渤海海域常压油藏实测地层压力与流体性质关系

Relationship Between Measured Formation Pressure and Fluid Properties in Normal-pressure Reservoirs in the Bohai Sea

研究渤海海域诸多常压油藏的连续电缆测压数据发现,油层顶部实测地层压力数据增压现象普遍表现为实测地层压力不同程度高于其等深折算压力,压力—深度线性关系存在不确定性、流体性质认识不清。将水静力学基本原理、等压面概念拓展到常压油藏"U形水银测压计"物理模型,并建立地层压力—原油密度函数关系,理论上证明地层压力与原油密度为反比关系、油层顶部增压的原因是地层原油密度相对偏低。进一步结合原油PVT与连续测压数据并证实:(1)原油密度分异是常压油藏油层顶部增压的关键,同时连续测压数据能够反映常压油藏单相流体密度分异特征;(2)增压段(纯油区顶部)原油密度低于非增压段(中—深部),实测地层压力高于等深折算压力即出现增压;(3)非增压段(纯油区中—深部)原油密度相对稳定,实测地层压力与其折算压力接近。明确常压油藏实测地层压力与流体性质关系,利于合理解释压力—深度关系、精细研究流体性质与分布规律。

The study on the wireline pressure measurement data of many normal-pressue reservoirs in the Bohai Sea area found that the pressure-increase phenomenon of the measured formation pressure at the top of the oil layer was generally showed that the measured formation pressures are higher than the equivalent pressures at the same depth, the pressure-depth linear relationship uncertainty is observed and fluid properties are unclear. By applying the basic principles of hydrostatics and the isostatic surface concept to the physical model of the U-shaped mercury manometer of normal-pressure reservoir, and through establishing the relationship between formation pressure and crude oil density, it is theoretically proved that the formation pressure is inversely proportional to the density of crude oil and low crude oil density accounts for the pressure-increase of the oil layer top. Further combined with crude oil PVT and continuous pressure measurement data proved that：① The crude oil density differentiation is the key to the pressure increment of oil layer top in normal-pressure reservoirs; the continuous pressure measurement data can reveal the single-phase fluid density differentiation characteristics of normal-pressure reservoirs; ② The crude oil density in the pressure-increase section （top of the pure oil zone） is lower than that in the non-pressure-increase section （medium-deep section of the pure oil zone）; the pressure-increase is confirmed if the measured formation pressure is higher than the equivalent pressure at the same depth;③ The non-pressure-increase section （medium-deep section of the pure oil zone） has a relatively stable density, and has a close measured formation pressure and equivalent pressure at the same depth. Understanding the relationship between measured formation pressure and fluid properties in normal-pressure reservoirs is helpful for understanding pressure-depth relationship and fine study of fluid properties and distribution.