Research On Porous Media Reservoir Parameter Inversion And Fluid Identification Method

Seismic oil and gas prediction and exploration and development process aresynchronous. Different oil and gas prediction purposes are required in differentexploration and development phase. The oil and gas prediction based on seismic datarelies on seismic parameters that could reflect special physical properties of oil andgas reservoir. Therefore, reservoir parameters inversion and reservoir fluididentification is the core of seismic oil and gas prediction. Along with deeperexploration of oil and gas, the exploration precision is required even more higher, andthe exploration objects are also moved from structural reservoir to lithologic reservoir,fractured reservoir and other kind of complex oil and gas reservoir. The reservoircontaining oil and gas is porous medium, which is also named two-phase medium.Two-phase anisotropic medium theory can describe the actual stratum structure andproperties more accurately, thereby comprehensive study on the medium property oftwo-phase and anisotropy is helpful to deeply research the oil and gas reservoir, and itis also useful for reservoir prediction with relevant poroelastic parameters (orattribute). So reliably extracting and transforming these parameters from seismic datahas become the key to the success of the oil and gas prediction. Related reservoirparameters inversion and reservoir fluid identification of porous medium areresearched in this paper, which could provide some technical support to oil and gasdirectly finding with seismic exploration. It is also helpful to reduce the risk of oil andgas exploration and development and improve the success rate to a certain extent.The research on seismic wave numerical modeling is of great significance toimproving our understanding of seismic wave propagation law and solving variousproblems encountered in the oil and gas exploration and development. Seismic wavenumerical modeling is the basis of seismic inversion and migration imaging, and italso plays an important role in seismic data acquisition, processing and interpretationof complicated area. Therefore, on the basis of fractured anisotropic theory and porousmedium model based on BISQ (Biot-Squirt) mechanism, elastic wave propagationequation in fracture porous medium based on BISQ mechanism is established in this paper. What is more, seismic wave field numerical simulation and feature analysis insingle-layered and two-layered fracture porous medium models are carried out withhigh precision staggered grid finite difference method. It also makes preparations forreservoir parameters inversion in fracture porous medium based on BISQ mechanism,providing forward operator.Porosity, fluid phase density and solid phase density are the key parameters in oiland gas reservoir identification, and the reservoir parameters inversion has greatsignificance to seismic oil and gas prediction. At present, porous medium reservoirparameters inversion methods could be generally divided into two types, one iscarried out based on wave equation (or non-wave equation) and isotropic (oranisotropic) Biot model, and the other one is carried out based on non-wave equationand isotropic (or anisotropic) BISQ (or modified BISQ) model. Porous mediumreservoir parameters inversion based on wave equation which is also named porousmedium reservoir parameters full waveform inversion in this paper, can rebuildunderground related poroelastic parameters structure while utilizing the kinematic anddynamic information of pre-stack seismic data, which could reveal detail informationof the physical properties of oil and gas reservoir under complex geologicalbackground. What is more, Biot flow and squirt flow are the two main fluid flowmechanisms in a reservoir medium containing fluid, and the BISQ model, whichincludes both of these dynamic flow mechanisms, can describe the wave propagationin reservoir medium more realistically and more accurately than the Biot model.Therefore, similarly to the extension of the BISQ theory application and the solutionof practical problems in oil and gas exploration and development, the implementationof the porous medium reservoir parameters inversion using the BISQ model based onwave equation has important practical significance. For this reason, on the basis offull waveform inversion idea, this paper presents fracture porous medium reservoirparameters full waveform inversion method based on BISQ mechanism for the firsttime. In this paper we calculate a synthetic medium surface seismic response that isconsistent with real measurement data by applying the least-square principle and aniche genetic algorithm. We propose a niche genetic multi-parameter (includingporosity, solid phase density and fluid phase density) joint inversion algorithm in afracture porous medium based on BISQ mechanism. We take the single-layered andtwo-layered fracture porous medium models based on BISQ mechanism as examples, and carry out the numerical analysis of reservoir parameters inversion, based onwhich we compare convergence and inversion effect between the simple geneticalgorithm and niche genetic algorithm. The numerical simulation inversion resultsindicate that the parameters inversion based on niche genetic algorithm in fractureporous medium reservoir is stably convergent, whose convergence speed is muchfaster and inversion precision is much higher than the inversion based on simplegenetic algorithm. However, there is also a shortcoming existed in the reservoirparameters inversion based on niche genetic algorithm in fracture porous medium.The calculating amount is quite large, and the inversion costs much time.To address the above problems, the major cause that influences computationalefficiency has been found after further research and analysis. During the reservoirparameters inversion in fracture porous medium, as the fitness calculation of nichegenetic algorithm is extremely large, its optimization efficiency is quite low, and it isvery time-consuming. In order to solve this problem, this paper proposes two methodsto improve the computational efficiency of parameters inversion in fracture porousmedium reservoir, and systematically discusses the basic theory and realizationprocess. The first method is based on the inherent parallel-ability of genetic algorithm,and it combines the high-speed parallel-ability of computer and inherentparallel-ability of genetic algorithm together with MPI program to build a nichemaster-slave parallel genetic algorithm. The second method introduces multi-sourceblended acquisition technology, which means that multiple sources in different spatiallocation are constituted to super-shot with random linear coding. It could improvecomputational efficiency of multiple shots forward modeling in fracture porousmedium reservoir parameters inversion, which could quicken the inversion calculationspeed. The proposed two methods are tested with simulated data in this paper, and thenumerical simulation examples prove that applying the niche master-slave parallelgenetic algorithm and multi-source blended acquisition technology to the fractureporous medium reservoir parameters inversion could successfully solve the largetime-consuming problem of niche genetic algorithm, and both the computation resultsand time efficiency reach much better effect.The low frequency information of reflection seismic data is extremely importantto the seismic oil and gas prediction, which contains plenty of information related toreservoir and fluid. Then how to fully make use of the low frequency information ofthe seismic data has great significance to seismic oil and gas identification. Aiming at this problem, the asymptotic analysis theory of frequency-dependent reflectioncoefficient in saturate porous medium is discussed in this paper. And on the basis ofthis theory, the calculation method of reservoir fluid mobility based on high resolutionsparse inversion spectral decomposition is deduced, and the reservoir and fluididentifications with reservoir fluid mobility attribute are also researched. The actualdata processing results show that the reservoir fluid mobility information based onhigh resolution sparse inversion spectral decomposition has well imaging capability tooil and gas reservoir and high resolution, which could be used to describe the oil andgas reservoir location and distribution, and also reduce the multi solutions anduncertainty of reservoir fluid identification.