MTDs that could disaggregate the seal competence and promote vertical fluid flow. The investigated MTD referred to as MTD-a lies directly over a large hydrocarbon reservoir that is located within the Central Canyon of northern South China Sea, which is examined by using high-resolution 3D seismic and borehole data. Thrust faults and irregular blocks composed of coarse-grained sandstones are observed in the compressional zone of the MTD-a’s toe. More importantly, seismic evidence (e.g., enhanced seismic reflections) suggests that a large amount of hydrocarbons from the underlying reservoir penetrated through the MTD-a along these thrust faults and charged into the coarse-grained sandstone blocks. This clear evidence of thrust faults compromising the MTD’s seal effectiveness and thus facilitating the vertical fluid flow through the non-permeable strata demonstrate the importance of reassessing the seal capacity of MTD.

Seismic Attribute Analyses and Attenuation Applications for Detecting Gas Hydrate Presence

Identifying gas hydrates in the oceanic subsurface using seismic reflection data supported by the presence of a bottom simulating reflector (BSR) is not an easy task, given the wide range of geophysical methods that have been applied to do so. Though the presence of the BSR is attributed to the attenuation response, as seismic waves transition from hydrate-filled sediment within the gas hydrate stability zone (GHSZ) to free gas-bearing sediment below, few studies have applied a direct attenuation measurement. To improve the detection of gas hydrates and associated features, including the BSR and free gas accumulation beneath the gas hydrates, we apply a recently developed method known as Sparse-Spike Decomposition (SSD) that directly measures attenuation from estimating the quality factor (Q) parameter. In addition to performing attribute analyses using frequency attributes and a spectral decomposition method to improve BSR imaging, using a comprehensive analysis of the three methods, we make several key observations. These include the following: (1) low-frequency shadow zones seem to correlate with large values of attenuation; (2) there is a strong relationship between the amplitude strength of the BSR and the increase of the attenuation response; (3) the resulting interpretation of migration pathways of the free gas using the direct attenuation measurement method; and (4) for the data analyzed, the gas hydrates themselves do not give rise to either impedance or attenuation anomalies that fully differentiate them from nearby non-hydrate zones. From this last observation, we find that, although the SSD method may not directly detect in situ gas hydrates, the same gas hydrates often form an effective seal trapping and deeper free gas accumulation, which can exhibit a large attenuation response, allowing us to infer the likely presence of the overlying hydrates themselves.

Innovative Techniques for Optimization of Far-Field Diverter Materials to Enhance Fracture Geometry in Carbonate Reservoirs

The technique of employing specialized particulates for far-field diversion is well-established during hydraulic fracturing treatments in unconventional formations and is being investigated for use in conventional formations. Far-field diverters (FFD) divert fluid away from the wellbore far into the formation. The injection of FFD at the beginning of the treatment provides an additional stress barrier between the producing interval and adjacent layers by depositing at the layer boundaries where higher leak-off is encountered. The ensuing restriction in height growth maximizes fracture extension within the producing zone, optimizing geometry for increased hydrocarbon production while limiting excess water. Polylactic Acid (PLA) polymer is self-degradable, compatible with reservoir fluids, and has a variety of compositions for different temperature applications. Blending proppant with PLA has been seen to significantly improve the strength of the deposited far-field diverter. Therefore, PLA powder and silica proppant are blended to develop Generation-1 far-field diverter (FFD-Gen1). However, many silica proppants have greater density than PLA, leading to separation during transport which prevents these two components from depositing evenly at the upper fracture boundary. This results in a situation in which excessive downward growth is prevented while upward growth is left unchecked. For this reason, both components need to be simultaneously deposited in order to develop an effective seal. Generation-2 far-field diverter (FFD-Gen2) is developed by replacing silica proppant of FFD-Gen1 with a deformable proppant having a density nearly equal to the polymer, which enables uniform deposition on all adjacent formation boundaries where leakoff is encountered. The deformable characteristic improves the pressure withstanding capacity of the diverter pack. The deposition and degradation behaviors are investigated in the laboratory by performing HTHP filter press and plug stability experiments. Experimental findings suggest that the primary selection criteria for acceptable performance are the material's mechanical properties. This methodology is used to select the appropriate FFD materials to optimize fracture geometry in carbonate reservoirs. Successful applications prevent excessive water production and substantially increase hydrocarbon production as illustrated in a three well case studies.

Sodium Silicate Based Drilling Fluid Application in Gulf of Thailand to Stabilise Wellbore: A Case Study

Sodium Silicate were first used in water-based drilling fluids to stabilize claystone formations in the 1930's, but found favour in the 1990's in high performance, non dispersed water based systems for drilling problematic claystone formations as an alternative to oil-based drilling fluids. In Bongkot South field, Gulf of Thailand, sodium silicate-based drilling fluid (SSBDF) were used with mixed success in shallow gas drilling. Typically, platform WP-33, the claystone formation of the 12¼" section were drilled with 5% v/v Sodium Silicate in the water based drilling fluid together with excessive circulation as intention to improve hole cleaning frequently result in a wellbore that was overgauge by upto 18.9% in some case. This led to further hole cleaning problem that also compromised cement job quality. A further 6 well campaign on WPS-16 required a re-evaulation of the SSBDF coupled to an understanding of the wellbore instability mechanisms that leads to hole enlargement. To overcome better wellbore stability, sodium silicate has been designed by increased concentration to 8% v/v sodium silicate treated drilling fluid showed optimal design for application base on application of SSBDF has been used on platform WP-11 in 2002. Rheology, hydraulic and flow regime was adjusted for laminar flow that reduced the erosion of fragile claystone formation in the wellbore. The revised SSBDF formulation at WPS-16 result in a significant reduction of hole enlargement to 3.2% in the claystone section through a combination of chemicals and mechanical inhibition that contribute improved hole cleaning. The addition of wellbore strengthening material also provide an effective seal to minimize gas invasion. This paper describes the field trials in the Gulf of Thailand drilled with revised sodium sodium silicate based drilling fluid, the use of wellbore strengthening materials to manage gas influxes, better drilling practice and hydraclic simulation concluded that high performance water based drilling fluid of this nature have wider application where oil-base drilling fluid have traditionally been used.

Gas Migration Mechanisms and Their Effects on Caprock Seal Capacity: A Case Study in Depleted Gas Fields in the Sarawak Basin, Offshore Malaysia

This paper focuses on the gas characteristics in caprock interval and the gas migration mechanisms from the carbonate reservoir into the caprock and its effects on caprock seal capacity. The workflow mainly includes three methods:(1) Gas geochemistry analysis from the GWD (Gas While Drilling) data to understand the gas composition, their distribution and mechanism for gas migration; (2) Petrophysical analysis to understand the rock types, petrophysical properties and the pore-throat system; and (3) Pore pressure prediction to understand the pressure sealing capacity of the caprock. Integrating the results from these three aspects, the sealing capacity can be evaluated by capillary pressure sealing, pore pressure sealing and the effects on the sealing efficiency for CO2. There are two gas migration mechanisms in the area: gas diffusion and gas advection. The gas in the caprock of Field A shows decreasing molecular weight trend from deep to shallow depths implying migration from the underlying carbonate reservoir by gas diffusion. However, the gas in the caprock of Field B where there is a gas chimney visible in the seismic data, has composition similar to the gas in carbonate reservoir, suggesting that the gas came from carbonate reservoir below by gas advection through faults and induced fractures and occurred simultaneously with the gas accumulation in the reservoir. There is also gas in the caprock above the gas chimney with lighter molecular weight representing gas that migrated from the gas chimney by gas diffusion. The caprock seal capability in the two fields are different. The gas in the carbonate reservoir in Field A can be sealed and trapped by the high displacement/entry pressure of the capillary pore-throat system and the abnormally high pore pressure in the caprock. The gas chimney at Field B would be connected to the carbonate reservoir below over geological time and there is effective seal enough to contain hundreds ft of gas column in the carbonate reservoir. The understanding of the leaking mechanism in these two fields is helpful for understanding the leakage scale, the effects on the sealing capacity, the risk evaluation and mitigation amendment.

Appendix gap losses in Stirling engines – review of recent findings

The appendix gap loss in Stirling cycle machines is generated by the annular gap around the thermally insulating, thin-walled dome typically attached to a piston or displacer plunging into the hot cylinder volume of an engine or the cold volume of a cryocooler. It was considered to be of minor importance for decades. Thus, simplified analytical models were considered sufficiently accurate for its description, until numerical simulations and experimental results gave rise to a more detailed analysis revealing that, neglecting entrance and end effects, the flow is typically laminar, but unsteady. Subsequently, an enhanced analytical model accounting for fluidic and thermal inertia effects as well as the volumetric displacement by the seal was developed. Compared to the previous ones, this model predicts a shift of the optimum width to smaller values, a higher minimum overall loss and furthermore, an option to decrease the loss by reducing the effective seal diameter. This could be experimentally confirmed as well as the unsteady gas temperature profiles predicted by this model. Subsequently, both theoretically and experimentally founded correlations for the radial and axial energy transport in the gap were derived and implemented in a differential simulation of the gap within a third order code.

Use of Thin Dressings Under N95 Respirators: Exploring Their Effect on Quantitative Fit Testing Results to Guide Hospital Practice During the COVID-19 Pandemic

At the beginning of the coronavirus disease-19 pandemic, health care staff at a level 1 trauma center in the state of New York experienced facial irritation and skin breakdown under their N95 respirators due to increased and prolonged use. PURPOSE: Members of the Certified Wound and Ostomy Nurse, Nurse Practitioners staff were charged with developing recommendations within 48 hours to help prevent and manage facial skin issues using available products that would not compromise the seal of the respirators. METHOD: With the assistance of a health care safety specialist from the Environmental Health and Safety Department of the hospital, an ambient particle counting device was used to measure the N95 fit factor following application of a liquid skin barrier, transparent film dressing, light silicone-based adhesive dressing, or an extra-thin hydrocolloid dressing on the bridge of the nose and the cheekbones underneath an N95 respirator of 2 hospital staff members who volunteered to test the dressings. RESULTS: All thin dressings tested showed a fit factor over 100, reflecting an effective seal. The highest fit factors were seen with the liquid skin barrier in the 2 volunteers (200 and 198, respectively). Thin dressing usage information was included in the hospital guidelines for N95 respirators and shared with staff. Subsequent feedback suggests that the light silicone-based adhesive dressing and the extra-thin hydrocolloid dressing were preferred. CONCLUSION: Thin dressing use may help reduce skin complications among hospital staff during periods of extended N95 respirator wear time. Because use of the dressings did not result in failure of the quantitative fit test, they were permitted for use by health care staff under their N95 respirators. Studies are needed to help health care facilities optimize N95 respirator use to protect staff from coronavirus disease-19 and respirator-related skin complications while supply shortages remain.

Osteoclasts’ Ability to Generate Trenches Rather Than Pits Depends on High Levels of Active Cathepsin K and Efficient Clearance of Resorption Products

Until recently, it was well-accepted that osteoclasts resorb bone according to the resorption cycle model. This model is based on the assumption that osteoclasts are immobile during bone erosion, allowing the actin ring to be firmly attached and thereby provide an effective seal encircling the resorptive compartment. However, through time-lapse, it was recently documented that osteoclasts making elongated resorption cavities and trenches move across the bone surface while efficiently resorbing bone. However, it was also shown that osteoclasts making rounded cavities and pits indeed resorb bone while they are immobile. Only little is known about what distinguishes these two different resorption modes. This is of both basic and clinical interest because these resorption modes are differently sensitive to drugs and are affected by the gender as well as age of the donor. In the present manuscript we show that: 1. levels of active cathepsin K determine the switch from pit to trench mode; 2. pit and trench mode depend on clathrin-mediated endocytosis; and 3. a mechanism integrating release of resorption products and membrane/integrin recycling is required for prolongation of trench mode. Our study therefore contributes to an improved understanding of the molecular and cellular determinants for the two osteoclastic bone resorption modes.