Abstract: To address the problem that single-sand-body characterization in Block Z,southwestern Ordos Basin,cannot meet the needs of efficient reservoir development,a systematic method for single-sand-body study constrained by ultra-short-term base-level cycles was proposed by taking the Chang 8₁ sand-layer group in this area as an example and using core,outcrop,mud-logging,well-logging,and production-performance data.The results show that seven ultra-short-term base-level cycles are developed in the Chang 8₁ sand-layer group in the study area,corresponding to seven sets of sequence single sand bodies.Single-sand-body interfaces were identified using electrical-log characteristics,and seven stable reservoir single sand bodies were identified through lateral correlation of sequence single sand bodies.The strength of lateral connectivity between single sand bodies mainly depends on the lateral contact relationships of sand bodies.Under the influence of the distribution and scale of underwater distributary channels,individual branches of single sand bodies are generally narrow in plan view,and channel width-to-thickness ratio exhibits a good positive correlation.Oil layers with injection-production relationship types such as injection without production,production without injection,and neither injection nor production have low producing degrees,which is closely related to the low degree of single-sand-body study.In single sand body 2-1 of the study area,targeted supplementary perforation adjustment increased the well-pattern connectivity rate to as high as 66%,effectively improving the producing degree of oil layers.This study expands the characterization of reservoir single sand bodies and provides technical support for optimizing injection-production adjustment measures.

Key words: ultra-short-term base-level cycle, single-sand-body division, identification and correlation, single-sand-body characterization, injection-production adjustment