Research On BFA-CM Hybrid Optimization Log Interpretation Method In Sandstone Reservoirs Of Sulige Area

With the exploration and development of large-scale oil and gas field, the reserve ofconventional oil and gas is reducing increasingly, and more attention is paid to unconventionaloil and gas resources. Tight sandstone gas is a typical unconventional oil and gas resources,which has a large reserves and a broad prospects for development. Tight sandstone gasreservoir has strong heterogeneity, low porosity and permeability, complex pore structure andvariety of shale distributions, which causes its logging evaluation difficulty and reservoirparameter calculation not easy to get results.Optimization log interpretation method is an effective way to evaluate tight sandstonereservoirs. Different from the tradition log interpretation methods by which limited logsinformation is used in turn, Optimization log interpretation method is based on geophysicalinversion theory. By this method, the logging information, geological information and workingexperience are taken full advantage of, and the optimization method is applied to calculatereservoir parameters. A high utilization rate for logging information is got by optimization loginterpretation method has, and its interpretation model and method are changed flexibly. Theself-checking can also be realized by itself, so its advantages are shown in the practice and ithas been widely used.P2h and P1s of tight sandstone gas reservoirs are regarded as the research objectives. Thelog data, mercury penetration and phase permeability testing data, physical property analysis ofcore and gas conclusion in research area are organized and analyzed, so the characteristic ofgas reservoirs and the lower limits of effective reservoirs are got, and BFA-CM hybridoptimization log interpretation method is applied to effective reservoirs for interpretation.The distributed of shale have a significant impact on the reservoir parameters, so it can betaken into account into the reservoir log interpretation model to improve the calculatedaccuracy of the unknown reservoir parameters. The log response equations of neutron, densityand sonic are got according to the interpretation model. It is necessary to set limits on theunknown parameter in the solution process in order to get reasonable results of theoptimization log interpretation. In addition to the fundamental mathematical physicsconstraints, the two response equations which are derived from Thomas-Stieber structure areregarded as the structure constraints of the optimization log interpretation method,so that volume content and shale texture are solved at the same time. By virtue of rolling up thecomponent volume content and the shale textural analyses into a single step, a morecompositional and reasonable analysis is achieved.After the mathematical model of optimization log interpretation method is established, anappropriate optimization method needs to be chosen for solving the optimal solution of themathematical model. Bacterial foraging algorithm(BFA) is a new bionics algorithm whichiterates to search for the optimal solution by simulating the survival of bacterial in biologicalbody, and it has not been applied to optimization log interpretation method. It has been provedthat bacterial foraging algorithm converges slowly in the latter part of the optimization process.In order to improve the precision and efficiency of calculation, it has been combined with thecomplex algorithm(CM) algorithm which has strong local search ability to form BFA-CMalgorithm as the optimization method of optimization log interpretation method.BFA-CM optimization log interpretation method which is based on structure constraint isapplied to tight sand reservoirs in Sulige gas field. Compared to the optimization loginterpretation method which is not based on structure constraint, the results by the methodbased on structure constraint are more stable and have better coincidence with the core dataand the thin section analysis.