Damage Mechanism And Evaluation Under Complex Geological Conditions

In recent years, the formation characteristics of high and low pressure reservoir are complex in our exploration and development, most of them are fractured carbonate reservoirs, and content higher hydrogen sulfide, it makes a large amount of drilling and completion fluids leak in the drilling process, directly or indirectly affect seepage ability of the surrounding rock near wellbore reservoir, which cause severe damage to reservoir and lead to the low recovery efficiency of late production. Due to a series of problems casing by abnormal pressure in the process of drilling, more and more attention are paid. But so far, the damage mechanism and degree for this kind of reservoir are not very clear, and the suitable reservoir damage evaluation method for it is also not worked out, oil fields usually use conventional sandstone evaluation method in the study of reservoir protection technology, not considering abnormal pressure and seepage characteristics of fractured rock. Therefore, it is necessary for conducting thorough research to the reservoir damage mechanism of the two types of reservoirs in the process of drilling, establishing a suitable reservoir damage evaluation method for fractured reservoir rock pore structure, in order to reduce reservoir damage in the process of drilling and completion,increase the production of oil and gas.Fistly,in this paper, on the basis of investigating the literature at home and abroard,sort through and analysis the datas, introduce the research of reservoir damage mechanism and evaluation technology under complex geological conditions. And describe the high pressure and low pressure of reservoir geology, reservoir lithology, reservoir space, pressure and temperature characteristics in detail.Secondly, research on the typical reservoir damage evaluation method. In a long-term practice of oil and gas field development, the whole production process are prone to damage after drilling the oil and gas layer.The skin factor is an important parameter for reservoir damage degree evaluation, occupies a very important position in terms of evaluation reservoir perfection. The total skin factor, the blockage ratio and pressure drop, effective well radius, flow efficiency, capacity ratio, condition than damage radius method were always used to quantitative evaluation of reservoir damage degree, and be considered as even damage. But the skin factor got from well test includes skin effects caused by all deviations from ideal seepage, in addition to the skin factor of damage made by drilling and completion fluids near the bottom hole zone, partly opened formation, perforation, hole deviation and phase behavior change, non-darcy seepage factors. To correctly evaluate hydrocarbon reservoir protection, skin factor decomposition is essential. Through decompositing total skin factor got from analyzing well test datas, removing skin factors caused by other elements, formation damage skin factor due to the drilling and completion fluids on the bottom area of can be calculated,the evaluation method can accurately evaluate formation damage.Thirdly, making study of typical reservoir damage evaluation method. In the long-term practice of oil and gas field development, it can be found that drilling oil layer of the whole production process are prone to damage oil and gas layer, and skin factor is an important parameter for reservoir damage degree evaluation, in terms of evaluation reservoir perfection occupies a very important position. We always use the total skin factor, the blockage ratio and pressure drop, effective well radius, flow efficiency, capacity ratio, condition than damage radius method to quantitative evaluation of reservoir damage degree, and be considered to be homogeneous. But the skin factor of well test includes all deviations from the ideal flow generated by skin effect, In addition to the drilling fluid and completion fluid on the near bottom hole area outside of the skin factor of formation damage, and partly opened formation, perforation, drift, phase change, non-darcy seepage factors such as the skin factor. To correctly evaluate hydrocarbon reservoir protection, skin factor decomposition is necessary. Now through analyzing well test data of total skin factor science decomposition, removing skin factor, etc. Calculating only due to the drilling and completion fluid on the bottom area of formation damage skin factor evaluation method, which can accurate evaluation of formation damageFinally, on the basis of the theoretical and experimental research, under the environment of Windows7, hydrocarbon reservoir damage evaluation software is compiled using Visual c#4.0, and analysis the example on site, the quantitative evaluation result is consistent with the test results.