Ingenious Method for Water Injection Optimization on Mature Carbonate Reservoir with Rapid Pressure Decline Problem, Case Study: XJN Field - South Sumatra, Indonesia

XJN field has implemented water injection as pressure maintenance since 1987, only one year after initial production. XJN is carbonate reservoir with weak aquifer underlying the oil zone. Initial reservoir pressure was 2,700 psi and peak production was 27,000 BOPD. Reservoir pressure was drop to 1,800 psi within 5 years of production. During 1991-2007, better injection management was performed to provide negative voidage. This action has managed to bring reservoir pressure back to its initial pressure, eventually enabling all wells to be converted from gaslift to naturalflow. In 2013, watercut has increased to 97% and several naturally flowing wells began to ceased-to-flow, then production mode was changed gradually from naturalflow to artificial lift using Electric Submersible Pump (ESP). In 2017-2020, there was rapid reservoir pressure decline around 300 psi/year while XJN water injection performance considered flawless. Voidage Replacement Ratio (VRR) was 1.3, but reservoir pressure was kept declining. This situation will cause ESP pump off on producer wells which in turn means big production loss. This paper will elaborate about the simple-uncommon-yet effective methods for problem detection and its solution to revive pressure and production. Analysis was began with observing the deviation of VRR and reservoir pressure, this was to estimate "leak" time of water injection. Next analysis was evaluation of injection rate leak off using material balance with reverse history matching. Reverse here means making reservoir pressure as main constraint rather than history matching goal. After that, it was continued with water injection flow path analysis. This was done by plotting production-injection-pressure data then make several small groups of injector-producer based on visible relationships. The purposes were to find key injector wells and to shut-in all inefficient ones. Furthermore, injection re-distribution was also performed based on VRR calculation on groups from previous step, water distribution priority was focused on key injector wells. These analysis have also paved the way for searching channeling possibility on injector wells. The results, XJN reservoir pressure showed an increasing trend of 100 psi/year after optimization was performed, with current pressure around 2000 psi. The increase in reservoir pressure has also made it possible to optimize ESP, field lifting has increased for 5000 BLPD. This project has also successfully secured XJN remaining oil. This project was racing with rapid pressure decline that will lead to early ESP pump off and production loss. The integrated subsurface analytical methods and actions being taken were simple but effective. Close monitoring on reservoir pressure, water injection and ESP parameters will be needed as field surveillance. Integrated analysis with surface facility engineering should also be carried out in the future in regards to surface network, injection rate and reservoir pressure.

Study of Pluto’s atmosphere based on 2020 stellar occultation light curve results

On 6 June 2020, Pluto’s stellar occultation was successfully observed at a ground-based observatory in Iran, and Pluto’s atmospheric parameters were investigated. We used an atmospheric model of Pluto, assuming a spherical and transparent pure N2 atmosphere. Using ray-tracing code, the stellar occultation light curve was satisfactorily fit to this model. We found that Pluto’s atmospheric pressure at the reference radius of 1215 km was 6.72 ± 0.48 μbar in June 2020. Our estimated pressure shows a continuation of the pressure increase trend observed since 1988 and does not confirm the rapid pressure decrease tentatively reported in 2019. The pressure evolution is consistent with a seasonal transport model. We conclude that the N2 sublimation process from Sputnik Planitia is continuing. This study’s result is shown on the diagram of the annual evolution of atmospheric pressure.

Reducing pressure oscillation in high-load HCCI combustion via air injection before compression

Pressure oscillation often occurs in high-load homogeneous charge compression ignition (HCCI) combustion, which is a challenge in the development of HCCI engines for automobiles. This work proposes a novel method of reducing the pressure oscillation in HCCI combustion at high loads. The proposed technique injects air into homogeneous mixtures before compression, thereby giving local fuel concentration gradient. The fuel concentration gradient is expected to suppress a rapid pressure rise, resulting in reduced pressure oscillation. High-load HCCI combustion was simulated via a rapid compression machine with a high compression ratio. Varying the period from air injection to compression, that is, the waiting time, controlled the magnitude of fuel concentration gradient. The pressure oscillation was quantified and evaluated via the knock intensity (KI) and the averaged pressure rise rate. For the short waiting time; in other words, when the local fuel concentration gradient was large, the KI was very lower than that for no air injection. The KI, however, increased with the waiting time to approach that for no air injection. The oscillation modes were also different with and without air injection according to a modal analysis. The in-cylinder temperature distribution was visualized via the infrared radiometry to better understand the effect of air injection. For no air injection, the temperature in the cylinder uniformly increased, and the whole mixtures were ignited instantaneously. With air injection and for the short waiting time, on the other hand, hot spots developed on the rim of the injected air where the specific heat ratio was higher and then gradually spread throughout the chamber. Therefore, retarded auto-ignition and subsequently slow spread would limit a rapid pressure rise, resulting in reduced pressure oscillation in HCCI combustion. In conclusion, the proposed technique is effective for reducing the pressure oscillation in high-load HCCI combustion only for the short waiting time.

Effect of Computational Constraints on Zero-Dimensional Computations for the Nanosecond-Order Ignition Process of the CH4/Air Mixture

Zero-dimensional computations of nanosecond-order ignition using a nanosecond discharge are performed with two constraints. The effects of these constraints are assessed to study the experimental rapid pressure change properly at the initial stages. The computations are carried out with the following constraints: constant internal energy and volume (U&V) and constant enthalpy and pressure (H&P), revealing differences between the two solutions. As the pressure remains constant under the H&P constraint, the total number density of all species decreases during ignition. In this case, O radicals are less generated and consumed. The progression of all reactions and temperatures increases under the H&P constraint less intensely than under the U&V constraint. Significant differences are found between the results calculated under the U&V and H&P constraints. Therefore, large discrepancies with real phenomena can be caused if the loss due to pressure reduction is not treated well.

Identification of a Pressure-Strain Correlation Based Bypass Transition Onset Marker

Temporally developing direct numerical simulations are performed for bypass transition flow with zero pressure gradient over a flat plate boundary layer for a range of free-stream turbulence intensities (Tu) of 1.4% to 6%. The objective is to understand the role of pressure-strain terms on bypass transition onset, and to propose and validate a phenomenological hypothesis for the identification of a robust transition onset marker for use in transition-sensitive Reynolds-averaged Navier-Stokes (RANS) simulations. Results show that transition initiates at a location where the slow pressure-strain term becomes more dominant than the rapid term in the pre-transitional boundary layer region. A simple transition onset marker based on one-point statistical quantities is derived from the scaling of the ratio of the slow and rapid pressure fluctuation source terms. The critical value of the marker is found to vary within a narrow range (+/- 3.2%), and satisfies previously identified criteria for a robust transition onset marker.

Nanoscale disintegration kinetics of mesoglobules in aqueous poly(N-isopropylacrylamide) solutions revealed by small-angle neutron scattering and pressure jumps

Two types of disintegration processes are revealed for polymeric nanoparticles using rapid pressure jumps and kinetic small-angle neutron scattering, namely chain release or swelling of the nanoparticle, depending on the target pressure.

Peptide–carbon hybrid membranes for highly efficient and selective extraction of actinides from rare earth elements

A cost-effective peptide–carbon hybrid membrane was developed to selectively extract uranium (U(vi)) and thorium (Th(iv)) from rare earth elements (REEs) through rapid pressure-driven filtration.