鄂尔多斯大牛地气田上古生界储层成岩作用评价

DIAGENESIS AND RESERVOIR EVALUATION ON THE UPPER PALAEOZONIC RESERVOIR SANDSTONES IN DANIUDI GAS FIELD,THE ORDOS BASIN

对鄂尔多斯盆地北部大牛地气田上古生界地层的成岩作用阶段进行了综合研究,结果显示,太原组-山一段地层煤镜质体反射率在1.4%～1.5%之间,包裹体均一温度为140 ℃,伊/蒙混层矿物中蒙脱石层含量一般小于30%,属晚成岩作用阶段B期;下石盒子组(包括盒一、二、三段)-山二段地层中煤镜质体反射率在1.3%～1.4%之间,盒一、二、三段包裹体均一温度为126 ℃,伊/蒙混层矿物中蒙脱石层含量主要在32%～36%之间,属晚成岩作用阶段A期;山二段包裹体均一温度比较复杂,认为也为晚成岩作用阶段A期.大牛地上古生界储集层成岩作用类型主要有压实作用、胶结作用(包括硅质胶结、碳酸盐胶结、粘土胶结)、溶解溶蚀作用以及微裂隙作用,储集岩石的孔隙类型主要有(剩余的)原生粒间孔隙、粒间(晶间)微孔隙、粒间(粒内)溶蚀孔隙(包括铸模孔隙),微裂隙包括切穿颗粒的和粒缘微裂隙.储层物性主要属低孔、低渗储层,孔隙结构参数显示盒三、盒二、太一和太二平均喉道半径和中值压力评价好于盒一、山一、山二段,排驱压力和最大连通半径也具有相似的特征;盒三、盒二段产能高、压降慢,与微裂隙作用造成渗透率增加有关.

The diagenesis stages of the reservoir sandstones in the Upper Palaeozonic strata in Daniudi Gasfield,northern Ordos Basin,were studied.The results show that the vitrinite reflectance(Ro) of the Taiyuan Formation and the First Member of Shanxi Formation is between 1.4% and 1.5%,the inclusion homogenation temperature is 140 ℃ and the percentage of montmorillonite is usualy less than 30% in illite-montmorillonite mixed-layer mineral,indicating the stage B of metarmosis.The Lower Shihezi Formation(including P1x1,P1x2 and P1x3 Members) is in the stage A of metarmosis with the Ro being 1.3%-1.4%,the inclusion homogenation temperature being 126 ℃ and the percentage of montmorillonite being 32%-36% in illite-montmorillonite mixed-layer mineral.The inclusion homogenation temperature of the Second Member of Shanxi Formation is complicated,but still can be considered as in the stage A of metarmosis.The main diagenesis processes that control the reservoir properties include compaction,cementation(silicide,carbonates,clay minerals),dissolution and fracturing.The types of pores are primary intergrain pore(residual),intercrystalline micro-pore and intergrain or intragrain solution pore(including moldic pore).The reservoir generally belongs to the type of low-porosity and low-permeability.The microfractures in formation greatly improve the reservoir properties and contribute to higher gas yield in P1x3 and P1x2 than in P1x1 and other reservoirs.