Fast imaging and inversion of on and off shore electromagnetic data

We consider thin layer algorithms for inversion of electromagnetic data acquired on large experimental grids. These algorithms do not involve targeted search of the model parameters. Instead, they determine an integrated characteristic of the model, i.e. heterogeneous conductance or transverse resistance, using a filtration technique developed for thin layer models, which adequately represent the geo-electric situation by a sequence of laterally homogeneous and heterogeneous layers. The corresponding filter reflects impedance/admittance relations between different components of the electromagnetic field in the stratified part of the model. Convolution of such filters with the data obtained from experimental measurements represents the most time consuming part of the computation. The convolution is carried out using a high performance algorithm, which makes the process of inversion extremely fast. The choice of a particular inversion algorithm is dictated by the specific geo-electric situation in the area of interest and the electromagnetic data subject to interpretation. Typically, most computations can be carried out in up to several minutes using a regular desktop or laptop PC.We restrict our consideration to two simplest algorithms for determination of the conductance of heterogeneous conductive layers (S-algorithm) and the transverse resistance of heterogeneous resistive layer (T-algorithm). The algorithms can be useful for interpretation of data acquired in on- and off-shore conditions with natural and controlled sources. Inversion can be jointly carried out for data sets collected for different source locations, at different frequencies, etc. Likewise, the algorithms can be used for interpreting the data collected using a moving source.Performance of the algorithms is demonstrated on a set of test inversions of numerically simulated data sets. The first group of the examples is typical for environmental applications. It is studied using the S-algorithm applied to natural and controlled source measurements for shallow and deep targets. The T-algorithm is applied for delineation of a gas hydrate type of reservoir using the data numerically simulated for such a problem.In geo-electrical situations that can be addressed using thin layer models, results of inversion hardly require any further elaboration. For instance, this happens when parameters of the heterogeneous layer satisfy thin layer conditions and its thickness can be determined from seismic measurements. When this is not the case, the model found by a thin layer inversion usually reveals correct location of the anomalous body and provides reasonable estimate of its integrated electric properties. In such situations the algorithm works as an imaging technique, which together with seismic information on the layer boundaries provides a justified initial model for a full scale 3D inversion and hopefully allows for avoiding pitfalls associated with a straightforward application of more traditional 3D inversion algorithms.     

水平井生产测井组合仪模拟井测量数据分析与模型建立

由于水平油水两相流局部流速及局部相含率沿管径方向存在复杂分布,致使其流量及相含率测量非常困难.本文利用伞集流涡轮流量计、电导传感器、过流式电容传感器构成的生产测井组合仪,在水平油水两相流模拟井中开展了动态实验,分析了流动特性及管子角度倾斜对涡轮流量计及含水率传感器响应特性的影响.根据电容及电导传感器在不同总流量及含水率范围的响应分辨特性,分别采用变系数漂移模型及统计模型预测分相流量,发现变系数漂移模型能够自适应调整模型中的流型参数,且对油水两相分相流量具有较高预测精度.     

土星磁层等离子体径向输运的数值模拟

本文建立了一个包含离心力效应的自洽稳态土星磁层模型,并且用等离子体细丝模型对土星磁层等离子体径向输运进行了数值模拟.模拟结果表明,Dione（土卫四）附近的等离子体可能因为发生离心交换不稳定性（Centrifugal Interchange Instability）而被输运到离土星更远的地方.这种输运现象的发生是由离心力主导的,等离子体的黏滞效应和能量转移对输运过程的影响非常小（几乎可以忽略不计）,但土星电离层电导率对输运过程有重要影响,电导率越低,径向输运过程越快,反之,高电导率在一定程度上会阻碍输运的进行.在土星电离层电导率σ=2 S时,Dione（距离土星6.3R_S, R_S为土星半径）附近的等离子体在5.52个小时中被输运到距离土星10R_S的地方.本文的模拟结果还表明,密度受到扰动的等离子体是不稳定的,如果洛仑兹力和等离子体热压强梯度不能与离心力平衡,径向输运就会发生.密度大的等离子体在向外输运过程中会绝热膨胀而温度降低,密度小的等离子体则在注入磁层过程中因为绝热压缩而温度升高.