Interpretation of S-wave data from Tai′anXinzhou DSS profile and its relationship with Xingtai earthquakes

On the basis of S wave information from Tai′an Xinzhou DSS profile and with reference to the results from P wave interpretation, the 2 D structures , including S wave velocity V s, ratio γ between V p and V s; and Poisson′s ratio σ , are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the above results. Upwarping mantle districts (V s≈4.30 km/s)and sloping mantle districts (V s≈4.50 km/s) of the profile with velocity difference about 4% at the top of upper mantle are divided according to the differences of V s , γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of Niujiaqiao Dongwang high angle ultra crustal fault zone is reaffirmed; the properties of low and high velocity blocks(zones) including the crust mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps, thermal material upwells through the high angle fault, the primary hypocenter was located at the crust mantle juncture 30.0～33.0 km deep, and additional stress excited the M S=6.8 and M S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao Dongwang, the earthquakes took place around the high angle ultra crustal fault and centered in the brittle media and rock strata with low γ and low σ values.

Structural Characteristics of the Andaman Forearc Inferred from Interpretation of Multichannel Seismic Reflection Data

The Andaman Forearc Basin （AFB） is asymmetric in configuration and filled with a-6 km-thick pile of Neogene to Recent sediments （-4 s in two-way travel time： TWT） with distinct zonation. It shows gradual thinning up to -3 km （0.8 s in TWT） towards the eastern end with a seabed gradient of 1：30. Thick deformed sediments -2 s （TWT） of the Outerarc are associated with intense faulting and occasional folding caused by recent tectonics. Development of a series of faults within the upwarped sedimentary column of Oligocene top to Recent is observed with a rotated fault block. These features are manifestations of Recent igneous intrusion, and reveal the presence of a mild N-S compressional regime. Its effect on the AFB resulted in further uplift of sediments, which can now be seen as the Invisible Bank. Forward gravity modelling supporting our seismic interpretation reveals that it is associated with igneous intrusion from the Moho （-9 km depth）, and also suggests that continental crust underlies the AFB. Strong Bottom Simulating Reflector （BSR）-like features in the Miocene sediments of Outerarc and Forearc basin at a depth of 0.6 s below the seabed suggest the inferred probable occurrence of gas hydrates in the AFB.

Correct understanding and application of waterflooding characteristic curves

Through reviewing the generation process and essential characteristics of waterflooding curves, the essence and characteristics of Zhang Jinqing waterflooding curve and Yu Qitai waterflooding curve recommended in Chinese Petroleum Industry Standard 'Calculation methods for Recoverable Oil Reserves(SY/T5367—1998)' were discussed, and some technical issues related to the curves were examined in-depth. We found that:(1) All the waterflooding curves are based on empirical formulas derived from oilfield production experience and statistics methods, and can characterize oil displacement features by water quite well.(2) A new waterflooding curve can be derived by combining waterflooding parameters and using different mathematical calculations as long as the parameter combinations and mathematical operation meet a linear relationship, so proposing new waterflooding curves by changing the combination mode has no practical significance anymore.(3) The upwarp of waterflooding curve in the extremely high water cut stage is because the mobility ratio curve has an inflection point with the rapid rise of water cut after reaching a certain value, and the later rapid rise of mobility ratio changes the original two-phase flow dynamics.(4) After entering into water cut stage, all the waterflooding curves with linear relationship can be used to make prediction, even curves with inflection points, as long as they have a straight section above the inflection point.(5) Actual data of waterflooding oilfields has proved that Type A, Zhang Jinqing and Yu Qitai waterflooding curves all can predict accurately oil recoverable reserves in extremely high water cut stage and can be promoted.