Field gas huff-n-puff for enhancing oil recovery in Eagle Ford shales – Effect of reservoir rock and crude properties

Cyclic gas injection methods have been shown to improve oil recovery in conventional reservoirs. Even though similar technologies have been used in unconventional reservoirs with some success stories in shale resources, cyclic gas injection enhanced oil recovery (EOR) is still a little-understood subject in boosting oil recovery from unconventional reservoirs. During gas injection, asphaltenes start to deposit and precipitate, which causes pore plugging and reduces oil recovery. Studies of asphaltene deposition challenges during cyclic nitrogen (N 2 ) gas injection and oil production in unconventional reservoirs are yet relatively limited. Therefore, a comprehensive experimental study was conducted using 12 Eagle Ford shale cores (dynamic mode), and filter paper membranes (static mode) were used to evaluate whether miscible and immiscible huff-n-puff (cyclic) N 2 injection increases oil recovery and aggravates asphaltene precipitation. To ensure that miscibility can be examined in cyclic experiments, N 2 minimum miscibility pressure (MMP) was determined using a slim tube technique. The factors studied included the injection pressure, number of cycles, production time, and injection cyclic mode, all conducted at 70 °C. The findings showed that a high asphaltene weight percent was calculated during static experiments (i.e., using filter membranes), and this increase was severe on smaller pore size structures. Dynamic tests (i.e., using shale cores) showed that miscibility increased oil recovery, but a stronger intermediate-wet system was observed when measuring the wettability of cores after N 2 cyclic tests. When starting with shorter soaking times, more oil recovery could be achieved. Oil recovery reduction and asphaltene depositions were observed at later cycles. Microscopy and scanning electron microscopy (SEM) imaging of the Eagle Ford cores showed asphaltene clusters inside the cores after cyclic tests. A mercury porosimeter emphasized the degree of pore plugging after cyclic tests, and the findings revealed a smaller pore size distribution after N 2 tests due to the asphaltene deposition process when compared to cores that had not been pressured. This extensive study focuses on the effects of asphaltene deposition on oil recovery under cyclic N 2 -miscible and immiscible conditions in shale resources.

Section: Introductionmentioning

confidence: 99%

Asphaltene Precipitation and Deposition during Nitrogen Gas Cyclic Miscible and Immiscible Injection in Eagle Ford Shale and Its Impact on Oil Recovery

Elturki

Imqam

2022

“…The materials and the crude oil properties can be found in Sie and Nguyen. 29 The result from a standard test for n-heptane insolubles (ASTM D3279) indicates that crude oil does not contain asphaltenes. Table 1 shows the properties of the two side-wall cores (both are 2 in.…”

Section: Methodsmentioning

confidence: 99%

“…A detailed description of core plug cleaning, oil saturation, gas synthesis, and effluent analysis can be found in ref 29. Briefly, the cleaned plug is vacuumed, and then saturated with the crude oil in a highpressure cell at 77 °C and 3500 psia.…”

Section: Experimental Procedurementioning

confidence: 99%

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Field Gas Huff-n-Puff for Improving Oil Recovery in the Eagle Ford Shale─The Effect of Injection Gas Composition and Cycle

Sie

Nguyen

2023

Self Cite

This work is a continuation of our previous works aiming to advance the understanding of field gas huff-n-puff for enhanced oil recovery in shale reservoirs, which focuses on the effect of injection gas composition and the huff-n-puff cycle (i.e., huff time and puff time). Three injection gases (methane and two synthetic field gases from two different shale formations) were used in the single-cycle huff-n-puff experiments. In addition, a series of multicycle huff-n-puff experiments were conducted with varying huff and puff times to investigate the effect of cycle duration on production. The core plugs and crude oil used in this work were retrieved from an Eagle Ford shale formation. Oil production was evaluated based on the crude oil properties as well as the ultimate recovery factor (URF). The average URF for the (34.0 mol % of C2 +) enriched gas huff-n-puff is 41.4% higher than that of methane huff-n-puff. Additionally, more than 90% of crude could be recovered by a very rich field gas with a composition similar to natural gas liquid. Such an increase in URF with the gas composition enrichment could be attributed to the enhanced phase partitioning as well as the increased molecular diffusion. The results of multicycle huff-n-puff show that the cycle duration has a minor impact on URF. However, an increased puff time could be beneficial to the oil production rate due to the redistribution of the saturation and composition profile in the matrix during the low-pressure shut-in. Additionally, a more frequent puff operation has a positive impact on the oil recovery rate, which could be attributed to injection gas refreshing and crude component removal in the matrix. Moreover, a comparison between single- and multicycle huff-n-puff further confirms that a long soaking without puff may not be favorable for the oil recovery rate.

“…Recently, gas huff-n-puff and flooding processes have been studied extensively in shale resources by various approaches, including experimental studies, − field pilots, , and simulation work. − Using N 2 and Eagle Ford shale cores, Yu and Sheng carried out an experimental investigation. They used mineral oil to saturate the cores and to perform the study.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO₂ Huff-n-Puff Gas Injection

Elturki

Imqam

2023

One of the challenges in extracting oil from unconventional resources using hydraulic fracturing and horizontal drilling techniques is the low primary recovery rate, which is caused by the ultra-small permeability of these resources. Consequently, it is essential to investigate gas injection methods to produce the trapped oil in shale formations. However, the injection process can cause asphaltene depositions inside the reservoir, leading to plugging of pores and oil recovery (OR) reduction. There has been limited research on using gas injection techniques to improve oil production in tight/unconventional resources, although carbon dioxide (CO2) and gas-enhanced oil recovery methods have been used in conventional resources. In order to determine whether or not the cyclic (huff-n-puff) CO2 process improves OR and aggravates asphaltene precipitation, a rigorous experimental investigation was undertaken utilizing filter membranes and Eagle Ford shale cores. After the minimum miscibility pressure was calculated for CO2, various injection pressures were selected to perform CO2 huff-n-puff experiments. Investigations were carried out at 70 °C on injection pressure, cycle number, production time, and huff-and-puff mode injection. The results demonstrated that when the pore size structure of the membranes used was smaller and gas injection cycles increased, a higher asphaltene weight percent (wt %) was determined during the static experiments (i.e., employing filter paper membranes). Miscibility improved OR in dynamic testing (i.e., using shale cores), but a more oil-wet system was detected in wettability measurements taken following CO2 huff-and-puff tests. The plugging impact of asphaltene particles on the pore structure was studied using optical microscopy and scanning electron microscopy imaging. Following the huff-and-puff tests, a mercury porosimeter revealed how severely the pores were plugged, and after the CO2 tests, the pore size distribution reduced as a consequence of asphaltene deposition. This study examines the significance of CO2 injection in OR under miscible/immiscible conditions to identify the critical parameters that could impact the effectiveness of CO2 huff-n-puff operation in unconventional formations.