Improved Hydrocarbon Recovery Using Mixtures of Energizing Chemicals in Unconventional Reservoirs

Abstract

Summary The objective of this work is to design and evaluate an effective blend of chemicals that can be injected into shale (black oil or critical fluid) reservoirs to enhance hydrocarbon recovery. The blend can be implemented as a prepad fluid ahead of hydraulic–fracturing fluid or as a remedial fluid later in the life of a well. A chemical blend (CB) consisting of an organic solvent (OS), a surfactant, and an oxidizing agent (OA) (in conjunction with an acid) was designed, developed, and tested in the laboratory on crushed rocks, core plugs, and fractured cores to evaluate the interactions of the chemicals with the shale samples. Microcomputed–tomography (micro–CT) scanning, scanning electron microscopy, and Brinell hardness tests were used to evaluate surface changes in the shales. The results of laboratory experiments demonstrate that the CB extracts up to 30% of mobile oil in crushed rocks and improves permeability by 25 to 100% in thin core plugs. Some of the mechanisms that might support the CB application are as follows: (1) pressurization of the formation and reopening of the closed fractures, thus improving well productivity; (2) extraction and mobilization of low–mobility oil, remnants of the original kerogen, removal of deposited salt, and trapped water in matrix and fracture network that impedes fluid flow; (3) creation of pathways to high–pressure liquid–rich small organic pores, where hydrocarbon liquids are trapped, adsorbed, and dissolved in the kerogen; (4) creation of flow pathways for the intrusion of aqueous–based fluids in oil–wet organic–rich rocks with wettability alteration to accelerate the injection, countercurrent imbibition, and osmotic processes; and (5) enhancement of porosity and permeability of fracture surfaces by the introduction of a delayed reaction mechanism to deliver acids deeper into the microfracture network without compromising rock mechanical properties. The presence of sulfate ions in the OA did not contribute to any noticeable scale deposit while delaying the reactivity of acid with inorganic components of shale surfaces. Several field trials have been conducted successfully in the Eagle Ford (EF) Formation.

Effects of Pressurizing Cryogenic Treatments on Physical and Mechanical Properties of Shale Core Samples—An Experimental Study

“…It is worth noting that the highest decreases in the velocities were observed at the highest treatment pressure (4.14 MPa) owing to the creation of longer and wider cracks leading to the highest porosity and permeability enhancements. The mechanical properties of the samples are functions of the compressional and shear velocities as shown in Equations (1)- (3). Thus, changes in ultrasonic velocities cause changes in the core samples dynamic mechanical properties (Young's modulus, Poisson's ratio, and bulk compressibility).…”

“…According to Energy Information Administration (EIA) [1], the USA oil and gas production from unconventional reservoirs, which have ultra-low permeability (nano-Darcy (nD) to micro-Darcy (µD)), have been considerably improved since 2007. Even though horizontal drilling and multistage-hydraulic fracturing are necessary to produce with economical rates from such reservoirs [2][3][4][5], the oil and gas production rates significantly decrease by 90% in the first two to three years of production [5]. Despite implementing horizontal drilling and multi-stage hydraulic fracturing, unconventional hydrocarbon recovery factors are still low, with 10% in oil reservoirs and 25% in gas reservoirs [5,6].…”

“…Since 2007, oil and gas production from unconventional resources (extremely low permeability formations) started to significantly increase [1]. Economical production from such resources requires drilling horizontally as well as implementing multistage hydraulic fracture treatments [2][3][4][5]21,22]. Wang et al [23] stated that more than 90% of gas wells and 70% of oil wells are hydraulically fractured worldwide.…”

Experimental Investigation on Cyclic Huff-n-Puff with Surfactants Based on Complex Fracture Networks in Water-Wet Oil Reservoirs with Extralow Permeability

“…During the secondary stage, an external fluid such as water and gas is injected into the reservoir. However, it can be much difficult to connect an injector to other producers in the extralow-permeability reservoirs without developed natural fractures or hydraulic fractures [9][10][11]. Through the effective hydraulic fracturing, the fluid can be injected in a larger volume into the reservoir, however, the reservoir heterogeneity will simultaneously be aggravated by the hydraulic fracturing, and the fluid will mostly flow through the fractures to the producers rather than displace the oil in matrix because of extralow matrix permeability [8,12,13], especially for the gas injection owing to low-gas viscosity [14][15][16][17].…”

“…Both of more injection and effective water exchange for more oil in matrix can perform better and then achieve a higher oil recovery. Based on the fracture networks, the injected fluid can enter into more high oil saturation areas near the fractures [11,22,23]. In order to exchange for more oil, the addition of the preferred surfactants will reduce the IFT and result in wettability alteration as well as water-oil emulsification [24][25][26][27][28][29][30] and thus achieve more sufficient mixture of oil and water by efficient displacement and imbibition in matrix, which can be a proper way to enhance oil recovery of huff-n-puff for extralow-permeability oil reservoirs.…”