油气同采方式下气顶油藏原油侵入状况的判断与调整

Judgment and adjustment of crude oil invasion for oil and gas commingled production in gas cap reservoir

东海西湖凹陷AC气顶油藏采用利用天然能量、同一套井网同时开采气顶和油区的开发方式,动态跟踪过程中难以判断原油侵入气顶状况。基于物质平衡原理,推导出了计算原油侵入气顶体积的公式,并构建了原油侵入指示曲线(原油侵入气顶体积百分数-生产时间关系曲线),该曲线与X轴交点即为原油侵入气顶的起始时间,曲线单调性反映流体的移动方向,斜率则反映移动速度。利用本文方法对AC气顶油藏原油侵入情况进行了分析,结果表明在原油采出程度为4.3%时,原油即已快速侵入气顶。综合AC气顶油藏采气速度的敏感性分析、现场系统试井结果,认识到通过降低采油速度可降低生产气油比,从而达到降低采气速度遏制原油进一步快速侵入气顶的目的,最终现场实施效果明显。本文方法对指导同类气顶油藏的开发具有重要的借鉴意义。

AC gas cap reservoir in Xihu sag simultaneously develops gas cap and oil in the same well pattern with natural energy, thus causing the difficulty to judge crude oil invasion gas cap in dynamic tracking process. Based on material balance theory, volume equation of crude oil invasion gas cap is derived, and oil invasion index curves with definite physical meaning （curves of volume percentage of crude oil invasion gas cap and production time） are established, in which the intersections of curves with X-axis are start time of crude oil invasion gas cap, monotonicity of curves reflect fluid movement direction, and the slopes reflect movement speed. Result shows crude oil has invaded gas cap quickly when oil recovery factor is 4. 3% in AC gas cap reservoir. Combing sensitivity analysis of comprehensive production velocity of AC gas cap res-ervoir with systematic well testing results, the knowledge of reducing GOR by decreasing production ve-locity is obtained, which can restrain crude oil to invade gas cap further rapidly. The effect of field applica-tion is obvious, which indicates the proposed method can guide development of similar gas cap reservoirs.