Su Zezhong, Li Tiantai, Bai Mingxing, Zhou Zhenjiang
School of Petroleum Engineering, Xi'an Shiyou University, 710065 Xi'an, China.
Cooperative Innovation Center of Unconventional Oil and Gas Exploration and Development, Xi'an Shiyou University, 710065 Xi'an, China.
ACS Omega. 2024 Feb 17;9(8):9269-9285. doi: 10.1021/acsomega.3c08439. eCollection 2024 Feb 27.
Revealing the impact of core mineral composition on the initiation pressure of waterflood-induced fractures (WIFs) in tight sandstone reservoirs is a crucial aspect of studying the initiation mechanism of WIFs. In this paper, through quantitative characterization of the core mineral composition from six samples of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, and modified experimental cores and displacement equipment for WIF experiments, the influence of the core mineral composition on the initiation pressure of WIFs in tight oil reservoirs is investigated. The conclusions are as follows. (1) The rock mineral composition of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, includes quartz, feldspar calcite, and clay, characterizing it as a typical feldspar sandstone reservoir. Quartz and calcite are considered as brittle minerals, while feldspar and clay are categorized as lithologic minerals. (2) For feldspar sandstone reservoirs, including quartz, feldspar, calcite, and clay minerals, when the combined content of quartz and feldspar exceeds 600% of the total mineral content, the changes of quartz and feldspar content will affect the initiation pressure of WIFs. As the ratio of the quartz content to feldspar content increases, the initiation pressure of WIFs exhibits a logarithmic function decrease. (3) Considering the contribution of diagenetic minerals to rock brittleness, the calculation method for the brittleness index of feldspar tight sandstone reservoirs is improved. (4) The relationships between , brittleness index, and initiation pressure of induced fractures suggest that an increase in leads to a power-law increase in the brittleness index, while the initiation pressure of WIFs relative to the brittleness index shows a power-law decrease. This phenomenon indicates an increased likelihood of WIFs occurring during the long-term water injection process in feldspar sandstone reservoirs. This work contributes to understanding how core minerals affect the initiation pressure of WIFs in tight sandstone reservoirs.
揭示核心矿物成分对致密砂岩油藏注水诱发裂缝（WIFs）起裂压力的影响是研究WIFs起裂机制的关键环节。本文通过对鄂尔多斯盆地西部吴起油田长6油藏6个样品的岩心矿物成分进行定量表征，以及对用于WIF实验的岩心和驱替设备进行改进，研究了岩心矿物成分对致密油藏WIFs起裂压力的影响。研究结论如下：（1）鄂尔多斯盆地西部吴起油田长6油藏的岩石矿物成分包括石英、长石、方解石和黏土，为典型的长石砂岩油藏。石英和方解石被视为脆性矿物，长石和黏土则归类为造岩矿物。（2）对于含有石英、长石、方解石和黏土矿物的长石砂岩油藏，当石英和长石的总含量超过矿物总量的600%时，石英和长石含量的变化会影响WIFs的起裂压力。随着石英含量与长石含量之比的增加，WIFs的起裂压力呈对数函数下降。（3）考虑成岩矿物对岩石脆性的贡献，改进了长石致密砂岩油藏脆性指数的计算方法。（4）孔隙度、脆性指数与诱导裂缝起裂压力之间的关系表明，孔隙度的增加导致脆性指数呈幂律增加，而WIFs的起裂压力相对于脆性指数呈幂律下降。这一现象表明，在长石砂岩油藏长期注水过程中WIFs发生的可能性增加。该研究有助于理解岩心矿物如何影响致密砂岩油藏中WIFs的起裂压力。
