浅水条件下浅层气走航式海洋电阻率法探测结果模拟分析

Simulationand Analysis of Detection Results of Shallow Gas Under Shallow Water with a Navigated DC Marine Resistivity Method

为分析海面走航式海洋电阻率探测技术对浅水条件下海底浅层气的探测能力,以舟山火山列岛海域浅层气分布区为研究区,根据电测井资料分别构建不同埋深和尺寸的气层、气囊地电模型进行正、反演计算,并对计算结果进行对比分析。计算结果显示,海面走航式电法探测剖面在一定条件下能够有效区分出浅层气的赋存形式,基于实测数据二次处理的电阻率变化比剖面能够有效反映层状浅层气的赋存状态及厚度、气囊尺寸的变化;当含气土与非含气土的电阻率变化比与含气层厚度值的1.2%相近时,其对应的等值线能够与含气区域良好吻合,可以有效判定含气区的底界埋深。

After the rock and soil inflated, the conductivity of the rock and soil will change accordingly. Based on this physical property change, the resistivity imaging technology has many applications in the detection and monitoring of shallow gas in the terrestrial area.In order to analyze the ability of asea surface navigated DC resistivity survey method to detect seabed shallow gas under shallow water, the shallow gas distribution area in the Zhoushan volcanic islands area was used as the research area.In this method, the electrode system is dragged on the tail of the ship and floats on the water.During the voyage, the supply electrode on the electrode system is continuously powered, and other potentials are simultaneously collected in parallel to realize resistivity profile measurement.According to the electric logging data of the research area, the geoelectric models of layered and saccate gas-bearing soil with different depths and sizes were constructed to carry out forward and inverse calculations. Through comparison and analysis, the calculation results show thatelectricity detection profile with a sea surface navigated DC resistivitysurvey method can effectively distinguish the shape of shallow gas, the resistivity change ratio based on the measured data with secondary processingcan effectively reflect the occurrence state, thickness of layered shallow gas,and the change in the size of the air sac. When the resistivity change ratio of gas-bearing soil and non-gas-bearing soil is close to 1.2% of the thickness of gas-bearing area, the corresponding isoline can well agree with the gas-bearing area, which can effectively determine the bottom boundary of the gas-bearing area.