Impact of Matrix Acidizing on Shale Formations

Abstract

Matrix acidizing is typically used to remove drilling and completion damage to reservoir conductivity around the wellbore and dissolve calcite in natural fractures. Despite being a common procedure, few studies have investigated the effect of matrix acidizing on the physical properties and oil recovery factors in shales. This paper describes the effect of HCl treatment on porosity, spontaneous imbibition, and crack distribution in samples from the Eagle Ford, Mancos, Barnett and Marcellus shale formations. Samples measuring 2.54-3.81 cm in diameter and 2.54-5.08 cm in length were exposed to acid with concentrations between 0.8-3% active HCl (4 and 15% of 20% diluted HCl). Active acid concentrations of 0.8% were optimal for balancing enhanced oil recovery while maintaining samples structural stability and integrity. The Pre and post HCl treated samples were saturated with Soltrol 130 TM . Oil recovery was determined by measuring the quantities of oil displaced by uptake of saline water. Recovery factors for Mancos and Eagle Ford shale samples improved from 4 and 16% for non-treated samples to 36 and 71% for the treated samples. In contrast, no change in Barnett and Marcellus shale recovery factors were observed. Porosities were calculated using X-ray computed tomography (CT-scanning). Average porosities prior to acid treatment were 1.6 -3.7% versus 1.6-10.7% after acid treatment. The CT-scanning studies of treated samples also shows that in the Mancos shale randomly oriented cracks developed, while in the Barnett and Marcellus shales cracks developed along bedding planes; very little crack development was observed in Eagle Ford shales. These results are encouraging for the application of matrix acidizing in shale formations to improve microfractures conductivity at distances along strike from the wellbore. Pre HCl Post 3% Active HCl Post 3% Active HCl Pre HCl Post 3% Active HCl Pre HCl Post 3% Active HCl Pre HCl

Effect of Matrix Acidizing on The Performance of Selected Niger Delta Reservoirs

“…Several techniques for selecting stimulation candidates exist in literature and also in the industry. [10] [11] [12] [13] It is important to consider damage mechanisms when designing a matrix treatment, as dissolving calcites, quartz, or clay minerals may affect the reservoir differently [14]. A limited number of studies have quantified the effect of HCL matrix acidizing on recoverability and physical properties of formations [15].…”

Geochemical element mobilisation by interaction of Bowland shale with acidic fluids

“…4) (e.g. [13,41]). In the experiments with starting fluid pH of 1.0, the amount of calcite in the RC673 sample is not sufficient to neutralise the acid, resulting in a low pH throughout the 100 hours duration of the experiment (Fig.…”

“…Hydrochloric acid (HCl) is the major component of fracturing fluids and can dissolve the reactive minerals and initiate cracks in the shale formation, thus providing a dissolution space to maximise the growth and connectivity of the fracture networks [6,[10][11]. Hence, the pressurised acidic fluids can physically fracture the target rock [12] and also dissolve minerals to increase the permeability [13]. Acid fracturing treatment is an effective method to stimulate the production of carbonate reservoirs.…”

Effects of Carbonate Minerals on Shale-Hydraulic Fracturing Fluid Interactions in the Marcellus Shale

“…Carbonate minerals play a dominant role by buffering the pH of shale-HFF interactions, which significantly impacts most reactions taking place in the reservoir and affects the stability of all other reactive components. The Marcellus Shale has a variable composition of carbonate minerals with calcite (CaCO 3 ) ranging from 3 to 48% and dolomite (CaMg(CO 3 ) 2 ) ranging from 0 to 10%, as well as trace amounts of other carbonates such as siderite (Morsy et al, 2013;U.S. EIA, 2017).…”