The simulation of gas production from oceanic gas hydrate reservoir by the combination of ocean surface warm water flooding with depressurization

A new method is proposed to produce gas from oceanic gas hydrate reservoir by combining the ocean surface warm water flooding with depressurization which can efficiently utilize the synthetic effects of thermal, salt and depressurization on gas hydrate dissociation. The method has the advantage of high efficiency, low cost and enhanced safety. Based on the proposed conceptual method, the physical and mathematical models are established, in which the effects of the flow of multiphase fluid, the kinetic process of hydrate dissociation, the endothermic process of hydrate dissociation, ice-water phase equilibrium, salt inhibition, dispersion, convection and conduction on the hydrate disso- ciation and gas and water production are considered. The gas and water rates, formation pressure for the combination method are compared with that of the single depressurization, which is referred to the method in which only depres- surization is used. The results show that the combination method can remedy the deficiency of individual producing methods. It has the advantage of longer stable period of high gas rate than the single depressurization. It can also reduce the geologic hazard caused by the formation defor- mation due to the maintaining of the formation pressure by injected ocean warm water.

Study on Sequence Stratigraphy of Zhujiang and Zhuhai Formations, Zhu

The early Miocene in the Zhu Ⅲ subbasin, the Pearl River Mouth basin, includes two formations-Zhujiang and Zhuhai. There are 8 third-order sequences, S1, S2, S3, S4, S5, S6, S7 and S8 from the bottom of Zhuhai to the top of Zhujiang in thee two formations. There are only one transgressive systems tract (TST) and one highstand systems tract (HST) in each sequence because the whole Zhu Ⅲ subbasin was located updip the shelf break during sequence deposition. The boundaries and maximum flooding surfaces (mfs) are in good response to both gamma and acoustic log curves in the study area. In seismic profile 1249, sediments obviously onlap over the unconformity (SB0, the bottom of Zhuhai Fm), SB1 and SB2, but obviously over only SB2 in seismic profile 1283 since the well- devel-oped faults in the subbasin. The sand bodies with high porosity and permeability for Petroleum migration and accumulation had been reworked by tidal currents before their burial. Hence, the tidal influenced parasequence sets occur both in TST and HST. Through detailed analysis, the sand bodies in TST are more favorable for Petroleum to migrate and accumulate than those in HST.

Surface Flood and Underground Flood in Xiangxi River Karst Basin： Characteristics, Models, and Comparisons

Xiangxi River Basin, located in western Hubei Province in central China, is a karst ridge-trough area with an inhomogeneous and complicated distribution of water resources. This paper compares the characteristics of surface and subsurface floods in this karst basin, utilizing a one-parameter Darcian model and the traditional exponential model. The observed hydrographs and inferred water components are strikingly similar for surface and subsurface floods. The Darcian model and the exponential model are based on different views of the flood generation process, with the former fitting the entire hydrograph with a single time constant, and the latter fitting only the recession limb with multiple time constants. Due to the anisotropy and heterogeneity of karst media, a combination of physical and chemical techniques including the use of 3S（remote sensing, geographical information system, global positioning system） method is proposed for an enhanced hydrological investigation to assess and characterize karst water resources in mountainous areas.

Magnetic properties of Holocene core ZK9 in the subaqueous Yangtze delta and their mechanisms and implications

We measured the magnetic properties of core ZK9 from the subaqueous Yangtze delta to examine the mechanisms and possibility of using magnetic proxies for the sedimentary environmental evolution controlled by the Holocene sea level. The results showed that low values of most magnetic parameters occurred and pyrite formed in the estuarine sediments during c. 10.5-8.4 cal ka BE reflecting the predominant early diagenesis in a tidaldominated depositional environment when the sea level rose rapidly. Sharp increases in the values of χARM （susceptibility of Anhysteresis Remanent Magnetisation）, χARM/χ, χARM/SIRM （Saturation Isothermal Remnant Magnetisation） and HIRM （Hard Isothermal Remnant Magnetisation） occurred immediately above the transitional zone from estuarine to deltaic system of c. 8.4--5.9 cal ka BP, which imply accumulation of single-domain magnetite and anti-ferromagnetic minerals. These magnetic properties indicate the enhanced freshwater processes at the core site as a result of the relatively stable sea level and the associated delta progradation since c. 5.9 cal ka BP. Therefore, magnetic proxies Of χARM and HIRM are useful to identify the maximum flooding surface. In addition, the intertidal-subtidal sediment of c. 13.2-10.5 cal ka BP had high values of χ, SIRM and HIRM, reflecting the features of a coastal environment. The sharp decline of the above parameters from c. 10.5 cal ka BP indicates possibly an event of rapid sea level rise.