砂岩油藏水淹过程中电阻率变化的实验模拟与规律分析

Resistivity changes during flooding in sandstone reservoirs experimental simulation and regular analysis

在油藏开发后期,水淹现象十分常见,随着开发程度不断提高,水淹程度发生不同变化致使地层水矿化度发生改变,引起地层电阻率的变化,造成水淹层评价困难.为此,探究砂岩油藏长岩心样品在不同矿化度注入水和不同注入时间条件下,距离注水口不同位置的电阻率变化规律,判断含水饱和度情况,进行水淹层级别的划分,进而评价水淹层来指导油田精细注水开发具有重大意义.利用全直径长岩心样品开展砂岩油藏水淹和污水回注模拟,实验表明,当采用污水回注时,岩石电阻率总是单调降低,呈“L”型,且与含水饱和度关系简单;而采用淡水驱替时,呈“U”型,且与含水饱和度关系复杂.对砂岩油藏进行淡水到污水水淹的整个过程中,电阻率曲线出现的从“U”型到“L”型的变化规律,为我们划分油藏中岩性相似的水淹层的级别提供了理论依据,极大的提高了我们评价水淹层的精度,避免了我们在淡水水淹的过程中,依靠单一的电阻率变化幅度法判断储层水淹程度,评价水淹层.

In the later stage of reservoir development,flooding phenomenon is very common,with the continuous improvement of the degree of development,different changes in the degree of flooding lead to changes in the degree of water mineralization of the formation,causing changes in the resistivity of the formation,resulting in difficulties in the evaluation of the flooded layer.Therefore,it is of great significance to explore the resistivity change law of sandstone reservoir long core samples at different positions from the water injection port under different mineralization degree injection water and different injection time conditions,judge the water saturation situation,divide the flooded layer level,and then evaluate the flooded layer to guide the development of fine water injection in the oilfield.The full-diameter long core samples were used to simulate flooding and sewage reinjection in sandstone reservoirs,and the experiments showed that when sewage reinjection was used,the rock resistivity was always monotonically reduced,showing an"L"shape,and the relationship with water saturation was simple.When fresh water is used,it is"U"shaped,and the relationship with water saturation is complex.In the whole process of freshwater to sewage flooding of sandstone reservoirs,the change law of resistivity curves from"U"shape to"L"shape provides a theoretical basis for us to divide the level of flooded layers with similar lithology in oil reservoirs,greatly improves the accuracy of our evaluation of flooded layers,and avoids us from relying on a single resistivity change amplitude method to judge the degree of flooding of reservoirs and evaluate flooded layers in the process of freshwater flooding.