基于动力学分析的致密油充注孔喉下限研究

Oil charging throat threshold is very important for tight oil exploration, development and resources potential assessment, while the actual oil charging throat threshold is difficult to be reflected by static analysis. Taking the tight oil near the source-and-reservoir interface and inside reservoirs of Yanchang formation, located in the Ordos Basin, as the research objects, tight oil occurrence space and its charging period will be studied by casting thin sections, ESEM, high-pressure mercury injection and fluid inclusion analysis. The overpressure development history will be analyzed by simulation experiment of pressurization during hydrocarbon generation and PVT simulation of fluid inclusions, then constrained by the fracturing pressure of formation rock, the history of oil charging force will be investigated. With reservoir pore throat radius regarded as a variate, capillary pressure and separating pressure of bound water film will be inferred in different reservoir conditions based on the factors such as reservoir wettability, bound water saturation and specific surface area obtained from experimental tests such as nuclear magnetic resonance and low temperature nitrogen adsorption, then the history of oil charging resistance evolution will be studied in combination with characteristics of evolution of temperature and pressure, oil charging and their effects on factors associated with oil charging resistance. The relationship between oil charging force and oil charging throat threshold in different reservoir conditions will be investigated on the basis of dynamical relationship of oil charging force and oil charging resistance, and the dynamics model for oil charging throat threshold will be established. The expected results can be served for oil exploration, development and resources potential assessment of tight reservoirs.

石油充注孔喉下限对致密油的勘探开发和资源潜力评价至关重要，而静态分析难以反映真正的石油充注孔喉下限。项目拟以鄂尔多斯盆地延长组致密砂岩为研究对象，针对源储界面和储层内部，通过铸体薄片、环境扫描电镜、高压压汞和包裹体分析，研究石油赋存孔喉空间与石油充注期；通过生烃增压模拟实验、包裹体PVT模拟，恢复超压发育历史，以岩石破裂压力为约束，研究石油充注动力演化过程；通过核磁共振、低温氮气吸附等测试，分析不同油藏条件下储层润湿性、束缚水饱和度、比表面积等参数，视孔喉半径为变量，计算毛细管力和束缚水膜分离压力，结合温压演化、石油充注及其对上述参数的影响，研究石油充注阻力演化过程。根据石油充注期的充注动力、阻力的动平衡关系，研究不同油藏条件下石油充注动力与充注孔喉下限的相互关系，建立石油充注孔喉下限的动力学模型，为致密油的勘探开发和资源潜力评价提供依据。

本项目着力于从动力学角度揭示致密油充注孔喉下限。选取鄂尔多斯盆地新安边地区长7段等典型致密油地层为研究对象，综合采用铸体薄片、扫描电镜、高压压汞、氮气吸附、核磁共振等实验，研究了储层微观孔喉结构表征及致密油赋存特征；借助生烃增压实验分析和包裹体数值模拟，剖析了典型烃源岩生烃增压演化及储层古压力；在储层物性演化及典型孔喉参数演化分析基础上，揭示了致密油充注阻力演化特征；通过致密油充注动阻力平衡关系分析，明确了致密油充注动力与充注孔喉下限的关系，建立了致密油充注孔喉下限的动力学模型。.通过研究，认为研究区致密油储层主要发育残余粒间孔、溶蚀孔及黏土晶间孔，划分出粒间孔-溶孔主导型、溶孔-晶间孔主导型和晶间孔主导型三类储集空间组合，建立了基于高压压汞、核磁共振的优势连通孔隙划分方法，揭示出上述三类储层优势连通孔隙体积分数平均为35%、26%和11%。致密油以游离态和吸附态为主，综合判别石油赋存的孔喉下限介于9~44nm。富有机质烃源生烃增压模拟实验结果表明，封闭条件下干酪根在主生烃期的生烃增压量可达62MPa，而在考虑地层破裂压力的情况下，源储界面充注动力介于7~27MPa；储层古压力恢复结果表明，致密储层内部的石油充注动力介于5~17MPa。通过毛细管阻力理论计算，认为研究区粒间孔-溶孔主导型、溶孔-晶间孔主导型及晶间孔主导型储层的石油充注阻力分别介于0.056~10.22MPa、0.035~14.76MPa、0.099~18.35MPa。基于致密油充注动力、阻力平衡关系剖析，揭示出源储界面位置的充注孔喉直径下限介于4.9~7.7nm，储层内部的充注孔喉直径下限介于7.7~26nm，并建立了充注孔喉下限动力学模型，明确了致密油充注动阻力变化对充注孔喉下限和储层有效储集空间的控制作用。该研究成果对于丰富致密油气充注成藏理论、预测致密油有利区具有较重要的应用价值。