克拉玛依油田530井区下乌尔禾组储层物性及油水分布控制因素

RESERVOIR'S PHYSICAL PROPERTY AND OIL-WATER DISTRIBUTION CONTROLLING FACTORS OF LOWER URH FORMATION IN WELL 530 DISTRICT OF KARAMAY OIL FIELD

克拉玛依油田530井区上二叠统下乌尔禾组为一厚层状的砂质砾状结构火山碎屑冲积扇沉积.油藏的储层物性变化大,油水分布关系复杂.通过岩石薄片、铸体、扫描电镜、物性等资料,分析了储层的成岩演化特征和孔隙成因类型,定量分析原生孔隙、次生孔隙与储层孔隙度、沉积相带之间的关系.在此基础上,根据试油和测井解释成果,综合分析油水分布的控制因素.

The Lower Urh Formation of upper Permian is around 600 to 750 meters thick in 530 well field of Karamay oil field. It is a thickly-bedded alluvial fan deposit formed by rapid accumulation of arenaceous conglomeratic pyroclastics near material source. The content of clastic particles is over 90 percent, and that of matrix and cement is 1.5~4 and 5.2~7.5 percents respectively. The clastic particles are mostly composed of tuffs (about 51 to 62 percent) followed by tuffites (around 11 to 12 percent). The results of core analysis show that the core porosity of Low Urh Formation is 4.8 to 18.8 percent with an average of 11.7 percent, and the core permeability ranges from 0.01×10-3μm2 to 13.01×10-3μm2 with an average of 0.35×10-3μm2 in 530 well field. Vertical fractures are dominant in the observed fractures on cores, followed by feather-like and cross-cutting fractures. The former ones are fresh in surface with none oil, while the latter two are filled by calcite and analcime partly or completely. Therefore the reservoirs of Lower Urh Formation belong to pore type. With the leaching and dissolving of pyroclastic grains and cement, and replacement by calcites and analcimes, secondary pores are formed, such as intra-grain solution cavity, intra-crystal and inter-crystal pores. A great change occurred in content of primary and secondary porosity in reservoirs. Microscopic observation of 68 casting-slice samples and analysis of their associated reservoir properties reveal that the higher the content of primary pores is, the higher the efficient porosity of reservoirs have. The efficient porosity is 8 to 10 percent when primary pores range from 10 percent to 40 percent, and over 12 percent in case of 40 percent to 70 percent. It indicates that the primary pore content is still the major factor in formation of fine reservoirs, although the dissolving of pyroclastic particles has a large effect on it during the diagenesis. The oil-water distribution of Lower Urh Formation is mainly controlled by sedimentary facies and reservoirs?physical property, and little affected by local structures and faults in 530 well field. The distribution of oil and water layers is not even on plane, and without uniform oil-water interface vertically. Oil layers are mainly distributed in typeⅠreservoir with fine physical property. Inter-layer water and edge water are distributed in type Ⅲ reservoir with worse physical property. TypeⅠreservoir formed at fan head and middle fan sub-facies, with development of oil and few inter-layer water; and type Ⅱ or Ⅲ revervior at edge and side fan sub-facies, with development of edge and side fan water.