高温高压高含酸性气体的海相裂缝性地层溢流机理研究

The marine fractured formations with high pressure and high temperature (HPHT) and high sour gas are widely distributed in China and have huge amount of resources, the overflow mechanism and quantity of overflow in the wellbore are one of the bottlenecks that restrict the well control. The existing researches on overflow mechanism for the fractured formations only consider the influence of gravity displacement, which has great limitation. The dynamic deformation law of fractures under the HPHT and fluid type is studied in this project, and the stress release effect of drilling fracture moment, gravity displacement effect under micro-overbalance and balance conditions, overflow after lost circulation effect under over-balance condition and under-balance effect were introduced to reveal overflow mechanism for the marine fractured formations with HPHT and high sour gas, meanwhile, mathematical model was established to predict overflow quantity in the wellbore and parametric studies were carried out. Overflow fracture-annulus coupling migration model was developed to predict overflow migration velocity and real-time annulus pressure profile and, explore the early overflow monitoring technologies and killing the well methods for marine fractured formations with HPHT and high sour gas. The research results have important academic value for enriching the basic theory of oil and gas well pressure control and have a guiding effect on the well control technologies for marine fractured formations.

高温高压高含酸性气体的海相裂缝性地层在我国分布广泛、资源量巨大，溢流机理和侵入井筒中的溢流量是制约该类地层井控安全的瓶颈之一。现有裂缝性地层溢流机理研究仅单一地考虑了重力置换等作用的影响，具有较大局限性。本项目拟研究高温高压等多重作用机制下的裂缝动态形变规律，揭示在高温高压高含酸性气体的海相裂缝性地层中钻开裂缝瞬间的应力释放效应、微过平衡或近平衡条件下的重力置换效应、过平衡条件下的先漏后溢效应和欠平衡效应作用下的溢流机理，建立侵入井筒中的溢流量预测数学模型，分析不同因素对溢流量的影响规律；建立深部海相裂缝性地层溢流裂缝-环空耦合运移模型，定量描述溢流运移速率和不同时刻的环空压力剖面，探索高温高压高含酸性气体的海相裂缝性地层的早期溢流监测技术和压井方法。研究成果对于丰富油气井压力控制基础理论具有重要学术价值，并对海相裂缝性地层的井控工艺具有指导作用。

高温高压高含酸性气体的海相裂缝性地层在我国分布广泛、资源量巨大，溢流机理和侵入井筒中的溢流量是制约该类地层井控安全的瓶颈之一。现有裂缝性地层溢流机理研究仅单一地考虑了重力置换等作用的影响，具有较大局限性，有必要对高温高压高含酸性气体的海相裂缝性地层溢流机理进行研究。本项目首先通过不同产状裂缝在温度场、应力场和流体等作用下的动态几何形变规律研究，建立多场多重作用机制下的裂缝几何形态参数定量表征模型，其次考虑裂缝闭合等因素，建立了高温高压高含酸性气体的海相裂缝性地层侵入井筒中的溢流量预测模型，最后综合考虑地层和井筒，建立高温高压高含酸性气体的海相裂缝性地层溢流裂缝-井筒耦合运移模型，模型精度较高能够准确描述溢流运移速率和不同时刻的环空压力剖面。项目组基于所建立的模型对高温高压高含酸性气体的海相裂缝性地层溢流机理进行了充分研究，得到的认识有：碳酸盐岩裂缝性地层气侵方式包括负压气侵、重力置换气侵、漏失性气侵三种主要方式，溢流侵入特征表现为储层压力敏感、气侵转化多样、井控操作反复；裂缝对于溢流量有较大的影响，裂缝开度越大、半径越大、负压值越大，溢流速率越大；裂缝开度越大、半径越小、负压值越大，裂缝压降越快；自然条件下，随着裂缝中气体流入井筒，裂缝会产生闭合，与不考虑裂缝闭合的情况相比，考虑裂缝闭合条件下压降减慢、溢流速率更快、溢流总量更多，溢流持续时间更长；环空形状对环空压降影响较小，无论是同心环空还是偏心环空，压力梯度均随内管转速的增大而减小，下降幅度随平均轴向速度的增大而减小；酸性气体对气体溢流有较大影响，含酸性气体越多压缩因子越小，在拟临界点附近变化越剧烈； H2S对井控风险影响最大，CO2次之，CH4最小。通过本项目的研究探索了高温高压高含酸性气体的海相裂缝性地层的早期溢流监测技术和压井方法。研究成果对于丰富油气井压力控制基础理论具有重要学术价值，并对海相裂缝性地层的井控工艺具有指导作用。