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Effect of Low-Concentration Hydrochloric Acid on Properties of Shale Rocks

Fig. 1—Experimental apparatus for measuring mechanical properties.

Matrix acidizing is commonly used as a preflush to the hydraulic-fracturing stimulation of shale formations. The process dissolves sediments and mud solids that inhibit the permeability of the rock, enlarging the natural pores of the reservoir and stimulating flow of hydrocarbons. In this paper, the mineralogical and physical responses to matrix acidizing of several important North American shale formations are evaluated.

Introduction

A few studies have quantified the effect of hydrochloric acid (HCl) matrix acidizing on mineralogical and physical properties of shale formations. However, less is known about the development of conductivity and the acid concentrations necessary to optimize conductivity and, by extension, the impact on production and rock stability. The mechanical properties of shale formations vary as a function of mineralogy, with shales rich in brittle minerals such as quartz and carbonates having higher Young’s-­modulus values. Increases in the clay content, total organic carbon (TOC) content, and porosity may lower the Young’s-­modulus values. Therefore, dissolution of brittle minerals, while improving short-term conductivity, may lower long-term shale rock stability. HCl reacts rapidly with calcite [Ca2(CO3)2] and, to a lesser extent, with dolomite [CaMg(CO3)2], and it is predicted that the main impact of HCl on shale will vary as a function of how much calcite is dissolving, which, in turn, is controlled by acid strength, temperature, and pressure.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 165689, “Effect of Low-Concentration Hydrochloric Acid on the Mineralogical, Mechanical, and Physical Properties of Shale Rocks,” by Samiha Morsy, SPE, C.J. Hetherington, and J.J. Sheng, Texas Tech University, prepared for the 2013 SPE Eastern Regional Meeting, Pittsburgh, Pennsylvania, USA, 20–22 August. The paper has not been peer reviewed.
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Effect of Low-Concentration Hydrochloric Acid on Properties of Shale Rocks

01 October 2014

Volume: 66 | Issue: 10

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