薄互层定点多级脉冲式压裂技术研究

RESEARCH ON MULTI-STAGE PULSED FRACTURING TECHNOLOGY FOR THIN INTERBEDS

鄂尔多斯盆地合水南地区长6-8油藏储层渗透率低(≤0.3 m D)、层内泥质及钙质隔夹层发育,薄互层特征明显,纵向上岩性高频率变化导致层间力学性质差异大,体积压裂效果不理想。根据致密薄互层的实际特点,开展大型物理模拟和可视化平行板实验突破了对薄互层裂缝扩展规律和支撑剂运移规律的传统认知,明确了提高纵向动用程度和增加横向有效支撑的增产技术方向;利用VTI数学模型剖析了薄互层间地应力、弹性模量与砂体岩性之间的对应关系;建立了多薄层可压性及物性综合评价体系;绘制了基于层间应力差和弹性模量差的压裂目标层射孔位置优选图版,最终形成了以"定点射孔、多级压裂、脉冲加砂"为核心的定点多级脉冲式压裂技术。现场试验70余口井,试油产量达到前期的2~3倍,初期日产油提高40%以上。通过裂缝拟合、现场测试等分析手段,证实了该技术可以提高储层纵向动用程度50%以上,增加横向有效支撑缝长30%以上,为致密薄互层增产开辟了新途径。

Reservoir Chang 6-8 at Heshui Southern region of the Ordos Basin is featured with low permeability( ≤0. 3 mD)and obvious muddy/calcareous septum interbeds. The high-frequency change in lithology in the longitudinal direction leads to large mechanics difference between zones and so not good volumetric fracturing results. According to the practical characteristics of dense thin interbreds,large-scale physical simulation and visualized parallel board experiment were made and they broke through the traditional knowledge regards the law of crack propagation and proppant migration in thin interbeds. Then the stimulation target of improving the development extent vertically and increasing effective horizontal support was decided. The relationship between stress,elastic modulus and lithology of sand bodies was set up using VTI model. The comprehensive evaluation system for multi-layer compressibility and physical properties was established. A chart was plotted on basis of the in-layer stress difference and elastic modulus difference to decide the optimum perforation points in the target zone to be perforated.Ultimately a new fixed-point multi-stage pulse fracturing technology is developed with the main idea of " fixed-point perforation,multi-stage fracturing,pulsed sand loading". It has been used in over 70 wells,tested oil production is 2 to 3 times the early stage rate,the initial daily production increased by over 40%. Through crack fitting and field test,the field tests confirm that the technology can improve the longitudinal development degree of the reservoir by over 50%,increase the effective lateral support length by over 30%,opening up a new way for stimulation in dense thin interbeds.