长庆致密油藏宽缝压裂技术研究

Research and Application of Enhancing Net-pressure Fracturing Technology for Tight Oil Reservoirs in Changqing Oilfield

鄂尔多斯盆地以华庆、姬塬、环江为代表的致密油藏普遍储层物性差、非均质性强、水平两向应力差大,采用常规压裂改造储量动用程度较低,投产后长期生产呈现低采油速度、低采出程度特征。为实现该类储层高效动用,创新提出了“宽缝压裂”的技术思路,即通过多轮次间歇压裂、级间放喷循环注入、梯级提高排量、不连续加砂、全程暂堵转向,应力“加载-卸载-加载”循环作用迫使岩石缝内净压力大幅提升,增加主裂缝宽度,开启侧向微裂缝,提高基质孔喉连通性,最终实现有效提高裂缝立体波及体积、缝网复杂指数和缝内导流能力的目的。本文以数值模拟和物理模拟为基础,应用大型可视化缝网支撑剂运移模拟装置,对比常规压裂与宽缝压裂对裂缝形态及支撑程度的影响。现场试验证实了该技术的可行性,综合分析了宽缝压裂的全过程压力响应、级间压降及水锤特征,试验井日产油量由实施前0.5 t大幅提高至2.5 t,达到初次改造投产的3倍以上,采油速度由0.2%提高至1.0%。该技术为致密油藏难动用储量大幅增产探索了一条有效的技术途径。

Tight oil reservoirs such as Huaqing,Jiyuan,and Huanjiang in the Ordos Basin generally exhibit poor reservoir physical properties,significant heterogeneity,and substantial differences in horizontal stress in two directions.Traditional fracturing stimulation exhibits limited reservoir utilization and is not conducive to production.Long-term production is expected to be characterized by a low oil recovery rate and degree of recovery.In order to achieve efficient utilization of this type of reservoir,the technical concept of"enhancing net-pressure fracturing technology"was innovatively proposed.This involves multiple rounds of intermittent fracturing,inter-stage blowout injection cycles,cascade increase in displacement,discontinuous sand addition,and temporary fracturing throughout the process.By blocking the steering,the stress"loading-unloading-loading"cycle significantly increases the net pressure in rock fractures,widens the main fractures,opens lateral micro-fractures,enhances connectivity of matrix pores and throats,ultimately leading to an effective increase in three-dimensional fracture volume and fracture volume.The study aims to investigate the network complexity index and in-slit conductivity.Through numerical simulation and physical experimentation,this paper utilizes a large-scale visual fracture network proppant migration simulation device to compare the impact of conventional fracturing with that of"enhancing net-pressure fracturing technology"on fracture morphology and support degree.The field test validated the feasibility of this technology and conducted a comprehensive analysis of the pressure response,interstage pressure drop,and water hammer characteristics throughout the entire process of"enhancing net-pressure fracturing technology".The daily oil production of the test well increased significantly from 0.5 tons before implementation to 2.5 tons,reaching the first level.This represents a more than threefold increase in transformation and production rate,with the oil production rate rising from 0.2%to 1.0%.This technology explores an effective technical approach for significantly enhancing production of challenging reserves in tight oil reservoirs.