Abstract
The challenges associated with unconventional reservoirs are related to their intrinsic nature: extremely low porosity and permeability. Combinations of horizontal wells and multistage hydraulic fracturing techniques have been developed to overcome the production obstacles and unlock the vast amount of oil in place in such formations. However, oil production still exhibits a sharp decline within the first 2 years after the stimulation, leading to an oil recovery of less than 15%. Thus, enhanced oil recovery methods need to be investigated to further increase the production rates and the recovery. In this study, laboratory experiments and numerical simulations were conducted to evaluate the performance of the CO2 foam huff and puff process and its impacts on oil recovery in tight oil formations. More specifically, the foam half-life was measured as a function of surfactant concentration and followed by the foam drainage ratio and its rheological properties in the subsequent tests. Reservoir simulations were conducted using the lab data and the field data collected from Cardium formation. Sensitivity analyses were finally carried out to investigate the effects of controlling variables on the CO2 foam performance. Experimental results revealed that the optimal surfactant concentration was found to be 0.2%, which is the critical micelle concentration point. Simulation results show that CO2 foam huff and puff can increase the oil recovery by more than 11% compared to that of the primary production. Moreover, sensitivity analyses show that the production time, injection time, and soaking time are the main effecting parameters, while the injection rate and the incremental injection rate are less important.
Highlights
Worldwide oil demand and decline in the well production rate has led to the implementation of improved oil recovery (IOR) and enhanced oil recovery (EOR) methods to sustain oil production (Golabi et al, 2012; Shabib-Asl et al, 2014; Ayoub et al, 2015; Hosseini et al, 2015a; Hosseini et al, 2015b; Shabib-Asl et al, 2015a; Shabib-Asl et al, 2015b; Dianatnasab et al, 2016; Shabib-AsL et al, 2019a; Shabib-Asl et al, 2019b)
The results showed that longer production is the key parameter to increase oil recovery, but longer soaking time is not guaranteed for more oil recovery
In the CO2 foam huff and puff, the injection of the EOR agent has already increased reservoir pressure, and the reservoir fluids properties have enhanced to some extent, based on the soaking time
Summary
Worldwide oil demand and decline in the well production rate has led to the implementation of improved oil recovery (IOR) and enhanced oil recovery (EOR) methods to sustain oil production (Golabi et al, 2012; Shabib-Asl et al, 2014; Ayoub et al, 2015; Hosseini et al, 2015a; Hosseini et al, 2015b; Shabib-Asl et al, 2015a; Shabib-Asl et al, 2015b; Dianatnasab et al, 2016; Shabib-AsL et al, 2019a; Shabib-Asl et al, 2019b). There are many parameters that can affect the huff and puff performance, including soaking time, injection rate, injection pressure, number of cycles, and injection fluid composition, which need to be optimized for its field application to achieve maximum oil recovery or profits. Researchers have conducted both experimental and numerical studies on CO2 injection performance under different conditions (Rahmanifard et al, 2014). A series of experimental tests were conducted to analyze the foam stability, foam quality, and foam rheological properties, and numerical simulation was used to model the effects of injection, soaking, and production times on the final oil recovery factor. An incremental injection rate ratio of 1.1 means that the first cycle injection rate is 10,000 scf/d, the second cycle is 11,000 scf/d, the third cycle is 12,100 scf/d, and so on
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