Numerical Simulation Study on Optimal Shut-In Time in Jimsar Shale Oil Reservoir

Chen, Xi; Liao, Kai; Zhao, Liang; Zhu, Jian; Wang, Junchao; Li, Yuqi; Wang, Fei

doi:10.3389/fenrg.2022.849064

Cited by 3 publications

(1 citation statement)

References 20 publications

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“…Currently, hydraulic fracturing is the main technology of economic and effective development of unconventional oil and gas reservoirs. Due to the large amount of fracturing fluid entering underground, the fluids still flow out of the wellbore with oil and gas for a long time, even after the flowback [3]. Therefore, operators are concerned with the flowback performance and its impact on productivity.…”

Section: Introductionmentioning

confidence: 99%

Flowback Characteristics Analysis and Rational Strategy Optimization for Tight Oil Fractured Horizontal Well Pattern in Mahu Sag

Tian,

Liao,

Liu

et al. 2023

Processes

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With the deep development of tight reservoir in Mahu Sag, the trend of rising water cut during flowback concerns engineers, and its control mechanism is not yet clear. For this purpose, the integrated numerical model of horizontal well pattern from fracturing to production was established, and its applicability has been demonstrated. Then the flowback performance from child wells to parent wells and single well to well pattern was simulated, and the optimization method of reasonable flowback strategy was discussed. The results show that the formation pressure coefficient decreases as well patterns were put into production year by year, so that the seepage driving force of the matrix is weakened. The pressure-sensitive reservoir is also accompanied by the decrease of permeability, resulting in the increase of seepage resistance, which is the key factor causing the prolongation of flowback period. With the synchronous fracturing mode of well patterns, the stimulated reservoir volume (SRV) is greatly increased compared with that of single well, which improves the reservoir recovery. However, when the well spacing is less than 200 m, well interference is easy to occur, resulting in the rapid entry and outflow of fracturing fluid, and the increased water cut during flowback. Additionally, the well patterns in target reservoir should adopt a drawdown management after fracturing, with an aggressive flowback in the early stage and a slow flowback in the middle and late stage. With pressure depletion in different development stages, the pressure drop rate should be further slowed down to ensure stable liquid supply from matrix. This research can provide a theoretical guidance for optimizing the flowback strategy of tight oil wells in Mahu sag.

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Section: Introductionmentioning

confidence: 99%

Flowback Characteristics Analysis and Rational Strategy Optimization for Tight Oil Fractured Horizontal Well Pattern in Mahu Sag

Tian,

Liao,

Liu

et al. 2023

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Experimental Investigation of Oil Displacement Caused by Fracturing Fluid Imbibition in Hydraulically Fractured Oil-Wet Shale Reservoirs

Jian,

Fei,

et al. 2024

Day 2 Tue, February 13, 2024

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Spontaneous imbibition (SI) has proven to be an effective method for enhancing oil recovery in water-wet shale reservoirs due to the capillary force. There are few articles that focus on the water imbibition and oil displacement for oil-wet reservoirs. However, we believe that the potential of oil displacement caused by water imbibition should not be neglected, since field observations from dozens of wells show strong positive relevance between initial oil production and post-fracturing well shut-in time in the oil-wet shale oil reservoir of Junggar Basin, China. In this paper, several experiments and numerical simulations are designed to shed light on the mechanism of oil displacement by fracturing fluid imbibition, including the driving force and the oil recovery of different pores. The real field fracturing fluid which is prepared by guar gel, anti-emulsifiers, anti-swelling, cleanup additives and gel breakers is used as the test fluid. Also, the oil-wet shale cores saturated with crude oil are used as the samples. Firstly, contact angle after different contact times and interfacial tension are measured to figure out the petrophysical properties of fracturing fluid and crude oil. Secondly, the SI experiments using the fracturing fluid made up of deuterium oxide as the imbibed fluid are conducted to discover the oil recovery of different sizes of pores with shale samples. The low-field nuclear magnetic resonance(LF-NMR) is used to describe the relative content of crude oil under different pores and different SI times. Finally, an experimental core model is established based on the above experimental results. The results show that wettability alteration appears in the oil-wet the core sample. As the contact time increases, the contact angle decreases continuously. The interfacial tension decreases from 72(water and crude oil) mN/m to 1.2(fracturing fluid and crude oil) mN/m. These two phenomena effectively explain the driving force of imbibition and displacement in oil-wet samples. The imbibition oil recovery is about 18.4% in the oil-wet core samples, which indicates that oil-wet cores have a certain oil displacement effect. The fracturing fluid enters the mesopore first because of the driving force produced by wettability alteration and the low frictional resistance, and the imbibition oil recovery in the mesopore is 35%, which is higher than that in micropore and small mesopore in oil-wet samples. This phenomenon and result show a sharp contrast with that of water-wet rock cores proved by previous studies. Finally, a new capillary force curve accounting for the effect of wettability alteration is fitted to characterize the oil displacement in oil-wet samples by the experimental core model simulation. This study aims to demonstrate the SI characteristics of oil-wet shale and helps to provide crucial theoretical foundations for developing oil-wet shale reservoirs.

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Numerical Investigation on Injected-Fluid Recovery and Production Performance following Hydraulic Fracturing in Shale Oil Wells

et al. 2022

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Currently, volume fracturing of horizontal wells is the main technology for shale oil development. A large amount of fracturing fluid is injected into the formation, but the flowback efficiency is very low. Besides, the impact of fluid retention on productivity is not fully clear. There is still a debate about fast-back or slow-back after fracturing, and the formulation of a reasonable cleanup scheme is lacking a theoretical basis. To illustrate the injected-fluid recovery and production performance of shale oil wells, an integrated workflow involving a complex fracture model and oil-water production simulation was presented, enabling a confident history match of flowback data. Then, the impacts of pumping rate, slick water ratio, cluster spacing, stage spacing and flowback rate were quantitatively analyzed. The results show that the pumping rate is negatively correlated with injected-fluid recovery, but positively correlated with oil production. A high ratio of slick water would induce a quite complex fracture configuration, resulting in a rather low flowback efficiency. Meanwhile, the overall conductivity of the fracture networks would also be reduced, as well as the productivity, which indicates that there is an optimal ratio for hybrid fracturing fluid. Due to the fracture interference, the design of stage or cluster spacing is not the smaller the better, and needs to be combined with the actual reservoir conditions. In addition, the short-term flowback efficiency and oil production increase with the flowback rate. However, considering the damage of pressure sensitivity to long-term production, a slow-back mode should be adopted for shale oil wells. The study results may provide support for the design of a fracturing scheme and the optimization of the flowback schedule for shale oil reservoirs.

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Numerical Simulation Study on Optimal Shut-In Time in Jimsar Shale Oil Reservoir

Cited by 3 publications

References 20 publications

Flowback Characteristics Analysis and Rational Strategy Optimization for Tight Oil Fractured Horizontal Well Pattern in Mahu Sag

Flowback Characteristics Analysis and Rational Strategy Optimization for Tight Oil Fractured Horizontal Well Pattern in Mahu Sag

Experimental Investigation of Oil Displacement Caused by Fracturing Fluid Imbibition in Hydraulically Fractured Oil-Wet Shale Reservoirs

Numerical Investigation on Injected-Fluid Recovery and Production Performance following Hydraulic Fracturing in Shale Oil Wells

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