水库

案例研究：了解 H2S 的发生：使用硫同位素进行 Bakken 开采

北达科他州能源与环境研究中心概述了石油和天然气行业在确定 H2S 生产源方面面临的困难。

硫化氢区域、抽油机、标志牌
来源：InStock/Getty Images/iStockphoto。

巴肯石油系统 (BPS) 生产过程中的硫化氢 (H 2 S) 生成因其偶尔发生以及相关的经济和 HSE 影响而成为石油生产商和管道运营商面临的问题。

矛盾的是，从 BPS 的 Middle Bakken (MB) 和下伏的 Three Forks (TF) 致密油藏中开采出来的原油历来质量较轻（40°API 至 50°API），含硫量低（<0.2 wt.%），通常 H2S 浓度为零到较低（<10 ppm ）。

此外，MB 和 TF 油藏均没有公开记录表明在钻杆测试 (DST) 期间存在 H 2 S。然而，根据北达科他大学能源与环境研究中心 (EERC) 之前的研究，BPS 油井中 H 2 S 出现的频率从 2010 年到 2023 年有所增加。尽管观察到的 H 2 S 增加与 BPS 中更大规模、多阶段的油井刺激和完井实践相关，但不清楚的地理和时间趋势使得导致恶化的确切机制成为一个悬而未决的研究问题。

至少有五种已知机制可能导致BPS 井的石油生产流中出现 H2S，包括：

  1. 热化学硫酸盐还原（TSR）
  2. 细菌硫酸盐还原（BSR）
  3. 源岩的生成
  4. 从较深或较浅的 H 2 S 储层运移
  5. 与储层改造工程相关的地球化学机制（表1）。
JPT_2024-10_CaseStudy_table.jpg

了解H2S的生成机制可能会降低新井的酸化风险，并使已经生产H2S的井能够制定更有效的缓解和管理策略。

研究中使用的样本

本研究重点关注威利斯顿盆地北达科他州部分的石油和天然气作业以及BPS 中的H2S实例，其中包括两个主要产油层：MB 和 TF。

在简化的地层序列中，BPS 包含三种不同的岩相。从最深到最浅，这些岩相分别是下巴肯页岩 (LBS)、MB 储层和上巴肯页岩 (UBS)。BPS 下方是 TF，其上部是富含石油的 TF 储层，被认为是 BPS 的一部分。UBS 和 LBS 是 MB 和 TF 储层中石油的源岩，由黑色、富含有机质的硅质碎屑泥岩（即页岩）组成。

直接覆盖在 BPS 上的是麦迪逊群，这是一个以碳酸盐为主的密西西比阶地段，细分为三个地层——Lodgepole (LP)、Mission Canyon (MC) 和 Charles。Birdbear 地层位于 TF 之下和 Duperow 地层之上。Duperow 和 Birdbear 地层均产油，主要由浅海石灰岩和白云岩的碳酸盐沉积物组成。

制定了采样程序来调查 BPS 中生产流中酸化程度不同的区域以及代表潜在烃源岩的多个富含有机质地层，包括 UBS、LBS、LP 和 MC。

样本是从具有不同岩性和成熟度的地点和地层采集的。

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Reservoir

Case Study: Understanding H2S Occurrence: Bakken Production Using Sulfur Isotopes

The Energy & Environmental Research Center in North Dakota outlines the difficulty that the oil and gas industry faces in pinpointing sources of H2S production.

Hydrogen sulphide area, pump jack, posted sign
Source: InStock/Getty Images/iStockphoto.

Souring—or H2S generation—in the Bakken petroleum system (BPS) production is becoming problematic for oil producers and pipeline operators because of the sporadic occurrence and associated economic and HSE impacts.

Paradoxically, crude oil produced from the tight Middle Bakken (MB) and underlying Three Forks (TF) reservoirs of the BPS has historically been light (40 °API to 50 °API) with low sulfur content (<0.2 wt.%), typically exhibiting nonexistent to low (<10 parts per million) H2S concentrations.

Additionally, neither the MB nor the TF reservoirs have public records indicating the presence of H2S during drillstem tests (DST). However, based on previous work performed by the University of North Dakota Energy & Environmental Research Center (EERC), the frequency of H2S occurrence in BPS wells has increased from 2010 to 2023. Even though the observed H2S increases correlate with larger, multistage well stimulation and completion practices in the BPS, the unclear geographical and temporal trends make the exact mechanisms responsible for souring an open research question.

At least five known mechanisms can potentially lead to H2S occurrence in the oil production stream of BPS wells, including:

  1. Thermochemical sulfate reduction (TSR)
  2. Bacterial sulfate reduction (BSR)
  3. Source rock generation
  4. Migration from deeper or shallower H2S reservoirs
  5. Geochemical mechanisms related to reservoir stimulation work (Table 1).
JPT_2024-10_CaseStudy_table.jpg

Understanding the mechanisms of H2S generation might reduce the risk of souring in new wells and enable more effective mitigation and management strategies in the wells already producing H2S.

Samples Used in the Study

This study is focused on oil and gas operations in the North Dakota portion of the Williston Basin and the H2S occurrences in the BPS, which includes two main oil-producing reservoirs: the MB and the TF.

In the simplified stratigraphic sequence, the BPS comprises three distinctive lithofacies. From deepest to shallowest, those lithofacies are the Lower Bakken Shale (LBS), the MB reservoir, and the Upper Bakken Shale (UBS). Underlying the BPS is the TF, the upper part of which is the oil-rich TF reservoir, considered part of the BPS. The UBS and LBS are the source rocks for the oil in MB and TF reservoirs and consist of black, organic-rich, siliciclastic mudstones (i.e., shale).

Directly overlying the BPS is the Madison Group, a carbonate-dominated Mississippian section that is subdivided into three formations—the Lodgepole (LP), Mission Canyon (MC), and Charles. The Birdbear Formation lies beneath the TF and on top of the Duperow Formation. Both the Duperow and Birdbear Formations produce oil and are dominated by carbonate deposits of shallow marine limestone and dolostones.

A sampling program was developed to investigate areas of the BPS with varying levels of souring in the production stream and multiple organic-rich formations representing potential source rocks, including the UBS, LBS, LP, and MC.

The samples were collected from locations and formations with different lithologies and maturity levels.

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