Understanding the Mechanisms of Huff-n-Puff, CO2-EOR in Liquid-Rich Shale Plays: Bakken Case Study

Abstract

A revolution of unconventional reservoirs is a turning point in the global oil and gas industry since these resources have massive reserves with large potential in contributing to hydrocarbon production. Previous EOR laboratory experiments and simulation studies in the literature illustrated promising results in terms of recovery factor for different EOR applications, such as CO2, surfactant, and natural gas. However, pilot tests performance reported contrast behavior due to misleading predicting for the EOR physics processes. This paper presents the experimental work to evaluate the feasibility of CO2-EOR using the huff-n-puff (HNP) protocol in the Middle Bakken (MB) Formation, the Mountrail County, Williston Basin, ND. We evaluate the oil recovery from CO2-EOR under several scenarios of operational and well/reservoir conditions. The parameters considered in the sensitivity study include temperatures, pressure, soak time, and number of injection cycles to obtain optimum conditions under which the incremental oil recovery from the MB Formation is increased. The wettability alteration (i.e. contact angle) was also studied using rock-chip samples before and after the HNP experiment at the Bakken reservoir conditions (present for example P & T in psi/F). The outcomes indicated on the effect of the reservoir temperature and pressure on the performance of the CO2, where the recoverable oil increases as the temperature and pressure increase until reach the optimum. As a previous research outcome, the number of cycling and soaking time are crucial design parameters for the HNP experiment and on the field as well to let the CO2 time to diffuse into the deep formation and swell more oil. In addition, the wettability alteration was changed by CO2-EOR as injection pressures increase and the wetting phase move from the oil-wet toward the water-wet system. As overall outcomes from this research, the CO2 HNP process has a good potential in the lab, and could be succeeded economically in field applications that might reduce the need for refracturing stimulation or infill drilling.

Unconventional Well Test Analysis for Assessing Individual Fracture Stages through Post-Treatment Pressure Falloffs: Case Study

“…This hydrocarbon production improvement has been driven by the application of modern horizontal drilling and multi-stage hydraulic fracturing (MSHF) techniques, which makes it possible to access low-porosity (<10%) and low-permeability (<0.1 mD) formations [1,2]. The creation of large stimulated reservoir volumes (SRVs) has been achieved through breakthroughs in hydraulic fracturing technology; however, fracture treatment is not necessarily effective [3]. Operators have started utilizing tighter spaced clusters, longer stage lengths, and greater proppant volumes in their stimulation designs [4,5].…”

“…An inappropriate ch may cause proppant deformation and/or crush under closure pressures. High-pres drawdown may also cause formation rock compression, which leads to a reductio matrix permeability with changes in reservoir pressure or stress [3,4,8]. The product of unconventional wells heavily relies on the effective fracture contact area or the prop fracture area per cluster, which is critical in evaluating hydraulic fracture treatment formance [9].…”

“…The majority of the previously published research is associated high uncertainty and lacks a thorough discussion of fracture network characterizat Only long-term production data were utilized in the past, the application of which ca ambiguity in understanding the hydraulic fracture performance [13,14]. This ambig was caused by the difficulty in utilizing conventional exploration and production niques to establish commercial production rates [3,15].…”

“…Only long-term production data were utilized in the past, the application of which caused ambiguity in understanding the hydraulic fracture performance [13,14]. This ambiguity was caused by the difficulty in utilizing conventional exploration and production techniques to establish commercial production rates [3,15].…”

Review on Phase Behavior in Tight Porous Media and Microscopic Flow Mechanism of CO2 Huff-n-Puff in Tight Oil Reservoirs

“…On the one hand, numerical simulation has been performed to optimize injection and production parameters [24][25][26]. On the other hand, physical experiments have been conducted to investigate the phase behavior and microscopic flow mechanism to improve the CO 2 huff-n-puff performance in tight oil reservoirs [27]. The phase behavior in a PVT cylinder is different from that in porous media.…”