姬塬地区长8砂岩储层渗流曲线特征及其影响因素分析

Analysis of the Percolation Characteristics and Their Influence Factors on the Chang-8 Sandstone Reservoir in Jiyuan Area

长8油组是鄂尔多斯盆地姬嫄地区延长组主力油层,但是储层非均质性强,单井产量变化迅速,因此对该区4口钻井岩样进行了相渗敏感性实验,研究了储层注水开发过程中,渗流曲线的特征以及影响因素。通过20片铸体薄片的显微镜下观察和图像粒度与孔喉分析,以及岩样的高压压汞、粘土矿物敏感性分析、X-射线衍射、扫描电镜、真实砂岩微观模型水驱油实验,重点分析了储层微观孔隙结构、粘土矿物以及成岩作用对渗流曲线的影响。结果表明,研究区渗流曲线可以细分为油相上凹型和直线型;上凹型曲线对应储层为分流河道微相,具有高骨架矿物含量、粗粒径,孔隙类型以原生粒间孔和各种溶孔为主,孔径大,孔隙间连通性好,颗粒间以点、点-线接触为主,喉道为粗长型,储层面孔率、渗透率高,流体连续性好。此外,发育裂缝的储层,适当的注入水流速可以提高驱油效率。对于高含量水敏、速敏性粘土矿物储层,应该采取逐渐加压的方式提高注入水压力,以解决粘土矿物对孔隙的堵塞问题。该研究成果对于油田开发初期储层渗流特征的认识,提高采收率具有重要的理论意义与参考价值。

The Chang-8 Unit of the Yanchang Formation is a major reservoir in Jiyuan area,Ordos Basin.However,the reservoir shows strong heterogeneity and oil production varies from well to well dramatically.In this paper,samples from 4 dr lling wells were selected to conduct relative permeability sensitivity test so that the percolation characteristics and their influence factors can be studied during the reservoir water-flooding process.Twenty casting thin sections were observed carefully,and the image analysis of grain size and the analysis of pore-throat were carried out.Other tests were also done including capillary pressure measurement,scanning electron microscope （SEM）,X-ray diffraction and sensitivity analysis of clay minerals in the sandstones,and the oil-water displacement experiment.The purpose of the work is to analyze micro-pore structures of the reservoir,clay minerals,and the impact of diagenesis on relative permeability curve.Results show that the permeability curve of the reservoir in the study area can be further divided into two types： the up-concaved and linear percolation curves.The up-concaved curve of the corresponding reservoir belongs to the distributary channel microfacies with a high content of skeleton minerals,coarse grain size,abundant primary intergranular pores and large-diameter dissolution pore and good connectivity between pores.Mineral grain contacts mainly occur as point to point and point to line,and the throat is coarse and long.The porosity and permeability of the reservoir are high,and the fluid percolation is good.In addition,as to reservoirs with micro-cracks,proper water-flooding rate can improve the efficiency of oil displacement.Because of the strong heterogeneity and high content of sensitive clay-minerals of the reservoir,pressure should be increased gradually to raise the water-flooding pressure to eventually solve the problem of clogging of pores by clay mineral.This research is important for understanding of reservoir percolation characteristics in the initial stage of exploitation and is useful to enhance oil recovery.