Study And Application Of Array Lateral Logging Inversion Method

The Array Lateral logging is a new logging mode which can provide five-six logging curves with different investigation depth simultaneously so as to obtain rich formation information. The Array Lateral logging whose apparent resistivity except shallow investigation depth is little affected by borehole is applied to thin layer and inhomogeneous formation around measured well. Some information, such as invasion radius, invasion resistivity, virgin zone resistivity are accurately obtained by inversion. Therefore, the research on inversion of Array Lateral logging has important theoretical and practical significance.The forward problem of Array Lateral logging is a kind of boundary value problem in partial differential equations which can be solved by finite element method after being transformed into minimum problem of norm function by variational principle. Using the automatic mesh generation and boundary processing method, the solution domain is discretized after building up the norm function suitable for the response of Array Lateral logging. The total matrix equation of solution domain is formed by unit assembly. The frontier solution of multiple cores parallel optimization is applied to achieve the forward calculation finally. Besides, the response of Array Lateral logging with invasion or non-invasion in deviated well and horizontal well is numerically simulated.In general the inversion problem of Array Lateral logging is solved by being transformed into optimization problem. By analyzing the traditional methods theoretically, such as gauss-newton method, Marquardt method, the existing disadvantages in inversion and corresponding correction measures are pointed out, especially some measures suitable for inversion of Array Lateral logging, like computing the Jacobi matrix and defining damping factor. The three parameters inversion (virgin zone resistivity, invading zone resistivity and invasion radius) and four parameters inversion (flushed zone resistivity, invasion radius of flushed zone, invasion radius of transitional zone and virgin zone resistivity) are carried out. By improving the inversion algorithm for thin layer, the calculation results with fast convergence are accurate.Whatever we improve the traditional methods, they still belong to local optimization. However, the differential evolution algorithm is a type of global optimization method with slow convergence at later stage and can’t be used for practical inversion. A hybrid inversion method of differential evolution algorithm is proposed in combination with traditional optimization methods and differential evolution algorithm. The calculation results show the hybrid inversion has characteristics of strong global searching ability, fast local searching speed and strong anti-noise ability.The coal bed methane is a kind of new energy and its exploration and development has attracted extensive attention. As a key to the evaluation of coal bed, the fracture evaluation plays an important role in exploration and development of coal bed methane and later stage management. The Array Lateral logging is applied to study the fracture parameters in coal bed. The results show that the logging response has good correlation with fracture porosity and fracture dip. Using Marquardt inversion for the response, the corresponding fracture porosity and fracture dip can be obtained.