石油与天然气地质 ›› 2025, Vol. 46 ›› Issue (1): 178-191.doi: 10.11743/ogg20250113

• 油气地质 • 上一篇    下一篇

川中地区侏罗系沙溪庙组二段富钙地层水成因及其对天然气运聚的指示意义

杨跃明1(), 王茂云2,3(), 吴长江1, 曾溅辉2,3, 潘珂1, 张欢乐4, 王小娟1, 陈冬霞2,3, 崔虎旺2,3   

  1. 1.中国石油 西南油气田分公司 勘探开发研究院,四川 成都 610041
    2.油气资源与工程全国重点实验室 中国石油大学(北京),北京 102249
    3.中国石油大学(北京) 地球科学学院,北京 102249
    4.中国石油 新疆油田分公司 勘探开发研究院,新疆 克拉玛依 834000
  • 收稿日期:2024-09-09 修回日期:2024-12-06 出版日期:2025-02-28 发布日期:2025-03-03
  • 通讯作者: 王茂云 E-mail:yangym@petrochina.com.cn;wmy950904@163.com
  • 第一作者简介:杨跃明(1963—),男,博士、正高级工程师,油气勘探开发生产管理及研究。E‑mail: yangym@petrochina.com.cn
  • 基金项目:
    中国石油西南油气田公司科研项目(JS2022-003)

Origin of calcium-rich formation water and its implications for natural gas migration and accumulation in the 2nd member of the Jurassic Shaximiao Formation, central Sichuan Basin

Yueming YANG1(), Maoyun WANG2,3(), Changjiang WU1, Jianhui ZENG2,3, Ke PAN1, Huanle ZHANG4, Xiaojuan WANG1, Dongxia CHEN2,3, Huwang CUI2,3   

  1. 1.Research Institute of Exploration and Development,Southwest Oil & Gasfield Company,PetroChina,Chengdu,Sichuan 610041,China
    2.State Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum (Beijing),Beijing 102249,China
    3.College of Geosciences,China University of Petroleum (Beijing),Beijing 102249,China
    4.Research Institute of Exploration and Development,Xinjiang Oilfield Company,PetroChina,Karamay,Xinjiang 834000,China
  • Received:2024-09-09 Revised:2024-12-06 Online:2025-02-28 Published:2025-03-03
  • Contact: Maoyun WANG E-mail:yangym@petrochina.com.cn;wmy950904@163.com

摘要:

基于34口井的地层水地球化学数据、含气饱和度数据和岩矿资料,分析了川中地区侏罗系沙溪庙组二段(沙二段)富钙地层水成因,探讨了地层水对源-储分离型致密砂岩气运聚的指示意义。研究结果表明:川中地区沙二段地层水较中国其他致密砂岩气藏具有明显的“钙富集和钠亏损”的特征。地层水矿化度为3.3 ~ 45.6 g/L,为CaCl2型,Ca2+当量比[γ(Ca2+)]为24.7 % ~ 69.5 %。根据γ(Ca2+)将研究区沙二段地层水划分为高钙地层水[γ(Ca2+)≥60 %]、中钙地层水[40 %≤γ(Ca2+)<60 %]和低钙地层水[γ(Ca2+)<40 %]3种类型。3类地层水的化学特征和分布存在明显的差异:高钙地层水主要分布在距角①断裂相对较近且与角①断裂连通的河道砂组,矿化度平均值为34.1 g/L,相对较高,阳离子以Ca2+为主,钠氯系数、脱硫酸系数和碳酸盐平衡系数最小;低钙地层水主要分布在距角①断裂较远或不与角①断裂直接连通的河道砂组,矿化度平均值为3.9 g/L,阳离子以Na+为主,钠氯系数、脱硫酸系数和碳酸盐平衡系数最大;中钙地层水矿化度平均值为17.7 g/L,Na+与Ca2+含量相差不大,钠氯系数、脱硫酸系数和碳酸盐平衡系数介于前两者之间。Ca2+含量较高的须家河组地层水的混入是沙二段地层水富钙的主要原因,后续的水-岩相互作用,尤其是斜长石的钠长石化导致钙进一步富集,而钠减少。川中地区沙二段地层水碳酸盐平衡系数、矿化度以及γ(Ca2+)沿着天然气侧向运移路径逐渐减少,表明富钙地层水化学指标对源-储分离型致密砂岩气藏具有较好的示踪能力。沙二段地层水中的钙越富集,储层的含气性越好,说明富钙地层水对天然气的富集具有指示意义。

关键词: 水-岩相互作用, 源-储分离型气藏, 富钙地层水, 天然气运聚, 沙溪庙组, 川中地区

Abstract:

Using data of the geochemistry, gas saturation, and rock and mineral compositions of formation water extracted from 34 wells, we discuss the origin of calcium-rich formation water in the 2nd member of the Jurassic Shaximiao Formation (hereafter referred to as the Sha 2 Member) in the central Sichuan Basin, and accordingly explore the implications of the formation water for natural gas migration and accumulation of tight-sand gas reservoirs with source-reservoir separated. The results indicate that the formation water in the Sha 2 Member exhibits pronounced calcium enrichment and sodium depletion compared to that in other tight-sand gas reservoirs in China. The formation water in the member displays total dissolved solids (TDS) ranging from 3.3 to 45.6 g/L (CaCl2 type) and equivalent concentration proportions of Ca2+γ(Ca2+)] ranging from 24.7 % to 69.5 %, based on which the formation water can be categorized into three types: high-calcium [γ(Ca2+) ≥ 60 %], medium-calcium [40 % ≤ γ(Ca2+) < 60 %], and low-calcium [γ(Ca2+) < 40 %] formation water. These three types of formation water differ greatly in chemical characteristics and distribution. Specifically, the high-calcium formation water is concentrated in channel sand bodies that are near and connected to Jiao ① fault. This type of formation water, among others, exhibits a high average TDS of 34.1 g/L, cations dominated by Ca2+, and the lowest Na+/Cl- ratio, desulfurization coefficient, and carbonate equilibrium coefficient. The low-calcium formation water principally occurs in channel sand bodies that are distant from or not directly connected to the Jiao ① fault. This type of formation water manifests an average TDS of 3.9 g/L, cations dominated by Na+, and the highest Na+/Cl- ratio, desulfurization coefficient, and carbonate equilibrium coefficient. The medium-calcium formation water exhibits an average TDS of 17.7 g/L and slightly different Na+ and Ca2+ concentrations, with Na+/Cl- ratios, desulfurization coefficients, and carbonate equilibrium coefficients falling between those of the high- and low-calcium formation water. The calcium enrichment in formation water of the Sha 2 Member is primarily attributed to the mixing of formation water with a high Ca2+ concentration from the Xujiahe Formation. Additionally, subsequent water-rock interactions, especially the albitization of plagioclase, further contribute to the calcium enrichment and sodium depletion in the formation water of Sha 2 Member. The carbonate equilibrium coefficients, TDS, and γ(Ca2+) of formation water in the Sha 2 Member decrease gradually along the lateral migration pathway of natural gas. This indicates that the chemical indices of calcium-rich formation water can serve as reliable tracers for tight-sand gas reservoirs of separated source-reservoir type. For the Sha 2 Member, higher calcium enrichment in formation water is associated with more favorable gas-bearing properties of reservoirs, suggesting that the calcium-rich formation water is indicative of natural gas accumulation.

Key words: water-rock interaction, gas reservoir of separated source-reservoir type, calcium-rich formation water, natural gas migration and accumulation, Shaximiao Formation, central Sichuan Basin

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