Study On The Law And Model Of Drilling Spillage And Coexisting Flow In Fractured Stratum

Loss circulation and well kick coexisting often occurs in fracture formation, causing downhole complexity, out of control for blowout, reservoir damage, well control difficulty, drilling cycle prolonging and cost-push. Drilling engineering fields ataches great importance to this problem, performs a large number of research and practice about leak stoppage, well killing and well control, gets many empirical achievements and theoretical achievements. However, the study for its objective laws is little, being lack of corresponding mathematical models as well. When loss circulation and well kick coexisting of multi-pressure system occurs, the condition for two phase flow in well and interaction between loss circulation and well kick is usually unknown. It is little studied for the mechanism and laws for loss circulation and well kick coexisting of gravity displacement mentioned in this paper.For loss circulation and well kick of multi-pressure system and gravity displacement in fracture formation, this paper builds basic theories of loss circulation and well kick of multi-pressure in fracture formation through theoretical study, computer emulation and experimental study, reveals its objective laws. The main research contents and achievements are as follows.(1) Study of fluid flow in single fracture. It is built for parameters computational method of fluid flow in flat fracture with several rheological models, such as frictional resistance, mean flow velocity, apparent viscosity. Natural fracture flow laws are studied by computer emulation, finding that fluid mainly flow in effective channels. Computational method of flow in natural fracture considering fracture surface characteristic lays foundation for the formation flow calculation of loss circulation and well kick.(2) Study of loss circulation and well kick of multi-pressure system. Computational method for leakage and well kick rate is built, simulated experiment and calculating case analysis reveals laws of loss circulation in fracture formation, computer emulation and experiment shows two phase flow laws at well and fracture intersection. Varying rate well multiphase flow for multi-pressure system is built, and discovers well pressure and flow pattern distribution rule, interaction law between loss circulation and well kick through calculating case analysis, provides theoretical support for well control of multi-pressure system.(3) Study of loss circulation and well kick coexisting of gravity displacement. Its ccurrence reason and conditions, flow field characters are stuied, revealing its mechanism. Basing on governing equation of incompressible fluid steady state flow, computational method is formed combining with boundary conditions and secondary equation. Hydrodynamics laws of gas and liquid two phase flow in fracture is obtained by visual simulated experiment, computer emulation, calculating case analysis. Calculating results match up to experimental results and leakage and well kick rate can be calculated with interrelated formation parameters. The research results provide theoretical foundation for seeking solution method, explaining its phenomenon and practical treating.