以前，我们检查了低含量（LS）EOR效应的潜在地层水（FW）Mg2+，其中FW中的二价阳离子的激怒正在降低LS水的影响。在本文中，我们证明了在注入水（FW和LS水）中相同的二价阳离子的重要性。我们还试图将注入水中的二价阳离子的百分比与FW中的百分比联系起来，以设计注射水的最佳浓度，并从砂岩储层中获得最大的油回收率。Berean砂岩核心在70°C下成功淹没了FW和LS水。在注射两种盐水时，分析了废水样品中的pH。双Ca2+和Mg2+浓度的油回收实验显示出较低的LS水作用，这意味着核心变得更加湿。但是，当HS水中的Ca2+和Mg2+的量减少一半时，LS水效应要大得多。这项工作的结果将石油回收与LS水化学成分，温度，离子交换和pH相关。

Enhanced oil recovery, LS water flooding, Petroleum geochemistry.

以前，我们检查了低含量（LS）EOR效应的潜在地层水（FW）Mg2+，其中FW中的二价阳离子的激怒正在降低LS水的影响。在本文中，我们证明了在注入水（FW和LS水）中相同的二价阳离子的重要性。我们还试图将注入水中的二价阳离子的百分比与FW中的百分比联系起来，以设计注射水的最佳浓度，并从砂岩储层中获得最大的油回收率。Berean砂岩核心在70°C下成功淹没了FW和LS水。在注射两种盐水时，分析了废水样品中的pH。双Ca2+和Mg2+浓度的油回收实验显示出较低的LS水作用，这意味着核心变得更加湿。但是，当HS水中的Ca2+和Mg2+的量减少一半时，LS水效应要大得多。这项工作的结果将石油回收与LS水化学成分，温度，离子交换和pH相关。

Enhanced oil recovery, LS water flooding, Petroleum geochemistry.

The improved oil recovery from using LS water flooding was 2-40% of the original oil in place (OOIP) [1,2]. The experimental observations of Tang and Morrow [3] for LS water flooding set out conditions for how LS water works. The conditions were: (1) the crude oil must contain acid and base numbers and (2) sandstone should contain clay such as illite and kaolinite. After several years, McGuire [4] and Lager and Web [5] added another condition, which was that divalent cations must be present in the FW. The second condition of Tang and Morrow was no longer valid after the investigations of Al-Saedi and Brady [6] and Sohrabi [7]. The observations from chromatographic columns of quartz showed an increase in the acetate detachment from the quartz surface [6]. The oil recovery observations from the quartz column supported the proposed mechanism [8]. Lager and Webb [5] examined the effect of LS water during brine injection into a sandstone oil reservoir that had an identical amount of Mg2+ in the injected brine and formation water. The objective of this study is to identify the important role of the divalent cations in the injected water for secondary and tertiary flooding.

Materials:The brines were prepared by dissolving the salts in deionized water. The brine compositions are listed in Table 1. Crude oil was delivered by Colt Energy from one of the Kansas oil fields. The viscosity of the oil was 14 cp at 20°C, the density is 0.815 gm/cc at 20°C. The experimental setup is shown in Figure 1. A syringe pump was used to injected water into the accumulators which contain the FW and LSW. The injected brines flow into the core mounted in the core holder and the effluent was collected from the other side. The whole system installed inside an oven.

核flooding:Berean砂岩核心被2个PV FW（96,100 ppm）淹没，作为次要洪水，然后以恒定速率注入2 PV LS水（4000 ppm）。在注射盐水时，分析了废水样品中的pH。实验如下：

In previous work [1], we investigated the role of the divalent cations (Ca2+ and Mg2+) in the FW on the LS EOR and found that the role of the Mg2+ in FW is more effective than the Ca2+ even at high concentrations. As the concentration of the divalent cations increases in the FW, the sandstone turned more water-wet and less LS EOR effect was observed. In the present study, the focus was on the divalent cations in the injected LS water. The oil recovery results have been discussed in relation to the concentrations of the injected divalent cations.

The outcrop core1 was successively flooded with FW and LS water at 70°C. No increased oil recovery was observed during LS water flooding (d3Mg2+) after core1 was flooded in secondary stage with FW. The ultimate oil recovery remained constant at 52.5% OOIP (Figure 2a). The measurements of the pH were logged for the FW and LS water. The pH reading for FW effluent was 6.8 (Figure 3a), which must be sufficiently low to promote adsorption of polar components onto the sandstone surface. The injection pressure was 41 psi during the FW flood. The LS water injection pressure increased to 47 psi (Figure 4a).

当从FW转换为LS水时，LS水流出物的pH值增加到7.3（图3），由于注射的LS盐水中的Mg2+高浓度显示出非常低的可食性可改变，这是小pH增量。根据Lager和Webb [5]以及Brady和Morrow [9]的说法，传统上，HS和LS水之间流出pH值向上变化的差异归因于H+在粘土表面上的二价阳离子的交换。我们以前的工作对自由粘土砂岩和丰富的粘土砂岩都表现出类似的态度[6]。由于pH值的跳跃，将引入更多的水湿砂岩。由于Mg2+的高浓度，注入的LS水似乎没有改变核心湿能。MG2+负责LS水流出物中的低pH值，依次没有获得额外的油回收率（表2）。

The core2 was flooded the same way as in core1 but with d10Mg2+ LS water. As pointed previously, core1 and core2 were saturated with FW containing 90 mmole Mg2+.The oil recovery during FW forced imbibition reached a plateau at 51.5% OOIP (Figure 2b). The oil recovery was similar to core1 because of both alike in petrophysical properties and the core preparations. Upon switching to LS water, the incremental oil recovery was 2.65% of OOIP (Figure 2b). Diluting the Mg2+ 10 times in the injected LS water improved the oil recovery from 0% to 2.65%. The initial pH of the FW was 6.9, and the pH increased to 7.9 when switching to LS water (Figure 3b), which was significantly higher than for the core1. The pH during FW flooding providing a favorable environment for creating mixed-wet media. The pressure profile had similar behavior to that in core1 (Figure 4a and 4b). In our previous work we conducted the same experiments under the same conditions but at 90°C. The results were quite similar for secondary oil recovery but it was greater for the LS water flooding when the Mg2+ was diluted 10 times in the LS water [10].

The authors thank the Higher Committee for Education Development in Iraq and the Iraqi Ministry of Oil/ Missan Oil Company for their permission to present this paper.