Comparative study of well soaking timing(pre vs.post flowback)for water blockage removal from matrix-fracture interface

Water blockage after hydraulic fracturing is one of the major challenges in shale oil recovery which affects the optimal production from the reservoir.The water blockage represents a higher water saturation near the matrixfracture interface,which decreases the hydrocarbon relative permeability.The removal of water blockage in the field is typically carried out by soaking the well(i.e.,shut-in)after hydraulic fracturing operation is finished.This soaking period allows water redistribution,which decreases the water saturation near the matrix-fracture interface.However,previous field reports show that there is not a strong consensus on whether shut-in is beneficial in terms of production rate or ultimate oil recovery.Due to the large number of parameters involved in hydraulic fracturing and tight formations,it is challenging to select which parameter plays the dominant role in determining the shut-in performance.Furthermore,literature on field case studies does not frequently report the parameters which are of researchers’interest.In other words,the challenge of evaluating shut-in performance not only lies on the complexity of parameters and effects involved within the reservoir,but also the limited number of field case studies which report a comprehensive list of fracturing and reservoir parameters.This paper aims to investigate the effect of well soaking timing on shut-in performance.This idea to investigate the shut-in timing effect is motivated by the fact that in the field,shut-in can take place either immediately after hydraulic fracturing but before the first flowback(i.e.,pre-flowback)or sometime after the first flowback(i.e.,post-flowback).The timing of shut-in is believed to influence the production performance,because it dictates how much water is allowed to imbibe from the fractures to the matrix before the extended production.A numerical model is built and validated by a successful history match with numerous data from core-flood experiments.Our previous study shows that shut-in performance depends heavily on the desiccation state of the formation:in non-desiccated formations,longer shut-in(pre-flowback)results in a lower regained hydrocarbon relative permeability,but in desiccated formations,longer shut-in(pre-flowback)does not affect the regained hydrocarbon relative permeability.In this study,our model further demonstrates that shut-in performed after the first flowback(i.e.,postflowback)can help ensure a higher regained oil relative permeability than shut-in performed before the first flowback(i.e.,pre-flowback)in such non-desiccated formations.A mechanistic analysis on the water blockage mitigation from these two shut-in timings is also presented.As a result,this study proposes that flowback should be carried out immediately following hydraulic fracturing,even if an extended shut-in is to be performed later.

The Conservation of Ground Water Levels in the Peat Swamp Forest at Ayer Hitam North Forest Reserve, Muar in Johor, Malaysia

The management of peat swamp forests in Malaysia contends with two major issues: forest fires and the effects of abandoned forest-logging drainage systems or canals. Forest fire occurs during low rainfall season related to the local people activities. The drainage networks change the hydrological function of the intact forest ecosystem. A key function of the hydrological system in the undisturbed forest is to absorb water during rainfall season, thus delaying downstream runoff and preventing flash floods. The objective of the project described here is to restore the hydrological function of peat swamp forest (PSF) at Ayer Hitam North Forest Reserve (AHNFR) in Muar, Johor, Malaysia. The oil palm plantations, especially in the southern part of the area affect the forest reserve. Water flows out of the forest reserve through the drainage system constructed for managing these plantations. In 2016 and 2017, two water block structures or check dams were constructed near the boundaries of the forest reserve to hold the water and raise the groundwater level in the forest reserve. The implementation of the check dams at the two locations has conserved the groundwater level and subsequently, about 1.2 million m3 of water was saved annually from leaving the forest reserve from each of the check dam. This project is also part of the Coca-Cola Company’s sustainability commitment for water strategy with the global that is to replenish 100% of the equivalent volume of water consumed in their products and production by 2020. Replenishment is the key sustainability commitment for the Company.

Hydrophobic nanochannel self-assembled by amphipathic Janus particles confined in aqueous nano-space

Hydrophobic nanochannel plays a significant role in many physical, biological, and geological phenomena and ex- hibits impressive applications due to both its ubiquitous distribution and great ability to transport hydrophobic molecules, including various oils and gases. Based on theoretical modeling, we herein reveal that the amphipathic Janus nanoparticles have a large probability to self-assemble into uninterrupted hydrophobic nanochannels inside the aqueous nano-space, al- though there are large portions of the Janus nanoparticles to be hydrophilic. The key to this observation is the attractions between the hydrophobic regimes on neighboring amphipathic Janus particles through hydrophobic interaction in aqueous nano-space. More surprisingly, the permeation efficiency of hydrophobic molecules through the uninterrupted hydrophobic channel in Janus particles aggregate is even higher than that in the aggregate of hydrophobic particles. We note that the proposed amphipathic Janus particles can be transported to the appropriate positions by the water since the hydrophilic regimes still remain a strong particle-water interaction. We also note that most natural subsurface rocks are not completely hydrophobic or hydrophilic but have complex surfaces with inhomogeneous wetting property. Our work therefore provides a detailed molecular level understanding of the formation of underground strata as well as the new insight for constructing the artificial hydrophobic channels for various applications, such as the design of proppants to enhance the recovery of the unconventional oil/gas.

The gas jet behavior in submerged Laval nozzle flow

The behavior of the combustion gas jet in a Laval nozzle flow is studied by numerical simulations. The Laval nozzle is installed in an engine and the combustion gas comes out of the engine through the nozzle and then injects into the surrounding environment. First, the jet injection into the air is simulated and the results are verified by the theoretical solutions of the 1-D isentropic flow. Then the behavior of the gas jet in a submerged Laval nozzle flow is simulated for various water depths. The stability of the jet and the jet evolution with a series of expansion waves and compression waves are analyzed, as well as the mechanism of the jet in a deep water depth. Finally, the numerical results are compared with existing experimental data and it is shown that the characteristics of the water blockage and the average values of the engine thrust are in good agreement and the unfixed engine in the experiment is the cause of the differences of the frequency and the amplitude of the oscillation.