南海东部特低渗油田压裂改造实践与效果评价

Practice and Effect Evaluation of Hydraulic Fracturing Technology in Ultra-low Permeability Oilfields in the Eastern South China Sea

南海东部F油田WC组属于特低渗油藏,具有埋藏深、渗透率低、储层跨度大的特征,常规测试产量低,需压裂改造提高产能。WC组A5井压裂时存在储层纵向改造不充分、裂缝失控风险高、砂堵风险高、井斜角大造成裂缝弯曲、压裂规模小等难题。在前置液中加入小粒径段塞,打磨射孔炮眼和弯曲裂缝,减小砂堵风险,同时降低压裂液滤失,增加隔层应力,避免裂缝向下延伸。优化施工排量为4m3/min、支撑剂加量为50m3,达到支撑裂缝半长125.9m,支撑缝高51.4m。优化海上平台压裂设备摆放,满足4台压裂泵作业需求,并采用连续补砂工艺,满足单次加砂50m3的要求。A5井压后初期平均日产油22m3/d,增产倍比达4倍以上。采用生产测井技术对压后效果进行评价,压后射孔段内有4个主要产液段,产液段长度占总射孔厚度的36%;4个产液段中,产液量占比最高达45%,最低为14%。分析认为,多裂缝、储层纵向非均质性是影响压后增产效果的主要因素。建议在该类储层后续压裂改造中,采用水平井或大斜度井,对储层进行精细划分,优选甜点段射孔和改造,提高对甜点层段的改造程度和裂缝规模。

The WC Formation of the F Oilfield in the eastern South China Sea belongs to an ultra-low per-meability reservoir,characterized by"deep burial,low permeability,and large reservoir span".Conventional test production is low,and hydraulic fracturing is needed to improve productivity.During the fracturing of Well A5 in WC Formation,there are difficulties such as insufficient longitudinal stimulation of the reservoirs,high risk of fracture control,high risk of sand plugging,bent fractures resulting from large well inclination angle,and small fracturing scale.Slugs with small particle sizes are added to the pad fluid,and perforations and bent fractures are polished to reduce the risk of sand plugging,reduce fracturing fluid filtration,increase interlayer stress,and prevent fractures from extending downward.The optimized construction displacement is 4m3/min and the addition of proppant is 50m^(3),reaching a half-length of 125.9m and a height of 51.4m for the propped fractures.The placement of fracturing equipment on the offshore platform is optimized to meet the operational requirements of four fracturing pumps.A continuous sand-filling process is adopted to meet the requirement of 50m^(3) of sand filling at a time.The average daily oil production in the early stage of Well A5 is 22m^(3)/d af-ter fracturing,with a production increase of more than four times.Production logging technology is used to e-valuate the post-fracturing effect.There are four main liquid-producing sections in the post-fracturing perfora-tion section,and the length of the liquid-producing section accounts for 36%of the total perforation thick-ness.Among the four liquid-producing sections,the highest and lowest liquid-producing sections account for 45%and 14%respectively.Analysis shows that multiple fractures and reservoir vertical heterogeneity are the main factors affecting the post-fracturing stimulation effect.It is recommended that horizontal wells or highly deviated wells should be used to finely divide the reservoirs,and the sweet spot sections should be selected for perforation and stimulation to improve the degree of stimulation and fracture scale of the sweet spot sec-tions in the subsequent fracturing stimulation of this type of reservoirs.