| The Bohai Oilfield has abundant heavy oil resources,and the efficient development of heavy oil reservoirs will become essential for the stable production of the Bohai Oilfield in the future.The high-temperature production conditions accompanying heavy oil thermal recovery pose great challenges to the integrity of the near-wellbore formation and sand control structure,resulting in remarkable sanding phenomena and making it difficult to achieve long-term sand control.This has become a key factor restricting the economic and efficient development of offshore heavy oil reservoirs.Targeting at long-term sand control heavy oil thermal recovery wells in the Bohai Oilfield’s,this thesis comprehensively conducts experiments,theoretical analysis,and numerical simulation,unveiling the rock mechanical properties of typical heavy oil reservoirs in the Bohai Oilfield,constructing a prediction model for deformation and failure of near-wellbore rock formation as well as sand production of heavy oil thermal recovery wells,revealing the sanding mechanism of heavy oil thermal recovery wells and the impact of injection parameters,exploring the failure mechanism and influencing factors of sand control structures in thermal recovery wells,and forming optimization design methods for injection parameters and sand control structure to achieve long-term sand control completion and efficient development of heavy oil thermal recovery wells.The research results show that the particle contact of typical heavy oil reservoir rocks in the Bohai Oilfield is loose,poorly cemented,and low in strength.When heated over 120 °C,they completely lose cohesion and only retain frictional strength.A mathematical model coupling the rock elastoplastic deformation,multiphase fluid flow in pores,and heat transfer and diffusion was constructed,and a hydro-thermo-mechamical prediction method for near-wellbore rock deformation and failure as well as sand production was developed.Quantitative analysis results show that with increasing injection rate,the pore pressure of the surrounding formation may increase,causing rock shear failure and leading to considerable sanding.With increasing injection rate,the drag force of injection steam may cause the wellbore to expand,resulting in a decrease in the compactness of the gravel pack and causing sand control failure.Considering the frictional force of the gravel on the screen pipe,an analysis model for predicting the thermal stress within the screen was constructed,and an innovative method was developed for calculating the spacing and compensation capability of the thermal stress compensator,forming a design chart for optimizing the parameters of the thermal stress compensator in typical heavy oil thermal recovery wells in the Bohai Oilfield.A series of experimental studies were conducted on the sand control parameters and fluid-passing capability of sand control media during steam injection and heavy oil production processes under the influence of thermal stress,particle erosion,particle blockage,and injection steam disturbance.The results show that the metal mesh of the sand control screen is less affected by thermal stress,and the risk of deformation leading to changes in sand control parameters is small under typical injection temperature(350 °C)conditions.The intermediate screen of the sand control screen is the most severely eroded and damaged,while the outer screen is less eroded and damaged.The higher the production rate and fluid viscosity of heavy oil thermal recovery wells,the more severe the gravel pack blockage,and a design chart is provided based on the experimental results for the specific oil recovery index and gravel packing blockage changing with the fluid velocity-viscosity index.During steam injection start-up and stoppage,the gravel pack may become unstable and local void may form under the impact of steam injection,leading to sand control failure.It is recommended that the compactness of the gravel pack should reach 96% to 97.5%. |
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